Doc. no:  P0112R1  (draft as of commit 0244f66975f0b8418584b4615fac2ba47ec8775e)
Date:     2015-10-23
Reply-To: Christopher Kohlhoff <chris@kohlhoff.com>

Networking Library (Revision 7)

1. Introduction

In the June 2014 committee meeting in Rapperswil, LEWG requested that Boost.Asio-based N2175 Networking Library Proposal for TR2 (Revision 1) be updated for C++14 and brought forward as a proposed Networking Technical Specification. This document is that revision. As well as updating the proposal for C++14, it incorporates improvements to Asio that are based on the widespread field experience accumulated since 2007.

The Boost.Asio library, from which this proposal is derived, has been deployed in numerous systems, from large (including internet-facing HTTP servers, instant messaging gateways and financial markets applications) to small (mobile phones and embedded systems). The Asio library supports, or has been ported to, many operating systems including Linux, Mac OS X, Windows (native), Windows Runtime, Solaris, FreeBSD, NetBSD, OpenBSD, HP-UX, Tru64, AIX, iOS, Android, WinCE, Symbian, vxWorks and QNX Neutrino.

2. Changes in this revision

This revision includes changes to address the remaining issues from the LWG wording review held in Cologne in February 2015, as well applying design changes following LEWG review in Lenexa. As the changes are too extensive to list here, readers may wish to view the GitHub page for this proposal at https://github.com/chriskohlhoff/asio-tr2/ for further information.

Since the previous revision, the design changes of note include:

  • Renaming io_service to io_context.
  • Renaming wrap() to bind_executor().
  • Changing package() to be the function call operator of use_future.
  • Removal of the const_buffers_1 and mutable_buffers_1 classes. The buffer sequence requirements have been updated, and const_buffer and mutable_buffer now satisfy these requirements directly.
  • Add new data() and size() member functions to const_buffer and mutable_buffer, replacing buffer_cast<>() and buffer_size() respectively.

3. Reference implementation

An almost complete implementation of the proposal text may be found in a variant of Asio that stands alone from Boost. This variant is available at https://github.com/chriskohlhoff/asio/tree/master.

4. Library examples

Unfamiliar readers are encouraged to look to the Boost.Asio documentation and examples for a more complete picture of the use of the library.

However, to give some idea of the flavour of the proposed library, consider the following sample code. This is part of a server program that echoes the characters it receives back to the client in upper case.

template <typename Iterator>
void uppercase(Iterator begin, Iterator end)
{
  std::locale loc("");
  for (Iterator iter = begin; iter != end; ++iter)
    *iter = std::toupper(*iter, loc);
}

void sync_connection(tcp::socket& socket)
{
  try
  {
    std::vector<char> buffer_space(1024);
    for (;;)
    {
      std::size_t length = socket.read_some(buffer(buffer_space));
      uppercase(buffer_space.begin(), buffer_space.begin() + length);
      write(socket, buffer(buffer_space, length));
    }
  }
  catch (std::system_error& e)
  {
    // ...
  }
}

The synchronous operations used above are functions that do not return control to the caller until the corresponding operating system operation completes. In Asio-based programs their use cases typically fall into two categories:

  • Simple programs that do not care about timeouts, or are happy to rely on the timeout behaviour provided by the underlying operating system.
  • Programs that require fine grained control over system calls, and are aware of the conditions under which synchronous operations will or will not block.

Next, the equivalent code developed using asynchronous operations might look something like this:

class async_connection
  : public std::enable_shared_from_this<async_connection>
{
public:
  async_connection(tcp::socket socket)
    : socket_(std::move(socket))
  {
  }

  void start()
  {
    do_read();
  }

private:
  void do_read()
  {
    auto self(shared_from_this());
    socket_.async_read_some(buffer(buffer_space_),
        [this, self](std::error_code ec, std::size_t length)
        {
          if (!ec)
          {
            uppercase(buffer_space_.begin(), buffer_space_.begin() + length);
            do_write(length);
          }
        });
  }

  void do_write(std::size_t length)
  {
    auto self(shared_from_this());
    async_write(socket_, buffer(buffer_space_, length),
        [this, self](std::error_code ec, std::size_t /*length*/)
        {
          if (!ec)
          {
            do_read();
          }
        });
  }

  tcp::socket socket_;
  std::vector<char> buffer_space_{1024};
};

Asynchronous operations do not block the caller, but instead involve the delivery of a notification to the program when the corresponding operating system operation completes. Most non-trivial Asio-based programs will make use of asynchronous operations.

While the code may appear more complex due to the inverted flow of control, it allows a knowledgeable programmer to write code that will scale to a great many concurrent connections. However, this proposal uses the asynchronous model described in [N4045]. This is an extensible model that allows the asynchronous operations to support a variety of composition and notification mechanisms, and these mechanisms may alleviate this complexity. This includes futures:

std::future<std::size_t> fut =
  socket.async_read_some(buffer(buffer_space), use_future);

// ...

std::size_t length = fut.get();

and, through library extensions, coroutines:

void coro_connection(tcp::socket& socket, yield_context yield)
{
  try
  {
    std::vector<char> buffer_space(1024);
    for (;;)
    {
      std::size_t length = socket.async_read_some(buffer(buffer_space), yield);
      uppercase(buffer_space.begin(), buffer_space.begin() + length);
      async_write(socket, buffer(buffer_space, length), yield);
    }
  }
  catch (std::system_error& e)
  {
    // ...
  }
}

Finally, for many applications, networking is not a core feature, nor is it seen as a core competency of the application’s programmers. To cater to these use cases, the proposal provides a high-level interface to TCP sockets that is designed around the familiar C++ I/O streams framework.

Using the library in this way is as easy as opening a stream object with the remote host’s details:

tcp::iostream s("www.boost.org", "http");

Once connected, you send and receive any data as needed. In this case you send a request:

s << "GET / HTTP/1.0\r\n";
s << "Host: www.boost.org\r\n";
s << "Accept: */*\r\n";
s << "Connection: close\r\n\r\n";

Then receive and process the response:

std::string header;
while (std::getline(s, header) && header != "\r")
  std::cout << header << "\n";
std::cout << s.rdbuf();

You can set a timeout to detect unresponsive connections:

s.expires_after(std::chrono::seconds(60));

And, if at any time there is an error, the tcp::iostream class’s error() member function may be used to obtain an error_code that identifies the reason for failure:

if (!s)
{
  std::cout << "Unable to connect: " << s.error().message() << "\n";
  return 1;
}

5. Scope

Problem areas addressed by this proposal include:

  • Networking using TCP and UDP, including support for multicast.
  • Client and server applications.
  • Scalability to handle many concurrent connections.
  • Protocol independence between IPv4 and IPv6.
  • Name resolution (i.e. DNS).
  • Timers.

Features that are considered outside the scope of this proposal include:

  • Protocol implementations such as HTTP, SMTP or FTP.
  • Encryption (e.g. SSL, TLS).
  • Operating system specific demultiplexing APIs.
  • Support for realtime environments.
  • QoS-enabled sockets.
  • Other TCP/IP protocols such as ICMP.
  • Functions and classes for enumerating network interfaces.
  • Other forms of asynchronous I/O, such as files. (However, the asynchronous model defined below is capable of supporting these facilities.)

6. Target audience

The bulk of the library interface is intended for use by developers with at least some understanding of networking concepts (or a willingness to learn). A high level iostreams interface supports simple use cases and permits novices to develop network code without needing to get into too much depth.

7. Related work

The interface is based on the BSD sockets API, which is widely implemented and supported by extensive literature. It is also used as the basis of networking APIs in other languages (e.g. Java). Unsafe practices of the BSD sockets API, e.g. lack of compile-time type safety, are not included.

Asynchronous support is derived from the Proactor design pattern as implemented by the ADAPTIVE Communication Environment [ACE], and is influenced by the design of the Symbian C++ sockets API [SYMBIAN], which supports synchronous and asynchronous operations side-by-side. The Microsoft .NET socket classes [MS-NET] and the Extended Sockets API [ES-API] developed by The Open Group support similar styles of network programming.

8. Impact on the standard

This is a pure library proposal. It does not add any new language features, nor does it alter any existing standard library headers. It makes additions to experimental headers that may also be modified by other Technical Specifications.

This library can be implemented using compilers that conform to the C++14 standard. An implementation of this library requires operating system-specific functions that lie outside the C++14 standard.

9. Relationship to other proposals

The asynchronous operations defined in this proposal use the asynchronous model previously described in [N4045]. With the extensible asynchronous model presented in that paper, the user has the ability to select an asynchronous approach that is appropriate to each use case. With these library foundations, a single extensible asynchronous model can support a variety of composition methods, including:

  • Callbacks, where minimal runtime penalty is desirable.
  • Futures, and not just std::future but also future classes supplied by other libraries.
  • Coroutines or resumable functions, without adding new keywords to the language.

To facilitate the coordination of asynchronous operations in multithreaded programs, the asynchronous model also utilises the executors design described and specified in [P0113].

As executors and the extensible asynchronous model are a prerequisite for the networking library, the proposed text below incorporates a complete specification of these facilities.

10. Proposed text

10.1. Scope
10.2. Conformance
10.2.1. POSIX conformance
10.2.2. Conditionally-supported features
10.3. Normative references
10.4. Namespaces and headers
10.5. Definitions
10.5.1. host byte order
10.5.2. network byte order
10.5.3. synchronous operation
10.5.4. asynchronous operation
10.5.5. orderly shutdown
10.6. Future plans (Informative)
10.7. Feature test macros (Informative)
10.8. Method of description (Informative)
10.8.1. Structure of each clause
10.8.1.1. Detailed specifications
10.8.2. Other conventions
10.8.2.1. Nested classes
10.9. Error reporting
10.9.1. Synchronous operations
10.9.2. Asynchronous operations
10.9.3. Error conditions
10.9.4. Suppression of signals
10.10. Library summary
10.11. Convenience header
10.11.1. Header <experimental/net> synopsis
10.12. Forward declarations
10.12.1. Header <experimental/netfwd> synopsis
10.13. Asynchronous model
10.13.1. Header <experimental/executor> synopsis
10.13.2. Requirements
10.13.2.1. Proto-allocator requirements
10.13.2.2. Executor requirements
10.13.2.3. Execution context requirements
10.13.2.4. Service requirements
10.13.2.5. Signature requirements
10.13.2.6. Associator requirements
10.13.2.7. Requirements on asynchronous operations
10.13.2.7.1. General asynchronous operation concepts
10.13.2.7.2. Completion tokens and handlers
10.13.2.7.3. Automatic deduction of initiating function return type
10.13.2.7.4. Production of initiating function return value
10.13.2.7.5. Lifetime of initiating function arguments
10.13.2.7.6. Non-blocking requirements on initiating functions
10.13.2.7.7. Associated executor
10.13.2.7.8. I/O executor
10.13.2.7.9. Completion handler executor
10.13.2.7.10. Outstanding work
10.13.2.7.11. Allocation of intermediate storage
10.13.2.7.12. Execution of completion handler on completion of asynchronous operation
10.13.2.7.13. Completion handlers and exceptions
10.13.3. Class template async_result
10.13.4. Class template async_completion
10.13.5. Class template associated_allocator
10.13.5.1. associated_allocator members
10.13.6. Function get_associated_allocator
10.13.7. Class execution_context
10.13.7.1. execution_context constructor
10.13.7.2. execution_context destructor
10.13.7.3. execution_context operations
10.13.7.4. execution_context protected operations
10.13.7.5. execution_context globals
10.13.8. Class execution_context::service
10.13.9. Class template is_executor
10.13.10. Executor argument tag
10.13.11. uses_executor
10.13.11.1. uses_executor trait
10.13.11.2. uses-executor construction
10.13.12. Class template associated_executor
10.13.12.1. associated_executor members
10.13.13. Function get_associated_executor
10.13.14. Class template executor_binder
10.13.14.1. executor_binder constructors
10.13.14.2. executor_binder access
10.13.14.3. executor_binder invocation
10.13.14.4. Class template partial specialization async_result
10.13.14.5. Class template partial specialization associated_allocator
10.13.14.6. Class template partial specialization associated_executor
10.13.15. Function bind_executor
10.13.16. Class template executor_work_guard
10.13.16.1. executor_work_guard members
10.13.17. Function make_work_guard
10.13.18. Class system_executor
10.13.18.1. system_executor operations
10.13.18.2. system_executor comparisons
10.13.19. Class system_context
10.13.20. Class bad_executor
10.13.21. Class executor
10.13.21.1. executor constructors
10.13.21.2. executor assignment
10.13.21.3. executor destructor
10.13.21.4. executor modifiers
10.13.21.5. executor operations
10.13.21.6. executor capacity
10.13.21.7. executor target access
10.13.21.8. executor comparisons
10.13.21.9. executor specialized algorithms
10.13.22. Function dispatch
10.13.23. Function post
10.13.24. Function defer
10.13.25. Class template strand
10.13.25.1. strand constructors
10.13.25.2. strand assignment
10.13.25.3. strand destructor
10.13.25.4. strand operations
10.13.25.5. strand comparisons
10.13.26. Class template use_future_t
10.13.26.1. use_future_t constructors
10.13.26.2. use_future_t members
10.13.26.3. Partial class template specialization async_result for use_future_t
10.13.27. Partial class template specialization async_result for packaged_task
10.14. Basic I/O services
10.14.1. Header <experimental/io_context> synopsis
10.14.2. Class io_context
10.14.2.1. io_context members
10.14.3. Class io_context::executor_type
10.14.3.1. io_context::executor_type constructors
10.14.3.2. io_context::executor_type assignment
10.14.3.3. io_context::executor_type operations
10.14.3.4. io_context::executor_type comparisons
10.15. Timers
10.15.1. Header <experimental/timer> synopsis
10.15.2. Requirements
10.15.2.1. Wait traits requirements
10.15.3. Class template wait_traits
10.15.4. Class template basic_waitable_timer
10.15.4.1. basic_waitable_timer constructors
10.15.4.2. basic_waitable_timer destructor
10.15.4.3. basic_waitable_timer assignment
10.15.4.4. basic_waitable_timer operations
10.16. Buffers
10.16.1. Header <experimental/buffer> synopsis
10.16.2. Requirements
10.16.2.1. Mutable buffer sequence requirements
10.16.2.2. Constant buffer sequence requirements
10.16.2.3. Dynamic buffer requirements
10.16.2.4. Requirements on read and write operations
10.16.3. Error codes
10.16.4. Class mutable_buffer
10.16.5. Class const_buffer
10.16.6. Buffer type traits
10.16.7. Buffer sequence access
10.16.8. Function buffer_size
10.16.9. Function buffer_copy
10.16.10. Buffer arithmetic
10.16.11. Buffer creation functions
10.16.12. Class template dynamic_vector_buffer
10.16.13. Class template dynamic_string_buffer
10.16.14. Dynamic buffer creation functions
10.17. Buffer-oriented streams
10.17.1. Requirements
10.17.1.1. Buffer-oriented synchronous read stream requirements
10.17.1.2. Buffer-oriented asynchronous read stream requirements
10.17.1.3. Buffer-oriented synchronous write stream requirements
10.17.1.4. Buffer-oriented asynchronous write stream requirements
10.17.1.5. Completion condition requirements
10.17.2. Class transfer_all
10.17.3. Class transfer_at_least
10.17.4. Class transfer_exactly
10.17.5. Synchronous read operations
10.17.6. Asynchronous read operations
10.17.7. Synchronous write operations
10.17.8. Asynchronous write operations
10.17.9. Synchronous delimited read operations
10.17.10. Asynchronous delimited read operations
10.18. Sockets
10.18.1. Header <experimental/socket> synopsis
10.18.2. Requirements
10.18.2.1. Requirements on synchronous socket operations
10.18.2.2. Requirements on asynchronous socket operations
10.18.2.3. Native handles
10.18.2.4. Endpoint requirements
10.18.2.5. Endpoint sequence requirements
10.18.2.6. Protocol requirements
10.18.2.7. Acceptable protocol requirements
10.18.2.8. Gettable socket option requirements
10.18.2.9. Settable socket option requirements
10.18.2.10. Boolean socket options
10.18.2.11. Integer socket options
10.18.2.12. I/O control command requirements
10.18.2.13. Connect condition requirements
10.18.3. Error codes
10.18.4. Class socket_base
10.18.5. Socket options
10.18.5.1. Class socket_base::linger
10.18.6. Class template basic_socket
10.18.6.1. basic_socket constructors
10.18.6.2. basic_socket destructor
10.18.6.3. basic_socket assignment
10.18.6.4. basic_socket operations
10.18.7. Class template basic_datagram_socket
10.18.7.1. basic_datagram_socket constructors
10.18.7.2. basic_datagram_socket assignment
10.18.7.3. basic_datagram_socket operations
10.18.8. Class template basic_stream_socket
10.18.8.1. basic_stream_socket constructors
10.18.8.2. basic_stream_socket assignment
10.18.8.3. basic_stream_socket operations
10.18.9. Class template basic_socket_acceptor
10.18.9.1. basic_socket_acceptor constructors
10.18.9.2. basic_socket_acceptor destructor
10.18.9.3. basic_socket_acceptor assignment
10.18.9.4. basic_socket_acceptor operations
10.19. Socket iostreams
10.19.1. Class template basic_socket_streambuf
10.19.1.1. basic_socket_streambuf constructors
10.19.1.2. basic_socket_streambuf members
10.19.1.3. basic_socket_streambuf overridden virtual functions
10.19.2. Class template basic_socket_iostream
10.19.2.1. basic_socket_iostream constructors
10.19.2.2. basic_socket_iostream members
10.20. Socket algorithms
10.20.1. Synchronous connect operations
10.20.2. Asynchronous connect operations
10.21. Internet protocol
10.21.1. Header <experimental/internet> synopsis
10.21.2. Requirements
10.21.2.1. Internet protocol requirements
10.21.2.2. Multicast group socket options
10.21.3. Error codes
10.21.4. Class ip::address
10.21.4.1. ip::address constructors
10.21.4.2. ip::address assignment
10.21.4.3. ip::address members
10.21.4.4. ip::address comparisons
10.21.4.5. ip::address creation
10.21.4.6. ip::address I/O
10.21.5. Class ip::address_v4
10.21.5.1. Struct ip::address_v4::bytes_type
10.21.5.2. ip::address_v4 constructors
10.21.5.3. ip::address_v4 members
10.21.5.4. ip::address_v4 static members
10.21.5.5. ip::address_v4 comparisons
10.21.5.6. ip::address_v4 creation
10.21.5.7. ip::address_v4 I/O
10.21.6. Class ip::address_v6
10.21.6.1. Struct ip::address_v6::bytes_type
10.21.6.2. ip::address_v6 constructors
10.21.6.3. ip::address_v6 members
10.21.6.4. ip::address_v6 static members
10.21.6.5. ip::address_v6 comparisons
10.21.6.6. ip::address_v6 creation
10.21.6.7. ip::address_v6 I/O
10.21.7. Class ip::bad_address_cast
10.21.8. Hash support
10.21.9. Class template ip::basic_address_iterator specializations
10.21.10. Class template ip::basic_address_range specializations
10.21.11. Class template ip::network_v4
10.21.11.1. ip::network_v4 constructors
10.21.11.2. ip::network_v4 members
10.21.11.3. ip::network_v4 comparisons
10.21.11.4. ip::network_v4 creation
10.21.11.5. ip::network_v4 I/O
10.21.12. Class template ip::network_v6
10.21.12.1. ip::network_v6 constructors
10.21.12.2. ip::network_v6 members
10.21.12.3. ip::network_v6 comparisons
10.21.12.4. ip::network_v6 creation
10.21.12.5. ip::network_v6 I/O
10.21.13. Class template ip::basic_endpoint
10.21.13.1. ip::basic_endpoint constructors
10.21.13.2. ip::basic_endpoint members
10.21.13.3. ip::basic_endpoint comparisons
10.21.13.4. ip::basic_endpoint I/O
10.21.13.5. ip::basic_endpoint members (extensible implementations)
10.21.14. Class template ip::basic_resolver_entry
10.21.14.1. ip::basic_resolver_entry constructors
10.21.14.2. ip::basic_resolver_entry members
10.21.14.3. op::basic_resolver_entry comparisons
10.21.15. Class template ip::basic_resolver_results
10.21.15.1. ip::basic_resolver_results constructors
10.21.15.2. ip::basic_resolver_results assignment
10.21.15.3. ip::basic_resolver_results size
10.21.15.4. ip::basic_resolver_results element access
10.21.15.5. ip::basic_resolver_results swap
10.21.15.6. ip::basic_resolver_results comparisons
10.21.16. Class ip::resolver_base
10.21.17. Class template ip::basic_resolver
10.21.17.1. ip::basic_resolver constructors
10.21.17.2. ip::basic_resolver destructor
10.21.17.3. ip::basic_resolver assignment
10.21.17.4. ip::basic_resolver operations
10.21.18. Host name functions
10.21.19. Class ip::tcp
10.21.19.1. ip::tcp comparisons
10.21.20. Class ip::udp
10.21.20.1. ip::udp comparisons
10.21.21. Internet socket options
10.21.21.1. Class ip::multicast::outbound_interface
10.22. Index

10.1. Scope

[scope]

This Technical Specification describes extensions to the C++ Standard Library. This Technical Specification specifies requirements for implementations of an interface that computer programs written in the C++ programming language may use to perform operations related to networking, such as operations involving sockets, timers, buffer management, host name resolution and internet protocols. This Technical Specification is applicable to information technology systems that can perform network operations, such as those with operating systems that conform to the POSIX interface. This Technical Specification is applicable only to vendors who wish to provide the interface it describes.

10.2. Conformance

[conformance]

Conformance is specified in terms of behavior. Ideal behavior is not always implementable, so the conformance sub-clauses take that into account.

10.2.1. POSIX conformance

[conformance.9945]

Some behavior is specified by reference to POSIX. How such behavior is actually implemented is unspecified.

[Note: This constitutes an "as if" rule allowing implementations to call native operating system or other APIs. —end note]

Implementations are encouraged to provide such behavior as it is defined by POSIX. Implementations shall document any behavior that differs from the behavior defined by POSIX. Implementations that do not support exact POSIX behavior are encouraged to provide behavior as close to POSIX behavior as is reasonable given the limitations of actual operating systems and file systems. If an implementation cannot provide any reasonable behavior, the implementation shall report an error as specified in Error Reporting.

[Note: This allows users to rely on an exception being thrown or an error code being set when an implementation cannot provide any reasonable behavior. —end note]

Implementations are not required to provide behavior that is not supported by a particular operating system.

10.2.2. Conditionally-supported features

[conformance.conditional]

This Technical Specification defines conditionally-supported features, in the form of additional member functions on types that satisfy Protocol, Endpoint, SettableSocketOption, GettableSocketOption or IoControlCommand requirements.

[Note: This is so that, when the additional member functions are available, C++ programs may extend the library to add support for other protocols and socket options. —end note]

For the purposes of this Technical Specification, implementations that provide all of the additional member functions are known as extensible implementations.

[Note: Implementations are encouraged to provide the additional member functions, where possible. It is intended that POSIX and Windows implementations will provide them. —end note]

10.3. Normative references

[references]

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

  • ISO/IEC 14882, Programming Language C++
  • ISO/IEC 9945, Information Technology — Portable Operating System Interface (POSIX)
  • C++ Extensions for Library Fundamentals

[Note: The programming language and library described in ISO/IEC 14882 is herein called the C++ Standard. References to clauses within the C++ Standard are written as "C++Std [xref]".
The operating system interface described in ISO/IEC 9945 is herein called POSIX. —end note]

This Technical Specification mentions commercially available operating systems for purposes of exposition. [1]

Unless otherwise specified, the whole of the C++ Standard's Library introduction (C++Std [library]) is included into this Technical Specification by reference.

10.4. Namespaces and headers

[namespaces]

The components described in this Technical Specification are experimental and not part of the C++ standard library. All components described in this Technical Specification are declared in namespace std::experimental::net::v1 or a sub-namespace thereof unless otherwise specified. The headers described in this technical specification shall import the contents of std::experimental::net::v1 into std::experimental::net as if by:

namespace std {
  namespace experimental {
    namespace net {
      inline namespace v1 {}
    }
  }
}

Unless otherwise specified, references to other entities described in this Technical Specification are assumed to be qualified with std::experimental::net::v1::, references to entities described in the C++ standard are assumed to be qualified with std::, and references to entities described in C++ Extensions for Library Fundamentals are assumed to be qualified with std::experimental::fundamentals_v1::.

10.5. Definitions

[defs]

10.5.1. host byte order

[defs.host.byte.order] See section 3.194 of POSIX Base Definitions, Host Byte Order.

10.5.2. network byte order

[defs.net.byte.order] See section 3.238 of POSIX Base Definitions, Network Byte Order.

10.5.3. synchronous operation

[defs.sync.op] A synchronous operation is one where control is not returned until the operation completes.

10.5.4. asynchronous operation

[defs.async.op] An asynchronous operation is one where control is returned immediately without waiting for the operation to complete. Multiple asynchronous operations may be executed concurrently.

10.5.5. orderly shutdown

[defs.orderly.shutdown] The procedure for shutting down a stream after all work in progress has been completed, without loss of data.

10.6. Future plans (Informative)

[plans]

This section describes tentative plans for future versions of this technical specification and plans for moving content into future versions of the C++ Standard.

The C++ committee may release new versions of this technical specification, containing networking library extensions we hope to add to a near-future version of the C++ Standard. Future versions will define their contents in std::experimental::net::v2, std::experimental::net::v3, etc., with the most recent implemented version inlined into std::experimental::net.

When an extension defined in this or a future version of this technical specification represents enough existing practice, it will be moved into the next version of the C++ Standard by replacing the experimental::net::vN segment of its namespace with net, and by removing the experimental/ prefix from its header's path.

10.7. Feature test macros (Informative)

[feature.test]

These macros allow users to determine which version of this Technical Specification is supported by the headers defined by the specification. All headers in this Technical Specification shall supply the following macro definition:

#define __cpp_lib_experimental_net yyyymm

If an implementation supplies all of the conditionally-supported features specified in [conformance.conditional], all headers in this Technical Specification shall supply the following macro definition:

#define __cpp_lib_experimental_net_extensible yyyymm

[Note: The value of the macros __cpp_lib_experimental_net and __cpp_lib_experimental_net_extensible is yyyymm where yyyy is the year and mm the month when the version of the Technical Specification was completed. —end note]

10.8. Method of description (Informative)

[description]

This subclause describes the conventions used to specify this Technical Specification, in addition to those conventions specified in C++Std [description].

10.8.1. Structure of each clause

[structure]

10.8.1.1. Detailed specifications

[structure.specifications]

In addition to the elements defined in C++Std [structure.specifications], descriptions of function semantics contain the following elements (as appropriate):

Completion signature: - if the function initiates an asynchronous operation, specifies the signature of a completion handler used to receive the result of the operation.

10.8.2. Other conventions

[conventions]

10.8.2.1. Nested classes

[nested.class]

Several classes defined in this Technical Specification are nested classes. For a specified nested class A::B, an implementation is permitted to define A::B as a synonym for a class with equivalent functionality to class A::B. [Note: When A::B is a synonym for another type A shall provide a nested type B, to emulate the injected class name. —end note]

10.9. Error reporting

[err.report]

10.9.1. Synchronous operations

[err.report.sync]

Most synchronous network library functions provide two overloads, one that throws an exception to report system errors, and another that sets an error_code (C++Std [syserr]).

[Note: This supports two common use cases:

— Uses where system errors are truly exceptional and indicate a serious failure. Throwing an exception is the most appropriate response.

— Uses where system errors are routine and do not necessarily represent failure. Returning an error code is the most appropriate response. This allows application specific error handling, including simply ignoring the error.

end note]

Functions not having an argument of type error_code& report errors as follows, unless otherwise specified:

— When a call by the implementation to an operating system or other underlying API results in an error that prevents the function from meeting its specifications, the function exits via an exception of a type that would match a handler of type system_error.

— Destructors throw nothing.

Functions having an argument of type error_code& report errors as follows, unless otherwise specified:

— If a call by the implementation to an operating system or other underlying API results in an error that prevents the function from meeting its specifications, the error_code& argument ec is set as appropriate for the specific error. Otherwise, the ec argument is set such that !ec is true.

Where a function is specified as two overloads, with and without an argument of type error_code&:

R f(A1 a1, A2 a2, ..., AN aN);
R f(A1 a1, A2 a2, ..., AN aN, error_code& ec);

then, when R is non-void, the effects of the first overload are as if:

error_code ec;
R r(f(a1, a2, ..., aN, ec));
if (ec) throw system_error(ec, S);
return r;

otherwise, when R is void, the effects of the first overload are as if:

error_code ec;
f(a1, a2, ..., aN, ec);
if (ec) throw system_error(ec, S);

except that the type thrown may differ as specified above. S is an NTBS indicating where the exception was thrown. [Note: A possible value for S is __func__. —end note]

For both overloads, failure to allocate storage is reported by throwing an exception as described in the C++ standard (C++Std [res.on.exception.handling]).

In this Technical Specification, when a type requirement is specified using two function call expressions f, with and without an argument ec of type error_code:

f(a1, a2, ..., aN)
f(a1, a2, ..., aN, ec)

then the effects of the first call expression of f shall be as described for the first overload above.

10.9.2. Asynchronous operations

[err.report.async]

Asynchronous network library functions in this Technical Specification are identified by having the prefix async_ and take a completion handler [async.reqmts.async.token]. These asynchronous operations report errors as follows:

— If a call by the implementation to an operating system or other underlying API results in an error that prevents the asynchronous operation from meeting its specifications, the completion handler is invoked with an error_code value ec that is set as appropriate for the specific error. Otherwise, the error_code value ec is set such that !ec is true.

— Asynchronous operations shall not fail with an error condition that indicates interruption of an operating system or underlying API by a signal [Note: Such as POSIX error number EINTRend note] . Asynchronous operations shall not fail with any error condition associated with non-blocking operations [Note: Such as POSIX error numbers EWOULDBLOCK, EAGAIN, or EINPROGRESS; Windows error numbers WSAEWOULDBLOCK or WSAEINPROGRESSend note] .

In this Technical Specification, when a type requirement is specified as a call to a function or member function having the prefix async_, then the function shall satisfy the error reporting requirements described above.

10.9.3. Error conditions

[err.report.conditions]

Unless otherwise specified, when the behavior of a synchronous or asynchronous operation is defined "as if" implemented by a POSIX function, the error_code produced by the function shall meet the following requirements:

— If the failure condition is one that is listed by POSIX for that function, the error_code shall compare equal to the error's corresponding enum class errc (C++Std [syserr]) or enum class resolver_errc constant.

— Otherwise, the error_code shall be set to an implementation-defined value that reflects the underlying operating system error.

[Example: The POSIX specification for shutdown lists EBADF as one of its possible errors. If a function that is specified "as if" implemented by shutdown fails with EBADF then the following condition holds for the error_code value ec: ec == errc::bad_file_descriptorend example]

When the description of a function contains the element Error conditions, this lists conditions where the operation may fail. The conditions are listed, together with a suitable explanation, as enum class constants. Unless otherwise specified, this list is a subset of the failure conditions associated with the function.

10.9.4. Suppression of signals

[err.report.signal]

Some POSIX functions referred to in this Technical Specification may report errors by raising a SIGPIPE signal. Where a synchronous or asynchronous operation is specified in terms of these POSIX functions, the generation of SIGPIPE is suppressed and an error condition corresponding to POSIX EPIPE is produced instead.

10.10. Library summary

[summary]

Table 1. Networking library summary

Clause

Header(s)

Convenience header

<experimental/net>

Forward declarations

<experimental/netfwd>

Asynchronous model

<experimental/executor>

Basic I/O services

<experimental/io_context>

Timers

<experimental/timer>

Buffers
Buffer-oriented streams

<experimental/buffer>

Sockets
Socket iostreams
Socket algorithms

<experimental/socket>

Internet protocol

<experimental/internet>


Throughout this Technical Specification, the names of the template parameters are used to express type requirements, as listed in the table below.

Table 2. Template parameters and type requirements

template parameter name

type requirements

AcceptableProtocol

acceptable protocol

Allocator

C++Std [allocator.requirements]

AsyncReadStream

buffer-oriented asynchronous read stream

AsyncWriteStream

buffer-oriented asynchronous write stream

Clock

C++Std [time.clock.req]

CompletionCondition

completion condition

CompletionToken

completion token

ConnectCondition

connect condition

ConstBufferSequence

constant buffer sequence

DynamicBuffer

dynamic buffer

EndpointSequence

endpoint sequence

ExecutionContext

execution context

Executor

executor

GettableSocketOption

gettable socket option

InternetProtocol

Internet protocol

IoControlCommand

I/O control command

MutableBufferSequence

mutable buffer sequence

ProtoAllocator

proto-allocator

Protocol

protocol

Service

service

SettableSocketOption

settable socket option

Signature

signature

SyncReadStream

buffer-oriented synchronous read stream

SyncWriteStream

buffer-oriented synchronous write stream

WaitTraits

wait traits


10.11. Convenience header

[convenience.hdr]

10.11.1. Header <experimental/net> synopsis

[convenience.hdr.synop]

#include <experimental/executor>
#include <experimental/io_context>
#include <experimental/timer>
#include <experimental/buffer>
#include <experimental/socket>
#include <experimental/internet>

[Note: This header is provided as a convenience for programs so that they may access all networking facilities via a single, self-contained #include. —end note]

10.12. Forward declarations

[fwd.decl]

10.12.1. Header <experimental/netfwd> synopsis

[fwd.decl.synop]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class execution_context;
  template<class T, class Executor>
    class executor_binder;
  template<class Executor>
    class executor_work_guard;
  class system_executor;
  class executor;
  template<class Executor>
    class strand;

  class io_context;

  template<class Clock> struct wait_traits;
  template<class Clock, class WaitTraits = wait_traits<Clock>>
    class basic_waitable_timer;
  typedef basic_waitable_timer<chrono::system_clock> system_timer;
  typedef basic_waitable_timer<chrono::steady_clock> steady_timer;
  typedef basic_waitable_timer<chrono::high_resolution_clock> high_resolution_timer;

  template<class Protocol>
    class basic_socket;
  template<class Protocol>
    class basic_datagram_socket;
  template<class Protocol>
    class basic_stream_socket;
  template<class Protocol>
    class basic_socket_acceptor;
  template<class Protocol, class Clock = chrono::steady_clock,
    class WaitTraits = wait_traits<Clock>>
      class basic_socket_streambuf;
  template<class Protocol, class Clock = chrono::steady_clock,
    class WaitTraits = wait_traits<Clock>>
      class basic_socket_iostream;

  namespace ip {

    class address;
    class address_v4;
    class address_v6;
    class address_iterator_v4;
    class address_iterator_v6;
    class address_range_v4;
    class address_range_v6;
    class network_v4;
    class network_v6;
    template<class InternetProtocol>
      class basic_endpoint;
    template<class InternetProtocol>
      class basic_resolver_entry;
    template<class InternetProtocol>
      class basic_resolver_results;
    template<class InternetProtocol>
      class basic_resolver;
    class tcp;
    class udp;

  } // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Default template arguments are described as appearing both in <netfwd> and in the synopsis of other headers but it is well-formed to include both <netfwd> and one or more of the other headers. [Note: It is the implementation’s responsibility to implement headers so that including <netfwd> and other headers does not violate the rules about multiple occurrences of default arguments. —end note]

10.13. Asynchronous model

[async]

10.13.1. Header <experimental/executor> synopsis

[async.synop]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class CompletionToken, class Signature, class = void>
    class async_result;

  template<class CompletionToken, class Signature>
    struct async_completion;

  template<class T, class ProtoAllocator = allocator<void>>
    struct associated_allocator;

  template<class T, class ProtoAllocator = allocator<void>>
    using associated_allocator_t = typename associated_allocator<T, ProtoAllocator>::type;

  // get_associated_allocator:

  template<class T>
    associated_allocator_t<T> get_associated_allocator(const T& t) noexcept;
  template<class T, class ProtoAllocator>
    associated_allocator_t<T, ProtoAllocator>
      get_associated_allocator(const T& t, const ProtoAllocator& a) noexcept;

  enum class fork_event {
    prepare,
    parent,
    child
  };

  class execution_context;

  class service_already_exists;

  template<class Service> Service& use_service(execution_context& ctx);
  template<class Service, class... Args> Service&
    make_service(execution_context& ctx, Args&&... args);
  template<class Service> bool has_service(execution_context& ctx) noexcept;

  template<class T> struct is_executor;

  struct executor_arg_t { };
  constexpr executor_arg_t executor_arg = executor_arg_t();

  template<class T, class Executor> struct uses_executor;

  template<class T, class Executor = system_executor>
    struct associated_executor;

  template<class T, class Executor = system_executor>
    using associated_executor_t = typename associated_executor<T, Executor>::type;

  // get_associated_executor:

  template<class T>
    associated_executor_t<T> get_associated_executor(const T& t) noexcept;
  template<class T, class Executor>
    associated_executor_t<T, Executor>
      get_associated_executor(const T& t, const Executor& ex) noexcept;
  template<class T, class ExecutionContext>
    associated_executor_t<T, typename ExecutionContext::executor_type>
      get_associated_executor(const T& t, ExecutionContext& ctx) noexcept;

  template<class T, class Executor>
    class executor_binder;

  template<class T, class Executor, class Signature>
    class async_result<executor_binder<T, Executor>, Signature>;

  template<class T, class Executor, class ProtoAllocator>
    struct associated_allocator<executor_binder<T, Executor>, ProtoAllocator>;

  template<class T, class Executor, class Executor1>
    struct associated_executor<executor_binder<T, Executor>, Executor1>;

  // bind_executor:

  template<class Executor, class T>
    executor_binder<decay_t<T>, Executor>
      bind_executor(const Executor& ex, T&& t);
  template<class ExecutionContext, class T>
    executor_binder<decay_t<T>, typename ExecutionContext::executor_type>
      bind_executor(ExecutionContext& ctx, T&& t);

  template<class Executor>
    class executor_work_guard;

  // make_work_guard:

  template<class Executor>
    executor_work_guard<Executor>
      make_work_guard(const Executor& ex);
  template<class ExecutionContext>
    executor_work_guard<typename ExecutionContext::executor_type>
      make_work_guard(ExecutionContext& ctx);
  template<class T>
    executor_work_guard<associated_executor_t<T>>
      make_work_guard(const T& t);
  template<class T, class U>
    auto make_work_guard(const T& t, U&& u)
      -> decltype(make_work_guard(get_associated_executor(t, forward<U>(u))));

  class system_executor;
  class system_context;

  bool operator==(const system_executor&, const system_executor&);
  bool operator!=(const system_executor&, const system_executor&);

  class bad_executor;

  class executor;

  bool operator==(const executor& a, const executor& b) noexcept;
  bool operator==(const executor& e, nullptr_t) noexcept;
  bool operator==(nullptr_t, const executor& e) noexcept;
  bool operator!=(const executor& a, const executor& b) noexcept;
  bool operator!=(const executor& e, nullptr_t) noexcept;
  bool operator!=(nullptr_t, const executor& e) noexcept;

  // dispatch:

  template<class CompletionToken>
    DEDUCED dispatch(CompletionToken&& token);
  template<class Executor, class CompletionToken>
    DEDUCED dispatch(const Executor& ex, CompletionToken&& token);
  template<class ExecutionContext, class CompletionToken>
    DEDUCED dispatch(ExecutionContext& ctx, CompletionToken&& token);

  // post:

  template<class CompletionToken>
    DEDUCED post(CompletionToken&& token);
  template<class Executor, class CompletionToken>
    DEDUCED post(const Executor& ex, CompletionToken&& token);
  template<class ExecutionContext, class CompletionToken>
    DEDUCED post(ExecutionContext& ctx, CompletionToken&& token);

  // defer:

  template<class CompletionToken>
    DEDUCED defer(CompletionToken&& token);
  template<class Executor, class CompletionToken>
    DEDUCED defer(const Executor& ex, CompletionToken&& token);
  template<class ExecutionContext, class CompletionToken>
    DEDUCED defer(ExecutionContext& ctx, CompletionToken&& token);

  template<class Executor>
    class strand;

  template<class Executor>
    bool operator==(const strand<Executor>& a, const strand<Executor>& b);
  template<class Executor>
    bool operator!=(const strand<Executor>& a, const strand<Executor>& b);

  template<class ProtoAllocator = allocator<void>>
    class use_future_t;

  constexpr use_future_t<> use_future = use_future_t<>();

  template<class ProtoAllocator, class Result, class... Args>
    class async_result<use_future_t<ProtoAllocator>, Result(Args...)>;

  template<class R, class... Args, class Signature>
    class async_result<packaged_task<Result(Args...)>, Signature>;

} // inline namespace v1
} // namespace net
} // namespace experimental

  template<class Allocator>
    struct uses_allocator<experimental::net::v1::executor, Allocator>
      : true_type {};

} // namespace std

10.13.2. Requirements

[async.reqmts]

10.13.2.1. Proto-allocator requirements

[async.reqmts.proto.allocator]

A type A meets the proto-allocator requirements if A is CopyConstructible (C++Std [copyconstructible]), Destructible (C++Std [destructible]), and allocator_traits<A>::rebind_alloc<U> meets the allocator requirements (C++Std [allocator.requirements]), where U is an object type. [Note: For example, std::allocator<void> meets the proto-allocator requirements but not the allocator requirements. —end note] No constructor, comparison operator, copy operation, move operation, or swap operation on these types shall exit via an exception.

10.13.2.2. Executor requirements

[async.reqmts.executor]

The library describes a standard set of requirements for executors. A type meeting the Executor requirements embodies a set of rules for determining how submitted function objects are to be executed.

A type X meets the Executor requirements if it satisfies the requirements of CopyConstructible (C++Std [copyconstructible]) and Destructible (C++Std [destructible]), as well as the additional requirements listed below.

No constructor, comparison operator, copy operation, move operation, swap operation, or member functions context, on_work_started, and on_work_finished on these types shall exit via an exception.

The executor copy constructor, comparison operators, and other member functions defined in these requirements shall not introduce data races as a result of concurrent calls to those functions from different threads.

Let ctx be the execution context returned by the executor's context() member function. An executor becomes invalid when the first call to ctx.shutdown() returns. The effect of calling on_work_started, on_work_finished, dispatch, post, or defer on an invalid executor is undefined. [Note: The copy constructor, comparison operators, and context() member function continue to remain valid until ctx is destroyed. —end note]

In the table below, x1 and x2 denote values of type X, cx1 and cx2 denote (possibly const) values of type X, mx1 denotes an xvalue of type X, f denotes a MoveConstructible (C++Std [moveconstructible]) function object callable with zero arguments, a denotes a (possibly const) value of type A meeting the Allocator requirements (C++Std [allocator.requirements]), and u denotes an identifier.

Table 3. Executor requirements

expression

type

assertion/note
pre/post-conditions

X u(cx1);

Shall not exit via an exception.

post: u == cx1 and std::addressof(u.context()) == std::addressof(cx1.context()).

X u(mx1);

Shall not exit via an exception.

post: u equals the prior value of mx1 and std::addressof(u.context()) equals the prior value of std::addressof(mx1.context()).

cx1 == cx2

bool

Returns true only if cx1 and cx2 can be interchanged with identical effects in any of the expressions defined in these type requirements. [Note: Returning false does not necessarily imply that the effects are not identical. —end note]

operator== shall be reflexive, symmetric, and transitive, and shall not exit via an exception.

cx1 != cx2

bool

Same as !(cx1 == cx2).

x1.context()

execution_context&, or E& where E is a type that satifisfies the ExecutionContext requirements.

Shall not exit via an exception.

The comparison operators and member functions defined in these requirements shall not alter the reference returned by this function.

x1.on_work_started()

Shall not exit via an exception.

x1.on_work_finished()

Shall not exit via an exception.

Precondition: A preceding call x2.on_work_started() where x1 == x2.

x1.dispatch(std::move(f),a)

Effects: Creates an object f1 initialized with DECAY_COPY(forward<Func>(f)) (C++Std [thread.decaycopy]) in the current thread of execution . Calls f1() at most once. The executor may block forward progress of the caller until f1() finishes execution.

Executor implementations should use the supplied allocator to allocate any memory required to store the function object. Prior to invoking the function object, the executor shall deallocate any memory allocated. [Note: Executors defined in this Technical Specification always use the supplied allocator unless otherwise specified. —end note]

Synchronization: The invocation of dispatch synchronizes with (C++Std [intro.multithread]) the invocation of f1.

x1.post(std::move(f),a)
x1.defer(std::move(f),a)

Effects: Creates an object f1 initialized with DECAY_COPY(forward<Func>(f)) in the current thread of execution. Calls f1() at most once. The executor shall not block forward progress of the caller pending completion of f1().

Executor implementations should use the supplied allocator to allocate any memory required to store the function object. Prior to invoking the function object, the executor shall deallocate any memory allocated. [Note: Executors defined in this Technical Specification always use the supplied allocator unless otherwise specified. —end note]

Synchronization: The invocation of post or defer synchronizes with (C++Std [intro.multithread]) the invocation of f1.

[Note: Although the requirements placed on defer are identical to post, the use of post conveys a preference that the caller does not block the first step of f1's progress, whereas defer conveys a preference that the caller does block the first step of f1. One use of defer is to convey the intention of the caller that f1 is a continuation of the current call context. The executor may use this information to optimize or otherwise adjust the way in which f1 is invoked. —end note]


10.13.2.3. Execution context requirements

[async.reqmts.executioncontext]

A type X meets the ExecutionContext requirements if it is publicly and unambiguously derived from execution_context, and satisfies the additional requirements listed below.

In the table below, x denotes a value of type X.

Table 4. ExecutionContext requirements

expression

return type

assertion/note
pre/post-condition

X::executor_type

type meeting Executor requirements

x.~X()

Destroys all unexecuted function objects that were submitted via an executor object that is associated with the execution context.

x.get_executor()

X::executor_type

Returns an executor object that is associated with the execution context.


10.13.2.4. Service requirements

[async.reqmts.service]

A class is a service if it is publicly and unambiguously derived from execution_context::service, or if it is publicly and unambiguously derived from another service. For a service S, S::key_type shall be valid and denote a type (C++Std [temp.deduct]), is_base_of_v<typename S::key_type, S> shall be true, and S shall satisfy the Destructible requirements (C++Std [destructible]).

The first parameter of all service constructors shall be an lvalue reference to execution_context. This parameter denotes the execution_context object that represents a set of services, of which the service object will be a member. [Note: These constructors may be called by the make_service function. —end note]

A service shall provide an explicit constructor with a single parameter of lvalue reference to execution_context. [Note: This constructor may be called by the use_service function. —end note]

[Example:

class my_service : public execution_context::service
{
public:
  typedef my_service key_type;
  explicit my_service(execution_context& ctx);
  my_service(execution_context& ctx, int some_value);
private:
  virtual void shutdown() noexcept override;
  ...
};

end example]

A service's shutdown member function shall destroy all copies of user-defined function objects that are held by the service.

10.13.2.5. Signature requirements

[async.reqmts.signature]

A type satisfies the signature requirements if it is a call signature (C++Std [func.def]).

10.13.2.6. Associator requirements

[async.reqmts.associator]

An associator defines a relationship between different types and objects where, given:

— a source object s of type S,

— type requirements R, and

— a candidate object c of type C meeting the type requirements R

an associated type A meeting the type requirements R may be computed, and an associated object a of type A may be obtained.

An associator shall be a class template that takes two template type arguments. The first template argument is the source type S. The second template argument is the candidate type C. The second template argument shall be defaulted to some default candidate type D that satisfies the type requirements R.

An associator shall additionally satisfy the requirements in the table below. In this table, X is a class template that meets the associator requirements, S is the source type, s is a (possibly const) value of type S, C is the candidate type, c is a (possibly const) value of type C, D is the default candidate type, and d is a (possibly const) value of type D that is the default candidate object.

Table 5. Associator requirements

expression

return type

assertion/note
pre/post-conditions

X<S>::type

X<S, D>::type

X<S, C>::type

The associated type.

X<S>::get(s)

X<S>::type

Returns X<S>::get(S, d).

X<S, C>::get(s, c)

X<S, C>::type

Returns the associated object.


The associator's primary template shall be defined. A program may partially specialize the associator class template for some user-defined type S.

Finally, the associator shall provide the following type alias and function template in the enclosing namespace:

template<class S, class C = D> using X_t = typename X<S, C>::type;

template<class S, class C = D>
typename X<S, C>::type get_X(const S& s, const C& c = d)
{
  return X<S, C>::get(s, c);
}

where X is replaced with the name of the associator class template. [Note: This function template is provided as a convenience, to automatically deduce the source and candidate types. —end note]

10.13.2.7. Requirements on asynchronous operations

[async.reqmts.async]

This section uses the names Alloc1, Alloc2, alloc1, alloc2, Args, CompletionHandler, completion_handler, Executor1, Executor2, ex1, ex2, f, i, N, Signature, token, Ti, ti, work1, and work2 as placeholders for specifying the requirements below.

10.13.2.7.1. General asynchronous operation concepts

[async.reqmts.async.concepts]

An initiating function is a function which may be called to start an asynchronous operation. A completion handler is a function object that will be invoked, at most once, with the result of the asynchronous operation.

The lifecycle of an asynchronous operation is comprised of the following events and phases:

— Event 1: The asynchronous operation is started by a call to the initiating function.

— Phase 1: The asynchronous operation is now outstanding.

— Event 2: The externally observable side effects of the asynchronous operation, if any, are fully established. The completion handler is submitted to an executor.

— Phase 2: The asynchronous operation is now completed.

— Event 3: The completion handler is called with the result of the asynchronous operation.

In this Technical Specification, all functions with the prefix async_ are initiating functions.

10.13.2.7.2. Completion tokens and handlers

[async.reqmts.async.token]

Initiating functions:

— are function templates with template parameter CompletionToken;

— accept, as the final parameter, a completion token object token of type CompletionToken;

— specify a completion signature, which is a call signature (C++Std [func.def]) Signature that determines the arguments to the completion handler.

An initiating function determines the type CompletionHandler of its completion handler function object by performing typename async_result<decay_t<CompletionToken>, Signature>::completion_handler_type. The completion handler object completion_handler is initialized with forward<CompletionToken>(token). [Note: No other requirements are placed on the type CompletionToken. —end note]

The type CompletionHandler must satisfy the requirements of Destructible (C++Std [destructible]) and MoveConstructible (C++Std [moveconstructible]), and be callable with the specified call signature.

In this Technical Specification, all initiating functions specify a Completion signature element that defines the call signature Signature. The Completion signature elements in this Technical Specification have named parameters, and the results of an asynchronous operation are specified in terms of these names.

10.13.2.7.3. Automatic deduction of initiating function return type

[async.reqmts.async.return.type]

The return type of an initiating function is typename async_result<decay_t<CompletionToken>, Signature>::return_type.

For the sake of exposition, this Technical Specification sometimes annotates functions with a return type DEDUCED. For every function declaration that returns DEDUCED, the meaning is equivalent to specifying the return type as typename async_result<decay_t<CompletionToken>, Signature>::return_type.

10.13.2.7.4. Production of initiating function return value

[async.reqmts.async.return.value]

An initiating function produces its return type as follows:

— constructing an object result of type async_result<decay_t<CompletionToken>, Signature>, initialized as result(completion_handler); and

— using result.get() as the operand of the return statement.

[Example: Given an asynchronous operation with Completion signature void(R1 r1, R2 r2), an initiating function meeting these requirements may be implemented as follows:

template<class CompletionToken>
auto async_xyz(T1 t1, T2 t2, CompletionToken&& token)
{
  typename async_result<decay_t<CompletionToken>, void(R1, R2)>::completion_handler_type
    completion_handler(forward<CompletionToken>(token));

  async_result<decay_t<CompletionToken>, void(R1, R2)> result(completion_handler);

  // initiate the operation and cause completion_handler to be invoked with
  // the result

  return result.get();
}

For convenience, initiating functions may be implemented using the async_completion template:

template<class CompletionToken>
auto async_xyz(T1 t1, T2 t2, CompletionToken&& token)
{
  async_completion<CompletionToken, void(R1, R2)> init(token);

  // initiate the operation and cause init.completion_handler to be invoked
  // with the result

  return init.result.get();
}

end example]

10.13.2.7.5. Lifetime of initiating function arguments

[async.reqmts.async.lifetime]

Unless otherwise specified, the lifetime of arguments to initiating functions shall be treated as follows:

— If the parameter has a pointer type or has a type of lvalue reference to non-const, the implementation may assume the validity of the pointee or referent, respectively, until the completion handler is invoked. [Note: In other words, the program must guarantee the validity of the argument until the completion handler is invoked. —end note]

— Otherwise, the implementation must not assume the validity of the argument after the initiating function completes. [Note: In other words, the program is not required to guarantee the validity of the argument after the initiating function completes. —end note] The implementation may make copies of the argument, and all copies shall be destroyed no later than immediately after invocation of the completion handler.

10.13.2.7.6. Non-blocking requirements on initiating functions

[async.reqmts.async.non.blocking]

An initiating function shall not block (C++Std [defns.block]) the calling thread pending completion of the outstanding operation.

[Note: Initiating functions may still block the calling thread for other reasons. For example, an initiating function may lock a mutex in order to synchronize access to shared data. —end note]

10.13.2.7.7. Associated executor

[async.reqmts.async.assoc.exec]

Certain objects that participate in asynchronous operations have an associated executor. These are obtained as specified below.

10.13.2.7.8. I/O executor

[async.reqmts.async.io.exec]

An asynchronous operation has an associated executor satisfying the Executor requirements. If not otherwise specified by the asynchronous operation, this associated executor is an object of type system_executor.

All asynchronous operations in this Technical Specification have an associated executor object that is determined as follows:

— If the initiating function is a member function, the associated executor is that returned by the get_executor member function on the same object.

— If the initiating function is not a member function, the associated executor is that returned by the get_executor member function of the first argument to the initiating function.

Let Executor1 be the type of the associated executor. Let ex1 be a value of type Executor1, representing the associated executor object obtained as described above.

10.13.2.7.9. Completion handler executor

[async.reqmts.async.handler.exec]

A completion handler object of type CompletionHandler has an associated executor of type Executor2 satisfying the Executor requirements. The type Executor2 is associated_executor_t<CompletionHandler, Executor1>. Let ex2 be a value of type Executor2 obtained by performing get_associated_executor(completion_handler, ex1).

10.13.2.7.10. Outstanding work

[async.reqmts.async.work]

Until the asynchronous operation has completed, the asynchronous operation shall maintain:

— an object work1 of type executor_work_guard<Executor1>, initialized as work1(ex1), and where work1.owns_work() == true; and

— an object work2 of type executor_work_guard<Executor2>, initialized as work2(ex2), and where work2.owns_work() == true.

10.13.2.7.11. Allocation of intermediate storage

[async.reqmts.async.alloc]

Asynchronous operations may allocate memory. [Note: Such as a data structure to store copies of the completion_handler object and the initiating function's arguments. —end note]

Let Alloc1 be a type, satisfying the ProtoAllocator requirements, that represents the asynchronous operation's default allocation strategy. [Note: Typically std::allocator<void>. —end note] Let alloc1 be a value of type Alloc1.

A completion handler object of type CompletionHandler has an associated allocator object alloc2 of type Alloc2 satisfying the ProtoAllocator requirements. The type Alloc2 is associated_allocator_t<CompletionHandler, Alloc1>. Let alloc2 be a value of type Alloc2 obtained by performing get_associated_allocator(completion_handler, alloc1).

The asynchronous operations defined in this Technical Specification:

— If required, allocate memory using only the completion handler's associated allocator.

— Prior to completion handler execution, deallocate any memory allocated using the completion handler's associated allocator.

[Note: The implementation may perform operating system or underlying API calls that perform memory allocations not using the associated allocator. Invocations of the allocator functions may not introduce data races (See C++Std [res.on.data.races]). —end note]

10.13.2.7.12. Execution of completion handler on completion of asynchronous operation

[async.reqmts.async.completion]

Let Args... be the argument types of the completion signature Signature and let N be sizeof...(Args). Let i be in the range [0,N). Let Ti be the ith type in Args... and let ti be the ith completion handler argument associated with Ti.

Let f be a function object, callable as f(), that invokes completion_handler as if by completion_handler(forward<T0>(t0), ..., forward<TN-1>(tN-1)).

If an asynchonous operation completes immediately (that is, within the thread of execution calling the initiating function, and before the initiating function returns), the completion handler shall be submitted for execution as if by performing ex2.post(std::move(f), alloc2). Otherwise, the completion handler shall be submitted for execution as if by performing ex2.dispatch(std::move(f), alloc2).

10.13.2.7.13. Completion handlers and exceptions

[async.reqmts.async.exceptions]

Completion handlers are permitted to throw exceptions. The effect of any exception propagated from the execution of a completion handler is determined by the executor which is executing the completion handler.

10.13.3. Class template async_result

[async.async.result]

The async_result class template is a customization point for asynchronous operations. Template parameter CompletionToken specifies the model used to obtain the result of the asynchronous operation. Template parameter Signature is the call signature (C++Std [func.def]) for the completion handler type invoked on completion of the asynchronous operation. The async_result template:

— transforms a CompletionToken into a completion handler type that is based on a Signature; and

— determines the return type and return value of an asynchronous operation's initiating function.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class CompletionToken, class Signature, class = void>
  class async_result
  {
  public:
    typedef CompletionToken completion_handler_type;
    typedef void return_type;

    explicit async_result(completion_handler_type&) {}
    async_result(const async_result&) = delete;
    async_result& operator=(const async_result&) = delete;

    return_type get() {}
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The template parameter CompletionToken shall be an object type. The template parameter Signature shall be a call signature (C++Std [func.def]).

Specializations of async_result shall satisfy the Destructible requirements (C++Std [destructible]) in addition to the requirements in the table below. In this table, R is a specialization of async_result; r is a modifiable lvalue of type R; and h is a modifiable lvalue of type R::completion_handler_type.

Table 6. async_result specialization requirements

Expression

Return type

Requirement

R::completion_handler_type

A type satisfying MoveConstructible requirements (C++Std [moveconstructible]), An object of type completion_handler_type shall be a function object with call signature Signature, and completion_handler_type shall be constructible with an rvalue of type CompletionToken.

R::return_type

void; or a type satisfying MoveConstructible requirements (C++Std [moveconstructible])

R r(h);

r.get()

R::return_type

[Note: An asynchronous operation's initiating function uses the get() member function as the sole operand of a return statement. —end note]


10.13.4. Class template async_completion

[async.async.completion]

Class template async_completion is provided as a convenience, to simplify the implementation of asynchronous operations that use async_result.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class CompletionToken, class Signature>
  struct async_completion
  {
    typedef async_result<decay_t<CompletionToken>,
      Signature>::completion_handler_type
        completion_handler_type;

    explicit async_completion(CompletionToken& t);
    async_completion(const async_completion&) = delete;
    async_completion& operator=(const async_completion&) = delete;

    see below completion_handler;
    async_result<decay_t<CompletionToken>, Signature> result;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The template parameter Signature shall be a call signature (C++Std [func.def]).

explicit async_completion(CompletionToken& t);

Effects: If CompletionToken and completion_handler_type are the same type, binds completion_handler to t; otherwise, initializes completion_handler with the result of forward<CompletionToken>(t). Initializes result with completion_handler.

see below completion_handler;

Type: completion_handler_type& if CompletionToken and completion_handler_type are the same type; otherwise, completion_handler_type.

10.13.5. Class template associated_allocator

[async.assoc.alloc]

Class template associated_allocator is an associator for the ProtoAllocator type requirements, with default candidate type allocator<void> and default candidate object allocator<void>().

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class ProtoAllocator = allocator<void>>
  struct associated_allocator
  {
    typedef see below type;

    static type get(const T& t, const ProtoAllocator& a = ProtoAllocator()) noexcept;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Specializations of associated_allocator shall satisfy the requirements in the table below. In this table, X is a specialization of associated_allocator for the template parameters T and ProtoAllocator; t is a value of (possibly const) T; and a is an object of type ProtoAllocator.

Table 7. associated_allocator specialization requirements

Expression

Return type

Note

typename X::type

A type meeting the proto-allocator requirements.

X::get(t)

X::type

Shall not exit via an exception.
Equivalent to X::get(t, ProtoAllocator()).

X::get(t, a)

X::type

Shall not exit via an exception.


10.13.5.1. associated_allocator members

[async.assoc.alloc.members]

typedef see below type;

Type: If T has a nested type allocator_type, typename T::allocator_type. Otherwise ProtoAllocator.

type get(const T& t, const ProtoAllocator& a = ProtoAllocator()) noexcept;

Returns: If T has a nested type allocator_type, t.get_allocator(). Otherwise a.

10.13.6. Function get_associated_allocator

[async.assoc.alloc.get]

template<class T>
  associated_allocator_t<T> get_associated_allocator(const T& t) noexcept;

Returns: associated_allocator<T>::get(t).

template<class T, class ProtoAllocator>
  associated_allocator_t<T, ProtoAllocator>
    get_associated_allocator(const T& t, const ProtoAllocator& a) noexcept;

Returns: associated_allocator<T, ProtoAllocator>::get(t, a).

10.13.7. Class execution_context

[async.exec.ctx]

Class execution_context implements an extensible, type-safe, polymorphic set of services, indexed by service type.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class execution_context
  {
  public:
    class service;

    // construct / copy / destroy:

    execution_context();
    execution_context(const execution_context&) = delete;
    execution_context& operator=(const execution_context&) = delete;
    virtual ~execution_context();

    // execution context operations:

    void notify_fork(fork_event e);

  protected:

    // execution context protected operations:

    void shutdown() noexcept;
    void destroy() noexcept;
  };

  // service access:
  template<class Service> typename Service::key_type&
    use_service(execution_context& ctx);
  template<class Service, class... Args> Service&
    make_service(execution_context& ctx, Args&&... args);
  template<class Service> bool has_service(const execution_context& ctx) noexcept;
  class service_already_exists : public logic_error { };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Access to the services of an execution_context is via three function templates, use_service<>, make_service<> and has_service<>.

In a call to use_service<Service>(), the type argument chooses a service. If the service is not present in an execution_context, an object of type Service is created and added to the execution_context. A program can check if an execution_context implements a particular service with the function template has_service<Service>().

Service objects may be explicitly added to an execution_context using the function template make_service<Service>(). If the service is already present, make_service exits via an exception of type service_already_exists.

Once a service reference is obtained from an execution_context object by calling use_service<>, that reference remains usable until a call to destroy().

10.13.7.1. execution_context constructor

[async.exec.ctx.cons]

execution_context();

Effects: Creates an object of class execution_context which contains no services. [Note: An implementation might preload services of internal service types for its own use. —end note]

10.13.7.2. execution_context destructor

[async.exec.ctx.dtor]

~execution_context();

Effects: Destroys an object of class execution_context. Performs shutdown() followed by destroy().

10.13.7.3. execution_context operations

[async.exec.ctx.ops]

void notify_fork(fork_event e);

Effects: For each service object svc in the set:
— If e == fork_event::prepare, performs svc->notify_fork(e) in reverse order of addition to the set.
— Otherwise, performs svc->notify_fork(e) in order of addition to the set.

10.13.7.4. execution_context protected operations

[async.exec.ctx.protected]

void shutdown() noexcept;

Effects: For each service object svc in the execution_context set, in reverse order of addition to the set, performs svc->shutdown(). For each service in the set, svc->shutdown() is called only once irrespective of the number of calls to shutdown on the execution_context.

void destroy() noexcept;

Effects: Destroys each service object in the execution_context set, and removes it from the set, in reverse order of addition to the set.

10.13.7.5. execution_context globals

[async.exec.ctx.globals]

The functions use_service, make_service, and has_service do not introduce data races as a result of concurrent calls to those functions from different threads.

template<class Service> typename Service::key_type&
  use_service(execution_context& ctx);

Effects: If an object of type Service::key_type does not already exist in the execution_context set identified by ctx, creates an object of type Service, initialized as Service(ctx), and adds it to the set.

Returns: A reference to the corresponding service of ctx.

Notes: The reference returned remains valid until a call to destroy.

template<class Service, class... Args> Service&
  make_service(execution_context& ctx, Args&&... args);

Requires: A service object of type Service::key_type does not already exist in the execution_context set identified by ctx.

Effects: Creates an object of type Service, initialized as Service(ctx, forward<Args>(args)...), and adds it to the execution_context set identified by ctx.

Throws: service_already_exists if a corresponding service object of type Key is already present in the set.

Notes: The reference returned remains valid until a call to destroy.

template<class Service> bool has_service(const execution_context& ctx) noexcept;

Returns: true if an object of type Service::key_type is present in ctx, otherwise false.

10.13.8. Class execution_context::service

[async.exec.ctx.svc]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class execution_context::service
  {
  protected:
    // construct / copy / destroy:

    explicit service(execution_context& owner);
    service(const service&) = delete;
    service& operator=(const service&) = delete;
    virtual ~service();

    // service observers:

    execution_context& context() noexcept;

  private:
    // service operations:

    virtual void shutdown() noexcept = 0;
    virtual void notify_fork(fork_event e) {}

    execution_context& context_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

explicit service(execution_context& owner);

Postconditions: std::addressof(context_) == std::addressof(owner).

execution_context& context() noexcept;

Returns: context_.

10.13.9. Class template is_executor

[async.is.exec]

The class template is_executor can be used to detect executor types satisfying the Executor type requirements.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T> struct is_executor;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

T shall be a complete type.

Class template is_executor is a UnaryTypeTrait (C++Std [meta.rqmts]) with a BaseCharacteristic of true_type if the type T meets the syntactic requirements for Executor, otherwise false_type.

10.13.10. Executor argument tag

[async.executor.arg]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  struct executor_arg_t { };
  constexpr executor_arg_t executor_arg = executor_arg_t();

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The executor_arg_t struct is an empty structure type used as a unique type to disambiguate constructor and function overloading. Specifically, types may have constructors with executor_arg_t as the first argument, immediately followed by an argument of a type that satisfies the Executor requirements.

10.13.11. uses_executor

[async.uses.executor]

10.13.11.1. uses_executor trait

[async.uses.executor.trait]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Executor> struct uses_executor;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Remark: Detects whether T has a nested executor_type that is convertible from Executor. Meets the BinaryTypeTrait requirements (C++Std [meta.rqmts]). The implementation provides a definition that is derived from true_type if a type T::executor_type exists and is_convertible<Executor, T::executor_type>::value != false, otherwise it is derived from false_type. A program may specialize this template to derive from true_type for a user-defined type T that does not have a nested executor_type but nonetheless can be constructed with an executor if the first argument of a constructor has type executor_arg_t and the second argument has type Executor.

10.13.11.2. uses-executor construction

[async.uses.executor.cons]

Uses-executor construction with executor Executor refers to the construction of an object obj of type T, using constructor arguments v1, v2, ..., vN of types V1, V2, ..., VN, respectively, and an executor ex of type Executor, according to the following rules:

— if uses_executor<T, Executor>::value is true and is_constructible<T, executor_arg_t, Executor, V1, V2, ..., VN>::value is true, then obj is initialized as obj(executor_arg, ex, v1, v2, ..., vN);

— otherwise, obj is initialized as obj(v1, v2, ..., vN).

10.13.12. Class template associated_executor

[async.assoc.exec]

Class template associated_allocator is an associator for the Executor type requirements, with default candidate type system_executor and default candidate object system_executor().

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Executor = system_executor>
  struct associated_executor
  {
    typedef see below type;

    static type get(const T& t, const Executor& e = Executor()) noexcept;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Specializations of associated_executor shall satisfy the requirements in the table below. In this table, X is a specialization of associated_executor for the template parameters T and Executor; t is a value of (possibly const) T; and e is an object of type Executor.

Table 8. associated_executor specialization requirements

Expression

Return type

Note

typename X::type

A type meeting Executor requirements.

X::get(t)

X::type

Shall not exit via an exception.
Equivalent to X::get(t, Executor()).

X::get(t, e)

X::type

Shall not exit via an exception.


10.13.12.1. associated_executor members

[async.assoc.exec.members]

typedef see below type;

Type: If T has a nested type executor_type, typename T::executor_type. Otherwise Executor.

type get(const T& t, const Executor& e = Executor()) noexcept;

Returns: If T has a nested type executor_type, t.get_executor(). Otherwise e.

10.13.13. Function get_associated_executor

[async.assoc.exec.get]

template<class T>
  associated_executor_t<T> get_associated_executor(const T& t) noexcept;

Returns: associated_executor<T>::get(t).

template<class T, class Executor>
  associated_executor_t<T, Executor>
    get_associated_executor(const T& t, const Executor& ex) noexcept;

Returns: associated_executor<T, Executor>::get(t, ex).

Remarks: This function shall not participate in overload resolution unless is_executor<Executor>::value is true.

template<class T, class ExecutionContext>
  associated_executor_t<T, typename ExecutionContext::executor_type>
    get_associated_executor(const T& t, ExecutionContext& ctx) noexcept;

Returns: get_associated_executor(t, ctx.get_executor()).

Remarks: This function shall not participate in overload resolution unless is_convertible<ExecutionContext&, execution_context&>::value is true.

10.13.14. Class template executor_binder

[async.exec.binder]

executor_binder<T, Executor> binds an executor of type Executor satisfying Executor requirements to an object or function of type T.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Executor>
  class executor_binder
  {
  public:
    // types:

    typedef T target_type;
    typedef Executor executor_type;

    // construct / copy / destroy:

    executor_binder(T t, const Executor& ex);
    executor_binder(const executor_binder& other) = default;
    executor_binder(executor_binder&& other) = default;
    template<class U, class OtherExecutor>
      executor_binder(const executor_binder<U, OtherExecutor>& other);
    template<class U, class OtherExecutor>
      executor_binder(executor_binder<U, OtherExecutor>&& other);
    template<class U, class OtherExecutor>
      executor_binder(executor_arg_t, const Executor& ex,
        const executor_binder<U, OtherExecutor>& other);
    template<class U, class OtherExecutor>
      executor_binder(executor_arg_t, const Executor& ex,
        executor_binder<U, OtherExecutor>&& other);

    ~executor_binder();

    // executor binder access:

    T& get() noexcept;
    const T& get() const noexcept;
    executor_type get_executor() const noexcept;

    // executor binder invocation:

    template<class... Args>
      result_of_t<T&(Args&&...)> operator()(Args&&... args);
    template<class... Args>
      result_of_t<const T&(Args&&...)> operator()(Args&&... args) const;

  private:
    Executor ex_; // exposition only
    T target_; // exposition only
  };

  template<class T, class Executor, class Signature>
    class async_result<executor_binder<T, Executor>, Signature>;

  template<class T, class Executor, class ProtoAllocator>
    struct associated_allocator<executor_binder<T, Executor>, ProtoAllocator>;

  template<class T, class Executor, class Executor1>
    struct associated_executor<executor_binder<T, Executor>, Executor1>;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
10.13.14.1. executor_binder constructors

[async.exec.binder.cons]

executor_binder(T t, const Executor& ex);

Effects: Initializes ex_ with ex. Initializes target_ by performing uses-executor construction, using the constructor argument std::move(t) and the executor ex_.

template<class U, class OtherExecutor>
  executor_binder(const executor_binder<U, OtherExecutor>& other);

Requires: If U is not convertible to T, or if OtherExecutor is not convertible to Executor, the program is ill-formed.

Effects: Initializes ex_ with other.get_executor(). Initializes target_ by performing uses-executor construction, using the constructor argument other.get() and the executor ex_.

template<class U, class OtherExecutor>
  executor_binder(executor_binder<U, OtherExecutor>&& other);

Requires: If U is not convertible to T, or if OtherExecutor is not convertible to Executor, the program is ill-formed.

Effects: Initializes ex_ with other.get_executor(). Initializes target_ by performing uses-executor construction, using the constructor argument std::move(other.get()) and the executor ex_.

template<class U, class OtherExecutor>
  executor_binder(executor_arg_t, const Executor& ex,
    const executor_binder<U, OtherExecutor>& other);

Requires: If U is not convertible to T the program is ill-formed.

Effects: Initializes ex_ with ex. Initializes target_ by performing uses-executor construction, using the constructor argument other.get() and the executor ex_.

template<class U, class OtherExecutor>
  executor_binder(executor_arg_t, const Executor& ex,
    executor_binder<U, OtherExecutor>&& other);

Requires: U is T or convertible to T.

Effects: Initializes ex_ with ex. Initializes target_ by performing uses-executor construction, using the constructor argument std::move(other.get()) and the executor ex_.

10.13.14.2. executor_binder access

[async.exec.binder.access]

T& get() noexcept;
const T& get() const noexcept;

Returns: target_.

executor_type get_executor() const noexcept;

Returns: executor_.

10.13.14.3. executor_binder invocation

[async.exec.binder.invocation]

template<class... Args>
  result_of_t<T&(Args&&...)> operator()(Args&&... args);
template<class... Args>
  result_of_t<const T&(Args&&...)> operator()(Args&&... args) const;

Returns: INVOKE(get(), forward<Args>(args)...) (C++Std [func.require]).

10.13.14.4. Class template partial specialization async_result

[async.exec.binder.async.result]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Executor, class Signature>
  class async_result<executor_binder<T, Executor>, Signature>
  {
  public:
    typedef executor_binder<
      typename async_result<T, Signature>::completion_handler_type,
        Executor> completion_handler_type;
    typedef typename async_result<T, Signature>::return_type return_type;

    explicit async_result(completion_handler_type& h);
    async_result(const async_result&) = delete;
    async_result& operator=(const async_result&) = delete;

    return_type get();

  private:
    async_result<T, Signature> target_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

explicit async_result(completion_handler_type& h);

Effects: Initializes target_ as target_(h.get()).

return_type get();

Returns: target_.get().

10.13.14.5. Class template partial specialization associated_allocator

[async.exec.binder.assoc.alloc]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Executor, class ProtoAllocator>
    struct associated_allocator<executor_binder<T, Executor>, ProtoAllocator>
  {
    typedef associated_allocator_t<T, ProtoAllocator> type;

    static type get(const executor_binder<T, Executor>& b,
                    const ProtoAllocator& a = ProtoAllocator()) noexcept;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

static type get(const executor_binder<T, Executor>& b,
                const ProtoAllocator& a = ProtoAllocator()) noexcept;

Returns: associated_allocator<T, ProtoAllocator>::get(b.get(), a).

10.13.14.6. Class template partial specialization associated_executor

[async.exec.binder.assoc.exec]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Executor, class Executor1>
    struct associated_executor<executor_binder<T, Executor>, Executor1>
  {
    typedef Executor type;

    static type get(const executor_binder<T, Executor>& b,
                    const Executor1& e = Executor1()) noexcept;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

static type get(const executor_binder<T, Executor>& b,
                const Executor1& e = Executor1()) noexcept;

Returns: b.get_executor().

10.13.15. Function bind_executor

[async.bind.executor]

template<class Executor, class T>
  executor_binder<decay_t<T>, Executor>
    bind_executor(const Executor& ex, T&& t);

Returns: executor_binder<decay_t<T>, Executor>(forward<T>(t), ex).

Remarks: This function shall not participate in overload resolution unless is_executor<Executor>::value is true.

template<class ExecutionContext, class CompletionToken>
  executor_binder<decay_t<T>, typename ExecutionContext::executor_type>
    bind_executor(ExecutionContext& ctx, T&& t);

Returns: bind_executor(ctx.get_executor(), forward<T>(t)).

Remarks: This function shall not participate in overload resolution unless is_convertible<ExecutionContext&, execution_context&>::value is true.

10.13.16. Class template executor_work_guard

[async.exec.work.guard]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Executor>
  class executor_work_guard
  {
  public:
    // types:

    typedef Executor executor_type;

    // construct / copy / destroy:

    explicit executor_work_guard(const executor_type& ex) noexcept;
    executor_work_guard(const executor_work_guard& other) noexcept;
    executor_work_guard(executor_work_guard&& other) noexcept;

    executor_work_guard& operator=(const executor_work_guard&) = delete;

    ~executor_work_guard();

    // executor work guard observers:

    executor_type get_executor() const noexcept;
    bool owns_work() const noexcept;

    // executor work guard modifiers:

    void reset() noexcept;

  private:
    Executor ex_; // exposition only
    bool owns_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
10.13.16.1. executor_work_guard members

[async.exec.work.guard.members]

explicit executor_work_guard(const executor_type& ex) noexcept;

Effects: Initializes ex_ with ex, and then performs ex_.on_work_started().

Postconditions: ex == ex_ and owns_ == true.

executor_work_guard(const executor_work_guard& other) noexcept;

Effects: Initializes ex_ with other.ex_. If other.owns_ == true, performs ex_.on_work_started().

Postconditions: ex_ == other.ex_ and owns_ == other.owns_.

executor_work_guard(executor_work_guard&& other) noexcept;

Effects: Initializes ex_ with std::move(other.ex_) and owns_ with other.owns_, and sets other.owns_ to false.

~executor_work_guard();

Effects: If owns_ is true, performs ex_.on_work_finished().

executor_type get_executor() const noexcept;

Returns: ex_.

bool owns_work() const noexcept;

Returns: owns_.

void reset() noexcept;

Effects: If owns_ is true, performs ex_.on_work_finished().

Postconditions: owns_ == false.

10.13.17. Function make_work_guard

[async.make.work.guard]

template<class Executor>
  executor_work_guard<Executor>
    make_work_guard(const Executor& ex);

Returns: executor_work_guard<Executor>(ex).

Remarks: This function shall not participate in overload resolution unless is_executor<Executor>::value is true.

template<class ExecutionContext>
  executor_work_guard<typename ExecutionContext::executor_type>
    make_work_guard(ExecutionContext& ctx);

Returns: make_work_guard(ctx.get_executor()).

Remarks: This function shall not participate in overload resolution unless is_convertible<ExecutionContext&, execution_context&>::value is true.

template<class T>
  executor_work_guard<associated_executor_t<T>>
    make_work_guard(const T& t);

Returns: make_work_guard(get_associated_executor(t)).

Remarks: This function shall not participate in overload resolution unless is_executor<T>::value is false and is_convertible<T&, execution_context&>::value is false.

template<class T, class U>
  auto make_work_guard(const T& t, U&& u)
    -> decltype(make_work_guard(get_associated_executor(t, forward<U>(u))));

Returns: make_work_guard(get_associated_executor(t, forward<U>(u))).

10.13.18. Class system_executor

[async.system.exec]

Class system_executor represents a set of rules where function objects are permitted to execute on any thread.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class system_executor
  {
  public:
    // constructors:

    system_executor() {}

    // executor operations:

    system_context& context() noexcept;

    void on_work_started() noexcept {}
    void on_work_finished() noexcept {}

    template<class Func, class ProtoAllocator>
      void dispatch(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void post(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void defer(Func&& f, const ProtoAllocator& a);
  };

  bool operator==(const system_executor&, const system_executor&) noexcept;
  bool operator!=(const system_executor&, const system_executor&) noexcept;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Class system_executor satisfies the Destructible (C++Std [destructible]), DefaultConstructible (C++Std [defaultconstructible]), and Executor type requirements.

To satisfy the Executor requirements for the post and defer member functions, the system executor may create thread objects to run the submitted function objects. These thread objects are collectively referred to as system threads.

10.13.18.1. system_executor operations

[async.system.exec.ops]

system_context& context() noexcept;

Returns: A reference to an object with static storage duration. All calls to this function return references to the same object.

template<class Func, class ProtoAllocator>
  void dispatch(Func&& f, const ProtoAllocator& a);

Effects: Equivalent to DECAY_COPY(forward<Func>(f))() (C++Std [thread.decaycopy]).

template<class Func, class ProtoAllocator>
  void post(Func&& f, const ProtoAllocator& a);
template<class Func, class ProtoAllocator>
  void defer(Func&& f, const ProtoAllocator& a);

Effects: If context().stopped() == false, creates an object f1 initialized with DECAY_COPY(forward<Func>(f)), and calls f1 as if in a thread of execution represented by a thread object. Any exception propagated from the execution of DECAY_COPY(forward<Func>(f))() results in a call to std::terminate.

10.13.18.2. system_executor comparisons

[async.system.exec.comparisons]

bool operator==(const system_executor&, const system_executor&) noexcept;

Returns: true.

bool operator!=(const system_executor&, const system_executor&) noexcept;

Returns: false.

10.13.19. Class system_context

[async.system.context]

Class system_context implements the execution context associated with system_executor objects.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class system_context : public execution_context
  {
  public:
    // types:

    typedef system_executor executor_type;

    // construct / copy / destroy:

    system_context() = delete;
    system_context(const system_context&) = delete;
    system_context& operator=(const system_context&) = delete;
    ~system_context();

    // system_context operations:

    executor_type get_executor() noexcept;

    void stop();
    bool stopped() const noexcept;
    void join();
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The class system_context satisfies the ExecutionContext type requirements.

The system_context member functions get_executor, stop, and stopped, and the system_executor copy constructors, member functions and comparison operators, do not introduce data races as a result of concurrent calls to those functions from different threads of execution.

~system_context();

Effects: Performs stop() followed by join().

executor_type get_executor() noexcept;

Returns: system_executor().

void stop();

Effects: Signals all system threads to exit as soon as possible. If a system thread is currently executing a function object, the thread will exit only after completion of that function object. Returns without waiting for the system threads to complete.

Postconditions: stopped() == true.

bool stopped() const noexcept;

Returns: true if the system_context has been stopped by a prior call to stop.

void join();

Effects: Blocks the calling thread (C++Std [defns.block]) until all system threads have completed.

Synchronization: The completion of each system thread synchronizes with (C++Std [intro.multithread]) the corresponding successful join() return.

10.13.20. Class bad_executor

[async.bad.exec]

An exception of type bad_executor is thrown by executor member functions dispatch, post, and defer when the executor object has no target.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class bad_executor : public exception
  {
  public:
    // constructor:
    bad_executor() noexcept;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

bad_executor() noexcept;

Effects: constructs a bad_executor object.

Postconditions: what() returns an implementation-defined NTBS.

10.13.21. Class executor

[async.executor]

The executor class provides a polymorphic wrapper for types that satisfy the Executor requirements.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class executor
  {
  public:
    // construct / copy / destroy:

    executor() noexcept;
    executor(nullptr_t) noexcept;
    executor(const executor& e) noexcept;
    executor(executor&& e) noexcept;
    template<class Executor> executor(Executor e);
    template<class Executor, class ProtoAllocator>
      executor(allocator_arg_t, const ProtoAllocator& a, Executor e);

    executor& operator=(const executor& e) noexcept;
    executor& operator=(executor&& e) noexcept;
    executor& operator=(nullptr_t) noexcept;
    template<class Executor> executor& operator=(Executor e);

    ~executor();

    // executor modifiers:

    void swap(executor& other) noexcept;
    template<class Executor, class ProtoAllocator>
      void assign(Executor e, const ProtoAllocator& a);

    // executor operations:

    execution_context& context() noexcept;

    void on_work_started() noexcept;
    void on_work_finished() noexcept;

    template<class Func, class ProtoAllocator>
      void dispatch(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void post(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void defer(Func&& f, const ProtoAllocator& a);

    // executor capacity:

    explicit operator bool() const noexcept;

    // executor target access:

    const type_info& target_type() const noexcept;
    template<class Executor> Executor* target() noexcept;
    template<class Executor> const Executor* target() const noexcept;
  };

  template<> struct is_executor<executor> : true_type {};

  // executor comparisons:

  bool operator==(const executor& a, const executor& b) noexcept;
  bool operator==(const executor& e, nullptr_t) noexcept;
  bool operator==(nullptr_t, const executor& e) noexcept;
  bool operator!=(const executor& a, const executor& b) noexcept;
  bool operator!=(const executor& e, nullptr_t) noexcept;
  bool operator!=(nullptr_t, const executor& e) noexcept;

  // executor specialized algorithms:

  void swap(executor& a, executor& b) noexcept;

} // inline namespace v1
} // namespace net
} // namespace experimental

  template<class Allocator>
    struct uses_allocator<experimental::net::v1::executor, Allocator>
      : true_type {};

} // namespace std

Class executor meets the requirements of Executor, DefaultConstructible (C++Std [defaultconstructible]), and CopyAssignable (C++Std [copyassignable]).

[Note: To meet the noexcept requirements for executor copy constructors and move constructors, implementations may share a target between two or more executor objects. —end note]

The target is the executor object that is held by the wrapper.

10.13.21.1. executor constructors

[async.executor.cons]

executor() noexcept;

Postconditions: !*this.

executor(nullptr_t) noexcept;

Postconditions: !*this.

executor(const executor& e) noexcept;

Postconditions: !*this if !e; otherwise, *this targets e.target() or a copy of e.target().

executor(executor&& e) noexcept;

Effects: If !e, *this has no target; otherwise, moves e.target() or move-constructs the target of e into the target of *this, leaving e in a valid state with an unspecified value.

template<class Executor> executor(Executor e);

Effects: *this targets a copy of e initialized with std::move(e).

template<class Executor, class ProtoAllocator>
  executor(allocator_arg_t, const ProtoAllocator& a, Executor e);

Effects: *this targets a copy of e initialized with std::move(e).

A copy of the allocator argument is used to allocate memory, if necessary, for the internal data structures of the constructed executor object.

10.13.21.2. executor assignment

[async.executor.assign]

executor& operator=(const executor& e) noexcept;

Effects: executor(e).swap(*this).

Returns: *this.

executor& operator=(executor&& e) noexcept;

Effects: Replaces the target of *this with the target of e, leaving e in a valid state with an unspecified value.

Returns: *this.

executor& operator=(nullptr_t) noexcept;

Effects: executor(nullptr).swap(*this).

Returns: *this.

template<class Executor> executor& operator=(Executor e);

Effects: executor(std::move(e)).swap(*this).

Returns: *this.

10.13.21.3. executor destructor

[async.executor.dtor]

~executor();

Effects: If *this != nullptr, releases shared ownership of, or destroys, the target of *this.

10.13.21.4. executor modifiers

[async.executor.modifiers]

void swap(executor& other) noexcept;

Effects: Interchanges the targets of *this and other.

template<class Executor, class ProtoAllocator>
  void assign(Executor e, const ProtoAllocator& a);

Effects: executor(allocator_arg, a, std::move(e)).swap(*this).

10.13.21.5. executor operations

[async.executor.ops]

execution_context& context() noexcept;

Requires: *this != nullptr.

Returns: e.context(), where e is the target object of *this.

void on_work_started() noexcept;

Requires: *this != nullptr.

Effects: e.on_work_started(), where e is the target object of *this.

void on_work_finished() noexcept;

Requires: *this != nullptr.

Effects: e.on_work_finished(), where e is the target object of *this.

template<class Func, class ProtoAllocator>
  void dispatch(Func&& f, const ProtoAllocator& a);

Let e be the target object of *this. Let a1 be the allocator that was specified when the target was set. Let fd be the result of DECAY_COPY(f) (C++Std [thread.decaycopy]).

Effects: e.dispatch(g, a1), where g is a function object of unspecified type that, when called as g(), performs fd(). The allocator a is used to allocate any memory required to implement g.

template<class Func, class ProtoAllocator>
  void post(Func&& f, const ProtoAllocator& a);

Let e be the target object of *this. Let a1 be the allocator that was specified when the target was set. Let fd be the result of DECAY_COPY(f).

Effects: e.post(g, a1), where g is a function object of unspecified type that, when called as g(), performs fd(). The allocator a is used to allocate any memory required to implement g.

template<class Func, class ProtoAllocator>
  void defer(Func&& f, const ProtoAllocator& a);

Let e be the target object of *this. Let a1 be the allocator that was specified when the target was set. Let fd be the result of DECAY_COPY(f).

Effects: e.defer(g, a1), where g is a function object of unspecified type that, when called as g(), performs fd(). The allocator a is used to allocate any memory required to implement g.

10.13.21.6. executor capacity

[async.executor.capacity]

explicit operator bool() const noexcept;

Returns: true if *this has a target, otherwise false.

10.13.21.7. executor target access

[async.executor.target]

const type_info& target_type() const noexcept;

Returns: If *this has a target of type T, typeid(T); otherwise, typeid(void).

template<class Executor> Executor* target() noexcept;
template<class Executor> const Executor* target() const noexcept;

Returns: If target_type() == typeid(Executor) a pointer to the stored executor target; otherwise a null pointer value.

10.13.21.8. executor comparisons

[async.executor.comparisons]

bool operator==(const executor& a, const executor& b) noexcept;

Returns:
true if !a and !b;
true if a and b share a target;
true if e and f are the same type and e == f, where e is the target of a and f is the target of b;
— otherwise false.

bool operator==(const executor& e, nullptr_t) noexcept;
bool operator==(nullptr_t, const executor& e) noexcept;

Returns: !e.

bool operator!=(const executor& a, const executor& b) noexcept;

Returns: !(a == b).

bool operator!=(const executor& e, nullptr_t) noexcept;
bool operator!=(nullptr_t, const executor& e) noexcept;

Returns: (bool) e.

10.13.21.9. executor specialized algorithms

[async.executor.algo]

void swap(executor& a, executor& b) noexcept;

Effects: a.swap(b).

10.13.22. Function dispatch

[async.dispatch]

[Note: The function dispatch satisfies the requirements for an asynchronous operation, except for the requirement that the operation uses post if it completes immediately. —end note]

template<class CompletionToken>
  DEDUCED dispatch(CompletionToken&& token);

Completion signature: void().

Effects:
— Constructs an object completion of type async_completion<CompletionToken, void()>, initialized with token.
— Performs ex.dispatch(std::move(completion.completion_handler), alloc), where ex is the result of get_associated_executor(completion.completion_handler), and alloc is the result of get_associated_allocator(completion.completion_handler).

Returns: completion.result.get().

template<class Executor, class CompletionToken>
  DEDUCED dispatch(const Executor& ex, CompletionToken&& token);

Completion signature: void().

Effects:
— Constructs an object completion of type async_completion<CompletionToken, void()>, initialized with token.
— Constructs a function object f containing as members:
    • a copy of the completion handler h, initialized with std::move(completion.completion_handler),
    • an executor_work_guard object w for the completion handler's associated executor, initialized with make_work_guard(h),
    and where the effect of f() is:
    • w.get_executor().dispatch(std::move(h), alloc), where alloc is the result of get_associated_allocator(h), followed by
    • w.reset().
— Performs ex.dispatch(std::move(f), alloc), where alloc is the result of get_associated_allocator(completion.completion_handler) prior to the construction of f.

Returns: completion.result.get().

Remarks: This function shall not participate in overload resolution unless is_executor<Executor>::value is true.

template<class ExecutionContext, class CompletionToken>
  DEDUCED dispatch(ExecutionContext& ctx, CompletionToken&& token);

Completion signature: void().

Returns: std::experimental::net::dispatch(ctx.get_executor(), forward<CompletionToken>(token)).

Remarks: This function shall not participate in overload resolution unless is_convertible<ExecutionContext&, execution_context&>::value is true.

10.13.23. Function post

[async.post]

[Note: The function post satisfies the requirements for an asynchronous operation. —end note]

template<class CompletionToken>
  DEDUCED post(CompletionToken&& token);

Completion signature: void().

Effects:
— Constructs an object completion of type async_completion<CompletionToken, void()>, initialized with token.
— Performs ex.post(std::move(completion.completion_handler), alloc), where ex is the result of get_associated_executor(completion.completion_handler), and alloc is the result of get_associated_allocator(completion.completion_handler).

Returns: completion.result.get().

template<class Executor, class CompletionToken>
  DEDUCED post(const Executor& ex, CompletionToken&& token);

Completion signature: void().

Effects:
— Constructs an object completion of type async_completion<CompletionToken, void()>, initialized with token.
— Constructs a function object f containing as members:
    • a copy of the completion handler h, initialized with std::move(completion.completion_handler),
    • an executor_work_guard object w for the completion handler's associated executor, initialized with make_work_guard(h),
    and where the effect of f() is:
    • w.get_executor().dispatch(std::move(h), alloc), where alloc is the result of get_associated_allocator(h), followed by
    • w.reset().
— Performs ex.post(std::move(f), alloc), where alloc is the result of get_associated_allocator(completion.completion_handler) prior to the construction of f.

Returns: completion.result.get().

Remarks: This function shall not participate in overload resolution unless is_executor<Executor>::value is true.

template<class ExecutionContext, class CompletionToken>
  DEDUCED post(ExecutionContext& ctx, CompletionToken&& token);

Completion signature: void().

Returns: std::experimental::net::post(ctx.get_executor(), forward<CompletionToken>(token)).

Remarks: This function shall not participate in overload resolution unless is_convertible<ExecutionContext&, execution_context&>::value is true.

10.13.24. Function defer

[async.defer]

[Note: The function defer satisfies the requirements for an asynchronous operation, except for the requirement that the operation uses post if it completes immediately. —end note]

template<class CompletionToken>
  DEDUCED defer(CompletionToken&& token);

Completion signature: void().

Effects:
— Constructs an object completion of type async_completion<CompletionToken, void()>, initialized with token.
— Performs ex.defer(std::move(completion.completion_handler), alloc), where ex is the result of get_associated_executor(completion.completion_handler), and alloc is the result of get_associated_allocator(completion.completion_handler).

Returns: completion.result.get().

template<class Executor, class CompletionToken>
  DEDUCED defer(const Executor& ex, CompletionToken&& token);

Completion signature: void().

Effects:
— Constructs an object completion of type async_completion<CompletionToken, void()>, initialized with token.
— Constructs a function object f containing as members:
    • a copy of the completion handler h, initialized with std::move(completion.completion_handler),
    • an executor_work_guard object w for the completion handler's associated executor, initialized with make_work_guard(h),
    and where the effect of f() is:
    • w.get_executor().dispatch(std::move(h), alloc), where alloc is the result of get_associated_allocator(h), followed by
    • w.reset().
— Performs ex.defer(std::move(f), alloc), where alloc is the result of get_associated_allocator(completion.completion_handler) prior to the construction of f.

Returns: completion.result.get().

Remarks: This function shall not participate in overload resolution unless is_executor<Executor>::value is true.

template<class ExecutionContext, class CompletionToken>
  DEDUCED defer(ExecutionContext& ctx, CompletionToken&& token);

Completion signature: void().

Returns: std::experimental::net::defer(ctx.get_executor(), forward<CompletionToken>(token)).

Remarks: This function shall not participate in overload resolution unless is_convertible<ExecutionContext&, execution_context&>::value is true.

10.13.25. Class template strand

[async.strand]

The class template strand is a wrapper around an object of type Executor satisfying the Executor requirements.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Executor>
  class strand
  {
  public:
    // types:

    typedef Executor inner_executor_type;

    // construct / copy / destroy:

    strand();
    explicit strand(Executor ex);
    template<class ProtoAllocator>
      strand(allocator_arg_t, const ProtoAllocator& alloc, Executor ex);
    strand(const strand& other) noexcept;
    strand(strand&& other) noexcept;
    template<class OtherExecutor> strand(const strand<OtherExecutor>& other) noexcept;
    template<class OtherExecutor> strand(strand<OtherExecutor>&& other) noexcept;

    strand& operator=(const strand& other) noexcept;
    strand& operator=(strand&& other) noexcept;
    template<class OtherExecutor> strand& operator=(const strand<OtherExecutor>& other) noexcept;
    template<class OtherExecutor> strand& operator=(strand<OtherExecutor>&& other) noexcept;

    ~strand();

    // strand operations:

    inner_executor_type get_inner_executor() const noexcept;

    bool running_in_this_thread() const noexcept;

    execution_context& context() noexcept;

    void on_work_started() noexcept;
    void on_work_finished() noexcept;

    template<class Func, class ProtoAllocator>
      void dispatch(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void post(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void defer(Func&& f, const ProtoAllocator& a);

  private:
    Executor inner_ex_; // exposition only
  };

  bool operator==(const strand<Executor>& a, const strand<Executor>& b);
  bool operator!=(const strand<Executor>& a, const strand<Executor>& b);

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

strand<Executor> satisfies the Executor requirements.

A strand provides guarantees of ordering and non-concurrency. Given:

— strand objects s1 and s2 such that s1 == s2

— a function object f1 added to the strand s1 using post or defer, or using dispatch when s1.running_in_this_thread() == false

— a function object f2 added to the strand s2 using post or defer, or using dispatch when s2.running_in_this_thread() == false

then the implementation invokes f1 and f2 such that:

— the invocation of f1 is not concurrent with the invocation of f2

— the invocation of f1 synchronizes with the invocation of f2.

Furthermore, if the addition of f1 happens before the addition of f2, then the invocation of f1 happens before the invocation of f2.

All member functions, except for the assignment operators and the destructor, do not introduce data races on *this, including its ordered, non-concurrent state. Additionally, constructors and assignment operators do not introduce data races on lvalue arguments.

If any function f executed by the strand throws an exception, the subsequent strand state is as if f had exited without throwing an exception.

10.13.25.1. strand constructors

[async.strand.cons]

strand();

Effects: Constructs an object of class strand<Executor> that represents a unique ordered, non-concurrent state. Initializes inner_ex_ with inner_ex_().

Remarks: This overload shall not participate in overload resolution unless Executor satisfies the DefaultConstructible requirements (C++Std [defaultconstructible]).

explicit strand(Executor ex);

Effects: Constructs an object of class strand<Executor> that represents a unique ordered, non-concurrent state. Initializes inner_ex_ as inner_ex_(ex).

template<class ProtoAllocator>
  strand(allocator_arg_t, const ProtoAllocator& a, Executor ex);

Effects: Constructs an object of class strand<Executor> that represents a unique ordered, non-concurrent state. Initializes inner_ex_ as inner_ex_(ex). A copy of the allocator argument a is used to allocate memory, if necessary, for the internal data structures of the constructed strand object.

strand(const strand& other) noexcept;

Effects: Initializes inner_ex_ as inner_ex_(other.inner_ex_).

Postconditions:
*this == other
get_inner_executor() == other.get_inner_executor()

strand(strand&& other) noexcept;

Effects: Initializes inner_ex_ with inner_ex_(std::move(other.inner_ex_)).

Postconditions:
*this is equal to the prior value of other
get_inner_executor() == other.get_inner_executor()

template<class OtherExecutor> strand(const strand<OtherExecutor>& other) noexcept;

Requires: OtherExecutor is convertible to Executor.

Effects: Initializes inner_ex_ with inner_ex_(other.inner_ex_).

Postconditions: *this == other.

template<class OtherExecutor> strand(strand<OtherExecutor>&& other) noexcept;

Requires: OtherExecutor is convertible to Executor.

Effects: Initializes inner_ex_ with inner_ex_(std::move(other.inner_ex_)).

Postconditions: *this is equal to the prior value of other.

10.13.25.2. strand assignment

[async.strand.assign]

strand& operator=(const strand& other) noexcept;

Requires: Executor is CopyAssignable (C++Std [copyassignable]).

Postconditions:
*this == other
get_inner_executor() == other.get_inner_executor()

Returns: *this.

strand& operator=(strand&& other) noexcept;

Requires: Executor is MoveAssignable (C++Std [moveassignable]).

Postconditions:
*this is equal to the prior value of other
get_inner_executor() == other.get_inner_executor()

Returns: *this.

template<class OtherExecutor> strand& operator=(const strand<OtherExecutor>& other) noexcept;

Requires: OtherExecutor is convertible to Executor. Executor is CopyAssignable (C++Std [copyassignable]).

Effects: Assigns other.inner_ex_ to inner_ex_.

Postconditions: *this == other.

Returns: *this.

template<class OtherExecutor> strand& operator=(strand<OtherExecutor>&& other) noexcept;

Requires: OtherExecutor is convertible to Executor. Executor is MoveAssignable (C++Std [moveassignable]).

Effects: Assigns std::move(other.inner_ex_) to inner_ex_.

Postconditions: *this is equal to the prior value of other.

Returns: *this.

10.13.25.3. strand destructor

[async.strand.dtor]

~strand();

Effects: Destroys an object of class strand<Executor>. After this destructor completes, objects that were added to the strand but have not yet been executed will be executed in a way that meets the guarantees of ordering and non-concurrency.

10.13.25.4. strand operations

[async.strand.ops]

inner_executor_type get_inner_executor() const noexcept;

Returns: inner_ex_.

bool running_in_this_thread() const noexcept;

Returns: true if the current thread of execution is running a function that was submitted to the strand, or to any other strand object s such that s == *this, using dispatch, post or defer; otherwise false. [Note: That is, the current thread of execution's call chain includes a function that was submitted to the strand. —end note]

execution_context& context() noexcept;

Returns: inner_ex_.context().

void on_work_started() noexcept;

Effects: Calls inner_ex_.on_work_started().

void on_work_finished() noexcept;

Effects: Calls inner_ex_.on_work_finished().

template<class Func, class ProtoAllocator>
  void dispatch(Func&& f, const ProtoAllocator& a);

Effects: If running_in_this_thread() == true, calls DECAY_COPY(forward<Func>(f))() (C++Std [thread.decaycopy]). [Note: If f exits via an exception, the exception propagates to the caller of dispatch(). —end note] Otherwise, requests invocation of f, as if by forwarding the function object f and allocator a to the executor inner_ex_, such that the guarantees of ordering and non-concurrency are met.

template<class Func, class ProtoAllocator>
  void post(Func&& f, const ProtoAllocator& a);

Effects: Requests invocation of f, as if by forwarding the function object f and allocator a to the executor inner_ex_, such that the guarantees of ordering and non-concurrency are met.

template<class Func, class ProtoAllocator>
  void defer(Func&& f, const ProtoAllocator& a);

Effects: Requests invocation of f, as if by forwarding the function object f and allocator a to the executor inner_ex_, such that the guarantees of ordering and non-concurrency are met.

10.13.25.5. strand comparisons

[async.strand.comparisons]

bool operator==(const strand<Executor>& a, const strand<Executor>& b);

Returns: true, if the strand objects share the same ordered, non-concurrent state; otherwise false.

bool operator!=(const strand<Executor>& a, const strand<Executor>& b);

Returns: !(a == b).

10.13.26. Class template use_future_t

[async.use.future]

The class template use_future_t defines a set of types that, when passed as a completion token to an asynchronous operation's initiating function, cause the result of the asynchronous operation to be delivered via a future (C++Std [futures.unique_future]).

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class ProtoAllocator = allocator<void>>
  class use_future_t
  {
  public:
    // use_future_t types:
    typedef ProtoAllocator allocator_type;

    // use_future_t members:
    constexpr use_future_t() noexcept(noexcept(allocator_type()));
    explicit use_future_t(const allocator_type& a) noexcept;
    template<class OtherProtoAllocator> use_future_t<OtherProtoAllocator>
      rebind(const OtherProtoAllocator& a) const noexcept;
    allocator_type get_allocator() const noexcept;
    template <class F> unspecified operator()(F&& f) const;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
10.13.26.1. use_future_t constructors

[async.use.future.cons]

constexpr use_future_t() noexcept(noexcept(allocator_type()));

Effects: Constructs a use_future_t with a default-constructed allocator.

explicit use_future_t(const allocator_type& a) noexcept;

Postconditions: get_allocator() == a.

10.13.26.2. use_future_t members

[async.use.future.members]

template<class OtherProtoAllocator> use_future_t<OtherProtoAllocator>
  rebind(const OtherProtoAllocator& a) const noexcept;

Returns: A use_future_t object where get_allocator() == a.

allocator_type get_allocator() const noexcept;

Returns: The associated allocator object.

template <class F> unspecified operator()(F&& f) const;

Let T be a completion token type. Let H be a completion handler type and let h be an object of type H. Let FD be the type decay_t<F> and let fd be an lvalue of type FD constructed with forward<F>(f). Let R(Args...) be the completion signature of an asynchronous operation using H and let N be sizeof...(Args). Let i be in the range [0,N) and let Ai be the ith type in Args. Let ai be the argument associated with Ai.

Returns: A completion token t of type T.

Remarks: The return type T satisfies the Destructible (C++Std [destructible]) and MoveConstructible (C++Std [moveconstructible]) requirements.

The object h of type H is an asynchronous provider with an associated shared state (C++Std [futures.state]). The effect of h(a0, ..., aN-1) is to atomically store the result of INVOKE(fd, forward<A0>(a0), ..., forward<AN-1>(aN-1)) (C++Std [func.require]) in the shared state and make the shared state ready. If fd exits via an exception then that exception is atomically stored in the shared state and the shared state is made ready.

The implementation provides a partial specialization template <class Result, class... Args> async_result<T, Result(Args...)> such that:
— the nested typedef completion_handler_type is a type H;
— the nested typedef return_type is future<result_of_t<FD(decay_t<Args>...)>>; and
— when an object r1 of type async_result<T, Result(Args...)> is constructed from h, the expression r1.get() returns a future with the same shared state as h.

For any executor type E, the associated object for the associator associated_executor<H, E> is an executor where, for function objects executed using the executor's dispatch(), post() or defer() functions, any exception thrown is caught by a function object and stored in the associated shared state.

10.13.26.3. Partial class template specialization async_result for use_future_t

[async.use.future.result]

template<class ProtoAllocator, class Result, class... Args>
class async_result<use_future_t<ProtoAllocator>, Result(Args...)>
{
  typedef see below completion_handler_type;
  typedef see below return_type;

  explicit async_result(completion_handler_type& h);
  async_result(const async_result&) = delete;
  async_result& operator=(const async_result&) = delete;

  return_type get();
};

Let R be the type async_result<use_future_t<ProtoAllocator>, Result(Args...)>. Let F be the nested function object type R::completion_handler_type.

An object t1 of type F is an asynchronous provider with an associated shared state (C++Std [futures.state]). The type F provides F::operator() such that the expression t1(declval<Args>()...) is well formed.

The implementation specializes associated_executor for F. For function objects executed using the associated executor's dispatch(), post() or defer() functions, any exception thrown is caught by the executor and stored in the associated shared state.

For any executor type E, the associated object for the associator associated_executor<F, E> is an executor where, for function objects executed using the executor's dispatch(), post() or defer() functions, any exception thrown by a function object is caught by the executor and stored in the associated shared state.

When an object r1 of type R is constructed from t1, the expression r1.get() returns a future with the same shared state as t1.

The type of R::return_type and the effects of F::operator() are defined in the table below. After establishing these effects, F::operator() makes the shared state ready. In this table, N is the value of sizeof...(Args); let i be in the range [0,N) and let Ti be the ith type in Args; let Ui be decay_t<Ti> for each type Ti in Args; let Ai be the deduced type of the ith argument to F::operator(); and let ai be the ith argument to F::operator().

Table 9. async_result<use_future_t<ProtoAllocator>, Result(Args...)> semantics

N

U0

R::return_type

F::operator() effects

0

future<void>

None.

1

error_code

future<void>

If a0 evaluates to true, atomically stores the exception pointer produced by make_exception_ptr(system_error(a0)) in the shared state.

1

exception_ptr

future<void>

If a0 is non-null, atomically stores the exception pointer a0 in the shared state.

1

all other types

future<U0>

Atomically stores forward<A0>(a0) in the shared state.

2

error_code

future<U1>

If a0 evaluates to true, atomically stores the exception pointer produced by make_exception_ptr(system_error(a0)) in the shared state; otherwise, atomically stores forward<A1>(a1) in the shared state.

2

exception_ptr

future<U1>

If a0 is non-null, atomically stores the exception pointer in the shared state; otherwise, atomically stores forward<A1>(a1) in the shared state.

2

all other types

future<tuple<U0,U1>>

Atomically stores forward_as_tuple(forward<A0>(a0),forward<A1>(a1)) in the shared state.

>2

error_code

future<tuple<U1,...,UN-1>>

If a0 evaluates to true, atomically stores the exception pointer produced by make_exception_ptr(system_error(a0)) in the shared state; otherwise, atomically stores forward_as_tuple(forward<A1>(a1),...,forward<AN-1>(aN-1)) in the shared state.

>2

exception_ptr

future<tuple<U1,...,UN-1>>

If a0 is non-null, atomically stores the exception pointer in the shared state; otherwise, atomically stores forward_as_tuple(forward<A1>(a1),...,forward<AN-1>(aN-1)) in the shared state.

>2

all other types

future<tuple<U0,...,UN-1>>

Atomically stores forward_as_tuple(forward<A0>(a0),...,forward<AN-1>(aN-1)) in the shared state.


10.13.27. Partial class template specialization async_result for packaged_task

[async.packaged.task.specializations]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Result, class... Args, class Signature>
  class async_result<packaged_task<Result(Args...)>, Signature>
  {
  public:
    typedef packaged_task<Result(Args...)> completion_handler_type;
    typedef future<Result> return_type;

    explicit async_result(completion_handler_type& h);
    async_result(const async_result&) = delete;
    async_result& operator=(const async_result&) = delete;

    return_type get();

  private:
    return_type future_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

explicit async_result(completion_handler_type& h);

Effects: Initializes future_ with h.get_future().

return_type get();

Returns: std::move(future_).

10.14. Basic I/O services

[io_context]

10.14.1. Header <experimental/io_context> synopsis

[io_context.synop]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class io_context;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

10.14.2. Class io_context

[io_context.io_context]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class io_context : public execution_context
  {
  public:
    // types:

    class executor_type;
    typedef implementation defined count_type;

    // construct / copy / destroy:

    io_context();
    explicit io_context(int concurrency_hint);
    io_context(const io_context&) = delete;
    io_context& operator=(const io_context&) = delete;

    // io_context operations:

    executor_type get_executor() noexcept;

    count_type run();
    template<class Rep, class Period>
      count_type run_for(const chrono::duration<Rep, Period>& rel_time);
    template<class Clock, class Duration>
      count_type run_until(const chrono::time_point<Clock, Duration>& abs_time);

    count_type run_one();
    template<class Rep, class Period>
      count_type run_one_for(const chrono::duration<Rep, Period>& rel_time);
    template<class Clock, class Duration>
      count_type run_one_until(const chrono::time_point<Clock, Duration>& abs_time);

    count_type poll();

    count_type poll_one();

    void stop();

    bool stopped() const noexcept;

    void restart();
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The class io_context satisfies the ExecutionContext type requirements.

count_type is an implementation-defined unsigned integral type of at least 32 bits.

The io_context member functions run, run_for, run_until, run_one, run_one_for, run_one_until, poll, and poll_one are collectively referred to as the run functions. The run functions must be called for the io_context to perform asynchronous operations on behalf of a C++ program. Notification that an asynchronous operation has completed is delivered by execution of the associated completion handler function object, as determined by the requirements for asynchronous operations.

For an object of type io_context, outstanding work is defined as the sum of:

— the total number of calls to the on_work_started function, less the total number of calls to the on_work_finished function, to any executor of the io_context.

— the number of function objects that have been added to the io_context via any executor of the io_context, but not yet executed; and

— the number of function objects that are currently being executed by the io_context.

If at any time the outstanding work falls to 0, the io_context is stopped as if by stop().

The io_context member functions get_executor, stop, and stopped, the run functions, and the io_context::executor_type copy constructors, member functions and comparison operators, do not introduce data races as a result of concurrent calls to those functions from different threads of execution. [Note: The restart member function is excluded from these thread safety requirements. —end note]

10.14.2.1. io_context members

[io_context.io_context.members]

io_context();
explicit io_context(int concurrency_hint);

Effects: Creates an object of class io_context.

Remarks: The concurrency_hint parameter is a suggestion to the implementation on the number of threads that should process asynchronous operations and execute function objects.

executor_type get_executor() noexcept;

Returns: An executor that may be used for submitting function objects to the io_context.

count_type run();

Requires: Must not be called from a thread that is currently calling a run function.

Effects: Equivalent to:

count_type n = 0;
while (run_one())
  if (n != numeric_limits<count_type>::max())
    ++n;

Returns: n.

template<class Rep, class Period>
  count_type run_for(const chrono::duration<Rep, Period>& rel_time);

Effects: Equivalent to:

return run_until(chrono::steady_clock::now() + rel_time);

template<class Clock, class Duration>
  count_type run_until(const chrono::time_point<Clock, Duration>& abs_time);

Effects: Equivalent to:

count_type n = 0;
while (run_one_until(abs_time))
  if (n != numeric_limits<count_type>::max())
    ++n;

Returns: n.

count_type run_one();

Requires: Must not be called from a thread that is currently calling a run function.

Effects: If the io_context object has no outstanding work, performs stop(). Otherwise, blocks while the io_context has outstanding work, or until the io_context is stopped, or until one function object has been executed.

If an executed function object throws an exception, the exception propagates to the caller of run_one(). The io_context state is as if the function object had returned normally.

Returns: 1 if a function object was executed, otherwise 0.

Notes: This function may invoke additional function objects through nested calls to the io_context executor's dispatch member function. These do not count towards the return value.

template<class Rep, class Period>
  count_type run_one_for(const chrono::duration<Rep, Period>& rel_time);

Effects: Equivalent to:

return run_one_until(chrono::steady_clock::now() + rel_time);

template<class Clock, class Duration>
  count_type run_one_until(const chrono::time_point<Clock, Duration>& abs_time);

Effects: If the io_context object has no outstanding work, performs stop(). Otherwise, blocks while the io_context has outstanding work, or until the expiration of the absolute timeout (C++Std [thread.req.timing]) specified by abs_time, or until the io_context is stopped, or until one function object has been executed.

If an executed function object throws an exception, the exception propagates to the caller of run_one(). The io_context state is as if the function object had returned normally.

Returns: 1 if a function object was executed, otherwise 0.

Notes: This function may invoke additional function objects through nested calls to the io_context executor's dispatch member function. These do not count towards the return value.

count_type poll();

Effects: Equivalent to:

count_type n = 0;
while (poll_one())
  if (n != numeric_limits<count_type>::max())
    ++n;

Returns: n.

count_type poll_one();

Effects: If the io_context object has no outstanding work, performs stop(). Otherwise, if there is a function object ready for immediate execution, executes it.

If an executed function object throws an exception, the exception propagates to the caller of poll_one(). The io_context state is as if the function object had returned normally.

Returns: 1 if a function object was invoked, otherwise 0.

Notes: This function may invoke additional function objects through nested calls to the io_context executor's dispatch member function. These do not count towards the return value.

void stop();

Effects: Stops the io_context. Concurrent calls to any run function will end as soon as possible. If a call to a run function is currently executing a function object, the call will end only after completion of that function object. The call to stop() returns without waiting for concurrent calls to run functions to complete.

Postconditions: stopped() == true.

[Note: When stopped() == true, subsequent calls to a run function will exit immediately with a return value of 0, without executing any function objects. An io_context remains in the stopped state until a call to restart(). —end note]

bool stopped() const noexcept;

Returns: true if the io_context is stopped.

void restart();

Postconditions: stopped() == false.

10.14.3. Class io_context::executor_type

[io_context.exec]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class io_context::executor_type
  {
  public:
    // construct / copy / destroy:

    executor_type(const executor_type& other) noexcept;
    executor_type(executor_type&& other) noexcept;

    executor_type& operator=(const executor_type& other) noexcept;
    executor_type& operator=(executor_type&& other) noexcept;

    // executor operations:

    bool running_in_this_thread() const noexcept;

    io_context& context() noexcept;

    void on_work_started() noexcept;
    void on_work_finished() noexcept;

    template<class Func, class ProtoAllocator>
      void dispatch(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void post(Func&& f, const ProtoAllocator& a);
    template<class Func, class ProtoAllocator>
      void defer(Func&& f, const ProtoAllocator& a);
  };

  bool operator==(const io_context::executor_type& a,
                  const io_context::executor_type& b) noexcept;
  bool operator!=(const io_context::executor_type& a,
                  const io_context::executor_type& b) noexcept;

  template<> struct is_executor<io_context::executor_type> : true_type {};

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

io_context::executor_type is a type satisfying Executor requirements. Objects of type io_context::executor_type are associated with an io_context, and function objects submitted using the dispatch, post, or defer member functions will be executed by the io_context from within a run function.]

10.14.3.1. io_context::executor_type constructors

[io_context.exec.cons]

executor_type(const executor_type& other) noexcept;

Postconditions: *this == other.

executor_type(executor_type&& other) noexcept;

Postconditions: *this is equal to the prior value of other.

10.14.3.2. io_context::executor_type assignment

[io_context.exec.assign]

executor_type& operator=(const executor_type& other) noexcept;

Postconditions: *this == other.

Returns: *this.

executor_type& operator=(executor_type&& other) noexcept;

Postconditions: *this is equal to the prior value of other.

Returns: *this.

10.14.3.3. io_context::executor_type operations

[io_context.exec.ops]

bool running_in_this_thread() const noexcept;

Returns: true if the current thread of execution is calling a run function of the associated io_context object. [Note: That is, the current thread of execution's call chain includes a run function. —end note]

io_context& context() noexcept;

Returns: A reference to the associated io_context object.

void on_work_started() noexcept;

Effects: Increment the count of outstanding work associated with the io_context.

void on_work_finished() noexcept;

Effects: Decrement the count of outstanding work associated with the io_context.

template<class Func, class ProtoAllocator>
  void dispatch(Func&& f, const ProtoAllocator& a);

Effects: If running_in_this_thread() is true, calls DECAY_COPY(forward<Func>(f))() (C++Std [thread.decaycopy]). [Note: If f exits via an exception, the exception propagates to the caller of dispatch(). —end note] Otherwise, calls post(forward<Func>(f), a).

template<class Func, class ProtoAllocator>
  void post(Func&& f, const ProtoAllocator& a);

Effects: Adds f to the io_context.

template<class Func, class ProtoAllocator>
  void defer(Func&& f, const ProtoAllocator& a);

Effects: Adds f to the io_context.

10.14.3.4. io_context::executor_type comparisons

[io_context.exec.comparisons]

bool operator==(const io_context::executor_type& a,
                const io_context::executor_type& b) noexcept;

Returns: addressof(a.context()) == addressof(b.context()).

bool operator!=(const io_context::executor_type& a,
                const io_context::executor_type& b) noexcept;

Returns: !(a == b).

10.15. Timers

[timer] This clause defines components for performing timer operations.

[Example: Performing a synchronous wait operation on a timer:

io_context c;
steady_timer t(c);
t.expires_after(seconds(5));
t.wait();

end example]

[Example: Performing an asynchronous wait operation on a timer:

void handler(error_code ec) { ... }
...
io_context c;
steady_timer t(c);
t.expires_after(seconds(5));
t.async_wait(handler);
c.run();

end example]

10.15.1. Header <experimental/timer> synopsis

[timer.synop]

#include <chrono>

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Clock> struct wait_traits;

  template<class Clock, class WaitTraits = wait_traits<Clock>>
    class basic_waitable_timer;

  typedef basic_waitable_timer<chrono::system_clock> system_timer;
  typedef basic_waitable_timer<chrono::steady_clock> steady_timer;
  typedef basic_waitable_timer<chrono::high_resolution_clock> high_resolution_timer;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

10.15.2. Requirements

[timer.reqmts]

10.15.2.1. Wait traits requirements

[timer.reqmts.waittraits]

The basic_waitable_timer template uses wait traits to allow programs to customize wait and async_wait behavior. [Note: Possible uses of wait traits include:
— To enable timers based on non-realtime clocks.
— Determining how quickly wallclock-based timers respond to system time changes.
— Correcting for errors or rounding timeouts to boundaries.
— Preventing duration overflow. That is, a program may set a timer's expiry e to be Clock::max() (meaning never reached) or Clock::min() (meaning always in the past). As a result, computing the duration until timer expiry as e - Clock::now() may cause overflow. —end note]

For a type Clock meeting the Clock requirements (C++Std [time.clock.req]), a type X meets the WaitTraits requirements if it satisfies the requirements listed below.

In the table below, t denotes a (possibly const) value of type Clock::time_point; and d denotes a (possibly const) value of type Clock::duration.

Table 10. WaitTraits requirements

expression

return type

assertion/note
pre/post-condition

X::to_wait_duration(d)

Clock::duration

Returns a Clock::duration value to be used in a wait or async_wait operation. [Note: The return value is typically representative of the duration d. —end note]

X::to_wait_duration(t)

Clock::duration

Returns a Clock::duration value to be used in a wait or async_wait operation. [Note: The return value is typically representative of the duration from Clock::now() until the time point t. —end note]


10.15.3. Class template wait_traits

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Clock>
  struct wait_traits
  {
    static typename Clock::duration to_wait_duration(
      const typename Clock::duration& d);

    static typename Clock::duration to_wait_duration(
      const typename Clock::time_point& t);
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Class template wait_traits satisfies the WaitTraits type requirements. Template argument Clock is a type meeting the Clock requirements (C++Std [time.clock.req]).

static typename Clock::duration to_wait_duration(
  const typename Clock::duration& d);

Returns: d.

static typename Clock::duration to_wait_duration(
  const typename Clock::time_point& t);

Returns: Let now be Clock::now(). If now + Clock::duration::max() is before t, Clock::duration::max(); if now + Clock::duration::min() is after t, Clock::duration::min(); otherwise, t - now.

10.15.4. Class template basic_waitable_timer

[timer.waitable]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Clock, class WaitTraits = wait_traits<Clock>>
  class basic_waitable_timer
  {
  public:
    // types:

    typedef io_context::executor_type executor_type;
    typedef Clock clock_type;
    typedef typename clock_type::duration duration;
    typedef typename clock_type::time_point time_point;
    typedef WaitTraits traits_type;

    // construct / copy / destroy:

    explicit basic_waitable_timer(io_context& ctx);
    basic_waitable_timer(io_context& ctx, const time_point& t);
    basic_waitable_timer(io_context& ctx, const duration& d);
    basic_waitable_timer(const basic_waitable_timer&) = delete;
    basic_waitable_timer(basic_waitable_timer&& rhs);

    ~basic_waitable_timer();

    basic_waitable_timer& operator=(const basic_waitable_timer&) = delete;
    basic_waitable_timer& operator=(basic_waitable_timer&& rhs);

    // basic_waitable_timer operations:

    executor_type get_executor() noexcept;

    size_t cancel();
    size_t cancel_one();

    time_point expiry() const;
    size_t expires_at(const time_point& t);
    size_t expires_after(const duration& d);

    void wait();
    void wait(error_code& ec);

    template<class CompletionToken>
      DEDUCED async_wait(CompletionToken&& token);
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_waitable_timer meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), and MoveAssignable (C++Std [moveassignable]).

10.15.4.1. basic_waitable_timer constructors

[timer.waitable.cons]

explicit basic_waitable_timer(io_context& ctx);

Effects: Equivalent to basic_waitable_timer(ctx, time_point()).

basic_waitable_timer(io_context& ctx, const time_point& t);

Postconditions:
get_executor() == ctx.get_executor().
expiry() == t.

basic_waitable_timer(io_context& ctx, const duration& d);

Effects: Sets the expiry time as if by calling expires_after(d).

Postconditions: get_executor() == ctx.get_executor().

basic_waitable_timer(basic_waitable_timer&& rhs);

Effects: Move constructs an object of class basic_waitable_timer<Clock, WaitTraits> that refers to the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
expiry() returns the same value as rhs.expiry() prior to the constructor invocation.
rhs.expiry() == time_point().

10.15.4.2. basic_waitable_timer destructor

[timer.waitable.dtor]

~basic_waitable_timer();

Effects: Destroys the timer, cancelling any asynchronous wait operations associated with the timer as if by calling cancel().

10.15.4.3. basic_waitable_timer assignment

[timer.waitable.assign]

basic_waitable_timer& operator=(basic_waitable_timer&& rhs);

Effects: Cancels any outstanding asynchronous operations associated with *this as if by calling cancel(), then moves into *this the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
expiry() returns the same value as rhs.expiry() prior to the assignment.
rhs.expiry() == time_point().

Returns: *this.

10.15.4.4. basic_waitable_timer operations

[timer.waitable.ops]

executor_type get_executor() noexcept;

Returns: The associated executor.

size_t cancel();

Effects: Causes any outstanding asynchronous wait operations to complete. Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Returns: The number of operations that were canceled.

Remarks: Does not block (C++Std [defns.block]) the calling thread pending completion of the canceled operations.

size_t cancel_one();

Effects: Causes the outstanding asynchronous wait operation that was initiated first, if any, to complete as soon as possible. The completion handler for the canceled operation is passed an error code ec such that ec == errc::operation_canceled yields true.

Returns: 1 if an operation was cancelled, otherwise 0.

Remarks: Does not block (C++Std [defns.block]) the calling thread pending completion of the canceled operation.

time_point expiry() const;

Returns: The expiry time associated with the timer, as previously set using expires_at() or expires_after().

size_t expires_at(const time_point& t);

Effects: Cancels outstanding asynchronous wait operations, as if by calling cancel(). Sets the expiry time associated with the timer.

Returns: The number of operations that were canceled.

Postconditions: expiry() == t.

size_t expires_after(const duration& d);

Returns: expires_at(clock_type::now() + d).

void wait();
void wait(error_code& ec);

Effects: Establishes the postcondition as if by repeatedly blocking the calling thread (C++Std [defns.block]) for the relative time produced by WaitTraits::to_wait_duration(expiry()).

Postconditions: ec || expiry() <= clock_type::now().

template<class CompletionToken>
  DEDUCED async_wait(CompletionToken&& token);

Completion signature: void(error_code ec).

Effects: Initiates an asynchronous wait operation to repeatedly wait for the relative time produced by WaitTraits::to_wait_duration(e), where e is a value of type time_point such that e <= expiry(). The completion handler is submitted for execution only when the condition ec || expiry() <= clock_type::now() yields true.

[Note: To implement async_wait, an io_context object ctx may maintain a priority queue for each specialization of basic_waitable_timer<Clock, WaitTraits> for which a timer object was initialized with ctx. Only the time point e of the earliest outstanding expiry need be passed to WaitTraits::to_wait_duration(e). —end note]

10.16. Buffers

[buffer]

10.16.1. Header <experimental/buffer> synopsis

[buffer.synop]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  enum class stream_errc {
    eof = an implementation defined non-zero value,
    not_found = an implementation defined non-zero value
  };

  const error_category& stream_category() noexcept;

  error_code make_error_code(stream_errc e) noexcept;
  error_condition make_error_condition(stream_errc e) noexcept;

  class mutable_buffer;
  class const_buffer;

  // buffer type traits:

  template<class T> is_mutable_buffer_sequence;
  template<class T> is_const_buffer_sequence;
  template<class T> is_dynamic_buffer;

  // buffer sequence access:

  const mutable_buffer* buffer_sequence_begin(const mutable_buffer& b);
  const const_buffer* buffer_sequence_begin(const const_buffer& b);
  const mutable_buffer* buffer_sequence_end(const mutable_buffer& b);
  const const_buffer* buffer_sequence_end(const const_buffer& b);
  template <class C> auto buffer_sequence_begin(C& c) -> decltype(c.begin());
  template <class C> auto buffer_sequence_begin(const C& c) -> decltype(c.begin());
  template <class C> auto buffer_sequence_end(C& c) -> decltype(c.end());
  template <class C> auto buffer_sequence_end(const C& c) -> decltype(c.end());

  // buffer size:

  template<class ConstBufferSequence>
    size_t buffer_size(const ConstBufferSequence& buffers) noexcept;

  // buffer copy:

  template<class MutableBufferSequence, class ConstBufferSequence>
    size_t buffer_copy(const MutableBufferSequence& dest,
                       const ConstBufferSequence& source) noexcept;
  template<class MutableBufferSequence, class ConstBufferSequence>
    size_t buffer_copy(const MutableBufferSequence& dest,
                       const ConstBufferSequence& source,
                       size_t max_size) noexcept;

  // buffer arithmetic:

  mutable_buffer operator+(const mutable_buffer& b, size_t n) noexcept;
  mutable_buffer operator+(size_t n, const mutable_buffer& b) noexcept;
  const_buffer operator+(const const_buffer&, size_t n) noexcept;
  const_buffer operator+(size_t, const const_buffer&) noexcept;

  // buffer creation:

  mutable_buffer buffer(void* p, size_t n) noexcept;
  const_buffer buffer(const void* p, size_t n) noexcept;

  mutable_buffer buffer(const mutable_buffer& b) noexcept;
  mutable_buffer buffer(const mutable_buffer& b, size_t n) noexcept;
  const_buffer buffer(const const_buffer& b) noexcept;
  const_buffer buffer(const const_buffer& b, size_t n) noexcept;

  template<class T, size_t N>
    mutable_buffer buffer(T (&data)[N]) noexcept;
  template<class T, size_t N>
    const_buffer buffer(const T (&data)[N]) noexcept;
  template<class T, size_t N>
    mutable_buffer buffer(array<T, N>& data) noexcept;
  template<class T, size_t N>
    const_buffer buffer(array<const T, N>& data) noexcept;
  template<class T, size_t N>
    const_buffer buffer(const array<T, N>& data) noexcept;
  template<class T, class Allocator>
    mutable_buffer buffer(vector<T, Allocator>& data) noexcept;
  template<class T, class Allocator>
    const_buffer buffer(const vector<T, Allocator>& data) noexcept;
  template<class CharT, class Traits, class Allocator>
    mutable_buffer buffer(basic_string<CharT, Traits, Allocator>& data) noexcept;
  template<class CharT, class Traits, class Allocator>
    const_buffer buffer(const basic_string<CharT, Traits, Allocator>& data) noexcept;
  template<class CharT, class Traits>
    const_buffer buffer(basic_string_view<CharT, Traits> data) noexcept;

  template<class T, size_t N>
    mutable_buffer buffer(T (&data)[N], size_t n) noexcept;
  template<class T, size_t N>
    const_buffer buffer(const T (&data)[N], size_t n) noexcept;
  template<class T, size_t N>
    mutable_buffer buffer(array<T, N>& data, size_t n) noexcept;
  template<class T, size_t N>
    const_buffer buffer(array<const T, N>& data, size_t n) noexcept;
  template<class T, size_t N>
    const_buffer buffer(const array<T, N>& data, size_t n) noexcept;
  template<class T, class Allocator>
    mutable_buffer buffer(vector<T, Allocator>& data, size_t n) noexcept;
  template<class T, class Allocator>
    const_buffer buffer(const vector<T, Allocator>& data, size_t n) noexcept;
  template<class CharT, class Traits, class Allocator>
    mutable_buffer buffer(basic_string<CharT, Traits, Allocator>& data,
                          size_t n) noexcept;
  template<class CharT, class Traits, class Allocator>
    const_buffer buffer(const basic_string<CharT, Traits, Allocator>& data,
                        size_t n) noexcept;
  template<class CharT, class Traits>
    const_buffer buffer(basic_string_view<CharT, Traits> data,
                        size_t n) noexcept;

  template<class T, class Allocator>
    class dynamic_vector_buffer;

  template<class CharT, class Traits, class Allocator>
    class dynamic_string_buffer;

  // dynamic buffer creation:

  template<class T, class Allocator>
    dynamic_vector_buffer<T, Allocator>
      dynamic_buffer(vector<T, Allocator>& vec) noexcept;
  template<class T, class Allocator>
    dynamic_vector_buffer<T, Allocator>
      dynamic_buffer(vector<T, Allocator>& vec, size_t n) noexcept;

  template<class CharT, class Traits, class Allocator>
    dynamic_string_buffer<CharT, Traits, Allocator>
      dynamic_buffer(basic_string<CharT, Traits, Allocator>& str) noexcept;
  template<class CharT, class Traits, class Allocator>
    dynamic_string_buffer<CharT, Traits, Allocator>
      dynamic_buffer(basic_string<CharT, Traits, Allocator>& str, size_t n) noexcept;

  class transfer_all;
  class transfer_at_least;
  class transfer_exactly;

  // synchronous read operations:

  template<class SyncReadStream, class MutableBufferSequence>
    size_t read(SyncReadStream& stream,
                const MutableBufferSequence& buffers);
  template<class SyncReadStream, class MutableBufferSequence>
    size_t read(SyncReadStream& stream,
                const MutableBufferSequence& buffers, error_code& ec);
  template<class SyncReadStream, class MutableBufferSequence,
    class CompletionCondition>
      size_t read(SyncReadStream& stream,
                  const MutableBufferSequence& buffers,
                  CompletionCondition completion_condition);
  template<class SyncReadStream, class MutableBufferSequence,
    class CompletionCondition>
      size_t read(SyncReadStream& stream,
                  const MutableBufferSequence& buffers,
                  CompletionCondition completion_condition,
                  error_code& ec);

  template<class SyncReadStream, class DynamicBuffer>
    size_t read(SyncReadStream& stream, DynamicBuffer&& b);
  template<class SyncReadStream, class DynamicBuffer>
    size_t read(SyncReadStream& stream, DynamicBuffer&& b, error_code& ec);
  template<class SyncReadStream, class DynamicBuffer, class CompletionCondition>
    size_t read(SyncReadStream& stream, DynamicBuffer&& b,
                CompletionCondition completion_condition);
  template<class SyncReadStream, class DynamicBuffer, class CompletionCondition>
    size_t read(SyncReadStream& stream, DynamicBuffer&& b,
                CompletionCondition completion_condition, error_code& ec);

  // asynchronous read operations:

  template<class AsyncReadStream, class MutableBufferSequence,
    class CompletionToken>
      DEDUCED async_read(AsyncReadStream& stream,
                      const MutableBufferSequence& buffers,
                      CompletionToken&& token);
  template<class AsyncReadStream, class MutableBufferSequence,
    class CompletionCondition, class CompletionToken>
      DEDUCED async_read(AsyncReadStream& stream,
                      const MutableBufferSequence& buffers,
                      CompletionCondition completion_condition,
                      CompletionToken&& token);

  template<class AsyncReadStream, class DynamicBuffer, class CompletionToken>
    DEDUCED async_read(AsyncReadStream& stream,
                    DynamicBuffer&& b, CompletionToken&& token);
  template<class AsyncReadStream, class DynamicBuffer,
    class CompletionCondition, class CompletionToken>
      DEDUCED async_read(AsyncReadStream& stream,
                      DynamicBuffer&& b,
                      CompletionCondition completion_condition,
                      CompletionToken&& token);

  // synchronous write operations:

  template<class SyncWriteStream, class ConstBufferSequence>
    size_t write(SyncWriteStream& stream,
                 const ConstBufferSequence& buffers);
  template<class SyncWriteStream, class ConstBufferSequence>
    size_t write(SyncWriteStream& stream,
                 const ConstBufferSequence& buffers, error_code& ec);
  template<class SyncWriteStream, class ConstBufferSequence,
    class CompletionCondition>
      size_t write(SyncWriteStream& stream,
                   const ConstBufferSequence& buffers,
                   CompletionCondition completion_condition);
  template<class SyncWriteStream, class ConstBufferSequence,
    class CompletionCondition>
      size_t write(SyncWriteStream& stream,
                   const ConstBufferSequence& buffers,
                   CompletionCondition completion_condition,
                   error_code& ec);

  template<class SyncWriteStream, class DynamicBuffer>
    size_t write(SyncWriteStream& stream, DynamicBuffer&& b);
  template<class SyncWriteStream, class DynamicBuffer>
    size_t write(SyncWriteStream& stream, DynamicBuffer&& b, error_code& ec);
  template<class SyncWriteStream, class DynamicBuffer, class CompletionCondition>
    size_t write(SyncWriteStream& stream, DynamicBuffer&& b,
                 CompletionCondition completion_condition);
  template<class SyncWriteStream, class DynamicBuffer, class CompletionCondition>
    size_t write(SyncWriteStream& stream, DynamicBuffer&& b,
                 CompletionCondition completion_condition, error_code& ec);

  // asynchronous write operations:

  template<class AsyncWriteStream, class ConstBufferSequence,
    class CompletionToken>
      DEDUCED async_write(AsyncWriteStream& stream,
                       const ConstBufferSequence& buffers,
                       CompletionToken&& token);
  template<class AsyncWriteStream, class ConstBufferSequence,
    class CompletionCondition, class CompletionToken>
      DEDUCED async_write(AsyncWriteStream& stream,
                       const ConstBufferSequence& buffers,
                       CompletionCondition completion_condition,
                       CompletionToken&& token);

  template<class AsyncWriteStream, class DynamicBuffer, class CompletionToken>
    DEDUCED async_write(AsyncWriteStream& stream,
                     DynamicBuffer&& b, CompletionToken&& token);
  template<class AsyncWriteStream, class DynamicBuffer,
    class CompletionCondition, class CompletionToken>
      DEDUCED async_write(AsyncWriteStream& stream,
                       DynamicBuffer&& b,
                       CompletionCondition completion_condition,
                       CompletionToken&& token);

  // synchronous delimited read operations:

  template<class SyncReadStream, class DynamicBuffer>
    size_t read_until(SyncReadStream& s, DynamicBuffer&& b, char delim);
  template<class SyncReadStream, class DynamicBuffer>
    size_t read_until(SyncReadStream& s, DynamicBuffer&& b,
                      char delim, error_code& ec);
  template<class SyncReadStream, class DynamicBuffer>
    size_t read_until(SyncReadStream& s, DynamicBuffer&& b, string_view delim);
  template<class SyncReadStream, class DynamicBuffer>
    size_t read_until(SyncReadStream& s, DynamicBuffer&& b,
                      string_view delim, error_code& ec);

  // asynchronous delimited read operations:

  template<class AsyncReadStream, class DynamicBuffer, class CompletionToken>
    DEDUCED async_read_until(AsyncReadStream& s,
                          DynamicBuffer&& b, char delim,
                          CompletionToken&& token);
  template<class AsyncReadStream, class DynamicBuffer, class CompletionToken>
    DEDUCED async_read_until(AsyncReadStream& s,
                          DynamicBuffer&& b, string_view delim,
                          CompletionToken&& token);

} // inline namespace v1
} // namespace net
} // namespace experimental

  template<> struct is_error_code_enum<
    experimental::net::v1::stream_errc>
      : public true_type {};

} // namespace std

10.16.2. Requirements

[buffer.reqmts]

10.16.2.1. Mutable buffer sequence requirements

[buffer.reqmts.mutablebuffersequence]

A mutable buffer sequence represents a set of memory regions that may be used to receive the output of an operation, such as the receive operation of a socket.

A type X meets the MutableBufferSequence requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and CopyConstructible (C++Std [copyconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a (possibly const) value of type X, and u denotes an identifier.

Table 11. MutableBufferSequence requirements

expression

return type

assertion/note
pre/post-condition

std::experimental::net::buffer_sequence_begin(x)
std::experimental::net::buffer_sequence_end(x)

An iterator type meeting the requirements for bidirectional iterators (C++Std [bidirectional.iterators]) whose value type is convertible to mutable_buffer.

X u(x);

post:

equal(
  std::experimental::net::buffer_sequence_begin(x),
  std::experimental::net::buffer_sequence_end(x),
  std::experimental::net::buffer_sequence_begin(u),
  std::experimental::net::buffer_sequence_end(u),
  [](const typename X::value_type& v1,
     const typename X::value_type& v2)
   {
     mutable_buffer b1(v1);
     mutable_buffer b2(v2);
     return b1.data() == b2.data()
         && b1.size() == b2.size();
   })


10.16.2.2. Constant buffer sequence requirements

[buffer.reqmts.constbuffersequence]

A constant buffer sequence represents a set of memory regions that may be used as input to an operation, such as the send operation of a socket.

A type X meets the ConstBufferSequence requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and CopyConstructible (C++Std [copyconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a (possibly const) value of type X, and u denotes an identifier.

Table 12. ConstBufferSequence requirements

expression

return type

assertion/note
pre/post-condition

std::experimental::net::buffer_sequence_begin(x)
std::experimental::net::buffer_sequence_end(x)

An iterator type meeting the requirements for bidirectional iterators (C++Std [bidirectional.iterators]) whose value type is convertible to const_buffer.

X u(x);

post:

equal(
  std::experimental::net::buffer_sequence_begin(x),
  std::experimental::net::buffer_sequence_end(x),
  std::experimental::net::buffer_sequence_begin(u),
  std::experimental::net::buffer_sequence_end(u),
  [](const typename X::value_type& v1,
     const typename X::value_type& v2)
   {
     const_buffer b1(v1);
     const_buffer b2(v2);
     return b1.data() == b2.data()
         && b1.size() == b2.size();
   })


10.16.2.3. Dynamic buffer requirements

[buffer.reqmts.dynamicbuffer]

A dynamic buffer encapsulates memory storage that may be automatically resized as required, where the memory is divided into two regions: readable bytes followed by writable bytes. These memory regions are internal to the dynamic buffer, but direct access to the elements is provided to permit them to be efficiently used with I/O operations. [Note: Such as the send or receive operations of a socket. The readable bytes would be used as the constant buffer sequence for send, and the writable bytes used as the mutable buffer sequence for receive. —end note] Data written to the writable bytes of a dynamic buffer object is appended to the readable bytes of the same object.

A type X meets the DynamicBuffer requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and MoveConstructible (C++Std [moveconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a value of type X, x1 denotes a (possibly const) value of type X, and n denotes a (possibly const) value of type size_t.

Table 13. DynamicBuffer requirements

expression

type

assertion/note
pre/post-conditions

X::const_buffers_type

type meeting ConstBufferSequence requirements.

This type represents the memory associated with the readable bytes.

X::mutable_buffers_type

type meeting MutableBufferSequence requirements.

This type represents the memory associated with the writable bytes.

x1.size()

size_t

Returns the number of readable bytes.

x1.max_size()

size_t

Returns the maximum number of bytes, both readable and writable, that can be held by x1.

x1.capacity()

size_t

Returns the maximum number of bytes, both readable and writeable, that can be held by x1 without requiring reallocation.

x1.data()

X::const_buffers_type

Returns a constant buffer sequence u that represents the readable bytes, and where buffer_size(u) == size().

x.prepare(n)

X::mutable_buffers_type

Returns a mutable buffer sequence u representing the writable bytes, and where buffer_size(u) == n. The dynamic buffer reallocates memory as required. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated.

Throws: length_error if size() + n exceeds max_size().

x.commit(n)

Appends n bytes from the start of the writable bytes to the end of the readable bytes. The remainder of the writable bytes are discarded. If n is greater than the number of writable bytes, all writable bytes are appended to the readable bytes. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated.

x.consume(n)

Removes n bytes from beginning of the readable bytes. If n is greater than the number of readable bytes, all readable bytes are removed. All constant or mutable buffer sequences previously obtained using data() or prepare() are invalidated.


10.16.2.4. Requirements on read and write operations

[buffer.reqmts.read.write]

A read operation is an operation that reads data into a mutable buffer sequence argument of a type meeting MutableBufferSequence requirements. The mutable buffer sequence specifies memory where the data should be placed. A read operation shall always fill a buffer in the sequence completely before proceeding to the next.

A write operation is an operation that writes data from a constant buffer sequence argument of a type meeting ConstBufferSequence requirements. The constant buffer sequence specifies memory where the data to be written is located. A write operation shall always write a buffer in the sequence completely before proceeding to the next.

If a read or write operation is also an asynchronous operation, the operation shall maintain one or more copies of the buffer sequence until such time as the operation no longer requires access to the memory specified by the buffers in the sequence. The program shall ensure the memory remains valid until:

— the last copy of the buffer sequence is destroyed, or

— the completion handler for the asynchronous operation is invoked,

whichever comes first.

10.16.3. Error codes

[buffer.err]

const error_category& stream_category() noexcept;

Returns: A reference to an object of a type derived from class error_category. All calls to this function return references to the same object.

The object's default_error_condition and equivalent virtual functions behave as specified for the class error_category. The object's name virtual function returns a pointer to the string "stream".

error_code make_error_code(stream_errc e) noexcept;

Returns: error_code(static_cast<int>(e), stream_category()).

error_condition make_error_condition(stream_errc e) noexcept;

Returns: error_condition(static_cast<int>(e), stream_category()).

10.16.4. Class mutable_buffer

[buffer.mutable]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class mutable_buffer
  {
  public:
    // constructors:
    mutable_buffer() noexcept;
    mutable_buffer(void* p, size_t n) noexcept;

    // members:
    void* data() const noexcept;
    size_t size() const noexcept;

  private:
    void* data_; // exposition only
    size_t size_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The mutable_buffer class satisfies requirements of MutableBufferSequence, DefaultConstructible (C++Std [defaultconstructible]), and CopyAssignable (C++Std [copyassignable]).

mutable_buffer() noexcept;

Postconditions: data_ == nullptr and size_ == 0.

mutable_buffer(void* p, size_t n) noexcept;

Postconditions: data_ == p and size_ == n.

void* data() const noexcept;

Returns: data_.

size_t size() const noexcept;

Returns: size_.

10.16.5. Class const_buffer

[buffer.const]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class const_buffer
  {
  public:
    // constructors:
    const_buffer() noexcept;
    const_buffer(const void* p, size_t n) noexcept;
    const_buffer(const mutable_buffer& b) noexcept;

    // members:
    const void* data() const noexcept;
    size_t size() const noexcept;

  private:
    const void* data_; // exposition only
    size_t size_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The const_buffer class satisfies requirements of ConstBufferSequence, DefaultConstructible (C++Std [defaultconstructible]), and CopyAssignable (C++Std [copyassignable]).

const_buffer() noexcept;

Postconditions: data_ == nullptr and size_ == 0.

const_buffer(const void* p, size_t n) noexcept;

Postconditions: data_ == p and size_ == n.

const_buffer(const mutable_buffer& b);

Postconditions: data_ == b.data() and size_ == b.size().

const void* data() const noexcept;

Returns: data_.

size_t size() const noexcept;

Returns: size_.

10.16.6. Buffer type traits

[buffer.traits]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T> struct is_mutable_buffer_sequence;
  template<class T> struct is_const_buffer_sequence;
  template<class T> struct is_dynamic_buffer;

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

This sub-clause contains templates that may be used to query the properties of a type at compile time. Each of these templates is a UnaryTypeTrait (C++Std [meta.rqmts]) with a BaseCharacteristic of true_type if the corresponding condition is true, otherwise false_type.

Table 14. Buffer type traits

Template

Condition

Preconditions

template<class T> is_mutable_buffer_sequence

T meets the syntactic requirements for mutable buffer sequence.

T is a complete type.

template<class T> is_const_buffer_sequence

T meets the syntactic requirements for constant buffer sequence.

T is a complete type.

template<class T> is_dynamic_buffer

T meets the syntactic requirements for dynamic buffer.

T is a complete type.


10.16.7. Buffer sequence access

[buffer.seq.access]

const mutable_buffer* buffer_sequence_begin(const mutable_buffer& b);
const const_buffer* buffer_sequence_begin(const const_buffer& b);

Returns: std::addressof(b).

const mutable_buffer* buffer_sequence_end(const mutable_buffer& b);
const const_buffer* buffer_sequence_end(const const_buffer& b);

Returns: std::addressof(b) + 1.

template <class C> auto buffer_sequence_begin(C& c) -> decltype(c.begin());
template <class C> auto buffer_sequence_begin(const C& c) -> decltype(c.begin());

Returns: c.begin().

template <class C> auto buffer_sequence_end(C& c) -> decltype(c.end());
template <class C> auto buffer_sequence_end(const C& c) -> decltype(c.end());

Returns: c.end().

10.16.8. Function buffer_size

[buffer.size]

template<class ConstBufferSequence>
  size_t buffer_size(const ConstBufferSequence& buffers) noexcept;

Returns: The total size of all buffers in the sequence, as if computed as follows:

size_t total_size = 0;
auto i = std::experimental::net::buffer_sequence_begin(buffers);
auto end = std::experimental::net::buffer_sequence_end(buffers);
for (; i != end; ++i)
{
  const_buffer b(*i);
  total_size += b.size();
}
return total_size;

10.16.9. Function buffer_copy

[buffer.copy]

template<class MutableBufferSequence, class ConstBufferSequence>
  size_t buffer_copy(const MutableBufferSequence& dest,
                     const ConstBufferSequence& source) noexcept;
template<class MutableBufferSequence, class ConstBufferSequence>
  size_t buffer_copy(const MutableBufferSequence& dest,
                     const ConstBufferSequence& source,
                     size_t max_size) noexcept;

Effects: Copies bytes from the buffer sequence source to the buffer sequence dest, as if by calls to memcpy.

The number of bytes copied is the lesser of:
buffer_size(dest);
buffer_size(source); and
max_size, if specified.

The mutable buffer sequence dest specifies memory where the data should be placed. The operation always fills a buffer in the sequence completely before proceeding to the next.

The constant buffer sequence source specifies memory where the data to be written is located. The operation always copies a buffer in the sequence completely before proceeding to the next.

Returns: The number of bytes copied from source to dest.

10.16.10. Buffer arithmetic

[buffer.arithmetic]

mutable_buffer operator+(const mutable_buffer& b, size_t n) noexcept;
mutable_buffer operator+(size_t n, const mutable_buffer& b) noexcept;

Returns: A mutable_buffer equivalent to

mutable_buffer(
  static_cast<char*>(b.data()) + min(n, b.size()),
  b.size() - min(n, b.size()));

const_buffer operator+(const const_buffer& b, size_t n) noexcept;
const_buffer operator+(size_t n, const const_buffer& b) noexcept;

Returns: A const_buffer equivalent to

const_buffer(
  static_cast<const char*>(b.data()) + min(n, b.size()),
  b.size() - min(n, b.size()));

10.16.11. Buffer creation functions

[buffer.creation]

In the functions below, T must be a trivially copyable or standard-layout type (C++Std [basic.types]).

For the function overloads below that accept an argument of type vector<>, the buffer objects returned are invalidated by any vector operation that also invalidates all references, pointers and iterators referring to the elements in the sequence (C++Std [vector]).

For the function overloads below that accept an argument of type basic_string<>, the buffer objects returned are invalidated according to the rules defined for invalidation of references, pointers and iterators referring to elements of the sequence (C++Std [string.require]).

mutable_buffer buffer(void* p, size_t n) noexcept;

Returns: mutable_buffer(p, n).

const_buffer buffer(const void* p, size_t n) noexcept;

Returns: const_buffer(p, n).

mutable_buffer buffer(const mutable_buffer& b) noexcept;

Returns: b.

mutable_buffer buffer(const mutable_buffer& b, size_t n) noexcept;

Returns: mutable_buffer(b.data(), min(b.size(), n)).

const_buffer buffer(const const_buffer& b) noexcept;

Returns: b.

const_buffer buffer(const const_buffer& b, size_t n) noexcept;

Returns: const_buffer(b.data(), min(b.size(), n)).

template<class T, size_t N>
  mutable_buffer buffer(T (&data)[N]) noexcept;
template<class T, size_t N>
  const_buffer buffer(const T (&data)[N]) noexcept;
template<class T, size_t N>
  mutable_buffer buffer(array<T, N>& data) noexcept;
template<class T, size_t N>
  const_buffer buffer(array<const T, N>& data) noexcept;
template<class T, size_t N>
  const_buffer buffer(const array<T, N>& data) noexcept;
template<class T, class Allocator>
  mutable_buffer buffer(vector<T, Allocator>& data) noexcept;
template<class T, class Allocator>
  const_buffer buffer(const vector<T, Allocator>& data) noexcept;
template<class CharT, class Traits, class Allocator>
  mutable_buffer buffer(basic_string<CharT, Traits, Allocator>& data) noexcept;
template<class CharT, class Traits, class Allocator>
  const_buffer buffer(const basic_string<CharT, Traits, Allocator>& data) noexcept;
template<class CharT, class Traits>
  const_buffer buffer(basic_string_view<CharT, Traits> data) noexcept;

Returns:

buffer(
  begin(data) != end(data) ? std::addressof(*begin(data)) : nullptr,
  (end(data) - begin(data)) * sizeof(*begin(data)));

template<class T, size_t N>
  mutable_buffer buffer(T (&data)[N], size_t n) noexcept;
template<class T, size_t N>
  const_buffer buffer(const T (&data)[N], size_t n) noexcept;
template<class T, size_t N>
  mutable_buffer buffer(array<T, N>& data, size_t n) noexcept;
template<class T, size_t N>
  const_buffer buffer(array<const T, N>& data, size_t n) noexcept;
template<class T, size_t N>
  const_buffer buffer(const array<T, N>& data, size_t n) noexcept;
template<class T, class Allocator>
  mutable_buffer buffer(vector<T, Allocator>& data, size_t n) noexcept;
template<class T, class Allocator>
  const_buffer buffer(const vector<T, Allocator>& data, size_t n) noexcept;
template<class CharT, class Traits, class Allocator>
  mutable_buffer buffer(basic_string<CharT, Traits, Allocator>& data,
                        size_t n) noexcept;
template<class CharT, class Traits, class Allocator>
  const_buffer buffer(const basic_string<CharT, Traits, Allocator>& data,
                      size_t n) noexcept;
template<class CharT, class Traits>
  const_buffer buffer(basic_string_view<CharT, Traits> data,
                      size_t n) noexcept;

Returns: buffer(buffer(data), n).

10.16.12. Class template dynamic_vector_buffer

[buffer.dynamic.vector]

Class template dynamic_vector_buffer is an adaptor used to automatically grow or shrink a vector object, to reflect the data successfully transferred in an I/O operation.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class T, class Allocator>
  class dynamic_vector_buffer
  {
  public:
    // types:
    typedef const_buffer const_buffers_type;
    typedef mutable_buffer mutable_buffers_type;

    // constructors:
    explicit dynamic_vector_buffer(vector<T, Allocator>& vec) noexcept;
    dynamic_vector_buffer(vector<T, Allocator>& vec,
                          size_t maximum_size) noexcept;
    dynamic_vector_buffer(dynamic_vector_buffer&&) = default;

    // members:
    size_t size() const noexcept;
    size_t max_size() const noexcept;
    size_t capacity() const noexcept;
    const_buffers_type data() const noexcept;
    mutable_buffers_type prepare(size_t n);
    void commit(size_t n);
    void consume(size_t n);

  private:
    vector<T, Allocator>& vec_; // exposition only
    size_t size_; // exposition only
    const size_t max_size_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The dynamic_vector_buffer class template meets the requirements of DynamicBuffer.

The dynamic_vector_buffer class template requires that T is a trivially copyable or standard-layout type (C++Std [basic.types]) and that sizeof(T) == 1.

explicit dynamic_vector_buffer(vector<T, Allocator>& vec) noexcept;

Effects: Initializes vec_ with vec, size_ with vec.size(), and max_size_ with vec.max_size().

dynamic_vector_buffer(vector<T, Allocator>& vec,
                      size_t maximum_size) noexcept;

Requires: vec.size() <= maximum_size.

Effects: Initializes vec_ with vec, size_ with vec.size(), and max_size_ with maximum_size.

size_t size() const noexcept;

Returns: size_.

size_t max_size() const noexcept;

Returns: max_size_.

size_t capacity() const noexcept;

Returns: vec_.capacity().

const_buffers_type data() const noexcept;

Returns: buffer(vec_, size_).

mutable_buffers_type prepare(size_t n);

Effects: Performs vec_.resize(size_ + n).

Returns: buffer(buffer(vec_) + size_, n).

Throws: length_error if size() + n exceeds max_size().

void commit(size_t n);

Effects: Performs:

size_ += min(n, vec_.size() - size_);
vec_.resize(size_);

void consume(size_t n);

Effects: Performs:

size_t m = min(n, size_);
vec_.erase(vec_.begin(), vec_.begin() + m);
size_ -= m;

10.16.13. Class template dynamic_string_buffer

[buffer.dynamic.string]

Class template dynamic_string_buffer is an adaptor used to automatically grow or shrink a basic_string object, to reflect the data successfully transferred in an I/O operation.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class CharT, class Traits, class Allocator>
  class dynamic_string_buffer
  {
  public:
    // types:
    typedef const_buffer const_buffers_type;
    typedef mutable_buffer mutable_buffers_type;

    // constructors:
    explicit dynamic_string_buffer(basic_string<CharT, Traits, Allocator>& str) noexcept;
    dynamic_string_buffer(basic_string<CharT, Traits, Allocator>& str,
                          size_t maximum_size) noexcept;
    dynamic_string_buffer(dynamic_string_buffer&&) = default;

    // members:
    size_t size() const noexcept;
    size_t max_size() const noexcept;
    size_t capacity() const noexcept;
    const_buffers_type data() const noexcept;
    mutable_buffers_type prepare(size_t n);
    void commit(size_t n) noexcept;
    void consume(size_t n);

  private:
    basic_string<CharT, Traits, Allocator>& str_; // exposition only
    size_t size_; // exposition only
    const size_t max_size_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The dynamic_string_buffer class template meets the requirements of DynamicBuffer.

The dynamic_string_buffer class template requires that sizeof(CharT) == 1.

explicit dynamic_string_buffer(basic_string<CharT, Traits, Allocator>& str) noexcept;

Effects: Initializes str_ with str, size_ with str.size(), and max_size_ with str.max_size().

dynamic_string_buffer(basic_string<CharT, Traits, Allocator>& str,
                      size_t maximum_size) noexcept;

Requires: str.size() <= maximum_size.

Effects: Initializes str_ with str, size_ with str.size(), and max_size_ with maximum_size.

size_t size() const noexcept;

Returns: size_.

size_t max_size() const noexcept;

Returns: max_size_.

size_t capacity() const noexcept;

Returns: str_.capacity().

const_buffers_type data() const noexcept;

Returns: buffer(str_, size_).

mutable_buffers_type prepare(size_t n);

Effects: Performs str_.resize(size_ + n).

Returns: buffer(buffer(str_) + size_, n).

Throws: length_error if size() + n exceeds max_size().

void commit(size_t n) noexcept;

Effects: Performs:

size_ += min(n, str_.size() - size_);
str_.resize(size_);

void consume(size_t n);

Effects: Performs:

size_t m = min(n, size_);
str_.erase(m);
size_ -= m;

10.16.14. Dynamic buffer creation functions

[buffer.dynamic.creation]

template<class T, class Allocator>
  dynamic_vector_buffer<T, Allocator>
    dynamic_buffer(vector<T, Allocator>& vec) noexcept;

Returns: dynamic_vector_buffer<T, Allocator>(vec).

template<class T, class Allocator>
  dynamic_vector_buffer<T, Allocator>
    dynamic_buffer(vector<T, Allocator>& vec, size_t n) noexcept;

Returns: dynamic_vector_buffer<T, Allocator>(vec, n).

template<class CharT, class Traits, class Allocator>
  dynamic_string_buffer<CharT, Traits, Allocator>
    dynamic_buffer(basic_string<CharT, Traits, Allocator>& str) noexcept;

Returns: dynamic_string_buffer<CharT, Traits, Allocator>(str).

template<class CharT, class Traits, class Allocator>
  dynamic_string_buffer<CharT, Traits, Allocator>
    dynamic_buffer(basic_string<CharT, Traits, Allocator>& str, size_t n) noexcept;

Returns: dynamic_string_buffer<CharT, Traits, Allocator>(str, n).

10.17. Buffer-oriented streams

[buffer.stream]

10.17.1. Requirements

[buffer.stream.reqmts]

10.17.1.1. Buffer-oriented synchronous read stream requirements

[buffer.stream.reqmts.syncreadstream]

A type X meets the SyncReadStream requirements if it satisfies the requirements listed below.

In the table below, a denotes a value of type X, mb denotes a (possibly const) value satisfying the MutableBufferSequence requirements, and ec denotes an object of type error_code.

Table 15. SyncReadStream requirements

operation

type

semantics, pre/post-conditions

a.read_some(mb)
a.read_some(mb,ec)

size_t

Meets the requirements for a read operation.

If buffer_size(mb) > 0, reads one or more bytes of data from the stream a into the buffer sequence mb. If successful, sets ec such that !ec is true, and returns the number of bytes read. If an error occurred, sets ec such that !!ec is true, and returns 0. If all data has been read from the stream, and the stream performed an orderly shutdown, sets ec to stream_errc::eof and returns 0.

If buffer_size(mb) == 0, the operation shall not block. Sets ec such that !ec is true, and returns 0.


10.17.1.2. Buffer-oriented asynchronous read stream requirements

[buffer.stream.reqmts.asyncreadstream]

A type X meets the AsyncReadStream requirements if it satisfies the requirements listed below.

In the table below, a denotes a value of type X, mb denotes a (possibly const) value satisfying the MutableBufferSequence requirements, and t is a completion token.

Table 16. AsyncReadStream requirements

operation

type

semantics, pre/post-conditions

a.get_executor()

A type satisfying the Executor requirements.

Returns the associated I/O executor.

a.async_read_some(mb,t)

The return type is determined according to the requirements for an asynchronous operation.

Meets the requirements for a read operation and an asynchronous operation with completion signature void(error_code ec, size_t n).

If buffer_size(mb) > 0, initiates an asynchronous operation to read one or more bytes of data from the stream a into the buffer sequence mb. If successful, ec is set such that !ec is true, and n is the number of bytes read. If an error occurred, ec is set such that !!ec is true, and n is 0. If all data has been read from the stream, and the stream performed an orderly shutdown, ec is stream_errc::eof and n is 0.

If buffer_size(mb) == 0, the operation completes immediately. ec is set such that !ec is true, and n is 0.


10.17.1.3. Buffer-oriented synchronous write stream requirements

[buffer.stream.reqmts.syncwritestream]

A type X meets the SyncWriteStream requirements if it satisfies the requirements listed below.

In the table below, a denotes a value of type X, cb denotes a (possibly const) value satisfying the ConstBufferSequence requirements, and ec denotes an object of type error_code.

Table 17. SyncWriteStream requirements

operation

type

semantics, pre/post-conditions

a.write_some(cb)
a.write_some(cb,ec)

size_t

Meets the requirements for a write operation.

If buffer_size(cb) > 0, writes one or more bytes of data to the stream a from the buffer sequence cb. If successful, sets ec such that !ec is true, and returns the number of bytes written. If an error occurred, sets ec such that !!ec is true, and returns 0.

If buffer_size(cb) == 0, the operation shall not block. Sets ec such that !ec is true, and returns 0.


10.17.1.4. Buffer-oriented asynchronous write stream requirements

[buffer.stream.reqmts.asyncwritestream]

A type X meets the AsyncWriteStream requirements if it satisfies the requirements listed below.

In the table below, a denotes a value of type X, cb denotes a (possibly const) value satisfying the ConstBufferSequence requirements, and t is a completion token.

Table 18. AsyncWriteStream requirements

operation

type

semantics, pre/post-conditions

a.get_executor()

A type satisfying the Executor requirements.

Returns the associated I/O executor.

a.async_write_some(cb,t)

The return type is determined according to the requirements for an asynchronous operation.

Meets the requirements for a write operation and an asynchronous operation with completion signature void(error_code ec, size_t n).

If buffer_size(cb) > 0, initiates an asynchronous operation to write one or more bytes of data to the stream a from the buffer sequence cb. If successful, ec is set such that !ec is true, and n is the number of bytes written. If an error occurred, ec is set such that !!ec is true, and n is 0.

If buffer_size(cb) == 0, the operation completes immediately. ec is set such that !ec is true, and n is 0.


10.17.1.5. Completion condition requirements

[buffer.stream.reqmts.completioncondition]

A completion condition is a function object that is used with the algorithms read, async_read, write, and async_write to determine when the algorithm has completed transferring data.

A type X meets the CompletionCondition requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and CopyConstructible (C++Std [copyconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a value of type X, ec denotes a (possibly const) value of type error_code, and n denotes a (possibly const) value of type size_t.

Table 19. CompletionCondition requirements

expression

return type

assertion/note
pre/post-condition

x(ec, n)

size_t

Let n be the total number of bytes transferred by the read or write algorithm so far.

Returns the maximum number of bytes to be transferred on the next read_some, async_read_some, write_some, or async_write_some operation performed by the algorithm. Returns 0 to indicate that the algorithm is complete.


10.17.2. Class transfer_all

[buffer.stream.transfer.all]

The class transfer_all is a completion condition that is used to specify that a read or write operation should continue until all of the data has been transferred, or until an error occurs.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class transfer_all
  {
  public:
    size_t operator()(const error_code& ec, size_t) const;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The class transfer_all satisfies the CompletionCondition requirements.

size_t operator()(const error_code& ec, size_t) const;

Returns: If !ec, an unspecified non-zero value. Otherwise 0.

10.17.3. Class transfer_at_least

[buffer.stream.transfer.at.least]

The class transfer_at_least is a completion condition that is used to specify that a read or write operation should continue until a minimum number of bytes has been transferred, or until an error occurs.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class transfer_at_least
  {
  public:
    explicit transfer_at_least(size_t m);
    size_t operator()(const error_code& ec, size_t s) const;
  private:
    size_t minimum_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The class transfer_at_least satisfies the CompletionCondition requirements.

explicit transfer_at_least(size_t m);

Postconditions: minimum_ == m.

size_t operator()(const error_code& ec, size_t n) const;

Returns: If !ec && n < minimum_, an unspecified non-zero value. Otherwise 0.

10.17.4. Class transfer_exactly

[buffer.stream.transfer.exactly]

The class transfer_exactly is a completion condition that is used to specify that a read or write operation should continue until an exact number of bytes has been transferred, or until an error occurs.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class transfer_exactly
  {
  public:
    explicit transfer_exactly(size_t e);
    size_t operator()(const error_code& ec, size_t s) const;
  private:
    size_t exact_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The class transfer_exactly satisfies the CompletionCondition requirements.

explicit transfer_exactly(size_t e);

Postconditions: exact_ == e.

size_t operator()(const error_code& ec, size_t n) const;

Returns: If !ec && n < exact_, the result of min(exact_ - n, N), where N is an unspecified non-zero value. Otherwise 0.

10.17.5. Synchronous read operations

[buffer.read]

template<class SyncReadStream, class MutableBufferSequence>
  size_t read(SyncReadStream& stream,
              const MutableBufferSequence& buffers);
template<class SyncReadStream, class MutableBufferSequence>
  size_t read(SyncReadStream& stream,
              const MutableBufferSequence& buffers, error_code& ec);
template<class SyncReadStream, class MutableBufferSequence,
  class CompletionCondition>
    size_t read(SyncReadStream& stream,
                const MutableBufferSequence& buffers,
                CompletionCondition completion_condition);
template<class SyncReadStream, class MutableBufferSequence,
  class CompletionCondition>
    size_t read(SyncReadStream& stream,
                const MutableBufferSequence& buffers,
                CompletionCondition completion_condition,
                error_code& ec);

Effects: Clears ec, then reads data from the buffer-oriented synchronous read stream object stream by performing zero or more calls to the stream's read_some member function.

The completion_condition parameter specifies a completion condition to be called prior to each call to the stream's read_some member function. The completion condition is passed the error_code value from the most recent read_some call, and the total number of bytes transferred in the synchronous read operation so far. The completion condition return value specifies the maximum number of bytes to be read on the subsequent read_some call. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The synchronous read operation continues until:

— the total number of bytes transferred is equal to buffer_size(buffers); or

— the completion condition returns 0.

On return, ec contains the error_code value from the most recent read_some call.

Returns: The total number of bytes transferred in the synchronous read operation.

Remarks: This function shall not participate in overload resolution unless is_mutable_buffer_sequence<MutableBufferSequence>::value is true.

template<class SyncReadStream, class DynamicBuffer>
  size_t read(SyncReadStream& stream, DynamicBuffer&& b);
template<class SyncReadStream, class DynamicBuffer>
  size_t read(SyncReadStream& stream, DynamicBuffer&& b, error_code& ec);
template<class SyncReadStream, class DynamicBuffer,
  class CompletionCondition>
    size_t read(SyncReadStream& stream, DynamicBuffer&& b,
                CompletionCondition completion_condition);
template<class SyncReadStream, class DynamicBuffer,
  class CompletionCondition>
    size_t read(SyncReadStream& stream, DynamicBuffer&& b,
                CompletionCondition completion_condition,
                error_code& ec);

Effects: Clears ec, then reads data from the synchronous read stream object stream by performing zero or more calls to the stream's read_some member function.

Data is placed into the dynamic buffer object b. A mutable buffer sequence is obtained prior to each read_some call using b.prepare(N), where N is an unspecified value less than or equal to b.max_size() - b.size(). [Note: Implementations are encouraged to use b.capacity() when determining N, to minimize the number of read_some calls performed on the stream. —end note] After each read_some call, the implementation performs b.commit(n), where n is the return value from read_some.

The completion_condition parameter specifies a completion condition to be called prior to each call to the stream's read_some member function. The completion condition is passed the error_code value from the most recent read_some call, and the total number of bytes transferred in the synchronous read operation so far. The completion condition return value specifies the maximum number of bytes to be read on the subsequent read_some call. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The synchronous read operation continues until:

b.size() == b.max_size(); or

— the completion condition returns 0.

On return, ec contains the error_code value from the most recent read_some call.

Returns: The total number of bytes transferred in the synchronous read operation.

Remarks: This function shall not participate in overload resolution unless is_dynamic_buffer<DynamicBuffer>::value is true.

10.17.6. Asynchronous read operations

[buffer.async.read]

template<class AsyncReadStream, class MutableBufferSequence,
  class CompletionToken>
    DEDUCED async_read(AsyncReadStream& stream,
                    const MutableBufferSequence& buffers,
                    CompletionToken&& token);
template<class AsyncReadStream, class MutableBufferSequence,
  class CompletionCondition, class CompletionToken>
    DEDUCED async_read(AsyncReadStream& stream,
                    const MutableBufferSequence& buffers,
                    CompletionCondition completion_condition,
                    CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Reads data from the buffer-oriented asynchronous read stream object stream by invoking the stream's async_read_some member function (henceforth referred to as asynchronous read_some operations) zero or more times.

The completion_condition parameter specifies a completion condition to be called prior to each asynchronous read_some operation. The completion condition is passed the error_code value from the most recent asynchronous read_some operation, and the total number of bytes transferred in the asynchronous read operation so far. The completion condition return value specifies the maximum number of bytes to be read on the subsequent asynchronous read_some operation. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

This asynchronous read operation is outstanding until:

— the total number of bytes transferred is equal to buffer_size(buffers); or

— the completion condition returns 0.

The program shall ensure the AsyncReadStream object stream is valid until the completion handler for the asynchronous operation is invoked.

On completion of the asynchronous operation, ec is the error_code value from the most recent asynchronous read_some operation, and n is the total number of bytes transferred.

Remarks: This function shall not participate in overload resolution unless is_mutable_buffer_sequence<MutableBufferSequence>::value is true.

template<class AsyncReadStream, class DynamicBuffer,
  class CompletionToken>
    DEDUCED async_read(AsyncReadStream& stream,
                    DynamicBuffer&& b, CompletionToken&& token);
template<class AsyncReadStream, class DynamicBuffer,
  class CompletionCondition, class CompletionToken>
    DEDUCED async_read(AsyncReadStream& stream,
                    DynamicBuffer&& b,
                    CompletionCondition completion_condition,
                    CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to read data from the buffer-oriented asynchronous read stream object stream by performing one or more asynchronous read_some operations on the stream.

Data is placed into the dynamic buffer object b. A mutable buffer sequence is obtained prior to each async_read_some call using b.prepare(N), where N is an unspecified value such that N is less than or equal to b.max_size() - b.size(). [Note: Implementations are encouraged to use b.capacity() when determining N, to minimize the number of asynchronous read_some operations performed on the stream. —end note] After the completion of each asynchronous read_some operation, the implementation performs b.commit(n), where n is the value passed to the asynchronous read_some operation's completion handler.

The completion_condition parameter specifies a completion condition to be called prior to each asynchronous read_some operation. The completion condition is passed the error_code value from the most recent asynchronous read_some operation, and the total number of bytes transferred in the asynchronous read operation so far. The completion condition return value specifies the maximum number of bytes to be read on the subsequent asynchronous read_some operation. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The asynchronous read operation is outstanding until:

b.size() == b.max_size(); or

— the completion condition returns 0.

The program shall ensure the AsyncReadStream object stream is valid until the completion handler for the asynchronous operation is invoked.

On completion of the asynchronous operation, ec is the error_code value from the most recent asynchronous read_some operation, and n is the total number of bytes transferred.

Remarks: This function shall not participate in overload resolution unless is_dynamic_buffer<DynamicBuffer>::value is true.

10.17.7. Synchronous write operations

[buffer.write]

template<class SyncWriteStream, class ConstBufferSequence>
  size_t write(SyncWriteStream& stream,
               const ConstBufferSequence& buffers);
template<class SyncWriteStream, class ConstBufferSequence>
  size_t write(SyncWriteStream& stream,
               const ConstBufferSequence& buffers, error_code& ec);
template<class SyncWriteStream, class ConstBufferSequence,
  class CompletionCondition>
    size_t write(SyncWriteStream& stream,
                 const ConstBufferSequence& buffers,
                 CompletionCondition completion_condition);
template<class SyncWriteStream, class ConstBufferSequence,
  class CompletionCondition>
    size_t write(SyncWriteStream& stream,
                 const ConstBufferSequence& buffers,
                 CompletionCondition completion_condition,
                 error_code& ec);

Effects: Writes data to the buffer-oriented synchronous write stream object stream by performing zero or more calls to the stream's write_some member function.

The completion_condition parameter specifies a completion condition to be called prior to each call to the stream's write_some member function. The completion condition is passed the error_code value from the most recent write_some call, and the total number of bytes transferred in the synchronous write operation so far. The completion condition return value specifies the maximum number of bytes to be written on the subsequent write_some call. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The synchronous write operation continues until:

— the total number of bytes transferred is equal to buffer_size(buffers); or

— the completion condition returns 0.

On return, ec contains the error_code value from the most recent write_some call.

Returns: The total number of bytes transferred in the synchronous write operation.

Remarks: This function shall not participate in overload resolution unless is_const_buffer_sequence<ConstBufferSequence>::value is true.

template<class SyncWriteStream, class DynamicBuffer>
  size_t write(SyncWriteStream& stream, DynamicBuffer&& b);
template<class SyncWriteStream, class DynamicBuffer>
  size_t write(SyncWriteStream& stream, DynamicBuffer&& b, error_code& ec);
template<class SyncWriteStream, class DynamicBuffer, class CompletionCondition>
  size_t write(SyncWriteStream& stream, DynamicBuffer&& b,
               CompletionCondition completion_condition);
template<class SyncWriteStream, class DynamicBuffer, class CompletionCondition>
  size_t write(SyncWriteStream& stream, DynamicBuffer&& b,
               CompletionCondition completion_condition,
               error_code& ec);

Effects: Writes data to the synchronous write stream object stream by performing zero or more calls to the stream's write_some member function.

Data is written from the dynamic buffer object b. A constant buffer sequence is obtained using b.data(). After the data has been written to the stream, the implementation performs b.consume(n), where n is the number of bytes successfully written.

The completion_condition parameter specifies a completion condition to be called after each call to the stream's write_some member function. The completion condition is passed the error_code value from the most recent write_some call, and the total number of bytes transferred in the synchronous write operation so far. The completion condition return value specifies the maximum number of bytes to be written on the subsequent write_some call. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The synchronous write operation continues until:

b.size() == 0; or

— the completion condition returns 0.

On return, ec contains the error_code value from the most recent write_some call.

Returns: The total number of bytes transferred in the synchronous write operation.

Remarks: This function shall not participate in overload resolution unless is_dynamic_buffer<DynamicBuffer>::value is true.

10.17.8. Asynchronous write operations

[buffer.async.write]

template<class AsyncWriteStream, class ConstBufferSequence,
  class CompletionToken>
    DEDUCED async_write(AsyncWriteStream& stream,
                     const ConstBufferSequence& buffers,
                     CompletionToken&& token);
template<class AsyncWriteStream, class ConstBufferSequence,
  class CompletionCondition, class CompletionToken>
    DEDUCED async_write(AsyncWriteStream& stream,
                     const ConstBufferSequence& buffers,
                     CompletionCondition completion_condition,
                     CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to write data to the buffer-oriented asynchronous write stream object stream by performing zero or more asynchronous operations on the stream using the stream's async_write_some member function (henceforth referred to as asynchronous write_some operations).

The completion_condition parameter specifies a completion condition to be called prior to each asynchronous write_some operation. The completion condition is passed the error_code value from the most recent asynchronous write_some operation, and the total number of bytes transferred in the asynchronous write operation so far. The completion condition return value specifies the maximum number of bytes to be written on the subsequent asynchronous write_some operation. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The asynchronous write operation continues until:

— the total number of bytes transferred is equal to buffer_size(buffers); or

— the completion condition returns 0.

The program must ensure the AsyncWriteStream object stream is valid until the completion handler for the asynchronous operation is invoked.

On completion of the asynchronous operation, ec is the error_code value from the most recent asynchronous write_some operation, and n is the total number of bytes transferred.

Remarks: This function shall not participate in overload resolution unless is_const_buffer_sequence<ConstBufferSequence>::value is true.

template<class AsyncWriteStream, class DynamicBuffer, class CompletionToken>
  DEDUCED async_write(AsyncWriteStream& stream,
                   DynamicBuffer&& b, CompletionToken&& token);
template<class AsyncWriteStream, class DynamicBuffer,
  class CompletionCondition, class CompletionToken>
    DEDUCED async_write(AsyncWriteStream& stream,
                     DynamicBuffer&& b,
                     CompletionCondition completion_condition,
                     CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to write data to the buffer-oriented asynchronous write stream object stream by performing zero or more asynchronous write_some operations on the stream.

Data is written from the dynamic buffer object b. A constant buffer sequence is obtained using b.data(). After the data has been written to the stream, the implementation performs b.consume(n), where n is the number of bytes successfully written.

The completion_condition parameter specifies a completion condition to be called prior to each asynchronous write_some operation. The completion condition is passed the error_code value from the most recent asynchronous write_some operation, and the total number of bytes transferred in the asynchronous write operation so far. The completion condition return value specifies the maximum number of bytes to be written on the subsequent asynchronous write_some operation. Overloads where a completion condition is not specified behave as if called with an object of class transfer_all.

The asynchronous write operation continues until:

b.size() == 0; or

— the completion condition returns 0.

The program must ensure both the AsyncWriteStream object stream and the memory associated with the dynamic buffer b are valid until the completion handler for the asynchronous operation is invoked.

On completion of the asynchronous operation, ec is the error_code value from the most recent asynchronous write_some operation, and n is the total number of bytes transferred.

Remarks: This function shall not participate in overload resolution unless is_dynamic_buffer<DynamicBuffer>::value is true.

10.17.9. Synchronous delimited read operations

[buffer.read.until]

template<class SyncReadStream, class DynamicBuffer>
  size_t read_until(SyncReadStream& s, DynamicBuffer&& b, char delim);
template<class SyncReadStream, class DynamicBuffer>
  size_t read_until(SyncReadStream& s, DynamicBuffer&& b,
                    char delim, error_code& ec);
template<class SyncReadStream, class DynamicBuffer>
  size_t read_until(SyncReadStream& s, DynamicBuffer&& b, string_view delim);
template<class SyncReadStream, class DynamicBuffer>
  size_t read_until(SyncReadStream& s, DynamicBuffer&& b,
                    string_view delim, error_code& ec);

Effects: Reads data from the buffer-oriented synchronous read stream object stream by performing zero or more calls to the stream's read_some member function, until the input sequence of the dynamic buffer object b contains the specified delimiter delim.

Data is placed into the dynamic buffer object b. A mutable buffer sequence is obtained prior to each read_some call using b.prepare(N), where N is an unspecified value such that N <= max_size() - size(). [Note: Implementations are encouraged to use b.capacity() when determining N, to minimize the number of read_some calls performed on the stream. —end note] After each read_some call, the implementation performs b.commit(n), where n is the return value from read_some.

The synchronous read_until operation continues until:

— the input sequence of b contains the delimiter delim; or

b.size() == b.max_size(); or

— an synchronous read_some operation fails.

On exit, if the input sequence of b contains the delimiter, ec is set such that !ec is true. Otherwise, if b.size() == b.max_size(), ec is set such that ec == stream_errc::not_found. If b.size() < b.max_size(), ec contains the error_code from the most recent read_some call.

Returns: The number of bytes in the input sequence of b up to and including the delimiter, if present. [Note: On completion, the buffer may contain additional bytes following the delimiter. —end note] Otherwise returns 0.

10.17.10. Asynchronous delimited read operations

[buffer.async.read.until]

template<class AsyncReadStream, class DynamicBuffer, class CompletionToken>
  DEDUCED async_read_until(AsyncReadStream& s,
                        DynamicBuffer&& b, char delim,
                        CompletionToken&& token);
template<class AsyncReadStream, class DynamicBuffer, class CompletionToken>
  DEDUCED async_read_until(AsyncReadStream& s,
                        DynamicBuffer&& b, string_view delim,
                        CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to read data from the buffer-oriented asynchronous read stream object stream by performing zero or more asynchronous read_some operations on the stream, until the readable bytes of the dynamic buffer object b contain the specified delimiter delim.

Data is placed into the dynamic buffer object b. A mutable buffer sequence is obtained prior to each async_read_some call using b.prepare(N), where N is an unspecified value such that N <= max_size() - size(). [Note: Implementations are encouraged to use b.capacity() when determining N, to minimize the number of asynchronous read_some operations performed on the stream. —end note] After the completion of each asynchronous read_some operation, the implementation performs b.commit(n), where n is the value passed to the asynchronous read_some operation's completion handler.

The asynchronous read_until operation continues until:

— the readable bytes of b contain the delimiter delim; or

b.size() == b.max_size(); or

— an asynchronous read_some operation fails.

The program shall ensure the AsyncReadStream object stream is valid until the completion handler for the asynchronous operation is invoked.

If delim is of type string_view, the implementation copies the underlying sequence of characters prior to initiating an asynchronous read_some operation on the stream. [Note: This means that the caller is not required to guarantee the validity of the delimiter string after the call to async_read_until returns. —end note]

On completion of the asynchronous operation, if the readable bytes of b contain the delimiter, ec is set such that !ec is true. Otherwise, if b.size() == b.max_size(), ec is set such that ec == stream_errc::not_found. If b.size() < b.max_size(), ec is the error_code from the most recent asynchronous read_some operation. n is the number of readable bytes in b up to and including the delimiter, if present, otherwise 0.

10.18. Sockets

[socket]

10.18.1. Header <experimental/socket> synopsis

[socket.synop]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  enum class socket_errc {
    already_open = an implementation defined non-zero value,
    not_found = an implementation defined non-zero value
  };

  const error_category& socket_category() noexcept;

  error_code make_error_code(socket_errc e) noexcept;
  error_condition make_error_condition(socket_errc e) noexcept;

  // Sockets:

  class socket_base;

  template<class Protocol>
    class basic_socket;

  template<class Protocol>
    class basic_datagram_socket;

  template<class Protocol>
    class basic_stream_socket;

  template<class Protocol>
    class basic_socket_acceptor;

  // Socket streams:

  template<class Protocol, class Clock = chrono::steady_clock,
    class WaitTraits = wait_traits<Clock>>
      class basic_socket_streambuf;

  template<class Protocol, class Clock = chrono::steady_clock,
    class WaitTraits = wait_traits<Clock>>
      class basic_socket_iostream;

  // synchronous connect operations:

  template<class Protocol, class EndpointSequence>
    typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                        const EndpointSequence& endpoints);
  template<class Protocol, class EndpointSequence>
    typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                        const EndpointSequence& endpoints,
                                        error_code& ec);
  template<class Protocol, class EndpointSequence, class ConnectCondition>
    typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                        const EndpointSequence& endpoints,
                                        ConnectCondition c);
  template<class Protocol, class EndpointSequence, class ConnectCondition>
    typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                        const EndpointSequence& endpoints,
                                        ConnectCondition c,
                                        error_code& ec);

  template<class Protocol, class InputIterator>
    InputIterator connect(basic_socket<Protocol>& s,
                          InputIterator first, InputIterator last);
  template<class Protocol, class InputIterator>
    InputIterator connect(basic_socket<Protocol>& s,
                          InputIterator first, InputIterator last,
                          error_code& ec);
  template<class Protocol, class InputIterator, class ConnectCondition>
    InputIterator connect(basic_socket<Protocol>& s,
                          InputIterator first, InputIterator last,
                          ConnectCondition c);
  template<class Protocol, class InputIterator, class ConnectCondition>
    InputIterator connect(basic_socket<Protocol>& s,
                          InputIterator first, InputIterator last,
                          ConnectCondition c,
                          error_code& ec);

  // asynchronous connect operations:

  template<class Protocol, class EndpointSequence, class CompletionToken>
    DEDUCED async_connect(basic_socket<Protocol>& s,
                          const EndpointSequence& endpoints,
                          CompletionToken&& token);
  template<class Protocol, class EndpointSequence,
    class ConnectCondition, class CompletionToken>
      DEDUCED async_connect(basic_socket<Protocol>& s,
                            const EndpointSequence& endpoints,
                            ConnectCondition c,
                            CompletionToken&& token);

  template<class Protocol, class InputIterator, class CompletionToken>
    DEDUCED async_connect(basic_socket<Protocol>& s,
                          InputIterator first, InputIterator last,
                          CompletionToken&& token);
  template<class Protocol, class InputIterator,
    class ConnectCondition, class CompletionToken>
      DEDUCED async_connect(basic_socket<Protocol>& s,
                            InputIterator first, InputIterator last,
                            ConnectCondition c,
                            CompletionToken&& token);

} // inline namespace v1
} // namespace net
} // namespace experimental

  template<> struct is_error_code_enum<
    experimental::net::v1::socket_errc>
      : public true_type {};

} // namespace std

The figure below illustrates relationships between various types described in this Technical Specification. A solid line from A to B that is terminated by an open arrow indicates that A is derived from B. A solid line from A to B that starts with a diamond and is terminated by a solid arrow indicates that A contains an object of type B. A dotted line from A to B indicates that A is a typedef for the class template B with the specified template argument.

sockets

10.18.2. Requirements

[socket.reqmts]

10.18.2.1. Requirements on synchronous socket operations

[socket.reqmts.sync]

In this section, synchronous socket operations are those member functions specified as two overloads, with and without an argument of type error_code&:

R f(A1 a1, A2 a2, ..., AN aN);
R f(A1 a1, A2 a2, ..., AN aN, error_code& ec);

For an object s, the conditions under which its synchronous socket operations may block the calling thread (C++Std [defns.block]) are determined as follows.

If:

s.non_blocking() == true,

— the synchronous socket operation is specified in terms of a POSIX function other than poll,

— that POSIX function lists EWOULDBLOCK or EAGAIN in its failure conditions, and

— the effects of the operation cannot be established immediately

then the synchronous socket operation shall not block the calling thread. [Note: And the effects of the operation are not established. —end note]

Otherwise, the synchronous socket operation shall block the calling thread until the effects are established.

10.18.2.2. Requirements on asynchronous socket operations

[socket.reqmts.async]

In this section, asynchronous socket operations are those member functions having prefix async_.

For an object s, a program may initiate asynchronous socket operations such that there are multiple simultaneously outstanding asynchronous operations.

When there are multiple outstanding asynchronous read operations on s:

— having no argument flags of type socket_base::message_flags, or

— having an argument flags of type socket_base::message_flags but where (flags & socket_base::message_out_of_band) == 0

then the buffers are filled in the order in which these operations were issued. The order of invocation of the completion handlers for these operations is unspecified.

When there are multiple outstanding asynchronous read operations on s having an argument flags of type socket_base::message_flags where (flags & socket_base::message_out_of_band) != 0 then the buffers are filled in the order in which these operations were issued.

When there are multiple outstanding asynchronous write operations on s, the buffers are transmitted in the order in which these operations were issued. The order of invocation of the completion handlers for these operations is unspecified.

10.18.2.3. Native handles

[socket.reqmts.native]

Several classes described in this Technical Specification have a member type native_handle_type, a member function native_handle, and member functions that accept arguments of type native_handle_type. The presence of these members and their semantics is implementation-defined.

[Note: These members allow implementations to provide access to their implementation details. Their names are specified to facilitate portable compile-time detection. Actual use of these members is inherently non-portable. For operating systems that are based on POSIX, implementations are encouraged to define the native_handle_type for sockets as int, representing the native file descriptor associated with the socket. —end note]

10.18.2.4. Endpoint requirements

[socket.reqmts.endpoint]

A type X meets the Endpoint requirements if it satisfies the requirements of Destructible (C++Std [destructible]), DefaultConstructible (C++Std [defaultconstructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]), as well as the additional requirements listed below.

In the table below, a denotes a (possibly const) value of type X, and u denotes an identifier.

Table 20. Endpoint requirements

expression

type

assertion/note
pre/post-conditions

X::protocol_type

type meeting Protocol requirements

a.protocol()

protocol_type


In the table below, a denotes a (possibly const) value of type X, b denotes a value of type X, and s denotes a (possibly const) value of a type that is convertible to size_t and denotes a size in bytes.

Table 21. Endpoint requirements for extensible implementations

expression

type

assertion/note
pre/post-conditions

a.data()

const void*

Returns a pointer suitable for passing as the address argument to functions such as POSIX connect, or as the dest_addr argument to functions such as POSIX sendto. The implementation shall perform a static_cast on the pointer to convert it to const sockaddr*.

b.data()

void*

Returns a pointer suitable for passing as the address argument to functions such as POSIX accept, getpeername, getsockname and recvfrom. The implementation shall perform a static_cast on the pointer to convert it to sockaddr*.

a.size()

size_t

Returns a value suitable for passing as the address_len argument to functions such as POSIX connect, or as the dest_len argument to functions such as POSIX sendto, after appropriate integer conversion has been performed.

b.resize(s)

pre: s >= 0
post: a.size() == s
Passed the value contained in the address_len argument to functions such as POSIX accept, getpeername, getsockname and recvfrom, after successful completion of the function. Permitted to throw an exception if the protocol associated with the endpoint object a does not support the specified size.

a.capacity()

size_t

Returns a value suitable for passing as the address_len argument to functions such as POSIX accept, getpeername, getsockname and recvfrom, after appropriate integer conversion has been performed.


10.18.2.5. Endpoint sequence requirements

[socket.reqmts.endpointsequence]

A type X meets the EndpointSequence requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and CopyConstructible (C++Std [copyconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a (possibly const) value of type X.

Table 22. EndpointSequence requirements

expression

return type

assertion/note
pre/post-condition

x.begin()
x.end()

A type meeting the requirements for forward iterators (C++Std [forward.iterators]) whose value type is convertible to a type satisfying the Endpoint requirements.

[x.begin(),x.end()) is a valid range.


10.18.2.6. Protocol requirements

[socket.reqmts.protocol]

A type X meets the Protocol requirements if it satisfies the requirements of Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]), as well as the additional requirements listed below.

Table 23. Protocol requirements

expression

return type

assertion/note
pre/post-conditions

X::endpoint

type meeting endpoint requirements


In the table below, a denotes a (possibly const) value of type X.

Table 24. Protocol requirements for extensible implementations

expression

return type

assertion/note
pre/post-conditions

a.family()

int

Returns a value suitable for passing as the domain argument to POSIX socket (or equivalent).

a.type()

int

Returns a value suitable for passing as the type argument to POSIX socket (or equivalent).

a.protocol()

int

Returns a value suitable for passing as the protocol argument to POSIX socket (or equivalent).


10.18.2.7. Acceptable protocol requirements

[socket.reqmts.acceptableprotocol]

A type X meets the AcceptableProtocol requirements if it satisfies the requirements of Protocol as well as the additional requirements listed below.

Table 25. AcceptableProtocol requirements

expression

return type

assertion/note
pre/post-conditions

X::socket

A type that satisfies the requirements of Destructible (C++Std [destructible]) and MoveConstructible (C++Std [moveconstructible]), and that is publicly and unambiguously derived from basic_socket<X>.


10.18.2.8. Gettable socket option requirements

[socket.reqmts.gettablesocketoption]

A type X meets the GettableSocketOption requirements if it satisfies the requirements listed below.

In the table below, a denotes a (possibly const) value of type X, b denotes a value of type X, p denotes a (possibly const) value that meets the Protocol requirements, and s denotes a (possibly const) value of a type that is convertible to size_t and denotes a size in bytes.

Table 26. GettableSocketOption requirements for extensible implementations

expression

type

assertion/note
pre/post-conditions

a.level(p)

int

Returns a value suitable for passing as the level argument to POSIX getsockopt (or equivalent).

a.name(p)

int

Returns a value suitable for passing as the option_name argument to POSIX getsockopt (or equivalent).

b.data(p)

void*

Returns a pointer suitable for passing as the option_value argument to POSIX getsockopt (or equivalent).

a.size(p)

size_t

Returns a value suitable for passing as the option_len argument to POSIX getsockopt (or equivalent), after appropriate integer conversion has been performed.

b.resize(p,s)

post: b.size(p) == s.
Passed the value contained in the option_len argument to POSIX getsockopt (or equivalent) after successful completion of the function. Permitted to throw an exception if the socket option object b does not support the specified size.


10.18.2.9. Settable socket option requirements

[socket.reqmts.settablesocketoption]

A type X meets the SettableSocketOption requirements if it satisfies the requirements listed below.

In the table below, a denotes a (possibly const) value of type X, p denotes a (possibly const) value that meets the Protocol requirements, and u denotes an identifier.

Table 27. SettableSocketOption requirements for extensible implementations

expression

type

assertion/note
pre/post-conditions

a.level(p)

int

Returns a value suitable for passing as the level argument to POSIX setsockopt (or equivalent).

a.name(p)

int

Returns a value suitable for passing as the option_name argument to POSIX setsockopt (or equivalent).

a.data(p)

const void*

Returns a pointer suitable for passing as the option_value argument to POSIX setsockopt (or equivalent).

a.size(p)

size_t

Returns a value suitable for passing as the option_len argument to POSIX setsockopt (or equivalent), after appropriate integer conversion has been performed.


10.18.2.10. Boolean socket options

[socket.reqmts.opt.bool]

A type X meets the BooleanSocketOption requirements if it satisfies the requirements of Destructible (C++Std [destructible]), DefaultConstructible (C++Std [defaultconstructible]), CopyConstructible (C++Std [copyconstructible]), CopyAssignable (C++Std [copyassignable]), GettableSocketOption, and SettableSocketOption, X is contextually convertible to bool, and X satisfies the additional requirements listed below.

In the table below, a denotes a (possibly const) value of type X, b denotes a (possibly const) value of type bool, and u denotes an identifier.

Table 28. BooleanSocketOption requirements

expression

type

assertion/note
pre/post-conditions

X u;

post: !u.value().

X u(b);

post: u.value() == b.

a.value()

bool

Returns the current boolean value of the socket option object.

static_cast<bool>(a)

bool

Returns a.value().

!a

bool

Returns !a.value().


In this Technical Specification, types that satisfy the BooleanSocketOption requirements are defined as follows.

class C
{
public:
  // constructors:
  C() noexcept;
  explicit C(bool v) noexcept;

  // members:
  C& operator=(bool v) noexcept;

  bool value() const noexcept;

  explicit operator bool() const noexcept;
  bool operator!() const noexcept;
};

Extensible implementations provide the following member functions:

class C
{
public:
  template<class Protocol> int level(const Protocol& p) const noexcept;
  template<class Protocol> int name(const Protocol& p) const noexcept;
  template<class Protocol> void* data(const Protocol& p) noexcept;
  template<class Protocol> const void* data(const Protocol& p) const noexcept;
  template<class Protocol> size_t size(const Protocol& p) const noexcept;
  template<class Protocol> void resize(const Protocol& p, size_t s);
  // remainder unchanged
private:
  int value_; // exposition only
};

Let L and N identify the POSIX macros to be passed as the level and option_name arguments, respectively, to POSIX setsockopt and getsockopt.

C() noexcept;

Postconditions: !value().

explicit C(bool v) noexcept;

Postconditions: value() == v.

C& operator=(bool v) noexcept;

Returns: *this.

Postconditions: value() == v.

bool value() const noexcept;

Returns: The stored socket option value. For extensible implementations, returns value_ != 0.

explicit operator bool() const noexcept;

Returns: value().

bool operator!() const noexcept;

Returns: !value().

template<class Protocol> int level(const Protocol& p) const noexcept;

Returns: L.

template<class Protocol> int name(const Protocol& p) const noexcept;

Returns: N.

template<class Protocol> void* data(const Protocol& p) noexcept;

Returns: std::addressof(value_).

template<class Protocol> const void* data(const Protocol& p) const noexcept;

Returns: std::addressof(value_).

template<class Protocol> size_t size(const Protocol& p) const noexcept;

Returns: sizeof(value_).

template<class Protocol> void resize(const Protocol& p, size_t s);

Throws: length_error if s is not a valid data size for the protocol specified by p.

10.18.2.11. Integer socket options

[socket.reqmts.opt.int]

A type X meets the IntegerSocketOption requirements if it satisfies the requirements of Destructible (C++Std [destructible]), DefaultConstructible (C++Std [defaultconstructible]), CopyConstructible (C++Std [copyconstructible]), CopyAssignable (C++Std [copyassignable]), GettableSocketOption, and SettableSocketOption, as well as the additional requirements listed below.

In the table below, a denotes a (possibly const) value of type X, b denotes a (possibly const) value of type int, and u denotes an identifier.

Table 29. IntegerSocketOption requirements

expression

type

assertion/note
pre/post-conditions

X u;

post: u.value() == 0.

X u(b);

post: u.value() == b.

a.value()

int

Returns the current integer value of the socket option object.


In this Technical Specification, types that satisfy the IntegerSocketOption requirements are defined as follows.

class C
{
public:
  // constructors:
  C() noexcept;
  explicit C(int v) noexcept;

  // members:
  C& operator=(int v) noexcept;

  int value() const noexcept;
};

Extensible implementations provide the following member functions:

class C
{
public:
  template<class Protocol> int level(const Protocol& p) const noexcept;
  template<class Protocol> int name(const Protocol& p) const noexcept;
  template<class Protocol> void* data(const Protocol& p) noexcept;
  template<class Protocol> const void* data(const Protocol& p) const noexcept;
  template<class Protocol> size_t size(const Protocol& p) const noexcept;
  template<class Protocol> void resize(const Protocol& p, size_t s);
  // remainder unchanged
private:
  int value_; // exposition only
};

Let L and N identify the POSIX macros to be passed as the level and option_name arguments, respectively, to POSIX setsockopt and getsockopt.

C() noexcept;

Postconditions: !value().

explicit C(int v) noexcept;

Postconditions: value() == v.

C& operator=(int v) noexcept;

Returns: *this.

Postconditions: value() == v.

int value() const noexcept;

Returns: The stored socket option value. For extensible implementations, returns value_.

template<class Protocol> int level(const Protocol& p) const noexcept;

Returns: L.

template<class Protocol> int name(const Protocol& p) const noexcept;

Returns: N.

template<class Protocol> void* data(const Protocol& p) noexcept;

Returns: std::addressof(value_).

template<class Protocol> const void* data(const Protocol& p) const noexcept;

Returns: std::addressof(value_).

template<class Protocol> size_t size(const Protocol& p) const noexcept;

Returns: sizeof(value_).

template<class Protocol> void resize(const Protocol& p, size_t s);

Throws: length_error if s is not a valid data size for the protocol specified by p.

10.18.2.12. I/O control command requirements

[socket.reqmts.iocontrolcommand]

A type X meets the IoControlCommand requirements if it satisfies the requirements listed below.

In the table below, a denotes a (possibly const) value of type X, and b denotes a value of type X.

Table 30. IoControlCommand requirements for extensible implementations

expression

type

assertion/note
pre/post-conditions

a.name()

int

Returns a value suitable for passing as the request argument to POSIX ioctl (or equivalent).

b.data()

void*


10.18.2.13. Connect condition requirements

[socket.reqmts.connectcondition]

A type X meets the ConnectCondition requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and CopyConstructible (C++Std [copyconstructible]), as well as the additional requirements listed below.

In the table below, x denotes a value of type X, ec denotes a (possibly const) value of type error_code, and ep denotes a (possibly const) value of some type satisfying the endpoint requirements.

Table 31. ConnectCondition requirements

expression

return type

assertion/note
pre/post-condition

x(ec, ep)

bool

Returns true to indicate that the connect or async_connect algorithm should attempt a connection to the endpoint ep. Otherwise, returns false to indicate that the algorithm should not attempt connection to the endpoint ep, and should instead skip to the next endpoint in the sequence.


10.18.3. Error codes

[socket.err]

const error_category& socket_category() noexcept;

Returns: A reference to an object of a type derived from class error_category. All calls to this function return references to the same object.

The object’s default_error_condition and equivalent virtual functions behave as specified for the class error_category. The object’s name virtual function returns a pointer to the string "socket".

error_code make_error_code(socket_errc e) noexcept;

Returns: error_code(static_cast<int>(e), socket_category()).

error_condition make_error_condition(socket_errc e) noexcept;

Returns: error_condition(static_cast<int>(e), socket_category()).

10.18.4. Class socket_base

[socket.base]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class socket_base
  {
  public:
    class broadcast;
    class debug;
    class do_not_route;
    class keep_alive;
    class linger;
    class out_of_band_inline;
    class receive_buffer_size;
    class receive_low_watermark;
    class reuse_address;
    class send_buffer_size;
    class send_low_watermark;

    typedef T1 shutdown_type;
    static constexpr shutdown_type shutdown_receive;
    static constexpr shutdown_type shutdown_send;
    static constexpr shutdown_type shutdown_both;

    typedef T2 wait_type;
    static constexpr wait_type wait_read;
    static constexpr wait_type wait_write;
    static constexpr wait_type wait_error;

    typedef T3 message_flags;
    static constexpr message_flags message_peek;
    static constexpr message_flags message_out_of_band;
    static constexpr message_flags message_do_not_route;

    static const int max_listen_connections;

  protected:
    socket_base();
    ~socket_base();
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

socket_base defines several member types:

— socket option classes broadcast, debug, do_not_route, keep_alive, linger, out_of_band_inline, receive_buffer_size, receive_low_watermark, reuse_address, send_buffer_size, and send_low_watermark;

— an enumerated type, shutdown_type, for use with the basic_socket<Protocol> class's shutdown member function.

— an enumerated type, wait_type, for use with the basic_socket<Protocol> and basic_socket_acceptor<Protocol> classes' wait and async_wait member functions,

— a bitmask type, message_flags, for use with the basic_stream_socket<Protocol> class's send, async_send,receive, and async_receive member functions, and the basic_datagram_socket<Protocol> class's send, async_send, send_to, async_send_to, receive, async_receive, receive_from, and async_receive_from member functions.

— a constant, max_listen_connections, for use with the basic_socket_acceptor<Protocol> class's listen member function.

Table 32. socket_base constants

Constant Name

POSIX macro

Definition or notes

shutdown_receive

SHUT_RD

Disables further receive operations.

shutdown_send

SHUT_WR

Disables further send operations.

shutdown_both

SHUT_RDWR

Disables further send and receive operations.

wait_read

Wait until the socket is ready-to-read.

For a given socket, when a wait or async_wait operation using wait_read completes successfuly, a subsequent call to the socket's receive or receive_from functions may complete without blocking.
Similarly, for a given acceptor, when a wait or async_wait operation using wait_read completes successfully, a subsequent call to the acceptor's accept function may complete without blocking.

wait_write

Wait until the socket is ready-to-write.

For a given socket, when a wait or async_wait operation using wait_write completes successfuly, a subsequent call to the socket's send or send_to functions may complete without blocking.

wait_error

Wait until the socket has a pending error condition.

For a given socket, when a wait or async_wait operation using wait_error completes successfuly, a subsequent call to one of the socket's synchronous operations may complete without blocking. The nature of the pending error condition determines which.

message_peek

MSG_PEEK

Leave received data in queue.

message_out_of_band

MSG_OOB

Out-of-band data.

message_do_not_route

MSG_DONTROUTE

Send without using routing tables.

max_listen_connections

SOMAXCONN

The implementation-defined limit on the length of the queue of pending incoming connections.


10.18.5. Socket options

[socket.opt]

In the table below, let C denote a socket option class; let L identify the POSIX macro to be passed as the level argument to POSIX setsockopt and getsockopt; let N identify the POSIX macro to be passed as the option_name argument to POSIX setsockopt and getsockopt; and let T identify the type of the value whose address will be passed as the option_value argument to POSIX setsockopt and getsockopt.

Table 33. socket options

C

L

N

T

Requirements, definition or notes

socket_base::broadcast

SOL_SOCKET

SO_BROADCAST

int

Satisfies the BooleanSocketOption type requirements.

Determines whether a socket permits sending of broadcast messages, if supported by the protocol.

socket_base::debug

SOL_SOCKET

SO_DEBUG

int

Satisfies the BooleanSocketOption type requirements.

Determines whether debugging information is recorded by the underlying protocol.

socket_base::do_not_route

SOL_SOCKET

SO_DONTROUTE

int

Satisfies the BooleanSocketOption type requirements.

Determines whether outgoing messages bypass standard routing facilities.

socket_base::keep_alive

SOL_SOCKET

SO_KEEPALIVE

int

Satisfies the BooleanSocketOption type requirements.

Determines whether a socket permits sending of keep_alive messages, if supported by the protocol.

socket_base::linger

SOL_SOCKET

SO_LINGER

linger

Controls the behavior when a socket is closed and unsent data is present.

socket_base::out_of_band_inline

SOL_SOCKET

SO_OOBINLINE

int

Satisfies the BooleanSocketOption type requirements.

Determines whether out-of-band data (also known as urgent data) is received inline.

socket_base::receive_buffer_size

SOL_SOCKET

SO_RCVBUF

int

Satisfies the IntegerSocketOption type requirements.

Specifies the size of the receive buffer associated with a socket.

socket_base::receive_low_watermark

SOL_SOCKET

SO_RCVLOWAT

int

Satisfies the IntegerSocketOption type requirements.

Specifies the minimum number of bytes to process for socket input operations.

socket_base::reuse_address

SOL_SOCKET

SO_REUSEADDR

int

Satisfies the BooleanSocketOption type requirements.

Determines whether the validation of endpoints used for binding a socket should allow the reuse of local endpoints, if supported by the protocol.

socket_base::send_buffer_size

SOL_SOCKET

SO_SNDBUF

int

Satisfies the IntegerSocketOption type requirements.

Specifies the size of the send buffer associated with a socket.

socket_base::send_low_watermark

SOL_SOCKET

SO_SNDLOWAT

int

Satisfies the IntegerSocketOption type requirements.

Specifies the minimum number of bytes to process for socket output operations.


10.18.5.1. Class socket_base::linger

[socket.opt.linger]

The linger class represents a socket option for controlling the behavior when a socket is closed and unsent data is present.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class socket_base::linger
  {
  public:
    // constructors:
    linger() noexcept;
    linger(bool e, chrono::seconds t) noexcept;

    // members:
    bool enabled() const noexcept;
    void enabled(bool e) noexcept;

    chrono::seconds timeout() const noexcept;
    void timeout(chrono::seconds t) noexcept;
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

linger satisfies the requirements of Destructible (C++Std [destructible]), DefaultConstructible (C++Std [defaultconstructible]), CopyConstructible (C++Std [copyconstructible]), CopyAssignable (C++Std [copyassignable]), GettableSocketOption, and SettableSocketOption.

Extensible implementations provide the following member functions:

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  class socket_base::linger
  {
  public:
    template<class Protocol> int level(const Protocol& p) const noexcept;
    template<class Protocol> int name(const Protocol& p) const noexcept;
    template<class Protocol> void data(const Protocol& p) noexcept;
    template<class Protocol> const void* data(const Protocol& p) const noexcept;
    template<class Protocol> size_t size(const Protocol& p) const noexcept;
    template<class Protocol> void resize(const Protocol& p, size_t s);
    // remainder unchanged
  private:
    ::linger value_;  // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

linger() noexcept;

Postconditions: !enabled() && timeout() == chrono::seconds(0).

linger(bool e, chrono::seconds t) noexcept;

Postconditions: enabled() == e && timeout() == t.

bool enabled() const noexcept;

Returns: value_.l_onoff != 0.

void enabled(bool e) noexcept;

Postconditions: enabled() == e.

chrono::seconds timeout() const noexcept;

Returns: chrono::seconds(value_.l_linger).

void timeout(chrono::seconds t) noexcept;

Postconditions: timeout() == t.

template<class Protocol> int level(const Protocol& p) const noexcept;

Returns: SOL_SOCKET.

template<class Protocol> int name(const Protocol& p) const noexcept;

Returns: SO_LINGER.

template<class Protocol> void* data(const Protocol& p) const noexcept;

Returns: std::addressof(value_).

template<class Protocol> const void* data(const Protocol& p) const noexcept;

Returns: std::addressof(value_).

template<class Protocol> size_t size(const Protocol& p) const noexcept;

Returns: sizeof(value_).

template<class Protocol> void resize(const Protocol& p, size_t s);

Throws: length_error if s != sizeof(value_).

10.18.6. Class template basic_socket

[socket.basic]

Class template basic_socket<Protocol> is used as the base class for the basic_datagram_socket<Protocol> and basic_stream_socket<Protocol> class templates. It provides functionality that is common to both types of socket.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Protocol>
  class basic_socket : public socket_base
  {
  public:
    // types:

    typedef io_context::executor_type executor_type;
    typedef implementation defined native_handle_type; // See native handles
    typedef Protocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;

    // basic_socket operations:

    executor_type get_executor() noexcept;

    native_handle_type native_handle(); // See native handles

    void open(const protocol_type& protocol = protocol_type());
    void open(const protocol_type& protocol, error_code& ec);

    void assign(const protocol_type& protocol,
                const native_handle_type& native_socket); // See native handles
    void assign(const protocol_type& protocol,
                const native_handle_type& native_socket,
                error_code& ec); // See native handles

    bool is_open() const noexcept;

    void close();
    void close(error_code& ec);

    void cancel();
    void cancel(error_code& ec);

    template<class SettableSocketOption>
      void set_option(const SettableSocketOption& option);
    template<class SettableSocketOption>
      void set_option(const SettableSocketOption& option, error_code& ec);

    template<class GettableSocketOption>
      void get_option(GettableSocketOption& option) const;
    template<class GettableSocketOption>
      void get_option(GettableSocketOption& option, error_code& ec) const;

    template<class IoControlCommand>
      void io_control(IoControlCommand& command);
    template<class IoControlCommand>
      void io_control(IoControlCommand& command, error_code& ec);

    void non_blocking(bool mode);
    void non_blocking(bool mode, error_code& ec);
    bool non_blocking() const;

    void native_non_blocking(bool mode);
    void native_non_blocking(bool mode, error_code& ec);
    bool native_non_blocking() const;

    bool at_mark() const;
    bool at_mark(error_code& ec) const;

    size_t available() const;
    size_t available(error_code& ec) const;

    void bind(const endpoint_type& endpoint);
    void bind(const endpoint_type& endpoint, error_code& ec);

    void shutdown(shutdown_type what);
    void shutdown(shutdown_type what, error_code& ec);

    endpoint_type local_endpoint() const;
    endpoint_type local_endpoint(error_code& ec) const;

    endpoint_type remote_endpoint() const;
    endpoint_type remote_endpoint(error_code& ec) const;

    void connect(const endpoint_type& endpoint);
    void connect(const endpoint_type& endpoint, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_connect(const endpoint_type& endpoint,
                            CompletionToken&& token);

    void wait(wait_type w);
    void wait(wait_type w, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_wait(wait_type w, CompletionToken&& token);

  protected:
    // construct / copy / destroy:

    explicit basic_socket(io_context& ctx);
    basic_socket(io_context& ctx, const protocol_type& protocol);
    basic_socket(io_context& ctx, const endpoint_type& endpoint);
    basic_socket(io_context& ctx, const protocol_type& protocol,
                 const native_handle_type& native_socket); // See native handles
    basic_socket(const basic_socket&) = delete;
    basic_socket(basic_socket&& rhs);
    template<class OtherProtocol>
      basic_socket(basic_socket<OtherProtocol>&& rhs);

    ~basic_socket();

    basic_socket& operator=(const basic_socket&) = delete;
    basic_socket& operator=(basic_socket&& rhs);
    template<class OtherProtocol>
      basic_socket& operator=(basic_socket<OtherProtocol>&& rhs);

  private:
    protocol_type protocol_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_socket meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), and MoveAssignable (C++Std [moveassignable]).

When an operation has its effects specified as if by passing the result of native_handle() to a POSIX function, then the operation fails with error condition errc::bad_file_descriptor if is_open() == false at the point in the effects when the POSIX function is called.

10.18.6.1. basic_socket constructors

[socket.basic.cons]

explicit basic_socket(io_context& ctx);

Postconditions:
get_executor() == ctx.get_executor().
is_open() == false.

basic_socket(io_context& ctx, const protocol_type& protocol);

Effects: Opens this socket as if by calling open(protocol).

Postconditions:
get_executor() == ctx.get_executor().
is_open() == true.
non_blocking() == false.
protocol_ == protocol.

basic_socket(io_context& ctx, const endpoint_type& endpoint);

Effects: Opens and binds this socket as if by calling:

open(endpoint.protocol());
bind(endpoint);

Postconditions:
get_executor() == ctx.get_executor().
is_open() == true.
non_blocking() == false.
protocol_ == endpoint.protocol().

basic_socket(io_context& ctx, const protocol_type& protocol,
             const native_handle_type& native_socket);

Requires: native_socket is a native handle to an open socket.

Effects: Assigns the existing native socket into this socket as if by calling assign(protocol, native_socket).

Postconditions:
get_executor() == ctx.get_executor().
is_open() == true.
non_blocking() == false.
protocol_ == protocol.

basic_socket(basic_socket&& rhs);

Effects: Move constructs an object of class basic_socket<Protocol> that refers to the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the constructor invocation.
non_blocking() returns the same value as rhs.non_blocking() prior to the constructor invocation.
native_handle() returns the prior value of rhs.native_handle().
protocol_ is the prior value of rhs.protocol_.
rhs.is_open() == false.

template<class OtherProtocol>
  basic_socket(basic_socket<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: Move constructs an object of class basic_socket<Protocol> that refers to the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the constructor invocation.
non_blocking() returns the same value as rhs.non_blocking() prior to the constructor invocation.
native_handle() returns the prior value of rhs.native_handle().
protocol_ is the result of converting the prior value of rhs.protocol_.
rhs.is_open() == false.

Remarks: This constructor shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.6.2. basic_socket destructor

[socket.basic.dtor]

~basic_socket();

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this socket, disables the linger socket option to prevent the destructor from blocking, and releases socket resources as if by POSIX close(native_handle()). Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true.

10.18.6.3. basic_socket assignment

[socket.basic.assign]

basic_socket& operator=(basic_socket&& rhs);

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this socket. Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true. Disables the linger socket option to prevent the assignment from blocking, and releases socket resources as if by POSIX close(native_handle()). Moves into *this the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the assignment.
non_blocking() returns the same value as rhs.non_blocking() prior to the assignment.
protocol_ is the prior value of rhs.protocol_.
rhs.is_open() == false.

Returns: *this.

template<class OtherProtocol>
  basic_socket& operator=(basic_socket<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this socket. Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true. Disables the linger socket option to prevent the assignment from blocking, and releases socket resources as if by POSIX close(native_handle()). Moves into *this the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the assignment.
non_blocking() returns the same value as rhs.non_blocking() prior to the assignment.
protocol_ is the result of converting the prior value of rhs.protocol_.
rhs.is_open() == false.

Returns: *this.

Remarks: This assignment operator shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.6.4. basic_socket operations

[socket.basic.ops]

executor_type get_executor() noexcept;

Returns: The associated executor.

native_handle_type native_handle();

Returns: The native representation of this socket.

void open(const protocol_type& protocol);
void open(const protocol_type& protocol, error_code& ec);

Effects: Establishes the postcondition, as if by POSIX socket(protocol.family(), protocol.type(), protocol.protocol()).

Postconditions:
is_open() == true.
non_blocking() == false.
protocol_ == protocol.

Error conditions:
socket_errc::already_open — if is_open() == true.

void assign(const protocol_type& protocol,
            const native_handle_type& native_socket);
void assign(const protocol_type& protocol,
            const native_handle_type& native_socket, error_code& ec);

Requires: native_socket is a native handle to an open socket.

Effects: Assigns the native socket handle to this socket object.

Postconditions:
is_open() == true.
non_blocking() == false.
protocol_ == protocol.

Error conditions:
socket_errc::already_open — if is_open() == true.

bool is_open() const noexcept;

Returns: A bool indicating whether this socket was opened by a previous call to open or assign.

void close();
void close(error_code& ec);

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this socket, and establishes the postcondition as if by POSIX close(native_handle()). Completion handlers for canceled asynchronous operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Postconditions: is_open() == false.

void cancel();
void cancel(error_code& ec);

Effects: Cancels all outstanding asynchronous operations associated with this socket. Completion handlers for canceled asynchronous operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

Remarks: Does not block (C++Std [defns.block]) the calling thread pending completion of the canceled operations.

template<class SettableSocketOption>
  void set_option(const SettableSocketOption& option);
template<class SettableSocketOption>
  void set_option(const SettableSocketOption& option, error_code& ec);

Effects: Sets an option on this socket, as if by POSIX setsockopt(native_handle(), option.level(protocol_), option.name(protocol_), option.data(protocol_), option.size(protocol_)).

template<class GettableSocketOption>
  void get_option(GettableSocketOption& option);
template<class GettableSocketOption>
  void get_option(GettableSocketOption& option, error_code& ec);

Effects: Gets an option from this socket, as if by POSIX:

socklen_t option_len = option.size(protocol_);
int result = getsockopt(native_handle(), option.level(protocol_),
                        option.name(protocol_), option.data(protocol_),
                        &option_len);
if (result == 0)
  option.resize(option_len);

template<class IoControlCommand>
  void io_control(IoControlCommand& command);
template<class IoControlCommand>
  void io_control(IoControlCommand& command, error_code& ec);

Effects: Executes an I/O control command on this socket, as if by POSIX ioctl(native_handle(), command.name(), command.data()).

void non_blocking(bool mode);
void non_blocking(bool mode, error_code& ec);

Effects: Sets the non-blocking mode of this socket. The non-blocking mode determines whether subsequent synchronous socket operations on *this block the calling thread.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

Postconditions: non_blocking() == mode.

[Note: The non-blocking mode has no effect on the behavior of asynchronous operations. —end note]

bool non_blocking() const;

Returns: The non-blocking mode of this socket.

void native_non_blocking(bool mode);
void native_non_blocking(bool mode, error_code& ec);

Effects: Sets the non-blocking mode of the underlying native socket, as if by POSIX:

int flags = fcntl(native_handle(), F_GETFL, 0);
if (flags >= 0)
{
  if (mode)
    flags |= O_NONBLOCK;
  else
    flags &= ~O_NONBLOCK;
  fcntl(native_handle(), F_SETFL, flags);
}

The native non-blocking mode has no effect on the behavior of the synchronous or asynchronous operations specified in this clause.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.
errc::invalid_argument — if mode == false and non_blocking() == true. [Note: As the combination does not make sense. —end note]

bool native_non_blocking() const;

Returns: The non-blocking mode of the underlying native socket.

Remarks: Implementations are permitted and encouraged to cache the native non-blocking mode that was applied through a prior call to native_non_blocking. Implementations may return an incorrect value if a program sets the non-blocking mode directly on the socket, by calling an operating system-specific function on the result of native_handle().

bool at_mark() const;
bool at_mark(error_code& ec) const;

Effects: Determines if this socket is at the out-of-band data mark, as if by POSIX sockatmark(native_handle()). [Note: The at_mark() function must be used in conjunction with the socket_base::out_of_band_inline socket option. —end note]

Returns: A bool indicating whether this socket is at the out-of-band data mark. false if an error occurs.

size_t available() const;
size_t available(error_code& ec) const;

Returns: An indication of the number of bytes that may be read without blocking, or 0 if an error occurs.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

void bind(const endpoint_type& endpoint);
void bind(const endpoint_type& endpoint, error_code& ec);

Effects: Binds this socket to the specified local endpoint, as if by POSIX bind(native_handle(), endpoint.data(), endpoint.size()).

void shutdown(shutdown_type what);
void shutdown(shutdown_type what, error_code& ec);

Effects: Shuts down all or part of a full-duplex connection for the socket, as if by POSIX shutdown(native_handle(), static_cast<int>(what)).

endpoint_type local_endpoint() const;
endpoint_type local_endpoint(error_code& ec) const;

Effects: Determines the locally-bound endpoint associated with the socket, as if by POSIX:

endpoint_type endpoint;
socklen_t endpoint_len = endpoint.capacity();
int result == getsockname(native_handle(), endpoint.data(), &endpoint_len);
if (result == 0)
  endpoint.resize(endpoint_len);

Returns: On success, endpoint. Otherwise endpoint_type().

endpoint_type remote_endpoint() const;
endpoint_type remote_endpoint(error_code& ec) const;

Effects: Determines the remote endpoint associated with this socket, as if by POSIX:

endpoint_type endpoint;
socklen_t endpoint_len = endpoint.capacity();
int result == getpeername(native_handle(), endpoint.data(), &endpoint_len);
if (result == 0)
  endpoint.resize(endpoint_len);

Returns: On success, endpoint. Otherwise endpoint_type().

void connect(const endpoint_type& endpoint);
void connect(const endpoint_type& endpoint, error_code& ec);

Effects: If is_open() is false, opens this socket by performing open(endpoint.protocol(), ec). If ec, returns with no further action. Connects this socket to the specified remote endpoint, as if by POSIX connect(native_handle(), endpoint.data(), endpoint.size()).

template<class CompletionToken>
  DEDUCED async_connect(const endpoint_type& endpoint, CompletionToken&& token);

Completion signature: void(error_code ec).

Effects: If is_open() is false, opens this socket by performing open(endpoint.protocol(), ec). If ec, the operation completes immediately with no further action. Initiates an asynchronous operation to connect this socket to the specified remote endpoint, as if by POSIX connect(native_handle(), endpoint.data(), endpoint.size()).

When an asynchronous connect operation on this socket is simultaneously outstanding with another asynchronous connect, read, or write operation on this socket, the behavior is undefined.

If a program performs a synchronous operation on this socket, other than close or cancel, while there is an outstanding asynchronous connect operation, the behavior is undefined.

void wait(wait_type w);
void wait(wait_type w, error_code& ec);

Effects: Waits for this socket to be ready to read, ready to write, or to have error conditions pending, as if by POSIX poll.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

template<class CompletionToken>
  DEDUCED async_wait(wait_type w, CompletionToken&& token);

Completion signature: void(error_code ec).

Effects: Initiates an asynchronous operation to wait for this socket to be ready to read, ready to write, or to have error conditions pending, as if by POSIX poll.

When there are multiple outstanding asynchronous wait operations on this socket with the same wait_type value, all of these operations complete when this socket enters the corresponding ready state. The order of invocation of the completion handlers for these operations is unspecified.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

10.18.7. Class template basic_datagram_socket

[socket.dgram]

The class template basic_datagram_socket<Protocol> is used to send and receive discrete messages of fixed maximum length.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Protocol>
  class basic_datagram_socket : public basic_socket<Protocol>
  {
  public:
    // types:

    typedef implementation defined native_handle_type; // See native handles
    typedef Protocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;

    // construct / copy / destroy:

    explicit basic_datagram_socket(io_context& ctx);
    basic_datagram_socket(io_context& ctx, const protocol_type& protocol);
    basic_datagram_socket(io_context& ctx, const endpoint_type& endpoint);
    basic_datagram_socket(io_context& ctx, const protocol_type& protocol,
                          const native_handle_type& native_socket);
    basic_datagram_socket(const basic_datagram_socket&) = delete;
    basic_datagram_socket(basic_datagram_socket&& rhs);
    template<class OtherProtocol>
      basic_datagram_socket(basic_datagram_socket<OtherProtocol>&& rhs);

    ~basic_datagram_socket();

    basic_datagram_socket& operator=(const basic_datagram_socket&) = delete;
    basic_datagram_socket& operator=(basic_datagram_socket&& rhs);
    template<class OtherProtocol>
      basic_datagram_socket& operator=(basic_datagram_socket<OtherProtocol>&& rhs);

    // basic_datagram_socket operations:

    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers);
    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers,
                     error_code& ec);

    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers,
                     socket_base::message_flags flags);
    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers,
                     socket_base::message_flags flags, error_code& ec);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_receive(const MutableBufferSequence& buffers,
                            CompletionToken&& token);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_receive(const MutableBufferSequence& buffers,
                            socket_base::message_flags flags,
                            CompletionToken&& token);

    template<class MutableBufferSequence>
      size_t receive_from(const MutableBufferSequence& buffers,
                          endpoint_type& sender);
    template<class MutableBufferSequence>
      size_t receive_from(const MutableBufferSequence& buffers,
                          endpoint_type& sender, error_code& ec);

    template<class MutableBufferSequence>
      size_t receive_from(const MutableBufferSequence& buffers,
                          endpoint_type& sender,
                          socket_base::message_flags flags);
    template<class MutableBufferSequence>
      size_t receive_from(const MutableBufferSequence& buffers,
                          endpoint_type& sender,
                          socket_base::message_flags flags,
                          error_code& ec);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_receive_from(const MutableBufferSequence& buffers,
                                 endpoint_type& sender,
                                 CompletionToken&& token);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_receive_from(const MutableBufferSequence& buffers,
                                 endpoint_type& sender,
                                 socket_base::message_flags flags,
                                 CompletionToken&& token);

    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers);
    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers, error_code& ec);

    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers,
                  socket_base::message_flags flags);
    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers,
                  socket_base::message_flags flags, error_code& ec);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_send(const ConstBufferSequence& buffers,
                         CompletionToken&& token);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_send(const ConstBufferSequence& buffers,
                         socket_base::message_flags flags,
                         CompletionToken&& token);

    template<class ConstBufferSequence>
      size_t send_to(const ConstBufferSequence& buffers,
                     const endpoint_type& recipient);
    template<class ConstBufferSequence>
      size_t send_to(const ConstBufferSequence& buffers,
                     const endpoint_type& recipient, error_code& ec);

    template<class ConstBufferSequence>
      size_t send_to(const ConstBufferSequence& buffers,
                     const endpoint_type& recipient,
                     socket_base::message_flags flags);
    template<class ConstBufferSequence>
      size_t send_to(const ConstBufferSequence& buffers,
                     const endpoint_type& recipient,
                     socket_base::message_flags flags, error_code& ec);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_send_to(const ConstBufferSequence& buffers,
                            const endpoint_type& recipient,
                            CompletionToken&& token);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_send_to(const ConstBufferSequence& buffers,
                            const endpoint_type& recipient,
                            socket_base::message_flags flags,
                            CompletionToken&& token);
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_datagram_socket meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), and MoveAssignable (C++Std [moveassignable]).

If a program performs a synchronous operation on this socket, other than close, cancel, shutdown, send, or send_to, while there is an outstanding asynchronous read operation, the behavior is undefined.

If a program performs a synchronous operation on this socket, other than close, cancel, shutdown, receive, or receive_from, while there is an outstanding asynchronous write operation, the behavior is undefined.

When an operation has its effects specified as if by passing the result of native_handle() to a POSIX function, then the operation fails with error condition errc::bad_file_descriptor if is_open() == false at the point in the effects when the POSIX function is called.

10.18.7.1. basic_datagram_socket constructors

[socket.dgram.cons]

explicit basic_datagram_socket(io_context& ctx);

Effects: Initializes the base class with basic_socket<Protocol>(ctx).

basic_datagram_socket(io_context& ctx, const protocol_type& protocol);

Effects: Initializes the base class with basic_socket<Protocol>(ctx, protocol).

basic_datagram_socket(io_context& ctx, const endpoint_type& endpoint);

Effects: Initializes the base class with basic_socket<Protocol>(ctx, endpoint).

basic_datagram_socket(io_context& ctx, const protocol_type& protocol,
                      const native_handle_type& native_socket);

Effects: Initializes the base class with basic_socket<Protocol>(ctx, protocol, native_socket).

basic_datagram_socket(basic_datagram_socket&& rhs);

Effects: Move constructs an object of class basic_datagram_socket<Protocol>, initializing the base class with basic_socket<Protocol>(std::move(rhs)).

template<class OtherProtocol>
  basic_datagram_socket(basic_datagram_socket<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: Move constructs an object of class basic_datagram_socket<Protocol>, initializing the base class with basic_socket<Protocol>(std::move(rhs)).

Remarks: This constructor shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.7.2. basic_datagram_socket assignment

[socket.dgram.assign]

basic_datagram_socket& operator=(basic_datagram_socket&& rhs);

Effects: Equivalent to basic_socket<Protocol>::operator=(std::move(rhs)).

Returns: *this.

template<class OtherProtocol>
  basic_datagram_socket& operator=(basic_datagram_socket<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: Equivalent to basic_socket<Protocol>::operator=(std::move(rhs)).

Returns: *this.

Remarks: This assignment operator shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.7.3. basic_datagram_socket operations

[socket.dgram.op]

template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers);
template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers,
                 error_code& ec);

Returns: receive(buffers, socket_base::message_flags(), ec).

template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers,
                 socket_base::message_flags flags);
template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers,
                 socket_base::message_flags flags, error_code& ec);

Effects: Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, and reads data from this socket as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
recvmsg(native_handle(), &message, static_cast<int>(flags));

Returns: On success, the number of bytes received. Otherwise 0.

[Note: This operation may be used with connection-mode or connectionless-mode sockets, but it is normally used with connection-mode sockets because it does not permit the application to retrieve the source endpoint of received data. —end note]

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_receive(const MutableBufferSequence& buffers,
                        CompletionToken&& token);

Returns: async_receive(buffers, socket_base::message_flags(), forward<CompletionToken>(token)).

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_receive(const MutableBufferSequence& buffers,
                        socket_base::message_flags flags,
                        CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to read data from this socket. Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, then reads data as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
recvmsg(native_handle(), &message, static_cast<int>(flags));

If the operation completes successfully, n is the number of bytes received. Otherwise n is 0.

[Note: This operation may be used with connection-mode or connectionless-mode sockets, but it is normally used with connection-mode sockets because it does not permit the application to retrieve the source endpoint of received data. —end note]

Error conditions:
errc::invalid_argument — if socket_base::message_peek is set in flags.

template<class MutableBufferSequence>
  size_t receive_from(const MutableBufferSequence& buffers,
                      endpoint_type& sender);
template<class MutableBufferSequence>
  size_t receive_from(const MutableBufferSequence& buffers,
                      endpoint_type& sender, error_code& ec);

Returns: receive_from(buffers, sender, socket_base::message_flags(), ec).

template<class MutableBufferSequence>
  size_t receive_from(const MutableBufferSequence& buffers,
                      endpoint_type& sender,
                      socket_base::message_flags flags);
template<class MutableBufferSequence>
  size_t receive_from(const MutableBufferSequence& buffers,
                      endpoint_type& sender,
                      socket_base::message_flags flags,
                      error_code& ec);

Effects: Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, and reads data from this socket as if by POSIX:

msghdr message;
message.msg_name = sender.data();
message.msg_namelen = sender.capacity();
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
ssize_t result = recvmsg(native_handle(), &message, static_cast<int>(flags));
if (result >= 0)
  sender.resize(message.msg_namelen);

Returns: On success, the number of bytes received. Otherwise 0.

[Note: This operation may be used with connection-mode or connectionless-mode sockets, but it is normally used with connectionless-mode sockets because it permits the application to retrieve the source endpoint of received data. —end note]

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_receive_from(const MutableBufferSequence& buffers,
                             endpoint_type& sender,
                             CompletionToken&& token);

Effects: Returns async_receive_from(buffers, sender, socket_base::message_flags(), forward<CompletionToken>(token)).

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_receive_from(const MutableBufferSequence& buffers,
                             endpoint_type& sender,
                             socket_base::message_flags flags,
                             CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to read data from this socket. Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, then reads data as if by POSIX:

msghdr message;
message.msg_name = sender.data();
message.msg_namelen = sender.capacity();
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
ssize_t result = recvmsg(native_handle(), &message, static_cast<int>(flags));
if (result >= 0)
  sender.resize(message.msg_namelen);

If the operation completes successfully, n is the number of bytes received. Otherwise n is 0.

[Note: This operation may be used with connection-mode or connectionless-mode sockets, but it is normally used with connectionless-mode sockets because it permits the application to retrieve the source endpoint of received data. —end note]

Error conditions:
errc::invalid_argument — if socket_base::message_peek is set in flags.

template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers);
template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers, error_code& ec);

Returns: send(buffers, socket_base::message_flags(), ec).

template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers,
              socket_base::message_flags flags);
template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers,
              socket_base::message_flags flags, error_code& ec);

Effects: Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, and writes data to this socket as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
sendmsg(native_handle(), &message, static_cast<int>(flags));

Returns: On success, the number of bytes sent. Otherwise 0.

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_send(const ConstBufferSequence& buffers, CompletionToken&& token);

Returns: async_send(buffers, socket_base::message_flags(), forward<CompletionToken>(token)).

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_send(const ConstBufferSequence& buffers,
                     socket_base::message_flags flags,
                     CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to write data to this socket. Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, then writes data as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
sendmsg(native_handle(), &message, static_cast<int>(flags));

If the operation completes successfully, n is the number of bytes sent. Otherwise n is 0.

template<class ConstBufferSequence>
  size_t send_to(const ConstBufferSequence& buffers,
                 const endpoint_type& recipient);
template<class ConstBufferSequence>
  size_t send_to(const ConstBufferSequence& buffers,
                 const endpoint_type& recipient, error_code& ec);

Returns: send_to(buffers, recipient, socket_base::message_flags(), ec).

template<class ConstBufferSequence>
  size_t send_to(const ConstBufferSequence& buffers,
                 const endpoint_type& recipient,
                 socket_base::message_flags flags);
template<class ConstBufferSequence>
  size_t send_to(const ConstBufferSequence& buffers,
                 const endpoint_type& recipient,
                 socket_base::message_flags flags, error_code& ec);

Effects: Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, and writes data to this socket as if by POSIX:

msghdr message;
message.msg_name = recipient.data();
message.msg_namelen = recipient.size();
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
sendmsg(native_handle(), &message, static_cast<int>(flags));

Returns: On success, the number of bytes sent. Otherwise 0.

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_send_to(const ConstBufferSequence& buffers,
                        const endpoint_type& recipient,
                        CompletionToken&& token);

Returns: async_send_to(buffers, recipient, socket_base::message_flags(), forward<CompletionToken>(token)).

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_send_to(const ConstBufferSequence& buffers,
                        const endpoint_type& recipient,
                        socket_base::message_flags flags,
                        CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to write data to this socket. Constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, then writes data as if by POSIX:

msghdr message;
message.msg_name = recipient.data();
message.msg_namelen = recipient.size();
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
sendmsg(native_handle(), &message, static_cast<int>(flags));

If the operation completes successfully, n is the number of bytes sent. Otherwise n is 0.

10.18.8. Class template basic_stream_socket

[socket.stream]

The class template basic_stream_socket<Protocol> is used to exchange data with a peer over a sequenced, reliable, bidirectional, connection-mode byte stream.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Protocol>
  class basic_stream_socket : public basic_socket<Protocol>
  {
  public:
    // types:

    typedef implementation defined native_handle_type; // See native handles
    typedef Protocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;

    // construct / copy / destroy:

    explicit basic_stream_socket(io_context& ctx);
    basic_stream_socket(io_context& ctx, const protocol_type& protocol);
    basic_stream_socket(io_context& ctx, const endpoint_type& endpoint);
    basic_stream_socket(io_context& ctx, const protocol_type& protocol,
                        const native_handle_type& native_socket);
    basic_stream_socket(const basic_stream_socket&) = delete;
    basic_stream_socket(basic_stream_socket&& rhs);
    template<class OtherProtocol>
      basic_stream_socket(basic_stream_socket<OtherProtocol>&& rhs);

    ~basic_stream_socket();

    basic_stream_socket& operator=(const basic_stream_socket&) = delete;
    basic_stream_socket& operator=(basic_stream_socket&& rhs);
    template<class OtherProtocol>
      basic_stream_socket& operator=(basic_stream_socket<OtherProtocol>&& rhs);

    // basic_stream_socket operations:

    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers);
    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers,
                     error_code& ec);

    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers,
                     socket_base::message_flags flags);
    template<class MutableBufferSequence>
      size_t receive(const MutableBufferSequence& buffers,
                     socket_base::message_flags flags, error_code& ec);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_receive(const MutableBufferSequence& buffers,
                            CompletionToken&& token);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_receive(const MutableBufferSequence& buffers,
                            socket_base::message_flags flags,
                            CompletionToken&& token);

    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers);
    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers, error_code& ec);

    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers,
                  socket_base::message_flags flags);
    template<class ConstBufferSequence>
      size_t send(const ConstBufferSequence& buffers,
                  socket_base::message_flags flags, error_code& ec);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_send(const ConstBufferSequence& buffers,
                         CompletionToken&& token);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_send(const ConstBufferSequence& buffers,
                         socket_base::message_flags flags,
                         CompletionToken&& token);

    template<class MutableBufferSequence>
      size_t read_some(const MutableBufferSequence& buffers);
    template<class MutableBufferSequence>
      size_t read_some(const MutableBufferSequence& buffers,
                       error_code& ec);

    template<class MutableBufferSequence, class CompletionToken>
      DEDUCED async_read_some(const MutableBufferSequence& buffers,
                              CompletionToken&& token);

    template<class ConstBufferSequence>
      size_t write_some(const ConstBufferSequence& buffers);
    template<class ConstBufferSequence>
      size_t write_some(const ConstBufferSequence& buffers,
                        error_code& ec);

    template<class ConstBufferSequence, class CompletionToken>
      DEDUCED async_write_some(const ConstBufferSequence& buffers,
                               CompletionToken&& token);
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_stream_socket meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), MoveAssignable (C++Std [moveassignable]), SyncReadStream, SyncWriteStream, AsyncReadStream, and AsyncWriteStream.

If a program performs a synchronous operation on this socket, other than close, cancel, shutdown, or send, while there is an outstanding asynchronous read operation, the behavior is undefined.

If a program performs a synchronous operation on this socket, other than close, cancel, shutdown, or receive, while there is an outstanding asynchronous write operation, the behavior is undefined.

When an operation has its effects specified as if by passing the result of native_handle() to a POSIX function, then the operation fails with error condition errc::bad_file_descriptor if is_open() == false at the point in the effects when the POSIX function is called.

10.18.8.1. basic_stream_socket constructors

[socket.stream.cons]

explicit basic_stream_socket(io_context& ctx);

Effects: Initializes the base class with basic_socket<Protocol>(ctx).

basic_stream_socket(io_context& ctx, const protocol_type& protocol);

Effects: Initializes the base class with basic_socket<Protocol>(ctx, protocol).

basic_stream_socket(io_context& ctx, const endpoint_type& endpoint);

Effects: Initializes the base class with basic_socket<Protocol>(ctx, endpoint).

basic_stream_socket(io_context& ctx, const protocol_type& protocol,
                      const native_handle_type& native_socket);

Effects: Initializes the base class with basic_socket<Protocol>(ctx, protocol, native_socket).

basic_stream_socket(basic_stream_socket&& rhs);

Effects: Move constructs an object of class basic_stream_socket<Protocol>, initializing the base class with basic_socket<Protocol>(std::move(rhs)).

template<class OtherProtocol>
  basic_stream_socket(basic_stream_socket<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: Move constructs an object of class basic_stream_socket<Protocol>, initializing the base class with basic_socket<Protocol>(std::move(rhs)).

Remarks: This constructor shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.8.2. basic_stream_socket assignment

[socket.stream.assign]

basic_stream_socket& operator=(basic_stream_socket&& rhs);

Effects: Equivalent to basic_socket<Protocol>::operator=(std::move(rhs)).

Returns: *this.

template<class OtherProtocol>
  basic_stream_socket& operator=(basic_stream_socket<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: Equivalent to basic_socket<Protocol>::operator=(std::move(rhs)).

Returns: *this.

Remarks: This assignment operator shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.8.3. basic_stream_socket operations

[socket.stream.ops]

template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers);
template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers,
                 error_code& ec);

Returns: receive(buffers, socket_base::message_flags(), ec).

template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers,
                 socket_base::message_flags flags);
template<class MutableBufferSequence>
  size_t receive(const MutableBufferSequence& buffers,
                 socket_base::message_flags flags, error_code& ec);

Effects: If buffer_size(buffers) == 0, returns immediately with no error. Otherwise, constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, and reads data from this socket as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
recvmsg(native_handle(), &message, static_cast<int>(flags));

Returns: On success, the number of bytes received. Otherwise 0.

Error conditions:
stream_errc::eof — if there is no data to be received and the peer performed an orderly shutdown.

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_receive(const MutableBufferSequence& buffers,
                        CompletionToken&& token);

Returns: async_receive(buffers, socket_base::message_flags(), forward<CompletionToken>(token)).

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_receive(const MutableBufferSequence& buffers,
                        socket_base::message_flags flags,
                        CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to read data from this socket. If buffer_size(buffers) == 0, the asynchronous operation completes immediately with no error and n == 0. Otherwise, constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, then reads data as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
recvmsg(native_handle(), &message, static_cast<int>(flags));

If the operation completes successfully, n is the number of bytes received. Otherwise n is 0.

Error conditions:
errc::invalid_argument — if socket_base::message_peek is set in flags. — stream_errc::eof — if there is no data to be received and the peer performed an orderly shutdown.

template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers);
template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers, error_code& ec);

Returns: send(buffers, socket_base::message_flags(), ec).

template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers,
              socket_base::message_flags flags);
template<class ConstBufferSequence>
  size_t send(const ConstBufferSequence& buffers,
              socket_base::message_flags flags, error_code& ec);

Effects: If buffer_size(buffers) == 0, returns immediately with no error. Otherwise, constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, and writes data to this socket as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
sendmsg(native_handle(), &message, static_cast<int>(flags));

Returns: On success, the number of bytes sent. Otherwise 0.

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_send(const ConstBufferSequence& buffers, CompletionToken&& token);

Returns: async_send(buffers, socket_base::message_flags(), forward<CompletionToken>(token)).

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_send(const ConstBufferSequence& buffers,
                     socket_base::message_flags flags,
                     CompletionToken&& token);

Completion signature: void(error_code ec, size_t n).

Effects: Initiates an asynchronous operation to write data to this socket. If buffer_size(buffers) == 0, the asynchronous operation completes immediately with no error and n == 0. Otherwise, constructs an array iov of POSIX type struct iovec and length iovlen, corresponding to buffers, then writes data as if by POSIX:

msghdr message;
message.msg_name = nullptr;
message.msg_namelen = 0;
message.msg_iov = iov;
message.msg_iovlen = iovlen;
message.msg_control = nullptr;
message.msg_controllen = 0;
message.msg_flags = 0;
sendmsg(native_handle(), &message, static_cast<int>(flags));

If the operation completes successfully, n is the number of bytes sent. Otherwise n is 0.

template<class MutableBufferSequence>
  size_t read_some(const MutableBufferSequence& buffers);
template<class MutableBufferSequence>
  size_t read_some(const MutableBufferSequence& buffers,
                   error_code& ec);

Returns: receive(buffers, ec).

template<class MutableBufferSequence, class CompletionToken>
  DEDUCED async_read_some(const MutableBufferSequence& buffers,
                          CompletionToken&& token);

Returns: async_receive(buffers, forward<CompletionToken>(token)).

template<class ConstBufferSequence>
  size_t write_some(const ConstBufferSequence& buffers);
template<class ConstBufferSequence>
  size_t write_some(const ConstBufferSequence& buffers,
                    error_code& ec);

Returns: send(buffers, ec).

template<class ConstBufferSequence, class CompletionToken>
  DEDUCED async_write_some(const ConstBufferSequence& buffers,
                           CompletionToken&& token);

Returns: async_send(buffers, forward<CompletionToken>(token)).

10.18.9. Class template basic_socket_acceptor

[socket.acceptor]

An object of class template basic_socket_acceptor<AcceptableProtocol> is used to listen for, and queue, incoming socket connections. Socket objects that represent the incoming connections are dequeued by calling accept or async_accept.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class AcceptableProtocol>
  class basic_socket_acceptor : public socket_base
  {
  public:
    // types:

    typedef io_context::executor_type executor_type;
    typedef implementation defined native_handle_type; // See native handles
    typedef AcceptableProtocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;
    typedef typename protocol_type::socket socket_type;

    // construct / copy / destroy:

    explicit basic_socket_acceptor(io_context& ctx);
    basic_socket_acceptor(io_context& ctx, const protocol_type& protocol);
    basic_socket_acceptor(io_context& ctx, const endpoint_type& endpoint,
                          bool reuse_addr = true);
    basic_socket_acceptor(io_context& ctx, const protocol_type& protocol,
                          const native_handle_type& native_acceptor);
    basic_socket_acceptor(const basic_socket_acceptor&) = delete;
    basic_socket_acceptor(basic_socket_acceptor&& rhs);
    template<class OtherProtocol>
      basic_socket_acceptor(basic_socket_acceptor<OtherProtocol>&& rhs);

    ~basic_socket_acceptor();

    basic_socket_acceptor& operator=(const basic_socket_acceptor&) = delete;
    basic_socket_acceptor& operator=(basic_socket_acceptor&& rhs);
    template<class OtherProtocol>
      basic_socket_acceptor& operator=(basic_socket_acceptor<OtherProtocol>&& rhs);

    // basic_socket_acceptor operations:

    executor_type get_executor() noexcept;

    native_handle_type native_handle(); // See native handles

    void open(const protocol_type& protocol = protocol_type());
    void open(const protocol_type& protocol, error_code& ec);

    void assign(const protocol_type& protocol,
                const native_handle_type& native_acceptor); // See native handles
    void assign(const protocol_type& protocol,
                const native_handle_type& native_acceptor,
                error_code& ec); // See native handles

    bool is_open() const;

    void close();
    void close(error_code& ec);

    void cancel();
    void cancel(error_code& ec);

    template<class SettableSocketOption>
      void set_option(const SettableSocketOption& option);
    template<class SettableSocketOption>
      void set_option(const SettableSocketOption& option, error_code& ec);

    template<class GettableSocketOption>
      void get_option(GettableSocketOption& option) const;
    template<class GettableSocketOption>
      void get_option(GettableSocketOption& option, error_code& ec) const;

    template<class IoControlCommand>
      void io_control(IoControlCommand& command);
    template<class IoControlCommand>
      void io_control(IoControlCommand& command, error_code& ec);

    void non_blocking(bool mode);
    void non_blocking(bool mode, error_code& ec);
    bool non_blocking() const;

    void native_non_blocking(bool mode);
    void native_non_blocking(bool mode, error_code& ec);
    bool native_non_blocking() const;

    void bind(const endpoint_type& endpoint);
    void bind(const endpoint_type& endpoint, error_code& ec);

    void listen(int backlog = max_listen_connections);
    void listen(int backlog, error_code& ec);

    endpoint_type local_endpoint() const;
    endpoint_type local_endpoint(error_code& ec) const;

    void enable_connection_aborted(bool mode);
    bool enable_connection_aborted() const;

    socket_type accept();
    socket_type accept(error_code& ec);
    socket_type accept(io_context& ctx);
    socket_type accept(io_context& ctx, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_accept(CompletionToken&& token);
    template<class CompletionToken>
      DEDUCED async_accept(io_context& ctx, CompletionToken&& token);

    socket_type accept(endpoint_type& endpoint);
    socket_type accept(endpoint_type& endpoint, error_code& ec);
    socket_type accept(io_context& ctx, endpoint_type& endpoint);
    socket_type accept(io_context& ctx, endpoint_type& endpoint,
                       error_code& ec);

    template<class CompletionToken>
      DEDUCED async_accept(endpoint_type& endpoint,
                           CompletionToken&& token);
    template<class CompletionToken>
      DEDUCED async_accept(io_context& ctx, endpoint_type& endpoint,
                           CompletionToken&& token);

    void wait(wait_type w);
    void wait(wait_type w, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_wait(wait_type w, CompletionToken&& token);

  private:
    protocol_type protocol_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_socket_acceptor meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), and MoveAssignable (C++Std [moveassignable]).

When there are multiple outstanding asynchronous accept operations the order in which the incoming connections are dequeued, and the order of invocation of the completion handlers for these operations, is unspecified.

When an operation has its effects specified as if by passing the result of native_handle() to a POSIX function, then the operation fails with error condition errc::bad_file_descriptor if is_open() == false at the point in the effects when the POSIX function is called.

10.18.9.1. basic_socket_acceptor constructors

[socket.acceptor.cons]

explicit basic_socket_acceptor(io_context& ctx);

Postconditions:
get_executor() == ctx.get_executor().
is_open() == false.

basic_socket_acceptor(io_context& ctx, const protocol_type& protocol);

Effects: Opens this acceptor as if by calling open(protocol).

Postconditions:
get_executor() == ctx.get_executor().
is_open() == true.
non_blocking() == false.
enable_connection_aborted() == false.
protocol_ == protocol.

basic_socket_acceptor(io_context& ctx, const endpoint_type& endpoint,
                      bool reuse_addr = true);

Effects: Opens and binds this acceptor as if by calling:

open(endpoint.protocol());
if (reuse_addr)
  set_option(reuse_address(true));
bind(endpoint);
listen();

Postconditions:
get_executor() == ctx.get_executor().
is_open() == true.
non_blocking() == false.
enable_connection_aborted() == false.
protocol_ == endpoint.protocol().

basic_socket_acceptor(io_context& ctx, const protocol_type& protocol,
                      const native_handle_type& native_acceptor);

Requires: native_acceptor is a native handle to an open acceptor.

Effects: Assigns the existing native acceptor into this acceptor as if by calling assign(protocol, native_acceptor).

Postconditions:
get_executor() == ctx.get_executor().
is_open() == true.
non_blocking() == false.
enable_connection_aborted() == false.
protocol_ == protocol.

basic_socket_acceptor(basic_socket_acceptor&& rhs);

Effects: Move constructs an object of class basic_socket_acceptor<AcceptableProtocol> that refers to the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the constructor invocation.
non_blocking() returns the same value as rhs.non_blocking() prior to the constructor invocation.
enable_connection_aborted() returns the same value as rhs.enable_connection_aborted() prior to the constructor invocation.
protocol_ is equal to the prior value of rhs.protocol_.
rhs.is_open() == false.

template<class OtherProtocol>
  basic_socket_acceptor(basic_socket_acceptor<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: Move constructs an object of class basic_socket_acceptor<AcceptableProtocol> that refers to the state originally represented by rhs.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the constructor invocation.
non_blocking() returns the same value as rhs.non_blocking() prior to the constructor invocation.
enable_connection_aborted() returns the same value as rhs.enable_connection_aborted() prior to the constructor invocation.
native_handle() returns the prior value of rhs.native_handle().
protocol_ is the result of converting the prior value of rhs.protocol_.
rhs.is_open() == false.

Remarks: This constructor shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.9.2. basic_socket_acceptor destructor

[socket.acceptor.dtor]

~basic_socket_acceptor();

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this acceptor, and releases acceptor resources as if by POSIX close(native_handle()). Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true.

10.18.9.3. basic_socket_acceptor assignment

[socket.acceptor.assign]

basic_socket_acceptor& operator=(basic_socket_acceptor&& rhs);

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this acceptor, and releases acceptor resources as if by POSIX close(native_handle()). Then moves into *this the state originally represented by rhs. Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the assignment.
non_blocking() returns the same value as rhs.non_blocking() prior to the assignment.
enable_connection_aborted() returns the same value as rhs.enable_connection_aborted() prior to the assignment.
native_handle() returns the same value as rhs.native_handle() prior to the assignment.
protocol_ is the same value as rhs.protocol_ prior to the assignment.
rhs.is_open() == false.

Returns: *this.

template<class OtherProtocol>
  basic_socket_acceptor& operator=(basic_socket_acceptor<OtherProtocol>&& rhs);

Requires: OtherProtocol is implicitly convertible to Protocol.

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this acceptor, and releases acceptor resources as if by POSIX close(native_handle()). Then moves into *this the state originally represented by rhs. Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Postconditions:
get_executor() == rhs.get_executor().
is_open() returns the same value as rhs.is_open() prior to the assignment.
non_blocking() returns the same value as rhs.non_blocking() prior to the assignment.
enable_connection_aborted() returns the same value as rhs.enable_connection_aborted() prior to the assignment.
native_handle() returns the same value as rhs.native_handle() prior to the assignment.
protocol_ is the result of converting the value of rhs.protocol_ prior to the assignment.
rhs.is_open() == false.

Returns: *this.

Remarks: This assignment operator shall not participate in overload resolution unless OtherProtocol is implicitly convertible to Protocol.

10.18.9.4. basic_socket_acceptor operations

[socket.acceptor.ops]

executor_type get_executor() noexcept;

Returns: The associated executor.

native_handle_type native_handle();

Returns: The native representation of this acceptor.

void open(const protocol_type& protocol);
void open(const protocol_type& protocol, error_code& ec);

Effects: Establishes the postcondition, as if by POSIX socket(protocol.family(), protocol.type(), protocol.protocol()).

Postconditions:
is_open() == true.
non_blocking() == false.
enable_connection_aborted() == false.
protocol_ == protocol.

Error conditions:
socket_errc::already_open — if is_open() is true.

void assign(const protocol_type& protocol,
            const native_handle_type& native_acceptor);
void assign(const protocol_type& protocol,
            const native_handle_type& native_acceptor, error_code& ec);

Requires: native_acceptor is a native handle to an open acceptor.

Effects: Assigns the native acceptor handle to this acceptor object.

Postconditions:
is_open() == true.
non_blocking() == false.
enable_connection_aborted() == false.
protocol_ == protocol.

Error conditions:
socket_errc::already_open — if is_open() is true.

bool is_open() const;

Returns: A bool indicating whether this acceptor was opened by a previous call to open or assign.

void close();
void close(error_code& ec);

Effects: If is_open() is true, cancels all outstanding asynchronous operations associated with this acceptor, and establishes the postcondition as if by POSIX close(native_handle()). Completion handlers for canceled asynchronous operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Postconditions: is_open() == false.

void cancel();
void cancel(error_code& ec);

Effects: Cancels all outstanding asynchronous operations associated with this acceptor. Completion handlers for canceled asynchronous operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.
errc::operation_not_supported — Current conditions do not permit cancelation. The conditions under which cancelation of asynchronous operations is permitted are implementation-defined.

Remarks: Does not block (C++Std [defns.block]) the calling thread pending completion of the canceled operations.

template<class SettableSocketOption>
  void set_option(const SettableSocketOption& option);
template<class SettableSocketOption>
  void set_option(const SettableSocketOption& option, error_code& ec);

Effects: Sets an option on this acceptor, as if by POSIX setsockopt(native_handle(), option.level(protocol_), option.name(protocol_), option.data(protocol_), option.size(protocol_)).

template<class GettableSocketOption>
  void get_option(GettableSocketOption& option);
template<class GettableSocketOption>
  void get_option(GettableSocketOption& option, error_code& ec);

Effects: Gets an option from this acceptor, as if by POSIX:

socklen_t option_len = option.size(protocol_);
int result = getsockopt(native_handle(), option.level(protocol_),
                        option.name(protocol_), option.data(protocol_),
                        &option_len);
if (result == 0)
  option.resize(option_len);

template<class IoControlCommand>
  void io_control(IoControlCommand& command);
template<class IoControlCommand>
  void io_control(IoControlCommand& command, error_code& ec);

Effects: Executes an I/O control command on this acceptor, as if by POSIX ioctl(native_handle(), command.name(), command.data()).

void non_blocking(bool mode);
void non_blocking(bool mode, error_code& ec);

Effects: Sets the non-blocking mode of this acceptor. The non-blocking mode determines whether subsequent synchronous socket operations on *this block the calling thread.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

Postconditions: non_blocking() == mode.

[Note: The non-blocking mode has no effect on the behavior of asynchronous operations. —end note]

bool non_blocking() const;

Returns: The non-blocking mode of this acceptor.

void native_non_blocking(bool mode);
void native_non_blocking(bool mode, error_code& ec);

Effects: Sets the non-blocking mode of the underlying native acceptor, as if by POSIX:

int flags = fcntl(native_handle(), F_GETFL, 0);
if (flags >= 0)
{
  if (mode)
    flags |= O_NONBLOCK;
  else
    flags &= ~O_NONBLOCK;
  fcntl(native_handle(), F_SETFL, flags);
}

The native non-blocking mode has no effect on the behavior of the synchronous or asynchronous operations specified in this clause.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.
errc::invalid_argument — if mode == false and non_blocking() == true. [Note: As the combination does not make sense. —end note]

bool native_non_blocking() const;

Returns: The non-blocking mode of the underlying native acceptor.

Remarks: Implementations are permitted and encouraged to cache the native non-blocking mode that was applied through a prior call to native_non_blocking. Implementations may return an incorrect value if a program sets the non-blocking mode directly on the acceptor, by calling an operating system-specific function on the result of native_handle().

void bind(const endpoint_type& endpoint);
void bind(const endpoint_type& endpoint, error_code& ec);

Effects: Binds this acceptor to the specified local endpoint, as if by POSIX bind(native_handle(), endpoint.data(), endpoint.size()).

void listen(int backlog = socket_base::max_connections);
void listen(int backlog, error_code& ec);

Effects: Marks this acceptor as ready to accept connections, as if by POSIX listen(native_handle(), backlog).

endpoint_type local_endpoint() const;
endpoint_type local_endpoint(error_code& ec) const;

Effects: Determines the locally-bound endpoint associated with this acceptor, as if by POSIX:

endpoint_type endpoint;
socklen_t endpoint_len = endpoint.capacity();
int result == getsockname(native_handle(), endpoint.data(), &endpoint_len);
if (result == 0)
  endpoint.resize(endpoint_len);

Returns: On success, endpoint. Otherwise endpoint_type().

void enable_connection_aborted(bool mode);

Effects: If mode is true, subsequent synchronous or asynchronous accept operations on this acceptor are permitted to fail with error condition errc::connection_aborted. If mode is false, subsequent accept operations will not fail with errc::connection_aborted. [Note: If mode is false, the implementation will restart the call to POSIX accept if it fails with ECONNABORTED. —end note]

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

bool enable_connection_aborted() const;

Returns: Whether accept operations on this acceptor are permitted to fail with errc::connection_aborted.

socket_type accept();
socket_type accept(error_code& ec);

Returns: accept(get_executor().context(), ec).

socket_type accept(io_context& ctx);
socket_type accept(io_context& ctx, error_code& ec);

Effects: Extracts a socket from the queue of pending connections of the acceptor, as if by POSIX:

native_handle_type h = accept(native_handle(), nullptr, 0);

Returns: On success, socket_type(ctx, protocol_, h). Otherwise socket_type(ctx).

template<class CompletionToken>
  DEDUCED async_accept(CompletionToken&& token);

Returns: async_accept(get_executor().context(), forward<CompletionToken>(token)).

template<class CompletionToken>
  DEDUCED async_accept(io_context& ctx, CompletionToken&& token);

Completion signature: void(error_code ec, socket_type s).

Effects: Initiates an asynchronous operation to extract a socket from the queue of pending connections of the acceptor, as if by POSIX:

native_handle_type h = accept(native_handle(), nullptr, 0);

On success, s is socket_type(ctx, protocol_, h). Otherwise, s is socket_type(ctx).

socket_type accept(endpoint_type& endpoint);
socket_type accept(endpoint_type& endpoint, error_code& ec);

Returns: accept(get_executor().context(), endpoint, ec).

socket_type accept(io_context& ctx, endpoint_type& endpoint);
socket_type accept(io_context& ctx, endpoint_type& endpoint,
                   error_code& ec);

Effects: Extracts a socket from the queue of pending connections of the acceptor, as if by POSIX:

socklen_t endpoint_len = endpoint.capacity();
native_handle_type h = accept(native_handle(),
                              endpoint.data(),
                              &endpoint_len);
if (h >= 0)
  endpoint.resize(endpoint_len);

Returns: On success, socket_type(ctx, protocol_, h). Otherwise socket_type(ctx).

template<class CompletionToken>
  DEDUCED async_accept(endpoint_type& endpoint,
                       CompletionToken&& token);

Returns: async_accept(get_executor().context(), endpoint, forward<CompletionToken>(token)).

template<class CompletionToken>
  DEDUCED async_accept(io_context& ctx, endpoint_type& endpoint,
                       CompletionToken&& token);

Completion signature: void(error_code ec, socket_type s).

Effects: Initiates an asynchronous operation to extract a socket from the queue of pending connections of the acceptor, as if by POSIX:

socklen_t endpoint_len = endpoint.capacity();
native_handle_type h = accept(native_handle(),
                              endpoint.data(),
                              &endpoint_len);
if (h >= 0)
  endpoint.resize(endpoint_len);

On success, s is socket_type(ctx, protocol_, h). Otherwise, s is socket_type(ctx)`.

void wait(wait_type w);
void wait(wait_type w, error_code& ec);

Effects: Waits for the acceptor to have a queued incoming connection, or to have error conditions pending, as if by POSIX poll.

template<class CompletionToken>
  DEDUCED async_wait(wait_type w, CompletionToken&& token);

Completion signature: void(error_code ec).

Effects: Initiates an asynchronous operation to wait for the acceptor to have a queued incoming connection, or to have error conditions pending, as if by POSIX poll.

When multiple asynchronous wait operations are initiated with the same wait_type value, all outstanding operations complete when the acceptor enters the corresponding ready state. The order of invocation of the completions handlers for these operations is unspecified.

Error conditions:
errc::bad_file_descriptor — if is_open() is false.

10.19. Socket iostreams

[socket.iostreams]

10.19.1. Class template basic_socket_streambuf

[socket.streambuf]

The class basic_socket_streambuf<Protocol, Clock, WaitTraits> associates both the input sequence and the output sequence with a socket. The input and output sequences do not support seeking. [Note: The input and output sequences are independent as a stream socket provides full duplex I/O. —end note]

[Note: This class is intended for sending and receiving bytes, not characters. The conversion from characters to bytes, and vice versa, must occur elsewhere. —end note]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Protocol, class Clock, class WaitTraits>
  class basic_socket_streambuf : public basic_streambuf<char>
  {
  public:
    // types:

    typedef Protocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;
    typedef Clock clock_type;
    typedef typename clock_type::time_point time_point;
    typedef typename clock_type::duration duration;
    typedef WaitTraits traits_type;

    // construct / copy / destroy:

    basic_socket_streambuf();
    explicit basic_socket_streambuf(basic_stream_socket<protocol_type> s);
    basic_socket_streambuf(const basic_socket_streambuf&) = delete;
    basic_socket_streambuf(basic_socket_streambuf&& rhs);

    virtual ~basic_socket_streambuf();

    basic_socket_streambuf& operator=(const basic_socket_streambuf&) = delete;
    basic_socket_streambuf& operator=(basic_socket_streambuf&& rhs);

    // members:

    basic_socket_streambuf* connect(const endpoint_type& e);
    template<class... Args> basic_socket_streambuf* connect(Args&&... );

    basic_socket_streambuf<protocol_type>* close();

    basic_socket<protocol_type>& socket();
    error_code error() const;

    time_point expiry() const;
    void expires_at(const time_point& t);
    void expires_after(const duration& d);

  protected:
    // overridden virtual functions:
    virtual int_type underflow() override;
    virtual int_type pbackfail(int_type c = traits_type::eof()) override;
    virtual int_type overflow(int_type c = traits_type::eof()) override;
    virtual int sync() override;
    virtual streambuf* setbuf(char_type* s, streamsize n) override;

  private:
    basic_stream_socket<protocol_type> socket_; // exposition only
    error_code ec_; // exposition only
    time_point expiry_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_socket_streambuf meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), and MoveAssignable (C++Std [moveassignable]).

10.19.1.1. basic_socket_streambuf constructors

[socket.streambuf.cons]

basic_socket_streambuf();

Effects: Initializes socket_ with ctx, where ctx is an unspecified object of class io_context.

Postconditions: expiry() == clock_type::max().

explicit basic_socket_streambuf(basic_stream_socket<protocol_type> s);

Effects: Initializes socket_ with std::move(s).

Postconditions: expiry() == clock_type::max().

basic_socket_streambuf(basic_socket_streambuf&& rhs);

Effects: Move constructs from the rvalue rhs. It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had. Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction. Additionally *this references the socket which rhs did before the construction, and rhs references no open socket after the construction.

Postconditions: Let rhs_p refer to the state of rhs just prior to this construction and let rhs_a refer to the state of rhs just after this construction.
is_open() == rhs_p.is_open()
rhs_a.is_open() == false
expiry() == rhs_p.expiry()
rhs_a.expiry() == clock_type::max()
gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
ptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
pptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
if (eback()) eback() != rhs_a.eback()
if (gptr()) gptr() != rhs_a.gptr()
if (egptr()) egptr() != rhs_a.egptr()
if (pbase()) pbase() != rhs_a.pbase()
if (pptr()) pptr() != rhs_a.pptr()
if (epptr()) epptr() != rhs_a.epptr()

virtual ~basic_socket_streambuf();

Effects: If a put area exists, calls overflow(traits_type::eof()) to flush characters. [Note: The socket is closed by the basic_stream_socket<protocol_type> destructor. —end note]

basic_socket_streambuf& operator=(basic_socket_streambuf&& rhs);

Effects: Calls this->close() then move assigns from rhs. After the move assignment *this has the observable state it would have had if it had been move constructed from rhs.

Returns: *this.

10.19.1.2. basic_socket_streambuf members

[socket.streambuf.members]

basic_socket_streambuf<protocol_type>* connect(const endpoint_type& e);

Effects: Initializes the basic_socket_streambuf as required, closes and re-opens the socket by performing socket_.close(ec_) and socket_.open(e.protocol(), ec_), then attempts to establish a connection as if by POSIX connect(socket_.native_handle(), static_cast<sockaddr*>(e.data()), e.size()). ec_ is set to reflect the error code produced by the operation. If the operation does not complete before the absolute timeout specified by expiry_, the socket is closed and ec_ is set to errc::timed_out.

Returns: if !ec_, this; otherwise, a null pointer.

template<class... Args>
  basic_socket_streambuf* connect(Args&&... args);

Effects: Initializes the basic_socket_streambuf as required and closes the socket as if by calling socket_.close(ec_). Obtains an endpoint sequence endpoints by performing protocol_type::resolver(ctx).resolve(forward<Args>(args)...), where ctx is an unspecified object of class io_context. For each endpoint e in the sequence, closes and re-opens the socket by performing socket_.close(ec_) and socket_.open(e.protocol(), ec_), then attempts to establish a connection as if by POSIX connect(socket_.native_handle(), static_cast<sockaddr*>(e.data()), e.size()). ec_ is set to reflect the error code produced by the operation. If the operation does not complete before the absolute timeout specified by expiry_, the socket is closed and ec_ is set to errc::timed_out.

Returns: if !ec_, this; otherwise, a null pointer.

Remarks: This function shall not participate in overload resolution unless Protocol meets the requirements for an internet protocol.

basic_socket_streambuf* close();

Effects: If a put area exists, calls overflow(traits_type::eof()) to flush characters. Regardless of whether the preceding call fails or throws an exception, the function closes the socket as if by basic_socket<protocol_type>::close(ec_). If any of the calls made by the function fail, close fails by returning a null pointer. If one of these calls throws an exception, the exception is caught and rethrown after closing the socket.

Returns: this on success, a null pointer otherwise.

Postconditions: is_open() == false.

basic_socket<protocol_type>& socket();

Returns: socket_.

error_code error() const;

Returns: ec_.

time_point expiry() const;

Returns: expiry_.

void expires_at(const time_point& t);

Postconditions: expiry_ == t.

void expires_after(const duration& d);

Effects: Equivalent to expires_at(clock_type::now() + d).

10.19.1.3. basic_socket_streambuf overridden virtual functions

[socket.streambuf.virtual]

virtual int_type underflow() override;

Effects: Behaves according to the description of basic_streambuf<char>::underflow(), with the specialization that a sequence of characters is read from the input sequence as if by POSIX recvmsg, and ec_ is set to reflect the error code produced by the operation. If the operation does not complete before the absolute timeout specified by expiry_, the socket is closed and ec_ is set to errc::timed_out.

Effects: Returns traits_type::eof() to indicate failure. Otherwise returns traits_type::to_int_type(*gptr()).

virtual int_type pbackfail(int_type c = traits_type::eof()) override;

Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:

— If traits_type::eq_int_type(c,traits_type::eof()) returns false, and if the function makes a putback position available, and if traits_type::eq(traits_type::to_char_type(c),gptr()[-1]) returns true, decrements the next pointer for the input sequence, gptr().
Returns: c.

— If traits_type::eq_int_type(c,traits_type::eof()) returns false, and if the function makes a putback position available, and if the function is permitted to assign to the putback position, decrements the next pointer for the input sequence, and stores c there.
Returns: c.

— If traits_type::eq_int_type(c,traits_type::eof()) returns true, and if either the input sequence has a putback position available or the function makes a putback position available, decrements the next pointer for the input sequence, gptr().
Returns: traits_type::not_eof(c).

Returns: traits_type::eof() to indicate failure.

Notes: The function does not put back a character directly to the input sequence. If the function can succeed in more than one of these ways, it is unspecified which way is chosen. The function can alter the number of putback positions available as a result of any call.

virtual int_type overflow(int_type c = traits_type::eof()) override;

Effects: Behaves according to the description of basic_streambuf<char>::overflow(c), except that the behavior of "consuming characters" is performed by output of the characters to the socket as if by one or more calls to POSIX sendmsg, and ec_ is set to reflect the error code produced by the operation. If the operation does not complete before the absolute timeout specified by expiry_, the socket is closed and ec_ is set to errc::timed_out.

Returns: traits_type::not_eof(c) to indicate success, and traits_type::eof() to indicate failure.

virtual int sync() override;

Effects: If a put area exists, calls overflow(traits_type::eof()) to flush characters.

virtual streambuf* setbuf(char_type* s, streamsize n) override;

Effects: If setbuf(nullptr, 0) is called on a stream before any I/O has occurred on that stream, the stream becomes unbuffered. Otherwise the results are unspecified. "Unbuffered" means that pbase() and pptr() always return null and output to the socket should appear as soon as possible.

10.19.2. Class template basic_socket_iostream

[socket.iostream]

The class template basic_socket_iostream<Protocol, Clock, WaitTraits> supports reading and writing on sockets. It uses a basic_socket_streambuf<Protocol, Clock, WaitTraits> object to control the associated sequences.

[Note: This class is intended for sending and receiving bytes, not characters. The conversion from characters to bytes, and vice versa, must occur elsewhere. —end note]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {

  template<class Protocol, class Clock, class WaitTraits>
  class basic_socket_iostream : public basic_iostream<char>
  {
  public:
    // types:

    typedef Protocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;
    typedef Clock clock_type;
    typedef typename clock_type::time_point time_point;
    typedef typename clock_type::duration duration;
    typedef WaitTraits traits_type;

    // construct / copy / destroy:

    basic_socket_iostream();
    explicit basic_socket_iostream(basic_stream_socket<protocol_type> s);
    basic_socket_iostream(const basic_socket_iostream&) = delete;
    basic_socket_iostream(basic_socket_iostream&& rhs);
    template<class... Args>
      explicit basic_socket_iostream(Args&&... args);

    basic_socket_iostream& operator=(const basic_socket_iostream&) = delete;
    basic_socket_iostream& operator=(basic_socket_iostream&& rhs);

    // members:

    template<class... Args> void connect(Args&&... args);

    void close();

    basic_socket_streambuf<protocol_type, clock_type, traits_type>* rdbuf() const;

    basic_socket<protocol_type>& socket();
    error_code error() const;

    time_point expiry() const;
    void expires_at(const time_point& t);
    void expires_after(const duration& d);

  private:
    basic_socket_streambuf<protocol_type, clock_type, traits_type> sb_; // exposition only
  };

} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of class template basic_socket_iostream meet the requirements of Destructible (C++Std [destructible]), MoveConstructible (C++Std [moveconstructible]), and MoveAssignable (C++Std [moveassignable]).

10.19.2.1. basic_socket_iostream constructors

[socket.iostream.cons]

basic_socket_iostream();

Effects: Initializes the base class as basic_iostream<char>(&sb_), sb_ as basic_socket_streambuf<Protocol, Clock, WaitTraits>(), and performs setf(std::ios_base::unitbuf).

explicit basic_socket_iostream(basic_stream_socket<protocol_type> s);

Effects: Initializes the base class as basic_iostream<char>(&sb_), sb_ as basic_socket_streambuf<Protocol, Clock, WaitTraits>(std::move(s)), and performs setf(std::ios_base::unitbuf).

basic_socket_iostream(basic_socket_iostream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_socket_streambuf. Next basic_iostream<char>::set_rdbuf(&sb_) is called to install the contained basic_socket_streambuf.

template<class... Args>
  explicit basic_socket_iostream(Args&&... args);

Effects: Initializes the base class as basic_iostream<char>(&sb_), initializes sb_ as basic_socket_streambuf<Protocol, Clock, WaitTraits>(), and performs setf(std::ios_base::unitbuf). Then calls rdbuf()->connect(forward<Args>(args)...). If that function returns a null pointer, calls setstate(failbit).

basic_socket_iostream& operator=(basic_socket_iostream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

Returns: *this.

10.19.2.2. basic_socket_iostream members

[socket.iostream.members]

template<class... Args>
  void connect(Args&&... args);

Effects: Calls rdbuf()->connect(forward<Args>(args)...). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure).

void close();

Effects: Calls rdbuf()->close(). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure).

basic_socket_streambuf<protocol_type, clock_type, traits_type>* rdbuf() const;

Returns: const_cast<basic_socket_streambuf<protocol_type, clock_type, traits_type>*>(std::addressof(sb_)).

basic_socket<protocol_type>& socket();

Returns: rdbuf()->socket().

error_code error() const;

Returns: rdbuf()->error().

time_point expiry() const;

Returns: rdbuf()->expiry().

void expires_at(const time_point& t);

Effects: Equivalent to rdbuf()->expires_at(t).

void expires_after(const duration& d);

Effects: Equivalent to rdbuf()->expires_after(d).

10.20. Socket algorithms

[socket.algo]

10.20.1. Synchronous connect operations

[socket.algo.connect]

template<class Protocol, class EndpointSequence>
  typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                      const EndpointSequence& endpoints);
template<class Protocol, class InputIterator>
  typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                      const EndpointSequence& endpoints,
                                      error_code& ec);

Returns: connect(s, endpoints, [](auto, auto){ return true; }, ec).

template<class Protocol, class EndpointSequence, class ConnectCondition>
  typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                      const EndpointSequence& endpoints,
                                      ConnectCondition c);
template<class Protocol, class InputIterator, class ConnectCondition>
  typename Protocol::endpoint connect(basic_socket<Protocol>& s,
                                      const EndpointSequence& endpoints,
                                      ConnectCondition c, error_code& ec);

Effects: Performs ec.clear(), then finds the first element ep in the sequence endpoints for which:
c(ec, ep) yields true;
s.close(ec) succeeds;
s.open(ep.protocol(), ec) succeeds; and
s.connect(ep, ec) succeeds.

Returns: typename Protocol::endpoint() if no such element is found, otherwise ep.

Error conditions:
socket_errc::not_found — if endpoints.empty() or if the function object c returned false for all elements in the sequence.

template<class Protocol, class InputIterator>
  InputIterator connect(basic_socket<Protocol>& s,
                        InputIterator first, InputIterator last);
template<class Protocol, class InputIterator>
  InputIterator connect(basic_socket<Protocol>& s,
                        InputIterator first, InputIterator last,
                        error_code& ec);

Returns: connect(s, first, last, [](auto, auto){ return true; }, ec).

template<class Protocol, class InputIterator, class ConnectCondition>
  InputIterator connect(basic_socket<Protocol>& s,
                        InputIterator first, InputIterator last,
                        ConnectCondition c);
template<class Protocol, class InputIterator, class ConnectCondition>
  InputIterator connect(basic_socket<Protocol>& s,
                        InputIterator first, InputIterator last,
                        ConnectCondition c, error_code& ec);

Effects: Performs ec.clear(), then finds the first iterator i in the range [first,last) for which:
c(ec, *i) yields true;
s.close(ec) succeeds;
s.open(typename Protocol::endpoint(*i).protocol(), ec) succeeds; and
s.connect(*i, ec) succeeds.

Returns: last if no such iterator is found, otherwise i.

Error conditions:
socket_errc::not_found — if first == last or if the function object c returned false for all iterators in the range.

10.20.2. Asynchronous connect operations

[socket.algo.async.connect]

template<class Protocol, class EndpointSequence, class CompletionToken>
  DEDUCED async_connect(basic_socket<Protocol>& s,
                        const EndpointSequence& endpoints,
                        CompletionToken&& token);

Returns: async_connect(s, endpoints, [](auto, auto){ return true; }, forward<CompletionToken>(token)).

template<class Protocol, class InputIterator,
  class ConnectCondition, class CompletionToken>
    DEDUCED async_connect(basic_socket<Protocol>& s,
                          const EndpointSequence& endpoints,
                          ConnectCondition c,
                          CompletionToken&& token);

Completion signature: void(error_code ec, typename Protocol::endpoint ep).

Effects: Performs ec.clear(), then finds the first element ep in the sequence endpoints for which:
c(ec, ep) yields true;
s.close(ec) succeeds;
s.open(ep.protocol(), ec) succeeds; and
— the asynchronous operation s.async_connect(ep, unspecified) succeeds.
ec is updated with the result of the s.async_connect(ep, unspecified) operation, if any. If no such element is found, or if the operation fails with one of the error conditions listed below, ep is set to typename Protocol::endpoint(). [Note: The underlying close, open, and async_connect operations are performed sequentially. —end note]

Error conditions:
socket_errc::not_found — if endpoints.empty() or if the function object c returned false for all elements in the sequence.
errc::operation_canceled — if s.is_open() == false immediately following an async_connect operation on the underlying socket.

template<class Protocol, class InputIterator, class CompletionToken>
  DEDUCED async_connect(basic_socket<Protocol>& s,
                        InputIterator first, InputIterator last,
                        CompletionToken&& token);

Returns: async_connect(s, first, last, [](auto, auto){ return true; }, forward<CompletionToken>(token)).

template<class Protocol, class InputIterator,
  class ConnectCondition, class CompletionToken>
    DEDUCED async_connect(basic_socket<Protocol>& s,
                          InputIterator first, InputIterator last,
                          ConnectCondition c,
                          CompletionToken&& token);

Completion signature: void(error_code ec, InputIterator i).

Effects: Performs ec.clear(), then finds the first iterator i in the range [first,last) for which:
c(ec, *i) yields true;
s.close(ec) succeeds;
s.open(typename Protocol::endpoint(*i).protocol(), ec) succeeds; and
— the asynchronous operation s.async_connect(*i, unspecified) succeeds.
ec is updated with the result of the s.async_connect(*i, unspecified) operation, if any. If no such iterator is found, or if the operation fails with one of the error conditions listed below, i is set to last. [Note: The underlying close, open, and async_connect operations are performed sequentially. —end note]

Error conditions:
socket_errc::not_found — if first == last or if the function object c returned false for all iterators in the range.
errc::operation_canceled — if s.is_open() == false immediately following an async_connect operation on the underlying socket.

10.21. Internet protocol

[internet]

10.21.1. Header <experimental/internet> synopsis

[internet.synop]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  enum class resolver_errc {
    host_not_found = an implementation defined non-zero value, // EAI_NONAME
    host_not_found_try_again = an implementation defined non-zero value, // EAI_AGAIN
    service_not_found = an implementation defined non-zero value // EAI_SERVICE
  };

  const error_category& resolver_category() noexcept;

  error_code make_error_code(resolver_errc e) noexcept;
  error_condition make_error_condition(resolver_errc e) noexcept;

  typedef uint_least16_t port_type;
  typedef uint_least32_t scope_id_type;

  struct v4_mapped_t {};
  constexpr v4_mapped_t v4_mapped;

  class address;
  class address_v4;
  class address_v6;

  class bad_address_cast;

  // address comparisons:
  constexpr bool operator==(const address&, const address&) noexcept;
  constexpr bool operator!=(const address&, const address&) noexcept;
  constexpr bool operator< (const address&, const address&) noexcept;
  constexpr bool operator> (const address&, const address&) noexcept;
  constexpr bool operator<=(const address&, const address&) noexcept;
  constexpr bool operator>=(const address&, const address&) noexcept;

  // address_v4 comparisons:
  constexpr bool operator==(const address_v4&, const address_v4&) noexcept;
  constexpr bool operator!=(const address_v4&, const address_v4&) noexcept;
  constexpr bool operator< (const address_v4&, const address_v4&) noexcept;
  constexpr bool operator> (const address_v4&, const address_v4&) noexcept;
  constexpr bool operator<=(const address_v4&, const address_v4&) noexcept;
  constexpr bool operator>=(const address_v4&, const address_v4&) noexcept;

  // address_v6 comparisons:
  constexpr bool operator==(const address_v6&, const address_v6&) noexcept;
  constexpr bool operator!=(const address_v6&, const address_v6&) noexcept;
  constexpr bool operator< (const address_v6&, const address_v6&) noexcept;
  constexpr bool operator> (const address_v6&, const address_v6&) noexcept;
  constexpr bool operator<=(const address_v6&, const address_v6&) noexcept;
  constexpr bool operator>=(const address_v6&, const address_v6&) noexcept;

  // address creation:
  address make_address(const char*);
  address make_address(const char*, error_code&) noexcept;
  address make_address(const string&);
  address make_address(const string&, error_code&) noexcept;
  address make_address(string_view);
  address make_address(string_view, error_code&) noexcept;

  // address_v4 creation:
  constexpr address_v4 make_address_v4(const address_v4::bytes_type&);
  constexpr address_v4 make_address_v4(address_v4::uint_type);
  constexpr address_v4 make_address_v4(v4_mapped_t, const address_v6&);
  address_v4 make_address_v4(const char*);
  address_v4 make_address_v4(const char*, error_code&) noexcept;
  address_v4 make_address_v4(const string&);
  address_v4 make_address_v4(const string&, error_code&) noexcept;
  address_v4 make_address_v4(string_view);
  address_v4 make_address_v4(string_view, error_code&) noexcept;

  // address_v6 creation:
  constexpr address_v6 make_address_v6(const address_v6::bytes_type&,
                                       scope_id_type = 0);
  constexpr address_v6 make_address_v6(v4_mapped_t, const address_v4&) noexcept;
  address_v6 make_address_v6(const char*);
  address_v6 make_address_v6(const char*, error_code&) noexcept;
  address_v6 make_address_v6(const string&);
  address_v6 make_address_v6(const string&, error_code&) noexcept;
  address_v6 make_address_v6(string_view);
  address_v6 make_address_v6(string_view, error_code&) noexcept;

  // address I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>&, const address&);

  // address_v4 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>&, const address_v4&);

  // address_v6 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>&, const address_v6&);

  template<class> class basic_address_iterator; // not defined
  template<> class basic_address_iterator<address_v4>;
  typedef basic_address_iterator<address_v4> address_v4_iterator;
  template<> class basic_address_iterator<address_v6>;
  typedef basic_address_iterator<address_v6> address_v6_iterator;

  template<class> class basic_address_range; // not defined
  template<> class basic_address_range<address_v4>;
  typedef basic_address_range<address_v4> address_v4_range;
  template<> class basic_address_range<address_v6>;
  typedef basic_address_range<address_v6> address_v6_range;

  class network_v4;
  class network_v6;

  // network_v4 comparisons:
  bool operator==(const network_v4&, const network_v4&) noexcept;
  bool operator!=(const network_v4&, const network_v4&) noexcept;

  // network_v6 comparisons:
  bool operator==(const network_v6&, const network_v6&) noexcept;
  bool operator!=(const network_v6&, const network_v6&) noexcept;

  // network_v4 creation:
  network_v4 make_network_v4(const address_v4&, int);
  network_v4 make_network_v4(const address_v4&, const address_v4&);
  network_v4 make_network_v4(const char*);
  network_v4 make_network_v4(const char*, error_code&) noexcept;
  network_v4 make_network_v4(const string&);
  network_v4 make_network_v4(const string&, error_code&) noexcept;
  network_v4 make_network_v4(string_view);
  network_v4 make_network_v4(string_view, error_code&) noexcept;

  // network_v6 creation:
  network_v6 make_network_v6(const address_v6&, int);
  network_v6 make_network_v6(const char*);
  network_v6 make_network_v6(const char*, error_code&) noexcept;
  network_v6 make_network_v6(const string&);
  network_v6 make_network_v6(const string&, error_code&) noexcept;
  network_v6 make_network_v6(string_view);
  network_v6 make_network_v6(string_view, error_code&) noexcept;

  // network_v4 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>&, const network_v4&);

  // network_v6 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>&, const network_v6&);

  template<class InternetProtocol>
    class basic_endpoint;

  // basic_endpoint comparisons:
  template<class InternetProtocol>
    bool operator==(const basic_endpoint<InternetProtocol>&,
                    const basic_endpoint<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator!=(const basic_endpoint<InternetProtocol>&,
                    const basic_endpoint<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator< (const basic_endpoint<InternetProtocol>&,
                    const basic_endpoint<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator> (const basic_endpoint<InternetProtocol>&,
                    const basic_endpoint<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator<=(const basic_endpoint<InternetProtocol>&,
                    const basic_endpoint<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator>=(const basic_endpoint<InternetProtocol>&,
                    const basic_endpoint<InternetProtocol>&);

  // basic_endpoint I/O:
  template<class CharT, class Traits, class InternetProtocol>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>&,
      const basic_endpoint<InternetProtocol>&);

  template<class InternetProtocol>
    class basic_resolver_entry;

  template<class InternetProtocol>
    bool operator==(const basic_resolver_entry<InternetProtocol>&,
                    const basic_resolver_entry<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator!=(const basic_resolver_entry<InternetProtocol>&,
                    const basic_resolver_entry<InternetProtocol>&);

  template<class InternetProtocol>
    class basic_resolver_results;

  template<class InternetProtocol>
    bool operator==(const basic_resolver_results<InternetProtocol>&,
                    const basic_resolver_results<InternetProtocol>&);
  template<class InternetProtocol>
    bool operator!=(const basic_resolver_results<InternetProtocol>&,
                    const basic_resolver_results<InternetProtocol>&);

  class resolver_base;

  template<class InternetProtocol>
    class basic_resolver;

  string host_name();
  string host_name(error_code&);
  template<class Allocator>
    basic_string<char, char_traits<char>, Allocator>
      host_name(const Allocator&);
  template<class Allocator>
    basic_string<char, char_traits<char>, Allocator>
      host_name(const Allocator&, error_code&);

  class tcp;

  // tcp comparisons:
  bool operator==(const tcp& a, const tcp& b);
  bool operator!=(const tcp& a, const tcp& b);

  class udp;

  // udp comparisons:
  bool operator==(const udp& a, const udp& b);
  bool operator!=(const udp& a, const udp& b);

  class v6_only;

  namespace unicast {

    class hops;

  } // namespace unicast

  namespace multicast {

    class join_group;

    class leave_group;

    class outbound_interface;

    class hops;

    class enable_loopback;

  } // namespace multicast
} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental

  template<> struct is_error_condition_enum<
    experimental::net::v1::ip::resolver_errc>
      : public true_type {};

  // hash support
  template<class T> struct hash;
  template<> struct hash<experimental::net::v1::ip::address>;
  template<> struct hash<experimental::net::v1::ip::address_v4>;
  template<> struct hash<experimental::net::v1::ip::address_v6>;

} // namespace std

10.21.2. Requirements

[internet.reqmts]

10.21.2.1. Internet protocol requirements

[internet.reqmts.protocol]

A type X meets the InternetProtocol requirements if it satisfies the requirements of AcceptableProtocol, as well as the additional requirements listed below.

In the table below, a denotes a (possibly const) value of type X, and b denotes a (possibly const) value of type X.

Table 34. InternetProtocol requirements

expression

return type

assertion/note
pre/post-conditions

X::resolver

ip::basic_resolver<X>

The type of a resolver for the protocol.

X::v4()

X

Returns an object representing the IP version 4 protocol.

X::v6()

X

Returns an object representing the IP version 6 protocol.

a == b

convertible to bool

Returns true if a and b represent the same IP protocol version, otherwise false.

a != b

convertible to bool

Returns !(a == b).


10.21.2.2. Multicast group socket options

[internet.reqmts.opt.mcast]

A type X meets the MulticastGroupSocketOption requirements if it satisfies the requirements of Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), CopyAssignable (C++Std [copyassignable]), and SettableSocketOption, as well as the additional requirements listed below.

In the table below, a denotes a (possibly const) value of type X, b denotes a (possibly const) value of type address, c and d denote (possibly const) values of type address_v4, e denotes a (possibly const) value of type address_v6, f denotes a (possibly const) value of type unsigned int, and u denotes an identifier.

Table 35. MulticastGroupSocketOption requirements

expression

type

assertion/note
pre/post-conditions

X u(b);

Constructs a multicast group socket option to join the group with the specified version-independent address.

X u(c, d);

Constructs a multicast group socket option to join the specified IPv4 address on a specified network interface.

X u(e, f);

Constructs a multicast group socket option to join the specified IPv6 address on a specified network interface.


In this Technical Specification, types that satisfy the MulticastGroupSocketOption requirements are defined as follows.

class C
{
public:
  // constructors:
  explicit C(const address& multicast_group) noexcept;
  explicit C(const address_v4& multicast_group,
             const address_v4& network_interface = address_v4::any()) noexcept;
  explicit C(const address_v6& multicast_group,
             unsigned int network_interface = 0) noexcept;
};

Extensible implementations provide the following member functions:

class C
{
public:
  template<class Protocol> int level(const Protocol& p) const noexcept;
  template<class Protocol> int name(const Protocol& p) const noexcept;
  template<class Protocol> const void* data(const Protocol& p) const noexcept;
  template<class Protocol> size_t size(const Protocol& p) const noexcept;
  // remainder unchanged
private:
  ip_mreq v4_value_; // exposition only
  ipv6_mreq v6_value_; // exposition only
};

Let L and N identify the POSIX macros to be passed as the level and option_name arguments, respectively, to POSIX setsockopt and getsockopt.

explicit C(const address& multicast_group) noexcept;

Effects: If multicast_group.is_v6() is true, calls C(multicast_group.to_v6()); otherwise, calls C(multicast_group.to_v4()).

explicit C(const address_v4& multicast_group,
           const address_v4& network_interface = address_v4::any()) noexcept;

Effects: For extensible implementations, v4_value_.imr_multiaddr is initialized to correspond to the address multicast_group, v4_value_.imr_interface is initialized to correspond to address network_interface, and v6_value_ is zero-initialized.

explicit C(const address_v6& multicast_group,
           unsigned int network_interface = 0) noexcept;

Effects: For extensible implementations, v6_value_.ipv6mr_multiaddr is initialized to correspond to the address multicast_group, v6_value_.ipv6mr_interface is initialized to network_interface, and v4_value_ is zero-initialized.

template<class Protocol> int level(const Protocol& p) const noexcept;

Returns: L.

template<class Protocol> int name(const Protocol& p) const noexcept;

Returns: N.

template<class Protocol> const void* data(const Protocol& p) const noexcept;

Returns: std::addressof(v6_value_) if p.family() == AF_INET6, otherwise std::addressof(v4_value_).

template<class Protocol> size_t size(const Protocol& p) const noexcept;

Returns: sizeof(v6_value_) if p.family() == AF_INET6, otherwise sizeof(v4_value_).

10.21.3. Error codes

[internet.resolver.err]

const error_category& resolver_category() noexcept;

Returns: A reference to an object of a type derived from class error_category. All calls to this function return references to the same object.

The object’s default_error_condition and equivalent virtual functions behave as specified for the class error_category. The object’s name virtual function returns a pointer to the string "resolver".

error_code make_error_code(resolver_errc e) noexcept;

Returns: error_code(static_cast<int>(e), resolver_category()).

error_condition make_error_condition(resolver_errc e) noexcept;

Returns: error_condition(static_cast<int>(e), resolver_category()).

10.21.4. Class ip::address

[internet.address]

The class address is a version-independent representation for an IP address. An object of class address holds either an IPv4 address, an IPv6 address, or no valid address.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class address
  {
  public:
    // constructors:
    constexpr address() noexcept;
    constexpr address(const address& a) noexcept;
    constexpr address(const address_v4& a) noexcept;
    constexpr address(const address_v6& a) noexcept;

    // assignment:
    address& operator=(const address& a) noexcept;
    address& operator=(const address_v4& a) noexcept;
    address& operator=(const address_v6& a) noexcept;

    // members:
    constexpr bool is_v4() const noexcept;
    constexpr bool is_v6() const noexcept;
    constexpr address_v4 to_v4() const;
    constexpr address_v6 to_v6() const;
    constexpr bool is_unspecified() const noexcept;
    constexpr bool is_loopback() const noexcept;
    constexpr bool is_multicast() const noexcept;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        to_string(const Allocator& a = Allocator()) const;

  private:
    address_v4 v4_; // exposition only
    address_v6 v6_; // exposition only
  };

  // address comparisons:
  constexpr bool operator==(const address& a, const address& b) noexcept;
  constexpr bool operator!=(const address& a, const address& b) noexcept;
  constexpr bool operator< (const address& a, const address& b) noexcept;
  constexpr bool operator> (const address& a, const address& b) noexcept;
  constexpr bool operator<=(const address& a, const address& b) noexcept;
  constexpr bool operator>=(const address& a, const address& b) noexcept;

  // address creation:
  address make_address(const char* str);
  address make_address(const char* str, error_code& ec) noexcept;
  address make_address(const string& str);
  address make_address(const string& str, error_code& ec) noexcept;
  address make_address(string_view str);
  address make_address(string_view str, error_code& ec) noexcept;

  // address I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>& os, const address& addr);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

address satisfies the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]).

10.21.4.1. ip::address constructors

[internet.address.cons]

constexpr address() noexcept;

Postconditions: is_v4() == true, is_v6() == false, and is_unspecified() == true.

constexpr address(const address_v4& a) noexcept;

Effects: Initializes v4_ with a.

Postconditions: is_v4() == true and is_v6() == false.

constexpr address(const address_v6& a) noexcept;

Effects: Initializes v6_ with a.

Postconditions: is_v4() == false and is_v6() == true.

10.21.4.2. ip::address assignment

[internet.address.assign]

constexpr address(const address_v4& a) noexcept;

Postconditions: is_v4() == true and is_v6() == false and to_v4() == a.

Returns: *this

constexpr address(const address_v6& a) noexcept;

Postconditions: is_v4() == false and is_v6() == true and to_v6() == a.

Returns: *this

10.21.4.3. ip::address members

[internet.address.members]

constexpr bool is_v4() const noexcept;

Returns: true if the object contains an IP version 4 address, otherwise false.

constexpr bool is_v6() const noexcept;

Returns: true if the object contains an IP version 6 address, otherwise false.

constexpr address_v4 to_v4() const;

Returns: v4_.

Throws: bad_address_cast if is_v4() == false.

constexpr address_v6 to_v6() const;

Returns: v6_.

Throws: bad_address_cast if is_v6() == false.

constexpr bool is_unspecified() const noexcept;

Returns: If is_v4(), returns v4_.is_unspecified(). Otherwise returns v6_.is_unspecified().

constexpr bool is_loopback() const noexcept;

Returns: If is_v4(), returns v4_.is_loopback(). Otherwise returns v6_.is_loopback().

constexpr bool is_multicast() const noexcept;

Returns: If is_v4(), returns v4_.is_multicast(). Otherwise returns v6_.is_multicast().

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    to_string(const Allocator& a = Allocator()) const;

Returns: If is_v4(), returns v4_.to_string(a). Otherwise returns v6_.to_string(a).

10.21.4.4. ip::address comparisons

[internet.address.comparisons]

constexpr bool operator==(const address& a, const address& b) noexcept;

Returns:
— if a.is_v4() != b.is_v4(), false;
— if a.is_v4(), the result of a.v4_ == b.v4_;
— otherwise, the result of a.v6_ == b.v6_.

constexpr bool operator!=(const address& a, const address& b) noexcept;

Returns: !(a == b).

constexpr bool operator< (const address& a, const address& b) noexcept;

Returns:
— if a.is_v4() && !b.is_v4(), true;
— if !a.is_v4() && b.is_v4(), false;
— if a.is_v4(), the result of a.v4_ < b.v4_;
— otherwise, the result of a.v6_ < b.v6_.

constexpr bool operator> (const address& a, const address& b) noexcept;

Returns: b < a.

constexpr bool operator<=(const address& a, const address& b) noexcept;

Returns: !(b < a).

constexpr bool operator>=(const address& a, const address& b) noexcept;

Returns: !(a < b).

10.21.4.5. ip::address creation

[internet.address.creation]

address make_address(const char* str);
address make_address(const char* str, error_code& ec) noexcept;
address make_address(const string& str);
address make_address(const string& str, error_code& ec) noexcept;
address make_address(string_view str);
address make_address(string_view str, error_code& ec) noexcept;

Effects: Converts a textual representation of an address into an object of class address, as if by calling:

address a;
address_v6 v6a = make_address_v6(str, ec);
if (!ec)
  a = v6a;
else
{
  address_v4 v4a = make_address_v4(str, ec);
  if (!ec)
    a = v4a;
}

Returns: a.

10.21.4.6. ip::address I/O

[internet.address.io]

template<class CharT, class Traits>
  basic_ostream<CharT, Traits>& operator<<(
    basic_ostream<CharT, Traits>& os, const address& addr);

Returns: os << addr.to_string().c_str().

10.21.5. Class ip::address_v4

[internet.address.v4]

The class address_v4 is a representation of an IPv4 address.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class address_v4
  {
  public:
    // types:
    typedef uint_least32_t uint_type;
    struct bytes_type;

    // constructors:
    constexpr address_v4() noexcept;
    constexpr address_v4(const address_v4& a) noexcept;
    constexpr address_v4(const bytes_type& bytes);
    explicit constexpr address_v4(uint_type val);

    // assignment:
    address_v4& operator=(const address_v4& a) noexcept;

    // members:
    constexpr bool is_unspecified() const noexcept;
    constexpr bool is_loopback() const noexcept;
    constexpr bool is_multicast() const noexcept;
    constexpr bytes_type to_bytes() const noexcept;
    constexpr uint_type to_uint() const noexcept;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        to_string(const Allocator& a = Allocator()) const;

    // static members:
    static constexpr address_v4 any() noexcept;
    static constexpr address_v4 loopback() noexcept;
    static constexpr address_v4 broadcast() noexcept;
  };

  // address_v4 comparisons:
  constexpr bool operator==(const address_v4& a, const address_v4& b) noexcept;
  constexpr bool operator!=(const address_v4& a, const address_v4& b) noexcept;
  constexpr bool operator< (const address_v4& a, const address_v4& b) noexcept;
  constexpr bool operator> (const address_v4& a, const address_v4& b) noexcept;
  constexpr bool operator<=(const address_v4& a, const address_v4& b) noexcept;
  constexpr bool operator>=(const address_v4& a, const address_v4& b) noexcept;

  // address_v4 creation:
  constexpr address_v4 make_address_v4(const address_v4::bytes_type& bytes);
  constexpr address_v4 make_address_v4(address_v4::uint_type val);
  constexpr address_v4 make_address_v4(v4_mapped_t, const address_v6& a);
  address_v4 make_address_v4(const char* str);
  address_v4 make_address_v4(const char* str, error_code& ec) noexcept;
  address_v4 make_address_v4(const string& str);
  address_v4 make_address_v4(const string& str, error_code& ec) noexcept;
  address_v4 make_address_v4(string_view str);
  address_v4 make_address_v4(string_view str, error_code& ec) noexcept;

  // address_v4 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>& os, const address_v4& addr);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

address_v4 satisfies the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]).

10.21.5.1. Struct ip::address_v4::bytes_type

[internet.address.v4.bytes]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  struct address_v4::bytes_type : array<unsigned char, 4>
  {
    template<class... T> explicit constexpr bytes_type(T... t)
      : array<unsigned char, 4>{{static_cast<unsigned char>(t)...}} {}
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The ip::address_v4::bytes_type type is a standard-layout struct that provides a byte-level representation of an IPv4 address in network byte order.

10.21.5.2. ip::address_v4 constructors

[internet.address.v4.cons]

constexpr address_v4() noexcept;

Postconditions: to_bytes() yields {0, 0, 0, 0} and to_uint() == 0.

constexpr address_v4(const bytes_type& bytes);

Throws: out_of_range if any element of bytes is not in the range [0, 0xFF]. [Note: For implementations where numeric_limits<unsigned char>::max() == 0xFF, no out-of-range detection is needed. —end note]

Postconditions: to_bytes() == bytes and to_uint() == (bytes[0] << 24) | (bytes[1] << 16) | (bytes[2] << 8) | bytes[3].

explicit constexpr address_v4(address_v4::uint_type val);

Throws: out_of_range if val is not in the range [0, 0xFFFFFFFF]. [Note: For implementations where numeric_limits<address_v4::uint_type>::max() == 0xFFFFFFFF, no out-of-range detection is needed. —end note]

Postconditions: to_uint() == val and to_bytes() is { (val >> 24) & 0xFF, (val >> 16) & 0xFF, (val >> 8) & 0xFF, val & 0xFF }.

10.21.5.3. ip::address_v4 members

[internet.address.v4.members]

constexpr bool is_unspecified() const noexcept;

Returns: to_uint() == 0.

constexpr bool is_loopback() const noexcept;

Returns: (to_uint() & 0xFF000000) == 0x7F000000.

constexpr bool is_multicast() const noexcept;

Returns: (to_uint() & 0xF0000000) == 0xE0000000.

constexpr bytes_type to_bytes() const noexcept;

Returns: A representation of the address in network byte order.

constexpr address_v4::uint_type to_uint() const noexcept;

Returns: A representation of the address in host byte order.

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    to_string(const Allocator& a = Allocator()) const;

Returns: If successful, the textual representation of the address, determined as if by POSIX inet_ntop when invoked with address family AF_INET. Otherwise basic_string<char, char_traits<char>, Allocator>(a).

10.21.5.4. ip::address_v4 static members

[internet.address.v4.static]

static constexpr address_v4 any() noexcept;

Returns: address_v4().

static constexpr address_v4 loopback() noexcept;

Returns: address_v4(0x7F000001).

static constexpr address_v4 broadcast() noexcept;

Returns: address_v4(0xFFFFFFFF).

10.21.5.5. ip::address_v4 comparisons

[internet.address.v4.comparisons]

constexpr bool operator==(const address_v4& a, const address_v4& b) noexcept;

Returns: a.to_uint() == b.to_uint().

constexpr bool operator!=(const address_v4& a, const address_v4& b) noexcept;

Returns: !(a == b).

constexpr bool operator< (const address_v4& a, const address_v4& b) noexcept;

Returns: a.to_uint() < b.to_uint().

constexpr bool operator> (const address_v4& a, const address_v4& b) noexcept;

Returns: b < a.

constexpr bool operator<=(const address_v4& a, const address_v4& b) noexcept;

Returns: !(b < a).

constexpr bool operator>=(const address_v4& a, const address_v4& b) noexcept;

Returns: !(a < b).

10.21.5.6. ip::address_v4 creation

[internet.address.v4.creation]

constexpr address_v4 make_address_v4(const address_v4::bytes_type& bytes);

Returns: address_v4(bytes).

constexpr address_v4 make_address_v4(address_v4::uint_type val);

Returns: address_v4(val).

constexpr address_v4 make_address_v4(v4_mapped_t, const address_v6& a);

Returns: An address_v4 object corresponding to the IPv4-mapped IPv6 address, as if computed by the following method:

address_v6::bytes_type v6b = a.to_bytes();
address_v4::bytes_type v4b(v6b[12], v6b[13], v6b[14], v6b[15]);
return address_v4(v4b);

Throws: bad_address_cast if a.is_v4_mapped() is false.

address_v4 make_address_v4(const char* str);
address_v4 make_address_v4(const char* str, error_code& ec) noexcept;
address_v4 make_address_v4(const string& str);
address_v4 make_address_v4(const string& str, error_code& ec) noexcept;
address_v4 make_address_v4(string_view str);
address_v4 make_address_v4(string_view str, error_code& ec) noexcept;

Effects: Converts a textual representation of an address into a corresponding address_v4 value, as if by POSIX inet_pton when invoked with address family AF_INET.

Returns: If successful, an address_v4 value corresponding to the string str. Otherwise address_v4().

Error conditions:
errc::invalid_argument — if str is not a valid textual representation of an IPv4 address.

10.21.5.7. ip::address_v4 I/O

[internet.address.v4.io]

template<class CharT, class Traits>
  basic_ostream<CharT, Traits>& operator<<(
    basic_ostream<CharT, Traits>& os, const address_v4& addr);

Returns: os << addr.to_string().c_str().

10.21.6. Class ip::address_v6

[internet.address.v6]

The class address_v6 is a representation of an IPv6 address.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class address_v6
  {
  public:
    // types:
    struct bytes_type;

    // constructors:
    constexpr address_v6() noexcept;
    constexpr address_v6(const address_v6& a) noexcept;
    constexpr address_v6(const bytes_type& bytes,
                         scope_id_type scope = 0);

    // assignment:
    address_v6& operator=(const address_v6& a) noexcept;

    // members:
    void scope_id(scope_id_type id) noexcept;
    constexpr scope_id_type scope_id() const noexcept;
    constexpr bool is_unspecified() const noexcept;
    constexpr bool is_loopback() const noexcept;
    constexpr bool is_multicast() const noexcept;
    constexpr bool is_link_local() const noexcept;
    constexpr bool is_site_local() const noexcept;
    constexpr bool is_v4_mapped() const noexcept;
    constexpr bool is_multicast_node_local() const noexcept;
    constexpr bool is_multicast_link_local() const noexcept;
    constexpr bool is_multicast_site_local() const noexcept;
    constexpr bool is_multicast_org_local() const noexcept;
    constexpr bool is_multicast_global() const noexcept;
    constexpr bytes_type to_bytes() const noexcept;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        to_string(const Allocator& a = Allocator()) const;

    // static members:
    static constexpr address_v6 any() noexcept;
    static constexpr address_v6 loopback() noexcept;
  };

  // address_v6 comparisons:
  constexpr bool operator==(const address_v6& a, const address_v6& b) noexcept;
  constexpr bool operator!=(const address_v6& a, const address_v6& b) noexcept;
  constexpr bool operator< (const address_v6& a, const address_v6& b) noexcept;
  constexpr bool operator> (const address_v6& a, const address_v6& b) noexcept;
  constexpr bool operator<=(const address_v6& a, const address_v6& b) noexcept;
  constexpr bool operator>=(const address_v6& a, const address_v6& b) noexcept;

  // address_v6 creation:
  constexpr address_v6 make_address_v6(const address_v6::bytes_type& bytes,
                                       scope_id_type scope_id = 0);
  constexpr address_v6 make_address_v6(v4_mapped_t, const address_v4& a) noexcept;
  address_v6 make_address_v6(const char* str);
  address_v6 make_address_v6(const char* str, error_code& ec) noexcept;
  address_v6 make_address_v6(const string& str);
  address_v6 make_address_v6(const string& str, error_code& ec) noexcept;
  address_v6 make_address_v6(string_view str);
  address_v6 make_address_v6(string_view str, error_code& ec) noexcept;

  // address_v6 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>& os, const address_v6& addr);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

address_v6 satisfies the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]).

[Note: The implementations of the functions is_unspecified, is_loopback, is_multicast, is_link_local, is_site_local, is_v4_mapped, is_multicast_node_local, is_multicast_link_local, is_multicast_site_local, is_multicast_org_local and is_multicast_global are determined by [RFC4291]. —end note]

10.21.6.1. Struct ip::address_v6::bytes_type

[internet.address.v6.bytes]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  struct address_v6::bytes_type : array<unsigned char, 16>
  {
    template<class... T> explicit constexpr bytes_type(T... t)
      : array<unsigned char, 16>{{static_cast<unsigned char>(t)...}} {}
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The ip::address_v6::bytes_type type is a standard-layout struct that provides a byte-level representation of an IPv6 address in network byte order.

10.21.6.2. ip::address_v6 constructors

[internet.address.v6.cons]

constexpr address_v6() noexcept;

Postconditions: is_unspecified() == true and scope_id() == 0.

constexpr address_v6(const bytes_type& bytes,
                     scope_id_type scope = 0);

Throws: out_of_range if any element of bytes is not in the range [0, 0xFF]. [Note: For implementations where numeric_limits<unsigned char>::max() == 0xFF, no out-of-range detection is needed. —end note]

Postconditions: to_bytes() == bytes and scope_id() == scope.

10.21.6.3. ip::address_v6 members

[internet.address.v6.members]

void scope_id(scope_id_type id) noexcept;

Postconditions: scope_id() == id.

constexpr scope_id_type scope_id() const noexcept;

Returns: The scope identifier associated with the address.

constexpr bool is_unspecified() const noexcept;

Returns: *this == make_address_v6("::").

constexpr bool is_loopback() const noexcept;

Returns: *this == make_address_v6("::1").

constexpr bool is_multicast() const noexcept;

Returns: A boolean indicating whether the address_v6 object represents a multicast address, as if computed by the following method:

bytes_type b = to_bytes();
return b[0] == 0xFF;

constexpr bool is_link_local() const noexcept;

Returns: A boolean indicating whether the address_v6 object represents a unicast link-local address, as if computed by the following method:

bytes_type b = to_bytes();
return b[0] == 0xFE && (b[1] & 0xC0) == 0x80;

constexpr bool is_site_local() const noexcept;

Returns: A boolean indicating whether the address_v6 object represents a unicast site-local address, as if computed by the following method:

bytes_type b = to_bytes();
return b[0] == 0xFE && (b[1] & 0xC0) == 0xC0;

constexpr bool is_v4_mapped() const noexcept;

Returns: A boolean indicating whether the address_v6 object represents an IPv4-mapped IPv6 address, as if computed by the following method:

bytes_type b = to_bytes();
return b[ 0] == 0 && b[ 1] == 0 && b[ 2] == 0    && b[ 3] == 0
    && b[ 4] == 0 && b[ 5] == 0 && b[ 6] == 0    && b[ 7] == 0
    && b[ 8] == 0 && b[ 9] == 0 && b[10] == 0xFF && b[11] == 0xFF;

constexpr bool is_multicast_node_local() const noexcept;

Returns: is_multicast() && (to_bytes()[1] & 0x0F) == 0x01.

constexpr bool is_multicast_link_local() const noexcept;

Returns: is_multicast() && (to_bytes()[1] & 0x0F) == 0x02.

constexpr bool is_multicast_site_local() const noexcept;

Returns: is_multicast() && (to_bytes()[1] & 0x0F) == 0x05.

constexpr bool is_multicast_org_local() const noexcept;

Returns: is_multicast() && (to_bytes()[1] & 0x0F) == 0x08.

constexpr bool is_multicast_global() const noexcept;

Returns: is_multicast() && (to_bytes()[1] & 0x0F) == 0x0E.

constexpr bytes_type to_bytes() const noexcept;

Returns: A representation of the address in network byte order.

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    to_string(const Allocator& a = Allocator()) const;

Effects: Converts an address into a textual representation. If scope_id() == 0, converts as if by POSIX inet_ntop when invoked with address family AF_INET6. If scope_id() != 0, the format is address%scope-id, where address is the textual representation of the equivalent address having scope_id() == 0, and scope-id is an implementation-defined textual representation of the scope identifier.

Returns: If successful, the textual representation of the address. Otherwise basic_string<char, char_traits<char>, Allocator>(a).

10.21.6.4. ip::address_v6 static members

[internet.address.v6.static]

static constexpr address_v6 any() noexcept;

Returns: An address a such that the a.is_unspecified() == true and a.scope_id() == 0.

static constexpr address_v6 loopback() noexcept;

Returns: An address a such that the a.is_loopback() == true and a.scope_id() == 0.

10.21.6.5. ip::address_v6 comparisons

[internet.address.v6.comparisons]

constexpr bool operator==(const address_v6& a, const address_v6& b) noexcept;

Returns: a.to_bytes() == b.to_bytes() && a.scope_id() == b.scope_id().

constexpr bool operator!=(const address_v6& a, const address_v6& b) noexcept;

Returns: !(a == b).

constexpr bool operator< (const address_v6& a, const address_v6& b) noexcept;

Returns: a.to_bytes() < b.to_bytes() || (!(b.to_bytes() < a.to_bytes()) && a.scope_id() < b.scope_id()).

constexpr bool operator> (const address_v6& a, const address_v6& b) noexcept;

Returns: b < a.

constexpr bool operator<=(const address_v6& a, const address_v6& b) noexcept;

Returns: !(b < a).

constexpr bool operator>=(const address_v6& a, const address_v6& b) noexcept;

Returns: !(a < b).

10.21.6.6. ip::address_v6 creation

[internet.address.v6.creation]

constexpr address_v6 make_address_v6(const address_v6::bytes_type& bytes,
                                     scope_id_type scope_id);

Returns: address_v6(bytes, scope_id).

constexpr address_v6 make_address_v6(v4_mapped_t, const address_v4& a) noexcept;

Returns: An address_v6 object containing the IPv4-mapped IPv6 address corresponding to the specified IPv4 address, as if computed by the following method:

address_v4::bytes_type v4b = a.to_bytes();
address_v6::bytes_type v6b(0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                           0xFF, 0xFF, v4b[0], v4b[1], v4b[2], v4b[3]);
return address_v6(v6b);

address_v6 make_address_v6(const char* str);
address_v6 make_address_v6(const char* str, error_code& ec) noexcept;
address_v4 make_address_v6(const string& str);
address_v4 make_address_v6(const string& str, error_code& ec) noexcept;
address_v6 make_address_v6(string_view str);
address_v6 make_address_v6(string_view str, error_code& ec) noexcept;

Effects: Converts a textual representation of an address into a corresponding address_v6 value. The format is either address or address%scope-id, where address is in the format specified by POSIX inet_pton when invoked with address family AF_INET6, and scope-id is an optional string specifying the scope identifier. All implementations accept as scope-id a textual representation of an unsigned decimal integer. It is implementation-defined whether alternative scope identifier representations are permitted. If scope-id is not supplied, an address_v6 object is returned such that scope_id() == 0.

Returns: If successful, an address_v6 value corresponding to the string str. Otherwise returns address_v6().

Error conditions:
errc::invalid_argument — if str is not a valid textual representation of an IPv6 address.

10.21.6.7. ip::address_v6 I/O

[internet.address.v6.io]

template<class CharT, class Traits>
  basic_ostream<CharT, Traits>& operator<<(
    basic_ostream<CharT, Traits>& os, const address_v6& addr);

Returns: os << addr.to_string().c_str().

10.21.7. Class ip::bad_address_cast

[internet.bad.address.cast]

An exception of type bad_address_cast is thrown by a failed address_cast.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class bad_address_cast : public bad_cast
  {
  public:
    // constructor:
    bad_address_cast() noexcept;
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

bad_address_cast() noexcept;

Effects: constructs a bad_address_cast object.

Postconditions: what() returns an implementation-defined NTBS.

10.21.8. Hash support

[internet.hash]

template<> struct hash<experimental::net::v1::ip::address>;
template<> struct hash<experimental::net::v1::ip::address_v4>;
template<> struct hash<experimental::net::v1::ip::address_v6>;

Requires: the template specializations shall meet the requirements of class template hash (C++Std [unord.hash]).

10.21.9. Class template ip::basic_address_iterator specializations

[internet.address.iter]

The class template basic_address_iterator enables iteration over IP addresses in network byte order. This clause defines two specializations of the class template basic_address_iterator: basic_address_iterator<address_v4> and basic_address_iterator<address_v6>. The members and operational semantics of these specializations are defined below.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<> class basic_address_iterator<Address>
  {
  public:
    // types:
    typedef Address value_type;
    typedef ptrdiff_t difference_type;
    typedef const Address* pointer;
    typedef const Address& reference;
    typedef input_iterator_tag iterator_category;

    // constructors:
    basic_address_iterator(const Address& a) noexcept;

    // members:
    reference operator*() const noexcept;
    pointer operator->() const noexcept;
    basic_address_iterator& operator++() noexcept;
    basic_address_iterator operator++(int) noexcept;
    basic_address_iterator& operator--() noexcept;
    basic_address_iterator operator--(int) noexcept;

    // other members as required by C++Std [input.iterators]

  private:
    Address address_; // exposition only
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Specializations of basic_address_iterator satisfy the requirements for input iterators (C++Std [input.iterators]).

basic_address_iterator(const Address& a) noexcept;

Effects: Initializes address_ with a.

reference operator*() const noexcept;

Returns: address_.

pointer operator->() const noexcept;

Returns: std::addressof(address_).

basic_address_iterator& operator++() noexcept;

Effects: Sets address_ to the next unique address in network byte order.

Returns: *this.

basic_address_iterator operator++(int) noexcept;

Effects: Sets address_ to the next unique address in network byte order.

Returns: The prior value of *this.

basic_address_iterator& operator--() noexcept;

Effects: Sets address_ to the prior unique address in network byte order.

Returns: *this.

basic_address_iterator operator--(int) noexcept;

Effects: Sets address_ to the prior unique address in network byte order.

Returns: The prior value of *this.

10.21.10. Class template ip::basic_address_range specializations

[internet.address.range]

The class template basic_address_range represents a range of IP addresses in network byte order. This clause defines two specializations of the class template basic_address_range: basic_address_range<address_v4> and basic_address_range<address_v6>. The members and operational semantics of these specializations are defined below.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<> class basic_address_range<Address>
  {
  public:
    // types:
    typedef basic_address_iterator<Address> iterator;

    // constructors:
    basic_address_range() noexcept;
    basic_address_range(const Address& first,
                        const Address& last) noexcept;

    // members:
    iterator begin() const noexcept;
    iterator end() const noexcept;
    bool empty() const noexcept;
    size_t size() const noexcept; // not always defined
    iterator find(const Address& addr) const noexcept;
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Specializations of basic_address_range satisfy the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]).

basic_address_range() noexcept;

Effects: Constructs an object of type basic_address_range<Address> that represents an empty range.

basic_address_range(const Address& first,
                    const Address& last) noexcept;

Effects: Constructs an object of type basic_address_range<Address> that represents the half open range [first,last).

iterator begin() const noexcept;

Returns: An iterator that points to the beginning of the range.

iterator end() const noexcept;

Returns: An iterator that points to the end of the range.

bool empty() const noexcept;

Returns: true if *this represents an empty range, otherwise false.

size_t size() const noexcept;

Returns: The number of unique addresses in the range.

Remarks: This member function is not defined when Address is type address_v6.

iterator find(const Address& addr) const noexcept;

Returns: If addr is in the range, an iterator that points to addr; otherwise, end().

Complexity: Constant time.

10.21.11. Class template ip::network_v4

[internet.network.v4]

The class network_v4 provides the ability to use and manipulate IPv4 network addresses.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class network_v4
  {
  public:
    // constructors:
    constexpr network_v4() noexcept;
    constexpr network_v4(const address_v4& addr, int prefix_len);
    constexpr network_v4(const address_v4& addr, const address_v4& mask);

    // members:
    constexpr address_v4 address() const noexcept;
    constexpr int prefix_length() const noexcept;
    constexpr address_v4 netmask() const noexcept;
    constexpr address_v4 network() const noexcept;
    constexpr address_v4 broadcast() const noexcept;
    address_v4_range hosts() const noexcept;
    constexpr network_v4 canonical() const noexcept;
    constexpr bool is_host() const noexcept;
    constexpr bool is_subnet_of(const network_v4& other) const noexcept;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        to_string(const Allocator& a = Allocator()) const;
  };

  // network_v4 comparisons:
  constexpr bool operator==(const network_v4& a, const network_v4& b) noexcept;
  constexpr bool operator!=(const network_v4& a, const network_v4& b) noexcept;

  // network_v4 creation:
  constexpr network_v4 make_network_v4(const address_v4& addr, int prefix_len);
  constexpr network_v4 make_network_v4(const address_v4& addr, const address_v4& mask);
  network_v4 make_network_v4(const char* str);
  network_v4 make_network_v4(const char* str, error_code& ec) noexcept;
  network_v4 make_network_v4(const string& str);
  network_v4 make_network_v4(const string& str, error_code& ec) noexcept;
  network_v4 make_network_v4(string_view str);
  network_v4 make_network_v4(string_view str, error_code& ec) noexcept;

  // network_v4 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>& os, const network_v4& addr);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

network_v4 satisfies the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]).

10.21.11.1. ip::network_v4 constructors

[internet.network.v4.cons]

constexpr network_v4() noexcept;

Postconditions: this->address().is_unspecified() == true and prefix_length() == 0.

constexpr network_v4(const address_v4& addr, int prefix_len);

Postconditions: this->address() == addr and prefix_length() == prefix_len.

Throws: out_of_range if prefix_len < 0 or prefix_len > 32.

constexpr network_v4(const address_v4& addr, const address_v4& mask);

Postconditions: this->address() == addr and prefix_length() is equal to the number of contiguous non-zero bits in mask.

Throws: invalid_argument if mask contains non-contiguous non-zero bits, or if the most significant bit is zero and any other bits are non-zero.

10.21.11.2. ip::network_v4 members

[internet.network.v4.members]

constexpr address_v4 address() const noexcept;

Returns: The address specified when the network_v4 object was constructed.

constexpr int prefix_length() const noexcept;

Returns: The prefix length of the network.

constexpr address_v4 netmask() const noexcept;

Returns: An address_v4 object with prefix_length() contiguous non-zero bits set, starting from the most significant bit in network byte order. All other bits are zero.

constexpr address_v4 network() const noexcept;

Returns: An address_v4 object with the first prefix_length() bits, starting from the most significant bit in network byte order, set to the corresponding bit value of this->address(). All other bits are zero.

constexpr address_v4 broadcast() const noexcept;

Returns: An address_v4 object with the first prefix_length() bits, starting from the most significant bit in network byte order, set to the corresponding bit value of this->address(). All other bits are non-zero.

address_v4_range hosts() const noexcept;

Returns: If is_host() == true, an address_v4_range object representing the single address this->address(). Otherwise, an address_v4_range object representing the range of unique host IP addresses in the network.

[Note: For IPv4, the network address and the broadcast address are not included in the range of host IP addresses. For example, given a network 192.168.1.0/24, the range returned by hosts() is from 192.168.1.1 to 192.168.1.254 inclusive, and neither 192.168.1.0 nor the broadcast address 192.168.1.255 are in the range. —end note]

constexpr network_v4 canonical() const noexcept;

Returns: network_v4(network(), prefix_length()).

constexpr bool is_host() const noexcept;

Returns: prefix_length() == 32.

constexpr bool is_subnet_of(const network_v4& other) const noexcept;

Returns: true if other.prefix_length() < prefix_length() and network_v4(this->address(), other.prefix_length()).canonical() == other.canonical(), otherwise false.

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    to_string(const Allocator& a = Allocator()) const;

Returns: this->address().to_string(a) + "/" + std::to_string(prefix_length()).

10.21.11.3. ip::network_v4 comparisons

[internet.network.v4.comparisons]

constexpr bool operator==(const network_v4& a, const network_v4& b) noexcept;

Returns: true if a.address() == b.address() and a.prefix_length() == b.prefix_length(), otherwise false.

constexpr bool operator!=(const network_v4& a, const network_v4& b) noexcept;

Returns: !(a == b).

10.21.11.4. ip::network_v4 creation

[internet.network.v4.creation]

constexpr network_v4 make_network_v4(const address_v4& addr, int prefix_len);

Returns: network_v4(addr, prefix_len).

constexpr network_v4 make_network_v4(const address_v4& addr, const address_v4& mask);

Returns: network_v4(addr, mask).

network_v4 make_network_v4(const char* str);
network_v4 make_network_v4(const char* str, error_code& ec) noexcept;
network_v4 make_network_v4(const string& str);
network_v4 make_network_v4(const string& str, error_code& ec) noexcept;
network_v4 make_network_v4(string_view str);
network_v4 make_network_v4(string_view str, error_code& ec) noexcept;

Returns: If str contains a value of the form address '/' prefix-length, a network_v4 object constructed with the result of applying make_address_v4() to the address portion of the string, and the result of converting prefix-length to an integer of type int. Otherwise returns network_v4() and sets ec to reflect the error.

Error conditions:
errc::invalid_argument — if str is not a valid textual representation of an IPv4 address and prefix length.

10.21.11.5. ip::network_v4 I/O

[internet.network.v4.io]

template<class CharT, class Traits>
  basic_ostream<CharT, Traits>& operator<<(
    basic_ostream<CharT, Traits>& os, const network_v4& net);

Returns: os << net.to_string().c_str().

10.21.12. Class template ip::network_v6

[internet.network.v6]

The class network_v6 provides the ability to use and manipulate IPv6 network addresses.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class network_v6
  {
  public:
    // constructors:
    constexpr network_v6() noexcept;
    constexpr network_v6(const address_v6& addr, int prefix_len);

    // members:
    constexpr address_v6 address() const noexcept;
    constexpr int prefix_length() const noexcept;
    constexpr address_v6 network() const noexcept;
    address_v6_range hosts() const noexcept;
    constexpr network_v6 canonical() const noexcept;
    constexpr bool is_host() const noexcept;
    constexpr bool is_subnet_of(const network_v6& other) const noexcept;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        to_string(const Allocator& a = Allocator()) const;
  };

  // network_v6 comparisons:
  constexpr bool operator==(const network_v6& a, const network_v6& b) noexcept;
  constexpr bool operator!=(const network_v6& a, const network_v6& b) noexcept;

  // network_v6 creation:
  constexpr network_v6 make_network_v6(const address_v6& addr, int prefix_len);
  network_v6 make_network_v6(const char* str);
  network_v6 make_network_v6(const char* str, error_code& ec) noexcept;
  network_v6 make_network_v6(const string& str);
  network_v6 make_network_v6(const string& str, error_code& ec) noexcept;
  network_v6 make_network_v6(const string_v6& str);
  network_v6 make_network_v6(const string_v6& str, error_code& ec) noexcept;

  // network_v6 I/O:
  template<class CharT, class Traits>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>& os, const network_v6& addr);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

network_v6 satisfies the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), and CopyAssignable (C++Std [copyassignable]).

10.21.12.1. ip::network_v6 constructors

[internet.network.v6.cons]

constexpr network_v6() noexcept;

Postconditions: this->address().is_unspecified() == true and prefix_length() == 0.

constexpr network_v6(const address_v6& addr, int prefix_len);

Postconditions: this->address() == addr and prefix_length() == prefix_len.

Throws: out_of_range if prefix_len < 0 or prefix_len > 128.

10.21.12.2. ip::network_v6 members

[internet.network.v6.members]

constexpr address_v6 address() const noexcept;

Returns: The address specified when the network_v6 object was constructed.

constexpr int prefix_length() const noexcept;

Returns: The prefix length of the network.

constexpr address_v6 network() const noexcept;

Returns: An address_v6 object with the first prefix_length() bits, starting from the most significant bit in network byte order, set to the corresponding bit value of this->address(). All other bits are zero.

address_v6_range hosts() const noexcept;

Returns: If is_host() == true, an address_v6_range object representing the single address this->address(). Otherwise, an address_v6_range object representing the range of unique host IP addresses in the network.

constexpr network_v6 canonical() const noexcept;

Returns: network_v6(network(), prefix_length()).

constexpr bool is_host() const noexcept;

Returns: prefix_length() == 128.

constexpr bool is_subnet_of(const network_v6& other) const noexcept;

Returns: true if other.prefix_length() < prefix_length() and network_v6(this->address(), other.prefix_length()).canonical() == other.canonical(), otherwise false.

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    to_string(const Allocator& a = Allocator()) const;

Returns: this->address().to_string(a) + "/" + to_string(prefix_length()).c_str().

10.21.12.3. ip::network_v6 comparisons

[internet.network.v6.comparisons]

constexpr bool operator==(const network_v6& a, const network_v6& b) noexcept;

Returns: true if a.address() == b.address() and a.prefix_length() == b.prefix_length(), otherwise false.

constexpr bool operator!=(const network_v6& a, const network_v6& b) noexcept;

Returns: !(a == b).

10.21.12.4. ip::network_v6 creation

[internet.network.v6.creation]

constexpr network_v6 make_network_v6(const address_v6& addr, int prefix_len);

Returns: network_v6(addr, prefix_len).

network_v6 make_network_v6(const char* str);
network_v6 make_network_v6(const char* str, error_code& ec) noexcept;
network_v6 make_network_v6(const string& str);
network_v6 make_network_v6(const string& str, error_code& ec) noexcept;
network_v6 make_network_v6(const string_v6& str);
network_v6 make_network_v6(const string_v6& str, error_code& ec) noexcept;

Returns: If str contains a value of the form address '/' prefix-length, a network_v6 object constructed with the result of applying make_address_v6() to the address portion of the string, and the result of converting prefix-length to an integer of type int. Otherwise returns network_v6() and sets ec to reflect the error.

Error conditions:
errc::invalid_argument — if str is not a valid textual representation of an IPv6 address and prefix length.

10.21.12.5. ip::network_v6 I/O

[internet.network.v6.io]

template<class CharT, class Traits>
  basic_ostream<CharT, Traits>& operator<<(
    basic_ostream<CharT, Traits>& os, const network_v6& net);

Returns: os << net.to_string().c_str().

10.21.13. Class template ip::basic_endpoint

[internet.endpoint]

An object of type basic_endpoint<InternetProtocol> represents a protocol-specific endpoint, where an endpoint consists of an IP address and port number. Endpoints may be used to identify sources and destinations for socket connections and datagrams.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<class InternetProtocol>
  class basic_endpoint
  {
  public:
    // types:
    typedef InternetProtocol protocol_type;

    // constructors:
    constexpr basic_endpoint() noexcept;
    constexpr basic_endpoint(const protocol_type& proto,
                             port_type port_num) noexcept;
    constexpr basic_endpoint(const ip::address& addr,
                             port_type port_num) noexcept;

    // members:
    constexpr protocol_type protocol() const noexcept;
    constexpr ip::address address() const noexcept;
    void address(const ip::address& addr) noexcept;
    constexpr port_type port() const noexcept;
    void port(port_type port_num) noexcept;
  };

  // basic_endpoint comparisons:
  template<class InternetProtocol>
    constexpr bool operator==(const basic_endpoint<InternetProtocol>& a,
                              const basic_endpoint<InternetProtocol>& b) noexcept;
  template<class InternetProtocol>
    constexpr bool operator!=(const basic_endpoint<InternetProtocol>& a,
                              const basic_endpoint<InternetProtocol>& b) noexcept;
  template<class InternetProtocol>
    constexpr bool operator< (const basic_endpoint<InternetProtocol>& a,
                              const basic_endpoint<InternetProtocol>& b) noexcept;
  template<class InternetProtocol>
    constexpr bool operator> (const basic_endpoint<InternetProtocol>& a,
                              const basic_endpoint<InternetProtocol>& b) noexcept;
  template<class InternetProtocol>
    constexpr bool operator<=(const basic_endpoint<InternetProtocol>& a,
                              const basic_endpoint<InternetProtocol>& b) noexcept;
  template<class InternetProtocol>
    constexpr bool operator>=(const basic_endpoint<InternetProtocol>& a,
                              const basic_endpoint<InternetProtocol>& b) noexcept;

  // basic_endpoint I/O:
  template<class CharT, class Traits, class InternetProtocol>
    basic_ostream<CharT, Traits>& operator<<(
      basic_ostream<CharT, Traits>& os,
      const basic_endpoint<InternetProtocol>& ep);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

Instances of the basic_endpoint class template meet the requirements for an Endpoint.

Extensible implementations provide the following member functions:

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<class InternetProtocol>
  class basic_endpoint
  {
  public:
    void* data() noexcept;
    const void* data() const noexcept;
    constexpr size_t size() const noexcept;
    void resize(size_t s);
    constexpr size_t capacity() const noexcept;
    // remainder unchanged
  private:
    union
    {
      sockaddr_in v4_;
      sockaddr_in6 v6_;
    } data_; // exposition only
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
10.21.13.1. ip::basic_endpoint constructors

[internet.endpoint.cons]

constexpr basic_endpoint() noexcept;

Postconditions: this->address() == ip::address() and port() == 0.

constexpr basic_endpoint(const protocol_type& proto,
                         port_type port_num) noexcept;

Requires: proto == protocol_type::v4() || proto == protocol_type::v6().

Postconditions:
— If proto == protocol_type::v6(), this->address() == ip::address_v6(); otherwise, this->address() == ip::address_v4().
port() == port_num.

constexpr basic_endpoint(const ip::address& addr,
                         port_type port_num) noexcept;

Postconditions: this->address() == addr and port() == port_num.

10.21.13.2. ip::basic_endpoint members

[internet.endpoint.members]

constexpr protocol_type protocol() const noexcept;

Returns: protocol_type::v6() if the expression this->address().is_v6() is true, otherwise protocol_type::v4().

constexpr ip::address address() const noexcept;

Returns: The address associated with the endpoint.

void address(const ip::address& addr) noexcept;

Postconditions: this->address() == addr.

constexpr port_type port() const noexcept;

Returns: The port number associated with the endpoint.

void port(port_type port_num) noexcept;

Postconditions: port() == port_num.

10.21.13.3. ip::basic_endpoint comparisons

[internet.endpoint.comparisons]

template<class InternetProtocol>
  constexpr bool operator==(const basic_endpoint<InternetProtocol>& a,
                            const basic_endpoint<InternetProtocol>& b) noexcept;

Returns: a.address() == b.address() && a.port() == b.port()).

template<class InternetProtocol>
  constexpr bool operator!=(const basic_endpoint<InternetProtocol>& a,
                            const basic_endpoint<InternetProtocol>& b) noexcept;

Returns: !(a == b).

template<class InternetProtocol>
  constexpr bool operator< (const basic_endpoint<InternetProtocol>& a,
                            const basic_endpoint<InternetProtocol>& b) noexcept;

Returns: a.address() < b.address() || (!(b.address() < a.address()) && a.port() < b.port()).

template<class InternetProtocol>
  constexpr bool operator> (const basic_endpoint<InternetProtocol>& a,
                            const basic_endpoint<InternetProtocol>& b) noexcept;

Returns: b < a.

template<class InternetProtocol>
  constexpr bool operator<=(const basic_endpoint<InternetProtocol>& a,
                            const basic_endpoint<InternetProtocol>& b) noexcept;

Returns: !(b < a).

template<class InternetProtocol>
  constexpr bool operator>=(const basic_endpoint<InternetProtocol>& a,
                            const basic_endpoint<InternetProtocol>& b) noexcept;

Returns: !(a < b).

10.21.13.4. ip::basic_endpoint I/O

[internet.endpoint.io]

template<class CharT, class Traits, class InternetProtocol>
  basic_ostream<CharT, Traits>& operator<<(
    basic_ostream<CharT, Traits>& os,
    const basic_endpoint<InternetProtocol>& ep);

Effects: Outputs a representation of the endpoint to the stream, as if it were implemented as follows:

basic_ostringstream<CharT, Traits> ss;
if (ep.protocol() == basic_endpoint<InternetProtocol>::protocol_type::v6())
  ss << "[" << ep.address() << "]";
else
  ss << ep.address();
ss << ":" << ep.port();
os << ss.str();

Returns: os.

[Note: The representation of the endpoint when it contains an IP version 6 address is based on [RFC2732]. —end note]

10.21.13.5. ip::basic_endpoint members (extensible implementations)

[internet.endpoint.extensible]

void* data() noexcept;

Returns: std::addressof(data_).

const void* data() const noexcept;

Returns: std::addressof(data_).

constexpr size_t size() const noexcept;

Returns: sizeof(sockaddr_in6) if protocol().family() == AF_INET6, otherwise sizeof(sockaddr_in).

void resize(size_t s);

Throws: length_error if the condition protocol().family() == AF_INET6 && s != sizeof(sockaddr_in6) || protocol().family() == AF_INET4 && s != sizeof(sockaddr_in) is true.

constexpr size_t capacity() const noexcept;

Returns: sizeof(data_).

10.21.14. Class template ip::basic_resolver_entry

[internet.resolver.entry]

An object of type basic_resolver_entry<InternetProtocol> represents a single element in the results returned by a name resolution operation.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<class InternetProtocol>
  class basic_resolver_entry
  {
  public:
    // types:
    typedef InternetProtocol protocol_type;
    typedef typename InternetProtocol::endpoint endpoint_type;

    // constructors:
    basic_resolver_entry();
    basic_resolver_entry(const endpoint_type& ep,
                         string_view h,
                         string_view s);

    // members:
    endpoint_type endpoint() const;
    operator endpoint_type() const;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        host_name(const Allocator& a = Allocator()) const;
    template<class Allocator = allocator<char>>
      basic_string<char, char_traits<char>, Allocator>
        service_name(const Allocator& a = Allocator()) const;
  };

  // basic_resolver_entry comparisons:
  template<class InternetProtocol>
    bool operator==(const basic_resolver_entry<InternetProtocol>& a,
                    const basic_resolver_entry<InternetProtocol>& b);
  template<class InternetProtocol>
    bool operator!=(const basic_resolver_entry<InternetProtocol>& a,
                    const basic_resolver_entry<InternetProtocol>& b);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
10.21.14.1. ip::basic_resolver_entry constructors

[internet.resolver.entry.cons]

basic_resolver_entry();

Effects: Equivalent to basic_resolver_entry<InternetProtocol>(endpoint_type(), "", "").

basic_resolver_entry(const endpoint_type& ep,
                     string_view h,
                     string_view s);

Postconditions:
endpoint() == ep.
host_name() == h.
service_name() == s.

10.21.14.2. ip::basic_resolver_entry members

[internet.resolver.entry.members]

endpoint_type endpoint() const;

Returns: The endpoint associated with the resolver entry.

operator endpoint_type() const;

Returns: endpoint().

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    host_name(const Allocator& a = Allocator()) const;

Returns: The host name associated with the resolver entry.

Remarks: Ill-formed unless allocator_traits<Allocator>::value_type is char.

template<class Allocator = allocator<char>>
  basic_string<char, char_traits<char>, Allocator>
    service_name(const Allocator& a = Allocator()) const;

Returns: The service name associated with the resolver entry.

Remarks: Ill-formed unless allocator_traits<Allocator>::value_type is char.

10.21.14.3. op::basic_resolver_entry comparisons

[internet.resolver.entry.comparisons]

template<class InternetProtocol>
  bool operator==(const basic_resolver_entry<InternetProtocol>& a,
                  const basic_resolver_entry<InternetProtocol>& b);

Returns: a.endpoint() == b.endpoint() && a.host_name() == b.host_name() && a.service_name() == b.service_name().

template<class InternetProtocol>
  bool operator!=(const basic_resolver_entry<InternetProtocol>& a,
                  const basic_resolver_entry<InternetProtocol>& b);

Returns: !(a == b).

10.21.15. Class template ip::basic_resolver_results

[internet.resolver.results]

An object of type basic_resolver_results<InternetProtocol> represents a sequence of basic_resolver_entry<InternetProtocol> elements resulting from a single name resolution operation.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<class InternetProtocol>
  class basic_resolver_results
  {
  public:
    // types:
    typedef InternetProtocol protocol_type;
    typedef typename protocol_type::endpoint endpoint_type;
    typedef basic_resolver_entry<protocol_type> value_type;
    typedef const value_type& const_reference;
    typedef value_type& reference;
    typedef implementation-defined const_iterator;
    typedef const_iterator iterator;
    typedef ptrdiff_t difference_type;
    typedef size_t size_type;

    // construct / copy / destroy:
    basic_resolver_results();
    basic_resolver_results(const basic_resolver_results& rhs);
    basic_resolver_results(basic_resolver_results&& rhs) noexcept;
    basic_resolver_results& operator=(const basic_resolver_results& rhs);
    basic_resolver_results& operator=(basic_resolver_results&& rhs);
    ~basic_resolver_results();

    // size:
    size_type size() const noexcept;
    size_type max_size() const noexcept;
    bool empty() const noexcept;

    // element access:
    const_iterator begin() const;
    const_iterator end() const;
    const_iterator cbegin() const;
    const_iterator cend() const;

    // swap:
    void swap(basic_resolver_results& that) noexcept;
  };

  // basic_resolver_results comparisons:
  template<class InternetProtocol>
    bool operator==(const basic_resolver_results<InternetProtocol>& a,
                    const basic_resolver_results<InternetProtocol>& b);
  template<class InternetProtocol>
    bool operator!=(const basic_resolver_results<InternetProtocol>& a,
                    const basic_resolver_results<InternetProtocol>& b);

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The class template basic_resolver_results satisfies the requirements of a sequence container (C++Std [sequence.reqmts]), except that only the operations defined for const-qualified sequence containers are supported. The class template basic_resolver_results supports forward iterators.

A default-constructed basic_resolver_results object is empty. A non-empty results object is obtained only by calling a basic_resolver object's wait or async_wait operations, or otherwise by copy construction, move construction, assignment, or swap from another non-empty results object.

10.21.15.1. ip::basic_resolver_results constructors

[internet.resolver.results.cons]

basic_resolver_results();

Postconditions: size() == 0.

basic_resolver_results(const basic_resolver_results& rhs);

Postconditions: *this == rhs.

basic_resolver_results(basic_resolver_results&& rhs) noexcept;

Postconditions: *this is equal to the prior value of rhs.

10.21.15.2. ip::basic_resolver_results assignment

[internet.resolver.results.assign]

basic_resolver_results& operator=(const basic_resolver_results& rhs);

Postconditions: *this == rhs.

Returns: *this.

basic_resolver_results& operator=(basic_resolver_results& rhs) noexcept;

Postconditions: *this is equal to the prior value of rhs.

Returns: *this.

10.21.15.3. ip::basic_resolver_results size

[internet.resolver.results.size]

size_type size() const noexcept;

Returns: The number of basic_resolver_entry elements in *this.

size_type max_size() const noexcept;

Returns: The maximum number of basic_resolver_entry elements that can be stored in *this.

bool empty() const noexcept;

Returns: size() == 0.

10.21.15.4. ip::basic_resolver_results element access

[internet.resolver.results.access]

const_iterator begin() const;
const_iterator cbegin() const;

Returns: A starting iterator that enumerates over all the basic_resolver_entry elements stored in *this.

const_iterator end() const;
const_iterator cend() const;

Returns: A terminating iterator that enumerates over all the basic_resolver_entry elements stored in *this.

10.21.15.5. ip::basic_resolver_results swap

[internet.resolver.results.swap]

void swap(basic_resolver_results& that) noexcept;

Postconditions: *this is equal to the prior value of that, and that is equal to the prior value of *this.

10.21.15.6. ip::basic_resolver_results comparisons

[internet.resolver.results.comparisons]

template<class InternetProtocol>
  bool operator==(const basic_resolver_results<InternetProtocol>& a,
                  const basic_resolver_results<InternetProtocol>& b);

Returns: a.size() == b.size() && equal(a.cbegin(), a.cend(), b.cbegin()).

template<class InternetProtocol>
  bool operator!=(const basic_resolver_results<InternetProtocol>& a,
                  const basic_resolver_results<InternetProtocol>& b);

Returns: !(a == b).

10.21.16. Class ip::resolver_base

[internet.resolver.base]

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class resolver_base
  {
  public:
    typedef T1 flags;
    static const flags passive;
    static const flags canonical_name;
    static const flags numeric_host;
    static const flags numeric_service;
    static const flags v4_mapped;
    static const flags all_matching;
    static const flags address_configured;

  protected:
    resolver_base();
    ~resolver_base();
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

resolver_base defines a bitmask type, flags, with the bitmask elements shown above.

Table 36. resolver flags

Constant name

POSIX macro

Definition or notes

passive

AI_PASSIVE

Returned endpoints are intended for use as locally bound socket endpoints.

canonical_name

AI_CANONNAME

Determine the canonical name of the host specified in the query.

numeric_host

AI_NUMERICHOST

Host name should be treated as a numeric string defining an IPv4 or IPv6 address and no host name resolution should be attempted.

numeric_service

AI_NUMERICSERV

Service name should be treated as a numeric string defining a port number and no service name resolution should be attempted.

v4_mapped

AI_V4MAPPED

If the protocol is specified as an IPv6 protocol, return IPv4-mapped IPv6 addresses on finding no IPv6 addresses.

all_matching

AI_ALL

If used with v4_mapped, return all matching IPv6 and IPv4 addresses.

address_configured

AI_ADDRCONFIG

Only return IPv4 addresses if a non-loopback IPv4 address is configured for the system. Only return IPv6 addresses if a non-loopback IPv6 address is configured for the system.


10.21.17. Class template ip::basic_resolver

[internet.resolver]

Objects of type basic_resolver<InternetProtocol> are used to perform name resolution. Name resolution is the translation of a host name and service name into a sequence of endpoints, or the translation of an endpoint into its corresponding host name and service name.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  template<class InternetProtocol>
  class basic_resolver : public resolver_base
  {
  public:
    // types:

    typedef io_context::executor_type executor_type;
    typedef InternetProtocol protocol_type;
    typedef typename InternetProtocol::endpoint endpoint_type;
    typedef basic_resolver_results<InternetProtocol> results_type;

    // construct / copy / destroy:

    explicit basic_resolver(io_context& ctx);
    basic_resolver(const basic_resolver&) = delete;
    basic_resolver(basic_resolver&& rhs) noexcept;

    ~basic_resolver();

    basic_resolver& operator=(const basic_resolver&) = delete;
    basic_resolver& operator=(basic_resolver&& rhs);

    // basic_resolver operations:

    executor_type get_executor() noexcept;

    void cancel();

    results_type resolve(string_view host_name, string_view service_name);
    results_type resolve(string_view host_name, string_view service_name,
                         error_code& ec);
    results_type resolve(string_view host_name, string_view service_name,
                         flags f);
    results_type resolve(string_view host_name, string_view service_name,
                         flags f, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_resolve(string_view host_name, string_view service_name,
                            CompletionToken&& token);
    template<class CompletionToken>
      DEDUCED async_resolve(string_view host_name, string_view service_name,
                            flags f, CompletionToken&& token);

    results_type resolve(const protocol_type& protocol,
                         string_view host_name, string_view service_name);
    results_type resolve(const protocol_type& protocol,
                         string_view host_name, string_view service_name,
                         error_code& ec);
    results_type resolve(const protocol_type& protocol,
                         string_view host_name, string_view service_name,
                         flags f);
    results_type resolve(const protocol_type& protocol,
                         string_view host_name, string_view service_name,
                         flags f, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_resolve(const protocol_type& protocol,
                            string_view host_name, string_view service_name,
                            CompletionToken&& token);
    template<class CompletionToken>
      DEDUCED async_resolve(const protocol_type& protocol,
                            string_view host_name, string_view service_name,
                            flags f, CompletionToken&& token);

    results_type resolve(const endpoint_type& e);
    results_type resolve(const endpoint_type& e, error_code& ec);

    template<class CompletionToken>
      DEDUCED async_resolve(const endpoint_type& e,
                            CompletionToken&& token);
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
10.21.17.1. ip::basic_resolver constructors

[internet.resolver.cons]

explicit basic_resolver(io_context& ctx);

Postconditions: get_executor() == ctx.get_executor().

basic_resolver(basic_resolver&& rhs) noexcept;

Effects: Move constructs an object of class basic_resolver<InternetProtocol> that refers to the state originally represented by rhs.

Postconditions: get_executor() == rhs.get_executor().

10.21.17.2. ip::basic_resolver destructor

[internet.resolver.dtor]

~basic_resolver();

Effects: Destroys the resolver, canceling all asynchronous operations associated with this resolver as if by calling cancel().

10.21.17.3. ip::basic_resolver assignment

[internet.resolver.assign]

basic_resolver& operator=(basic_resolver&& rhs);

Effects: Cancels all outstanding asynchronous operations associated with *this as if by calling cancel(), then moves into *this the state originally represented by rhs.

Postconditions: get_executor() == ctx.get_executor().

Returns: *this.

10.21.17.4. ip::basic_resolver operations

[internet.resolver.ops]

executor_type& get_executor() noexcept;

Returns: The associated executor.

void cancel();

Effects: Cancels all outstanding asynchronous resolve operations associated with *this. Completion handlers for canceled operations are passed an error code ec such that ec == errc::operation_canceled yields true.

Remarks: Does not block (C++Std [defns.block]) the calling thread pending completion of the canceled operations.

results_type resolve(string_view host_name, string_view service_name);
results_type resolve(string_view host_name, string_view service_name,
                     error_code& ec);

Returns: resolve(host_name, service_name, resolver_base::flags(), ec).

results_type resolve(string_view host_name, string_view service_name,
                     flags f);
results_type resolve(string_view host_name, string_view service_name,
                     flags f, error_code& ec);

Effects: If host_name.data() != nullptr, let H be an NTBS constructed from host_name; otherwise, let H be nullptr. If service_name.data() != nullptr, let S be an NTBS constructed from service_name; otherwise, let S be nullptr. Resolves a host name and service name, as if by POSIX:

addrinfo hints;
hints.ai_flags = static_cast<int>(f);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = endpoint_type().protocol().type();
hints.ai_protocol = endpoint_type().protocol().protocol();
hints.ai_addr = nullptr;
hints.ai_addrlen = 0;
hints.ai_canonname = nullptr;
hints.ai_next = nullptr;
addrinfo* result = nullptr;
getaddrinfo(H, S, &hints, &result);

Returns: On success, a non-empty results object containing the results of the resolve operation. Otherwise results_type().

template<class CompletionToken>
  DEDUCED async_resolve(string_view host_name, string_view service_name,
                        CompletionToken&& token);

Returns: async_resolve(host_name, service_name, resolver_base::flags(), forward<CompletionToken>(token)).

template<class CompletionToken>
  DEDUCED async_resolve(string_view host_name, string_view service_name,
                        flags f, CompletionToken&& token);

Completion signature: void(error_code ec, results_type r).

Effects: If host_name.data() != nullptr, let H be an NTBS constructed from host_name; otherwise, let H be nullptr. If service_name.data() != nullptr, let S be an NTBS constructed from service_name; otherwise, let S be nullptr. Initiates an asynchronous operation to resolve a host name and service name, as if by POSIX:

addrinfo hints;
hints.ai_flags = static_cast<int>(f);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = endpoint_type().protocol().type();
hints.ai_protocol = endpoint_type().protocol().protocol();
hints.ai_addr = nullptr;
hints.ai_addrlen = 0;
hints.ai_canonname = nullptr;
hints.ai_next = nullptr;
addrinfo* result = nullptr;
getaddrinfo(H, S, &hints, &result);

On success, r is a non-empty results object containing the results of the resolve operation. Otherwise, r is results_type().

results_type resolve(const protocol_type& protocol,
                     string_view host_name, string_view service_name);
results_type resolve(const protocol_type& protocol,
                     string_view host_name, string_view service_name,
                     error_code& ec);

Returns: resolve(protocol, host_name, service_name, resolver_base::flags(), ec).

results_type resolve(const protocol_type& protocol,
                     string_view host_name, string_view service_name,
                     flags f);
results_type resolve(const protocol_type& protocol,
                     string_view host_name, string_view service_name,
                     flags f, error_code& ec);

Effects: If host_name.data() != nullptr, let H be an NTBS constructed from host_name; otherwise, let H be nullptr. If service_name.data() != nullptr, let S be an NTBS constructed from service_name; otherwise, let S be nullptr. Resolves a host name and service name, as if by POSIX:

addrinfo hints;
hints.ai_flags = static_cast<int>(f);
hints.ai_family = protocol.family();
hints.ai_socktype = protocol.type();
hints.ai_protocol = protocol.protocol();
hints.ai_addr = nullptr;
hints.ai_addrlen = 0;
hints.ai_canonname = nullptr;
hints.ai_next = nullptr;
addrinfo* result = nullptr;
getaddrinfo(H, S, &hints, &result);

Returns: On success, a non-empty results object containing the results of the resolve operation. Otherwise results_type().

template<class CompletionToken>
  DEDUCED async_resolve(const protocol_type& protocol,
                        string_view host_name, string_view service_name,
                        CompletionToken&& token);

Returns: async_resolve(protocol, host_name, service_name, resolver_base::flags(), forward<CompletionToken>(token)).

template<class CompletionToken>
  DEDUCED async_resolve(const protocol& protocol,
                        string_view host_name, string_view service_name,
                        flags f, CompletionToken&& token);

Completion signature: void(error_code ec, results_type r).

Effects: If host_name.data() != nullptr, let H be an NTBS constructed from host_name; otherwise, let H be nullptr. If service_name.data() != nullptr, let S be an NTBS constructed from service_name; otherwise, let S be nullptr. Initiates an asynchronous operation to resolve a host name and service name, as if by POSIX:

addrinfo hints;
hints.ai_flags = static_cast<int>(f);
hints.ai_family = protocol.family();
hints.ai_socktype = protocol.type();
hints.ai_protocol = protocol.protocol();
hints.ai_addr = nullptr;
hints.ai_addrlen = 0;
hints.ai_canonname = nullptr;
hints.ai_next = nullptr;
addrinfo* result = nullptr;
getaddrinfo(H, S, &hints, &result);

On success, r is a non-empty results object containing the results of the resolve operation. Otherwise, r is results_type().

results_type resolve(const endpoint_type& e);
results_type resolve(const endpoint_type& e, error_code& ec);

Effects: Let S1 and S2 be implementation-defined values that are sufficiently large to hold the host name and service name respectively. Resolves an endpoint as if by POSIX:

char host_name[S1];
char service_name[S2];
int flags = 0;
if (endpoint_type().protocol().type() == SOCK_DGRAM)
  flags |= NI_DGRAM;
int result = getnameinfo((const sockaddr*)e.data(), e.size(),
                         host_name, S1,
                         service_name, S2,
                         flags);
if (result != 0)
{
  flags |= NI_NUMERICSERV;
  result = getnameinfo((const sockaddr*)e.data(), e.size(),
                       host_name, S1,
                       service_name, S2,
                       flags);
}

Returns: On success, a results object with size() == 1 containing the results of the resolve operation. Otherwise results_type().

template<class CompletionToken>
  DEDUCED async_resolve(const endpoint_type& e,
                        CompletionToken&& token);

Completion signature: void(error_code ec, results_type r).

Effects: Let S1 and S2 be implementation-defined values that are sufficiently large to hold the host name and service name respectively. Initiates an asynchronous operation to resolve an endpoint as if by POSIX:

char host_name[S1];
char service_name[S2];
int flags = 0;
if (endpoint_type().protocol().type() == SOCK_DGRAM)
  flags |= NI_DGRAM;
int result = getnameinfo((const sockaddr*)e.data(), e.size(),
                         host_name, S1,
                         service_name, S2,
                         flags);
if (result != 0)
{
  flags |= NI_NUMERICSERV;
  result = getnameinfo((const sockaddr*)e.data(), e.size(),
                       host_name, S1,
                       service_name, S2,
                       flags);
}

On success, r is a results object with size() == 1 containing the results of the resolve operation; otherwise, r is results_type().

10.21.18. Host name functions

[internet.host.name]

string host_name();
string host_name(error_code& ec);
template<class Allocator>
  basic_string<char, char_traits<char>, Allocator>
    host_name(const Allocator& a);
template<class Allocator>
  basic_string<char, char_traits<char>, Allocator>
    host_name(const Allocator& a, error_code& ec);

Returns: The standard host name for the current machine, determined as if by POSIX gethostname.

Remarks: In the last two overloads, ill-formed unless allocator_traits<Allocator>::value_type is char.

10.21.19. Class ip::tcp

[internet.tcp]

The class tcp encapsulates the types and flags necessary for TCP sockets.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class tcp
  {
  public:
    // types:
    typedef basic_endpoint<tcp> endpoint;
    typedef basic_resolver<tcp> resolver;
    typedef basic_stream_socket<tcp> socket;
    typedef basic_socket_acceptor<tcp> acceptor;
    typedef basic_socket_iostream<tcp> iostream;
    class no_delay;

    // static members:
    static constexpr tcp v4() noexcept;
    static constexpr tcp v6() noexcept;

    tcp() = delete;
  };

  // tcp comparisons:
  constexpr bool operator==(const tcp& a, const tcp& b) noexcept;
  constexpr bool operator!=(const tcp& a, const tcp& b) noexcept;

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The tcp class meets the requirements for an InternetProtocol.

Extensible implementations provide the following member functions:

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class tcp
  {
  public:
    constexpr int family() const noexcept;
    constexpr int type() const noexcept;
    constexpr int protocol() const noexcept;
    // remainder unchanged
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The return values for these member functions are listed in the table below.

Table 37. Behavior of extensible implementations

value

family()

type()

protocol()

tcp::v4()

AF_INET

SOCK_STREAM

IPPROTO_TCP

tcp::v6()

AF_INET6

SOCK_STREAM

IPPROTO_TCP


[Note: The constants AF_INET, AF_INET6 and SOCK_STREAM are defined in the POSIX header file sys/socket.h. The constant IPPROTO_TCP is defined in the POSIX header file netinet/in.h. —end note]

10.21.19.1. ip::tcp comparisons

[internet.tcp.comparisons]

constexpr bool operator==(const tcp& a, const tcp& b) noexcept;

Returns: A boolean indicating whether two objects of class tcp are equal, such that the expression tcp::v4() == tcp::v4() is true, the expression tcp::v6() == tcp::v6() is true, and the expression tcp::v4() == tcp::v6() is false.

constexpr bool operator!=(const tcp& a, const tcp& b) noexcept;

Returns: !(a == b).

10.21.20. Class ip::udp

[internet.udp]

The class udp encapsulates the types and flags necessary for UDP sockets.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class udp
  {
  public:
    // types:
    typedef basic_endpoint<udp> endpoint;
    typedef basic_resolver<udp> resolver;
    typedef basic_datagram_socket<udp> socket;

    // static members:
    static constexpr udp v4() noexcept;
    static constexpr udp v6() noexcept;

    udp() = delete;
  };

  // udp comparisons:
  constexpr bool operator==(const udp& a, const udp& b) noexcept;
  constexpr bool operator!=(const udp& a, const udp& b) noexcept;

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The udp class meets the requirements for an InternetProtocol.

Extensible implementations provide the following member functions:

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {

  class udp
  {
  public:
    constexpr int family() const noexcept;
    constexpr int type() const noexcept;
    constexpr int protocol() const noexcept;
    // remainder unchanged
  };

} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

The return values for these member functions are listed in the table below.

Table 38. Behavior of extensible implementations

value

family()

type()

protocol()

udp::v4()

AF_INET

SOCK_DGRAM

IPPROTO_UDP

udp::v6()

AF_INET6

SOCK_DGRAM

IPPROTO_UDP


[Note: The constants AF_INET, AF_INET6 and SOCK_DGRAM are defined in the POSIX header file sys/socket.h. The constant IPPROTO_UDP is defined in the POSIX header file netinet/in.h. —end note]

10.21.20.1. ip::udp comparisons

[internet.udp.comparisons]

constexpr bool operator==(const udp& a, const udp& b) noexcept;

Returns: A boolean indicating whether two objects of class udp are equal, such that the expression udp::v4() == udp::v4() is true, the expression udp::v6() == udp::v6() is true, and the expression udp::v4() == udp::v6() is false.

constexpr bool operator!=(const udp& a, const udp& b) noexcept;

Returns: !(a == b).

10.21.21. Internet socket options

[internet.socket.opt]

In the table below, let C denote a socket option class; let L identify the POSIX macro to be passed as the level argument to POSIX setsockopt and getsockopt; let N identify the POSIX macro to be passed as the option_name argument to POSIX setsockopt and getsockopt; let T identify the type of the value whose address will be passed as the option_value argument to POSIX setsockopt and getsockopt; let p denote a (possibly const) value of a type meeting the protocol requirements, as passed to the socket option's level and name member functions; and let F be the value of p.family().

Table 39. Internet socket options

C

L

N

T

Requirements, definition or notes

ip::tcp::no_delay

IPPROTO_TCP

TCP_NODELAY

int

Satisfies the BooleanSocketOption type requirements.

Determines whether a TCP socket will avoid coalescing of small segments. [Note: That is, setting this option disables the Nagle algorithm. —end note]

ip::v6_only

IPPROTO_IPV6

IPV6_V6ONLY

int

Satisfies the BooleanSocketOption type requirements.

Determines whether a socket created for an IPv6 protocol is restricted to IPv6 communications only.

Implementations are not required to support setting the v6_only option to false, and the initial value of the v6_only option for a socket is implementation-defined. [Note: As not all operating systems support dual stack IP networking. Some operating systems that do provide dual stack support offer a configuration option to disable it or to set the initial value of the v6_only socket option. —end note]

ip::unicast::hops

IPPROTO_IPV6 if F == AF_INET6, otherwise IPPROTO_IP

IPV6_UNICAST_HOPS if F == AF_INET6, otherwise IP_TTL

int

Satisfies the IntegerSocketOption type requirements.

Specifies the default number of hops (also known as time-to-live or TTL) on outbound datagrams.

The constructor and assignment operator for the ip::unicast::hops class throw out_of_range if the int argument is not in the range [0, 255].

ip::multicast::join_group

IPPROTO_IPV6 if F == AF_INET6, otherwise IPPROTO_IP

IPV6_JOIN_GROUP if F == AF_INET6, otherwise IP_ADD_MEMBERSHIP

ipv6_mreq if F == AF_INET6, otherwise ip_mreq

Satisfies the MulticastGroupSocketOption type requirements.

Requests that the socket join the specified multicast group.

ip::multicast::leave_group

IPPROTO_IPV6 if F == AF_INET6, otherwise IPPROTO_IP

IPV6_LEAVE_GROUP if F == AF_INET6, otherwise IP_DROP_MEMBERSHIP

ipv6_mreq if F == AF_INET6, otherwise ip_mreq

Satisfies the MulticastGroupSocketOption type requirements.

Requests that the socket leave the specified multicast group.

ip::multicast::outbound_interface

IPPROTO_IPV6 if F == AF_INET6, otherwise IPPROTO_IP

IPV6_MULTICAST_IF if F == AF_INET6, otherwise IP_MULTICAST_IF

unsigned int if F == AF_INET6, otherwise in_addr

Specifies the network interface to use for outgoing multicast datagrams.

ip::multicast::hops

IPPROTO_IPV6 if F == AF_INET6, otherwise IPPROTO_IP

IPV6_MULTICAST_HOPS if F == AF_INET6, otherwise IP_MULTICAST_TTL

int

Satisfies the IntegerSocketOption type requirements.

Specifies the default number of hops (also known as time-to-live or TTL) on outbound datagrams.

The constructor and assignment operator for the ip::multicast::hops class throw out_of_range if the int argument is not in the range [0, 255].

ip::multicast::enable_loopback

IPPROTO_IPV6 if F == AF_INET6, otherwise IPPROTO_IP

IPV6_MULTICAST_LOOP if F == AF_INET6, otherwise IP_MULTICAST_LOOP

int

Satisfies the BooleanSocketOption type requirements.

Determines whether multicast datagrams are delivered back to the local application.


10.21.21.1. Class ip::multicast::outbound_interface

[internet.multicast.outbound]

The outbound_interface class represents a socket option that specifies the network interface to use for outgoing multicast datagrams.

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {
namespace multicast {

  class outbound_interface
  {
  public:
    // constructors:
    explicit outbound_interface(const address_v4& network_interface) noexcept;
    explicit outbound_interface(unsigned int network_interface) noexcept;
  };

} // namespace multicast
} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std

outbound_interface satisfies the requirements for Destructible (C++Std [destructible]), CopyConstructible (C++Std [copyconstructible]), CopyAssignable (C++Std [copyassignable]), and SettableSocketOption.

Extensible implementations provide the following member functions:

namespace std {
namespace experimental {
namespace net {
inline namespace v1 {
namespace ip {
namespace multicast {

  class outbound_interface
  {
  public:
    template<class Protocol> int level(const Protocol& p) const noexcept;
    template<class Protocol> int name(const Protocol& p) const noexcept;
    template<class Protocol> const void* data(const Protocol& p) const noexcept;
    template<class Protocol> size_t size(const Protocol& p) const noexcept;
    // remainder unchanged
  private:
      in_addr v4_value_; // exposition only
      unsigned int v6_value_; // exposition only
  };

} // namespace multicast
} // namespace ip
} // inline namespace v1
} // namespace net
} // namespace experimental
} // namespace std
explicit outbound_interface(const address_v4& network_interface) noexcept;

Effects: For extensible implementations, v4_value_ is initialized to correspond to the IPv4 address network_interface, and v6_value_ is zero-initialized.

explicit outbound_interface(unsigned int network_interface) noexcept;

Effects: For extensible implementations, v6_value_ is initialized to network_interface, and v4_value_ is zero-initialized.

template<class Protocol> int level(const Protocol& p) const noexcept;

Returns: IPPROTO_IPV6 if p.family() == AF_INET6, otherwise IPPROTO_IP.

template<class Protocol> int name(const Protocol& p) const noexcept;

Returns: IPV6_MULTICAST_HOPS if p.family() == AF_INET6, otherwise IP_MULTICAST_HOPS.

template<class Protocol> const void* data(const Protocol& p) const noexcept;

Returns: std::addressof(v6_value_) if p.family() == AF_INET6, otherwise std::addressof(v4_value_).

template<class Protocol> size_t size(const Protocol& p) const noexcept;

Returns: sizeof(v6_value_) if p.family() == AF_INET6, otherwise sizeof(v4_value_).

10.22. Index

Cross references

A

async, Asynchronous model
async.assoc.alloc, Class template associated_allocator
async.assoc.alloc.get, Function get_associated_allocator
async.assoc.alloc.members, associated_allocator members
async.assoc.exec, Class template associated_executor
async.assoc.exec.get, Function get_associated_executor
async.assoc.exec.members, associated_executor members
async.async.completion, Class template async_completion
async.async.result, Class template async_result
async.bad.exec, Class bad_executor
async.bind.executor, Function bind_executor
async.defer, Function defer
async.dispatch, Function dispatch
async.exec.binder, Class template executor_binder
async.exec.binder.access, executor_binder access
async.exec.binder.assoc.alloc, Class template partial specialization associated_allocator
async.exec.binder.assoc.exec, Class template partial specialization associated_executor
async.exec.binder.async.result, Class template partial specialization async_result
async.exec.binder.cons, executor_binder constructors
async.exec.binder.invocation, executor_binder invocation
async.exec.ctx, Class execution_context
async.exec.ctx.cons, execution_context constructor
async.exec.ctx.dtor, execution_context destructor
async.exec.ctx.globals, execution_context globals
async.exec.ctx.ops, execution_context operations
async.exec.ctx.protected, execution_context protected operations
async.exec.ctx.svc, Class execution_context::service
async.exec.work.guard, Class template executor_work_guard
async.exec.work.guard.members, executor_work_guard members
async.executor, Class executor
async.executor.algo, executor specialized algorithms
async.executor.arg, Executor argument tag
async.executor.assign, executor assignment
async.executor.capacity, executor capacity
async.executor.comparisons, executor comparisons
async.executor.cons, executor constructors
async.executor.dtor, executor destructor
async.executor.modifiers, executor modifiers
async.executor.ops, executor operations
async.executor.target, executor target access
async.is.exec, Class template is_executor
async.make.work.guard, Function make_work_guard
async.packaged.task.specializations, Partial class template specialization async_result for packaged_task
async.post, Function post
async.reqmts, Requirements
async.reqmts.associator, Associator requirements
async.reqmts.async, Requirements on asynchronous operations
async.reqmts.async.alloc, Allocation of intermediate storage
async.reqmts.async.assoc.exec, Associated executor
async.reqmts.async.completion, Execution of completion handler on completion of asynchronous operation
async.reqmts.async.concepts, General asynchronous operation concepts
async.reqmts.async.exceptions, Completion handlers and exceptions
async.reqmts.async.handler.exec, Completion handler executor
async.reqmts.async.io.exec, I/O executor
async.reqmts.async.lifetime, Lifetime of initiating function arguments
async.reqmts.async.non.blocking, Non-blocking requirements on initiating functions
async.reqmts.async.return.type, Automatic deduction of initiating function return type
async.reqmts.async.return.value, Production of initiating function return value
async.reqmts.async.token, Completion tokens and handlers
async.reqmts.async.work, Outstanding work
async.reqmts.executioncontext, Execution context requirements
async.reqmts.executor, Executor requirements
async.reqmts.proto.allocator, Proto-allocator requirements
async.reqmts.service, Service requirements
async.reqmts.signature, Signature requirements
async.strand, Class template strand
async.strand.assign, strand assignment
async.strand.comparisons, strand comparisons
async.strand.cons, strand constructors
async.strand.dtor, strand destructor
async.strand.ops, strand operations
async.synop, Header <experimental/executor> synopsis
async.system.context, Class system_context
async.system.exec, Class system_executor
async.system.exec.comparisons, system_executor comparisons
async.system.exec.ops, system_executor operations
async.use.future, Class template use_future_t
async.use.future.cons, use_future_t constructors
async.use.future.members, use_future_t members
async.use.future.result, Partial class template specialization async_result for use_future_t
async.uses.executor, uses_executor
async.uses.executor.cons, uses-executor construction
async.uses.executor.trait, uses_executor trait

B

buffer, Buffers
buffer.arithmetic, Buffer arithmetic
buffer.async.read, Asynchronous read operations
buffer.async.read.until, Asynchronous delimited read operations
buffer.async.write, Asynchronous write operations
buffer.const, Class const_buffer
buffer.copy, Function buffer_copy
buffer.creation, Buffer creation functions
buffer.dynamic.creation, Dynamic buffer creation functions
buffer.dynamic.string, Class template dynamic_string_buffer
buffer.dynamic.vector, Class template dynamic_vector_buffer
buffer.err, Error codes
buffer.mutable, Class mutable_buffer
buffer.read, Synchronous read operations
buffer.read.until, Synchronous delimited read operations
buffer.reqmts, Requirements
buffer.reqmts.constbuffersequence, Constant buffer sequence requirements
buffer.reqmts.dynamicbuffer, Dynamic buffer requirements
buffer.reqmts.mutablebuffersequence, Mutable buffer sequence requirements
buffer.reqmts.read.write, Requirements on read and write operations
buffer.seq.access, Buffer sequence access
buffer.size, Function buffer_size
buffer.stream, Buffer-oriented streams
buffer.stream.reqmts, Requirements
buffer.stream.reqmts.asyncreadstream, Buffer-oriented asynchronous read stream requirements
buffer.stream.reqmts.asyncwritestream, Buffer-oriented asynchronous write stream requirements
buffer.stream.reqmts.completioncondition, Completion condition requirements
buffer.stream.reqmts.syncreadstream, Buffer-oriented synchronous read stream requirements
buffer.stream.reqmts.syncwritestream, Buffer-oriented synchronous write stream requirements
buffer.stream.transfer.all, Class transfer_all
buffer.stream.transfer.at.least, Class transfer_at_least
buffer.stream.transfer.exactly, Class transfer_exactly
buffer.synop, Header <experimental/buffer> synopsis
buffer.traits, Buffer type traits
buffer.write, Synchronous write operations

C

conformance, Conformance
conformance.9945, POSIX conformance
conformance.conditional, Conditionally-supported features
convenience.hdr, Convenience header
convenience.hdr.synop, Header <experimental/net> synopsis
conventions, Other conventions

D

defs, Definitions
defs.async.op, asynchronous operation
defs.host.byte.order, host byte order
defs.net.byte.order, network byte order
defs.orderly.shutdown, orderly shutdown
defs.sync.op, synchronous operation
description, Method of description (Informative)

E

err.report, Error reporting
err.report.async, Asynchronous operations
err.report.conditions, Error conditions
err.report.signal, Suppression of signals
err.report.sync, Synchronous operations

I

internet, Internet protocol
internet.address, Class ip::address
internet.address.assign, ip::address assignment
internet.address.comparisons, ip::address comparisons
internet.address.cons, ip::address constructors
internet.address.creation, ip::address creation
internet.address.io, ip::address I/O
internet.address.iter, Class template ip::basic_address_iterator specializations
internet.address.members, ip::address members
internet.address.range, Class template ip::basic_address_range specializations
internet.address.v4, Class ip::address_v4
internet.address.v4.bytes, Struct ip::address_v4::bytes_type
internet.address.v4.comparisons, ip::address_v4 comparisons
internet.address.v4.cons, ip::address_v4 constructors
internet.address.v4.creation, ip::address_v4 creation
internet.address.v4.io, ip::address_v4 I/O
internet.address.v4.members, ip::address_v4 members
internet.address.v4.static, ip::address_v4 static members
internet.address.v6, Class ip::address_v6
internet.address.v6.bytes, Struct ip::address_v6::bytes_type
internet.address.v6.comparisons, ip::address_v6 comparisons
internet.address.v6.cons, ip::address_v6 constructors
internet.address.v6.creation, ip::address_v6 creation
internet.address.v6.io, ip::address_v6 I/O
internet.address.v6.members, ip::address_v6 members
internet.address.v6.static, ip::address_v6 static members
internet.bad.address.cast, Class ip::bad_address_cast
internet.endpoint, Class template ip::basic_endpoint
internet.endpoint.comparisons, ip::basic_endpoint comparisons
internet.endpoint.cons, ip::basic_endpoint constructors
internet.endpoint.extensible, ip::basic_endpoint members (extensible implementations)
internet.endpoint.io, ip::basic_endpoint I/O
internet.endpoint.members, ip::basic_endpoint members
internet.hash, Hash support
internet.host.name, Host name functions
internet.multicast.outbound, Class ip::multicast::outbound_interface
internet.network.v4, Class template ip::network_v4
internet.network.v4.comparisons, ip::network_v4 comparisons
internet.network.v4.cons, ip::network_v4 constructors
internet.network.v4.creation, ip::network_v4 creation
internet.network.v4.io, ip::network_v4 I/O
internet.network.v4.members, ip::network_v4 members
internet.network.v6, Class template ip::network_v6
internet.network.v6.comparisons, ip::network_v6 comparisons
internet.network.v6.cons, ip::network_v6 constructors
internet.network.v6.creation, ip::network_v6 creation
internet.network.v6.io, ip::network_v6 I/O
internet.network.v6.members, ip::network_v6 members
internet.reqmts, Requirements
internet.reqmts.opt.mcast, Multicast group socket options
internet.reqmts.protocol, Internet protocol requirements
internet.resolver, Class template ip::basic_resolver
internet.resolver.assign, ip::basic_resolver assignment
internet.resolver.base, Class ip::resolver_base
internet.resolver.cons, ip::basic_resolver constructors
internet.resolver.dtor, ip::basic_resolver destructor
internet.resolver.entry, Class template ip::basic_resolver_entry
internet.resolver.entry.comparisons, op::basic_resolver_entry comparisons
internet.resolver.entry.cons, ip::basic_resolver_entry constructors
internet.resolver.entry.members, ip::basic_resolver_entry members
internet.resolver.err, Error codes
internet.resolver.ops, ip::basic_resolver operations
internet.resolver.results, Class template ip::basic_resolver_results
internet.resolver.results.access, ip::basic_resolver_results element access
internet.resolver.results.assign, ip::basic_resolver_results assignment
internet.resolver.results.comparisons, ip::basic_resolver_results comparisons
internet.resolver.results.cons, ip::basic_resolver_results constructors
internet.resolver.results.size, ip::basic_resolver_results size
internet.resolver.results.swap, ip::basic_resolver_results swap
internet.socket.opt, Internet socket options
internet.synop, Header <experimental/internet> synopsis
internet.tcp, Class ip::tcp
internet.tcp.comparisons, ip::tcp comparisons
internet.udp, Class ip::udp
internet.udp.comparisons, ip::udp comparisons
io_context, Basic I/O services
io_context.exec, Class io_context::executor_type
io_context.exec.assign, io_context::executor_type assignment
io_context.exec.comparisons, io_context::executor_type comparisons
io_context.exec.cons, io_context::executor_type constructors
io_context.exec.ops, io_context::executor_type operations
io_context.io_context, Class io_context
io_context.io_context.members, io_context members
io_context.synop, Header <experimental/io_context> synopsis

N

namespaces, Namespaces and headers
nested.class, Nested classes

S

scope, Scope
socket, Sockets
socket.acceptor, Class template basic_socket_acceptor
socket.acceptor.assign, basic_socket_acceptor assignment
socket.acceptor.cons, basic_socket_acceptor constructors
socket.acceptor.dtor, basic_socket_acceptor destructor
socket.acceptor.ops, basic_socket_acceptor operations
socket.algo, Socket algorithms
socket.algo.async.connect, Asynchronous connect operations
socket.algo.connect, Synchronous connect operations
socket.base, Class socket_base
socket.basic, Class template basic_socket
socket.basic.assign, basic_socket assignment
socket.basic.cons, basic_socket constructors
socket.basic.dtor, basic_socket destructor
socket.basic.ops, basic_socket operations
socket.dgram, Class template basic_datagram_socket
socket.dgram.assign, basic_datagram_socket assignment
socket.dgram.cons, basic_datagram_socket constructors
socket.dgram.op, basic_datagram_socket operations
socket.err, Error codes
socket.iostream, Class template basic_socket_iostream
socket.iostream.cons, basic_socket_iostream constructors
socket.iostream.members, basic_socket_iostream members
socket.iostreams, Socket iostreams
socket.opt, Socket options
socket.opt.linger, Class socket_base::linger
socket.reqmts, Requirements
socket.reqmts.acceptableprotocol, Acceptable protocol requirements
socket.reqmts.async, Requirements on asynchronous socket operations
socket.reqmts.connectcondition, Connect condition requirements
socket.reqmts.endpoint, Endpoint requirements
socket.reqmts.endpointsequence, Endpoint sequence requirements
socket.reqmts.gettablesocketoption, Gettable socket option requirements
socket.reqmts.iocontrolcommand, I/O control command requirements
socket.reqmts.native, Native handles
socket.reqmts.opt.bool, Boolean socket options
socket.reqmts.opt.int, Integer socket options
socket.reqmts.protocol, Protocol requirements
socket.reqmts.settablesocketoption, Settable socket option requirements
socket.reqmts.sync, Requirements on synchronous socket operations
socket.stream, Class template basic_stream_socket
socket.stream.assign, basic_stream_socket assignment
socket.stream.cons, basic_stream_socket constructors
socket.stream.ops, basic_stream_socket operations
socket.streambuf, Class template basic_socket_streambuf
socket.streambuf.cons, basic_socket_streambuf constructors
socket.streambuf.members, basic_socket_streambuf members
socket.streambuf.virtual, basic_socket_streambuf overridden virtual functions
socket.synop, Header <experimental/socket> synopsis
structure, Structure of each clause
structure.specifications, Detailed specifications
summary, Library summary

T

timer, Timers
timer.reqmts, Requirements
timer.reqmts.waittraits, Wait traits requirements
timer.synop, Header <experimental/timer> synopsis
timer.waitable, Class template basic_waitable_timer
timer.waitable.assign, basic_waitable_timer assignment
timer.waitable.cons, basic_waitable_timer constructors
timer.waitable.dtor, basic_waitable_timer destructor
timer.waitable.ops, basic_waitable_timer operations

11. Acknowledgements

In the eleven years since Asio's inception, hundreds of people have contributed to its development through design review, patches, feature suggestions, bug reports, and usage feedback from the field. With respect to the 2014 refresh of the Networking Library Proposal, the author would particularly like to thank Jamie Allsop for providing feedback during the drafting process, and Oliver Kowalke for contributing towards the design and implementation of the CIDR support.

The author would also like to thank Marshall Clow, Jens Maurer, Arash Partow, Jamie Allsop, Dietmar Kühl, Detlef Vollmann, Jonathan Wakely, Mikael Kilpeläinen, Jens Weller, Michael Wong, Eric Fisselier, and Jeffrey Yasskin for participating in the Cologne LWG wording review of the Networking Library TS proposal, which contributed significantly to the changes in this revision.

12. References

[POSIX] ISO/IEC 9945:2003, IEEE Std 1003.1-2001, and The Open Group Base Specifications, Issue 6. Also known as The Single Unix Specification, Version 3.

[N4045] Kohlhoff, Christopher, Library Foundations for Asynchronous Operations, Revision 2, 2014.

[P0113] Kohlhoff, Christopher, Executors and Asynchronous Operations, Revision 2, 2015.

[N4099] Draft Filesystem Technical Specification, 2014.

[ACE] Schmidt, Douglas C., ADAPTIVE Communication Environment, http://www.cs.wustl.edu/~schmidt/ACE.html.

[SYMBIAN] Symbian Ltd, Sockets Client, http://www.symbian.com/developer/techlib/v70sdocs/doc_source/reference/cpp/SocketsClient/index.html.

[MS-NET] Microsoft Corporation, .NET Framework Class Library, Socket Class, http://msdn2.microsoft.com/en-us/library/system.net.sockets.socket.aspx.

[ES-API] The Interconnect Software Consortium / The Open Group, Extended Sockets API (ES-API), Issue 1.0, 2005, http://opengroup.org/icsc/uploads/40/6415/ES_API_1_0.pdf.

[UNPV1] Stevens, W. Richard, UNIX Network Programming, Volume 1, 2nd Edition, Prentice Hall, 1998.

[POSA2] Schmidt, Douglas C. et al, Pattern Oriented Software Architecture, Volume 2, Wiley, 2000.

[RFC821] Postel, J., RFC 821: Simple Mail Transfer Protocol, 1982, http://www.ietf.org/rfc/rfc0821.txt.

[RFC959] Postel, J. and Reynolds, J., RFC 959: File Transfer Protocol (FTP), 1985, http://www.ietf.org/rfc/rfc0959.txt.

[RFC2616] Fielding, R. et al, RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1, 1999, http://www.ietf.org/rfc/rfc2616.txt.

[RFC2732] Hinden, R., Carpenter, B. and Masinter, L., RFC 2732: Format for Literal IPv6 Addresses in URL's, 1999, http://www.ietf.org/rfc/rfc2732.txt.

[RFC3513] Hinden, R. and Deering, S., RFC 3513: Internet Protocol Version 6 (IPv6) Addressing Architecture, 2003, http://www.ietf.org/rfc/rfc3513.txt.



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