[/
 / Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 /
 / Distributed under the Boost Software License, Version 1.0. (See accompanying
 / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 /]

[section:bsd_sockets The BSD Socket API and Asio]

The Asio library includes a low-level socket interface based on the BSD socket
API, which is widely implemented and supported by extensive literature. It is
also used as the basis for networking APIs in other languages, like Java. This
low-level interface is designed to support the development of efficient and
scalable applications. For example, it permits programmers to exert finer
control over the number of system calls, avoid redundant data copying, minimise
the use of resources like threads, and so on.

Unsafe and error prone aspects of the BSD socket API are not included. For
example, the use of `int` to represent all sockets lacks type safety. The
socket representation in Asio uses a distinct type for each protocol, e.g. for
TCP one would use `ip::tcp::socket`, and for UDP one uses `ip::udp::socket`.

The following table shows the mapping between the BSD socket API and Asio:

[table
  [
    [BSD Socket API Elements]
    [Equivalents in Asio]
  ]
  [
    [socket descriptor - `int` (POSIX) or `SOCKET` (Windows)]
    [ For TCP: [link asio.reference.ip__tcp.socket ip::tcp::socket],
               [link asio.reference.ip__tcp.acceptor ip::tcp::acceptor]

      For UDP: [link asio.reference.ip__udp.socket ip::udp::socket]

               [link asio.reference.basic_socket basic_socket],
               [link asio.reference.basic_stream_socket basic_stream_socket],
               [link asio.reference.basic_datagram_socket basic_datagram_socket],
               [link asio.reference.basic_raw_socket basic_raw_socket] ]
  ]
  [
    [`in_addr`,
     `in6_addr`]
    [          [link asio.reference.ip__address ip::address],
               [link asio.reference.ip__address ip::address_v4],
               [link asio.reference.ip__address ip::address_v6] ]
  ]
  [
    [`sockaddr_in`,
     `sockaddr_in6`]
    [ For TCP: [link asio.reference.ip__tcp.endpoint ip::tcp::endpoint]
    
      For UDP: [link asio.reference.ip__udp.endpoint ip::udp::endpoint]

               [link asio.reference.ip__basic_endpoint ip::basic_endpoint] ]
  ]
  [
    [`accept()`]
    [ For TCP: [link asio.reference.basic_socket_acceptor.accept ip::tcp::acceptor::accept()]

               [link asio.reference.basic_socket_acceptor.accept basic_socket_acceptor::accept()] ]
  ]
  [
    [`bind()`]
    [ For TCP: [link asio.reference.basic_socket.bind ip::tcp::acceptor::bind()],
               [link asio.reference.basic_socket.bind ip::tcp::socket::bind()]

      For UDP: [link asio.reference.basic_socket.bind ip::udp::socket::bind()]

               [link asio.reference.basic_socket.bind basic_socket::bind()] ]
  ]
  [
    [`close()`]
    [ For TCP: [link asio.reference.basic_socket.close ip::tcp::acceptor::close()],
               [link asio.reference.basic_socket.close ip::tcp::socket::close()]

      For UDP: [link asio.reference.basic_socket.close ip::udp::socket::close()]

               [link asio.reference.basic_socket.close basic_socket::close()] ]
  ]
  [
    [`connect()`]
    [ For TCP: [link asio.reference.basic_socket.connect ip::tcp::socket::connect()]

      For UDP: [link asio.reference.basic_socket.connect ip::udp::socket::connect()]

               [link asio.reference.basic_socket.connect basic_socket::connect()] ]
  ]
  [
    [`getaddrinfo()`,
     `gethostbyaddr()`,
     `gethostbyname()`,
     `getnameinfo()`,
     `getservbyname()`,
     `getservbyport()`]
    [ For TCP: [link asio.reference.ip__basic_resolver.resolve ip::tcp::resolver::resolve()],
               [link asio.reference.ip__basic_resolver.async_resolve ip::tcp::resolver::async_resolve()]

      For UDP: [link asio.reference.ip__basic_resolver.resolve ip::udp::resolver::resolve()],
               [link asio.reference.ip__basic_resolver.async_resolve ip::udp::resolver::async_resolve()]

               [link asio.reference.ip__basic_resolver.resolve ip::basic_resolver::resolve()],
               [link asio.reference.ip__basic_resolver.async_resolve ip::basic_resolver::async_resolve()] ]
  ]
  [
    [`gethostname()`]
    [          [link asio.reference.ip__host_name ip::host_name()] ]
  ]
  [
    [`getpeername()`]
    [ For TCP: [link asio.reference.basic_socket.remote_endpoint ip::tcp::socket::remote_endpoint()]

      For UDP: [link asio.reference.basic_socket.remote_endpoint ip::udp::socket::remote_endpoint()]

               [link asio.reference.basic_socket.remote_endpoint basic_socket::remote_endpoint()] ]
  ]
  [
    [`getsockname()`]
    [ For TCP: [link asio.reference.basic_socket.local_endpoint ip::tcp::acceptor::local_endpoint()],
               [link asio.reference.basic_socket.local_endpoint ip::tcp::socket::local_endpoint()]

      For UDP: [link asio.reference.basic_socket.local_endpoint ip::udp::socket::local_endpoint()]

               [link asio.reference.basic_socket.local_endpoint basic_socket::local_endpoint()] ]
  ]
  [
    [`getsockopt()`]
    [ For TCP: [link asio.reference.basic_socket.get_option ip::tcp::acceptor::get_option()],
               [link asio.reference.basic_socket.get_option ip::tcp::socket::get_option()]

      For UDP: [link asio.reference.basic_socket.get_option ip::udp::socket::get_option()]

               [link asio.reference.basic_socket.get_option basic_socket::get_option()] ]
  ]
  [
    [`inet_addr()`,
     `inet_aton()`,
     `inet_pton()`]
    [          [link asio.reference.ip__address.make_address ip::make_address()],
               [link asio.reference.ip__address_v4.make_address_v4 ip::make_address_v4()],
               [link asio.reference.ip__address_v6.make_address_v6 ip::make_address_v6()] ]
  ]
  [
    [`inet_ntoa()`,
     `inet_ntop()`]
    [          [link asio.reference.ip__address.to_string ip::address::to_string()],
               [link asio.reference.ip__address_v4.to_string ip::address_v4::to_string()],
               [link asio.reference.ip__address_v6.to_string ip::address_v6::to_string()] ]
  ]
  [
    [`ioctl()`]
    [ For TCP: [link asio.reference.basic_socket.io_control ip::tcp::socket::io_control()]

      For UDP: [link asio.reference.basic_socket.io_control ip::udp::socket::io_control()]

               [link asio.reference.basic_socket.io_control basic_socket::io_control()] ]
  ]
  [
    [`listen()`]
    [ For TCP: [link asio.reference.basic_socket_acceptor.listen ip::tcp::acceptor::listen()]

               [link asio.reference.basic_socket_acceptor.listen basic_socket_acceptor::listen()] ]
  ]
  [
    [`poll()`,
     `select()`,
     `pselect()`]
    [          [link asio.reference.io_context.run io_context::run()],
               [link asio.reference.io_context.run_one io_context::run_one()],
               [link asio.reference.io_context.poll io_context::poll()],
               [link asio.reference.io_context.poll_one io_context::poll_one()]

      Note: in conjunction with asynchronous operations. ]
  ]
  [
    [`readv()`,
     `recv()`,
     `read()`]
    [ For TCP: [link asio.reference.basic_stream_socket.read_some ip::tcp::socket::read_some()],
               [link asio.reference.basic_stream_socket.async_read_some ip::tcp::socket::async_read_some()],
               [link asio.reference.basic_stream_socket.receive ip::tcp::socket::receive()],
               [link asio.reference.basic_stream_socket.async_receive ip::tcp::socket::async_receive()]

      For UDP: [link asio.reference.basic_datagram_socket.receive ip::udp::socket::receive()],
               [link asio.reference.basic_datagram_socket.async_receive ip::udp::socket::async_receive()]

               [link asio.reference.basic_stream_socket.read_some basic_stream_socket::read_some()],
               [link asio.reference.basic_stream_socket.async_read_some basic_stream_socket::async_read_some()],
               [link asio.reference.basic_stream_socket.receive basic_stream_socket::receive()],
               [link asio.reference.basic_stream_socket.async_receive basic_stream_socket::async_receive()],
               [link asio.reference.basic_datagram_socket.receive basic_datagram_socket::receive()],
               [link asio.reference.basic_datagram_socket.async_receive basic_datagram_socket::async_receive()] ]
  ]
  [
    [`recvfrom()`]
    [ For UDP: [link asio.reference.basic_datagram_socket.receive_from ip::udp::socket::receive_from()],
               [link asio.reference.basic_datagram_socket.async_receive_from ip::udp::socket::async_receive_from()]

               [link asio.reference.basic_datagram_socket.receive_from basic_datagram_socket::receive_from()],
               [link asio.reference.basic_datagram_socket.async_receive_from basic_datagram_socket::async_receive_from()] ]
  ]
  [
    [`send()`,
     `write()`,
     `writev()`]
    [ For TCP: [link asio.reference.basic_stream_socket.write_some ip::tcp::socket::write_some()],
               [link asio.reference.basic_stream_socket.async_write_some ip::tcp::socket::async_write_some()],
               [link asio.reference.basic_stream_socket.send ip::tcp::socket::send()],
               [link asio.reference.basic_stream_socket.async_send ip::tcp::socket::async_send()]

      For UDP: [link asio.reference.basic_datagram_socket.send ip::udp::socket::send()],
               [link asio.reference.basic_datagram_socket.async_send ip::udp::socket::async_send()]

               [link asio.reference.basic_stream_socket.write_some basic_stream_socket::write_some()],
               [link asio.reference.basic_stream_socket.async_write_some basic_stream_socket::async_write_some()],
               [link asio.reference.basic_stream_socket.send basic_stream_socket::send()],
               [link asio.reference.basic_stream_socket.async_send basic_stream_socket::async_send()],
               [link asio.reference.basic_datagram_socket.send basic_datagram_socket::send()],
               [link asio.reference.basic_datagram_socket.async_send basic_datagram_socket::async_send()] ]
  ]
  [
    [`sendto()`]
    [ For UDP: [link asio.reference.basic_datagram_socket.send_to ip::udp::socket::send_to()],
               [link asio.reference.basic_datagram_socket.async_send_to ip::udp::socket::async_send_to()]

               [link asio.reference.basic_datagram_socket.send_to basic_datagram_socket::send_to()],
               [link asio.reference.basic_datagram_socket.async_send_to basic_datagram_socket::async_send_to()] ]
  ]
  [
    [`setsockopt()`]
    [ For TCP: [link asio.reference.basic_socket.set_option ip::tcp::acceptor::set_option()],
               [link asio.reference.basic_socket.set_option ip::tcp::socket::set_option()]

      For UDP: [link asio.reference.basic_socket.set_option ip::udp::socket::set_option()]

               [link asio.reference.basic_socket.set_option basic_socket::set_option()] ]
  ]
  [
    [`shutdown()`]
    [ For TCP: [link asio.reference.basic_socket.shutdown ip::tcp::socket::shutdown()]

      For UDP: [link asio.reference.basic_socket.shutdown ip::udp::socket::shutdown()]

               [link asio.reference.basic_socket.shutdown basic_socket::shutdown()] ]
  ]
  [
    [`sockatmark()`]
    [ For TCP: [link asio.reference.basic_socket.at_mark ip::tcp::socket::at_mark()]

               [link asio.reference.basic_socket.at_mark basic_socket::at_mark()] ]
  ]
  [
    [`socket()`]
    [ For TCP: [link asio.reference.basic_socket.open ip::tcp::acceptor::open()],
               [link asio.reference.basic_socket.open ip::tcp::socket::open()]

      For UDP: [link asio.reference.basic_socket.open ip::udp::socket::open()]

               [link asio.reference.basic_socket.open basic_socket::open()] ]
  ]
  [
    [`socketpair()`]
    [          [link asio.reference.local__connect_pair local::connect_pair()]

      Note: POSIX operating systems only. ]
  ]
]

[endsect]
