[/
 / Copyright (c) 2003-2022 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:protocols TCP, UDP and ICMP]

Asio provides off-the-shelf support for the internet protocols TCP, UDP and
ICMP.

[heading TCP Clients]

Hostname resolution is performed using a resolver, where host and service names
are looked up and converted into one or more endpoints:

  ip::tcp::resolver resolver(my_io_context);
  ip::tcp::resolver::query query("www.boost.org", "http");
  ip::tcp::resolver::iterator iter = resolver.resolve(query);
  ip::tcp::resolver::iterator end; // End marker.
  while (iter != end)
  {
    ip::tcp::endpoint endpoint = *iter++;
    std::cout << endpoint << std::endl;
  }

The list of endpoints obtained above could contain both IPv4 and IPv6 endpoints,
so a program should try each of them until it finds one that works. This keeps the
client program independent of a specific IP version.

To simplify the development of protocol-independent programs, TCP clients may
establish connections using the free functions [link asio.reference.connect
connect()] and [link asio.reference.async_connect async_connect()]. These
operations try each endpoint in a list until the socket is successfully
connected. For example, a single call:

  ip::tcp::socket socket(my_io_context);
  asio::connect(socket, resolver.resolve(query));

will synchronously try all endpoints until one is successfully connected.
Similarly, an asynchronous connect may be performed by writing:

  asio::async_connect(socket_, iter,
      boost::bind(&client::handle_connect, this,
        asio::placeholders::error));

  // ...

  void handle_connect(const error_code& error)
  {
    if (!error)
    {
      // Start read or write operations.
    }
    else
    {
      // Handle error.
    }
  }

When a specific endpoint is available, a socket can be created and connected:

  ip::tcp::socket socket(my_io_context);
  socket.connect(endpoint);

Data may be read from or written to a connected TCP socket using the [link
asio.reference.basic_stream_socket.receive receive()], [link
asio.reference.basic_stream_socket.async_receive async_receive()], [link
asio.reference.basic_stream_socket.send send()] or [link
asio.reference.basic_stream_socket.async_send async_send()] member functions.
However, as these could result in [link asio.overview.core.streams short writes
or reads], an application will typically use the following operations instead:
[link asio.reference.read read()], [link asio.reference.async_read
async_read()], [link asio.reference.write write()] and [link
asio.reference.async_write async_write()].

[heading TCP Servers]

A program uses an acceptor to accept incoming TCP connections:

  ip::tcp::acceptor acceptor(my_io_context, my_endpoint);
  ...
  ip::tcp::socket socket(my_io_context);
  acceptor.accept(socket);

After a socket has been successfully accepted, it may be read from or written
to as illustrated for TCP clients above.

[heading UDP]

UDP hostname resolution is also performed using a resolver:

  ip::udp::resolver resolver(my_io_context);
  ip::udp::resolver::query query("localhost", "daytime");
  ip::udp::resolver::iterator iter = resolver.resolve(query);
  ...

A UDP socket is typically bound to a local endpoint. The following code will
create an IP version 4 UDP socket and bind it to the "any" address on port
`12345`:

  ip::udp::endpoint endpoint(ip::udp::v4(), 12345);
  ip::udp::socket socket(my_io_context, endpoint);

Data may be read from or written to an unconnected UDP socket using the [link
asio.reference.basic_datagram_socket.receive_from receive_from()], [link
asio.reference.basic_datagram_socket.async_receive_from async_receive_from()],
[link asio.reference.basic_datagram_socket.send_to send_to()] or [link
asio.reference.basic_datagram_socket.async_send_to async_send_to()] member
functions. For a connected UDP socket, use the [link
asio.reference.basic_datagram_socket.receive receive()], [link
asio.reference.basic_datagram_socket.async_receive async_receive()], [link
asio.reference.basic_datagram_socket.send send()] or [link
asio.reference.basic_datagram_socket.async_send async_send()] member functions.

[heading ICMP]

As with TCP and UDP, ICMP hostname resolution is performed using a resolver:

  ip::icmp::resolver resolver(my_io_context);
  ip::icmp::resolver::query query("localhost", "");
  ip::icmp::resolver::iterator iter = resolver.resolve(query);
  ...

An ICMP socket may be bound to a local endpoint. The following code will create
an IP version 6 ICMP socket and bind it to the "any" address:

  ip::icmp::endpoint endpoint(ip::icmp::v6(), 0);
  ip::icmp::socket socket(my_io_context, endpoint);

The port number is not used for ICMP.

Data may be read from or written to an unconnected ICMP socket using the [link
asio.reference.basic_raw_socket.receive_from receive_from()], [link
asio.reference.basic_raw_socket.async_receive_from async_receive_from()],
[link asio.reference.basic_raw_socket.send_to send_to()] or [link
asio.reference.basic_raw_socket.async_send_to async_send_to()] member
functions.

[heading See Also]

[link asio.reference.ip__tcp ip::tcp],
[link asio.reference.ip__udp ip::udp],
[link asio.reference.ip__icmp ip::icmp],
[link asio.tutorial.tutdaytime1 daytime protocol tutorials],
[link asio.examples.cpp03_examples.icmp ICMP ping example].

[endsect]
