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<title>TCP, UDP and ICMP</title>
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table>
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<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="asio.overview.networking.protocols"></a><a class="link" href="protocols.html" title="TCP, UDP and ICMP">TCP, UDP and ICMP</a>
</h4></div></div></div>
<p>
Asio provides off-the-shelf support for the internet protocols TCP, UDP
and ICMP.
</p>
<h6>
<a name="asio.overview.networking.protocols.h0"></a>
<span><a name="asio.overview.networking.protocols.tcp_clients"></a></span><a class="link" href="protocols.html#asio.overview.networking.protocols.tcp_clients">TCP
Clients</a>
</h6>
<p>
Hostname resolution is performed using a resolver, where host and service
names are looked up and converted into one or more endpoints:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">resolver</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">query</span><span class="special">(</span><span class="string">"www.boost.org"</span><span class="special">,</span> <span class="string">"http"</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">resolver</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">query</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">end</span><span class="special">;</span> <span class="comment">// End marker.</span>
<span class="keyword">while</span> <span class="special">(</span><span class="identifier">iter</span> <span class="special">!=</span> <span class="identifier">end</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="identifier">endpoint</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">iter</span><span class="special">++;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">endpoint</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
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.
</p>
<p>
To simplify the development of protocol-independent programs, TCP clients
may establish connections using the free functions <a class="link" href="../../reference/connect.html" title="connect">connect()</a>
and <a class="link" href="../../reference/async_connect.html" title="async_connect">async_connect()</a>.
These operations try each endpoint in a list until the socket is successfully
connected. For example, a single call:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span> <span class="identifier">resolver</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">query</span><span class="special">));</span>
</pre>
<p>
will synchronously try all endpoints until one is successfully connected.
Similarly, an asynchronous connect may be performed by writing:
</p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_connect</span><span class="special">(</span><span class="identifier">socket_</span><span class="special">,</span> <span class="identifier">iter</span><span class="special">,</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&amp;</span><span class="identifier">client</span><span class="special">::</span><span class="identifier">handle_connect</span><span class="special">,</span> <span class="keyword">this</span><span class="special">,</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">placeholders</span><span class="special">::</span><span class="identifier">error</span><span class="special">));</span>
<span class="comment">// ...</span>
<span class="keyword">void</span> <span class="identifier">handle_connect</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">error</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(!</span><span class="identifier">error</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// Start read or write operations.</span>
<span class="special">}</span>
<span class="keyword">else</span>
<span class="special">{</span>
<span class="comment">// Handle error.</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<p>
When a specific endpoint is available, a socket can be created and connected:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">socket</span><span class="special">.</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">endpoint</span><span class="special">);</span>
</pre>
<p>
Data may be read from or written to a connected TCP socket using the <a class="link" href="../../reference/basic_stream_socket/receive.html" title="basic_stream_socket::receive">receive()</a>,
<a class="link" href="../../reference/basic_stream_socket/async_receive.html" title="basic_stream_socket::async_receive">async_receive()</a>,
<a class="link" href="../../reference/basic_stream_socket/send.html" title="basic_stream_socket::send">send()</a> or
<a class="link" href="../../reference/basic_stream_socket/async_send.html" title="basic_stream_socket::async_send">async_send()</a>
member functions. However, as these could result in <a class="link" href="../core/streams.html" title="Streams, Short Reads and Short Writes">short
writes or reads</a>, an application will typically use the following
operations instead: <a class="link" href="../../reference/read.html" title="read">read()</a>,
<a class="link" href="../../reference/async_read.html" title="async_read">async_read()</a>, <a class="link" href="../../reference/write.html" title="write">write()</a>
and <a class="link" href="../../reference/async_write.html" title="async_write">async_write()</a>.
</p>
<h6>
<a name="asio.overview.networking.protocols.h1"></a>
<span><a name="asio.overview.networking.protocols.tcp_servers"></a></span><a class="link" href="protocols.html#asio.overview.networking.protocols.tcp_servers">TCP
Servers</a>
</h6>
<p>
A program uses an acceptor to accept incoming TCP connections:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span> <span class="identifier">acceptor</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">,</span> <span class="identifier">my_endpoint</span><span class="special">);</span>
<span class="special">...</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">acceptor</span><span class="special">.</span><span class="identifier">accept</span><span class="special">(</span><span class="identifier">socket</span><span class="special">);</span>
</pre>
<p>
After a socket has been successfully accepted, it may be read from or written
to as illustrated for TCP clients above.
</p>
<h6>
<a name="asio.overview.networking.protocols.h2"></a>
<span><a name="asio.overview.networking.protocols.udp"></a></span><a class="link" href="protocols.html#asio.overview.networking.protocols.udp">UDP</a>
</h6>
<p>
UDP hostname resolution is also performed using a resolver:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">resolver</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">query</span><span class="special">(</span><span class="string">"localhost"</span><span class="special">,</span> <span class="string">"daytime"</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">resolver</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">query</span><span class="special">);</span>
<span class="special">...</span>
</pre>
<p>
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 <code class="computeroutput"><span class="number">12345</span></code>:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="identifier">endpoint</span><span class="special">(</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">v4</span><span class="special">(),</span> <span class="number">12345</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">,</span> <span class="identifier">endpoint</span><span class="special">);</span>
</pre>
<p>
Data may be read from or written to an unconnected UDP socket using the
<a class="link" href="../../reference/basic_datagram_socket/receive_from.html" title="basic_datagram_socket::receive_from">receive_from()</a>,
<a class="link" href="../../reference/basic_datagram_socket/async_receive_from.html" title="basic_datagram_socket::async_receive_from">async_receive_from()</a>,
<a class="link" href="../../reference/basic_datagram_socket/send_to.html" title="basic_datagram_socket::send_to">send_to()</a>
or <a class="link" href="../../reference/basic_datagram_socket/async_send_to.html" title="basic_datagram_socket::async_send_to">async_send_to()</a>
member functions. For a connected UDP socket, use the <a class="link" href="../../reference/basic_datagram_socket/receive.html" title="basic_datagram_socket::receive">receive()</a>,
<a class="link" href="../../reference/basic_datagram_socket/async_receive.html" title="basic_datagram_socket::async_receive">async_receive()</a>,
<a class="link" href="../../reference/basic_datagram_socket/send.html" title="basic_datagram_socket::send">send()</a>
or <a class="link" href="../../reference/basic_datagram_socket/async_send.html" title="basic_datagram_socket::async_send">async_send()</a>
member functions.
</p>
<h6>
<a name="asio.overview.networking.protocols.h3"></a>
<span><a name="asio.overview.networking.protocols.icmp"></a></span><a class="link" href="protocols.html#asio.overview.networking.protocols.icmp">ICMP</a>
</h6>
<p>
As with TCP and UDP, ICMP hostname resolution is performed using a resolver:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">resolver</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">query</span><span class="special">(</span><span class="string">"localhost"</span><span class="special">,</span> <span class="string">""</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">resolver</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">query</span><span class="special">);</span>
<span class="special">...</span>
</pre>
<p>
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:
</p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="identifier">endpoint</span><span class="special">(</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span><span class="special">::</span><span class="identifier">v6</span><span class="special">(),</span> <span class="number">0</span><span class="special">);</span>
<span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">,</span> <span class="identifier">endpoint</span><span class="special">);</span>
</pre>
<p>
The port number is not used for ICMP.
</p>
<p>
Data may be read from or written to an unconnected ICMP socket using the
<a class="link" href="../../reference/basic_raw_socket/receive_from.html" title="basic_raw_socket::receive_from">receive_from()</a>,
<a class="link" href="../../reference/basic_raw_socket/async_receive_from.html" title="basic_raw_socket::async_receive_from">async_receive_from()</a>,
<a class="link" href="../../reference/basic_raw_socket/send_to.html" title="basic_raw_socket::send_to">send_to()</a>
or <a class="link" href="../../reference/basic_raw_socket/async_send_to.html" title="basic_raw_socket::async_send_to">async_send_to()</a>
member functions.
</p>
<h6>
<a name="asio.overview.networking.protocols.h4"></a>
<span><a name="asio.overview.networking.protocols.see_also"></a></span><a class="link" href="protocols.html#asio.overview.networking.protocols.see_also">See
Also</a>
</h6>
<p>
<a class="link" href="../../reference/ip__tcp.html" title="ip::tcp">ip::tcp</a>, <a class="link" href="../../reference/ip__udp.html" title="ip::udp">ip::udp</a>,
<a class="link" href="../../reference/ip__icmp.html" title="ip::icmp">ip::icmp</a>, <a class="link" href="../../tutorial/tutdaytime1.html" title="Daytime.1 - A synchronous TCP daytime client">daytime
protocol tutorials</a>, <a class="link" href="../../examples/cpp03_examples.html#asio.examples.cpp03_examples.icmp">ICMP
ping example</a>.
</p>
</div>
<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
</div>
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