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<title>Daytime.3 - An asynchronous TCP daytime server</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.tutorial.tutdaytime3"></a><a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3 - An asynchronous
TCP daytime server</a>
</h3></div></div></div>
<h5>
<a name="asio.tutorial.tutdaytime3.h0"></a>
<span><a name="asio.tutorial.tutdaytime3.the_main___function"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.the_main___function">The
main() function</a>
</h5>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">try</span>
<span class="special">{</span>
</pre>
<p>
We need to create a server object to accept incoming client connections.
The <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> object provides
I/O services, such as sockets, that the server object will use.
</p>
<pre class="programlisting"> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span class="identifier">io_context</span><span class="special">;</span>
<span class="identifier">tcp_server</span> <span class="identifier">server</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">);</span>
</pre>
<p>
Run the <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> object
so that it will perform asynchronous operations on your behalf.
</p>
<pre class="programlisting"> <span class="identifier">io_context</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
<span class="special">}</span>
<span class="keyword">catch</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
<span class="special">{</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</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>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<h5>
<a name="asio.tutorial.tutdaytime3.h1"></a>
<span><a name="asio.tutorial.tutdaytime3.the_tcp_server_class"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.the_tcp_server_class">The
tcp_server class</a>
</h5>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">tcp_server</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
</pre>
<p>
The constructor initialises an acceptor to listen on TCP port 13.
</p>
<pre class="programlisting"> <span class="identifier">tcp_server</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">&amp;</span> <span class="identifier">io_context</span><span class="special">)</span>
<span class="special">:</span> <span class="identifier">io_context_</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">),</span>
<span class="identifier">acceptor_</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">v4</span><span class="special">(),</span> <span class="number">13</span><span class="special">))</span>
<span class="special">{</span>
<span class="identifier">start_accept</span><span class="special">();</span>
<span class="special">}</span>
<span class="keyword">private</span><span class="special">:</span>
</pre>
<p>
The function <code class="computeroutput"><span class="identifier">start_accept</span><span class="special">()</span></code> creates a socket and initiates an asynchronous
accept operation to wait for a new connection.
</p>
<pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">start_accept</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">pointer</span> <span class="identifier">new_connection</span> <span class="special">=</span>
<span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">create</span><span class="special">(</span><span class="identifier">io_context_</span><span class="special">);</span>
<span class="identifier">acceptor_</span><span class="special">.</span><span class="identifier">async_accept</span><span class="special">(</span><span class="identifier">new_connection</span><span class="special">-&gt;</span><span class="identifier">socket</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">tcp_server</span><span class="special">::</span><span class="identifier">handle_accept</span><span class="special">,</span> <span class="keyword">this</span><span class="special">,</span> <span class="identifier">new_connection</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="special">}</span>
</pre>
<p>
The function <code class="computeroutput"><span class="identifier">handle_accept</span><span class="special">()</span></code> is called when the asynchronous accept
operation initiated by <code class="computeroutput"><span class="identifier">start_accept</span><span class="special">()</span></code> finishes. It services the client request,
and then calls <code class="computeroutput"><span class="identifier">start_accept</span><span class="special">()</span></code> to initiate the next accept operation.
</p>
<pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">handle_accept</span><span class="special">(</span><span class="identifier">tcp_connection</span><span class="special">::</span><span class="identifier">pointer</span> <span class="identifier">new_connection</span><span class="special">,</span>
<span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</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="identifier">new_connection</span><span class="special">-&gt;</span><span class="identifier">start</span><span class="special">();</span>
<span class="special">}</span>
<span class="identifier">start_accept</span><span class="special">();</span>
<span class="special">}</span>
</pre>
<h5>
<a name="asio.tutorial.tutdaytime3.h2"></a>
<span><a name="asio.tutorial.tutdaytime3.the_tcp_connection_class"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.the_tcp_connection_class">The
tcp_connection class</a>
</h5>
<p>
We will use <code class="computeroutput"><span class="identifier">shared_ptr</span></code> and
<code class="computeroutput"><span class="identifier">enable_shared_from_this</span></code> because
we want to keep the <code class="computeroutput"><span class="identifier">tcp_connection</span></code>
object alive as long as there is an operation that refers to it.
</p>
<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">tcp_connection</span>
<span class="special">:</span> <span class="keyword">public</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_shared_from_this</span><span class="special">&lt;</span><span class="identifier">tcp_connection</span><span class="special">&gt;</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special">&lt;</span><span class="identifier">tcp_connection</span><span class="special">&gt;</span> <span class="identifier">pointer</span><span class="special">;</span>
<span class="keyword">static</span> <span class="identifier">pointer</span> <span class="identifier">create</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">&amp;</span> <span class="identifier">io_context</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">pointer</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">tcp_connection</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">));</span>
<span class="special">}</span>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">socket_</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
In the function <code class="computeroutput"><span class="identifier">start</span><span class="special">()</span></code>,
we call asio::async_write() to serve the data to the client. Note that we
are using asio::async_write(), rather than <a class="link" href="../reference/basic_stream_socket/async_write_some.html" title="basic_stream_socket::async_write_some">ip::tcp::socket::async_write_some()</a>,
to ensure that the entire block of data is sent.
</p>
<pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">start</span><span class="special">()</span>
<span class="special">{</span>
</pre>
<p>
The data to be sent is stored in the class member <code class="computeroutput"><span class="identifier">message_</span></code>
as we need to keep the data valid until the asynchronous operation is complete.
</p>
<pre class="programlisting"> <span class="identifier">message_</span> <span class="special">=</span> <span class="identifier">make_daytime_string</span><span class="special">();</span>
</pre>
<p>
When initiating the asynchronous operation, and if using <a class="link" href="boost_bind.html" title="boost::bind">boost::bind</a>,
you must specify only the arguments that match the handler's parameter list.
In this program, both of the argument placeholders (asio::placeholders::error
and asio::placeholders::bytes_transferred) could potentially have been removed,
since they are not being used in <code class="computeroutput"><span class="identifier">handle_write</span><span class="special">()</span></code>.
</p>
<pre class="programlisting"> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket_</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">message_</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">tcp_connection</span><span class="special">::</span><span class="identifier">handle_write</span><span class="special">,</span> <span class="identifier">shared_from_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="identifier">asio</span><span class="special">::</span><span class="identifier">placeholders</span><span class="special">::</span><span class="identifier">bytes_transferred</span><span class="special">));</span>
</pre>
<p>
Any further actions for this client connection are now the responsibility
of <code class="computeroutput"><span class="identifier">handle_write</span><span class="special">()</span></code>.
</p>
<pre class="programlisting"> <span class="special">}</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="identifier">tcp_connection</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">&amp;</span> <span class="identifier">io_context</span><span class="special">)</span>
<span class="special">:</span> <span class="identifier">socket_</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">)</span>
<span class="special">{</span>
<span class="special">}</span>
<span class="keyword">void</span> <span class="identifier">handle_write</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="comment">/*error*/</span><span class="special">,</span>
<span class="identifier">size_t</span> <span class="comment">/*bytes_transferred*/</span><span class="special">)</span>
<span class="special">{</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">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">message_</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<h5>
<a name="asio.tutorial.tutdaytime3.h3"></a>
<span><a name="asio.tutorial.tutdaytime3.removing_unused_handler_parameters"></a></span><a class="link" href="tutdaytime3.html#asio.tutorial.tutdaytime3.removing_unused_handler_parameters">Removing
unused handler parameters</a>
</h5>
<p>
You may have noticed that the <code class="computeroutput"><span class="identifier">error</span></code>,
and <code class="computeroutput"><span class="identifier">bytes_transferred</span></code> parameters
are not used in the body of the <code class="computeroutput"><span class="identifier">handle_write</span><span class="special">()</span></code> function. If parameters are not needed,
it is possible to remove them from the function so that it looks like:
</p>
<pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">handle_write</span><span class="special">()</span>
<span class="special">{</span>
<span class="special">}</span>
</pre>
<p>
The asio::async_write() call used to initiate the call can then be changed
to just:
</p>
<pre class="programlisting"> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket_</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">message_</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">tcp_connection</span><span class="special">::</span><span class="identifier">handle_write</span><span class="special">,</span> <span class="identifier">shared_from_this</span><span class="special">()));</span>
</pre>
<p>
See the <a class="link" href="tutdaytime3/src.html" title="Source listing for Daytime.3">full source listing</a>
</p>
<p>
Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
</p>
<p>
Previous: <a class="link" href="tutdaytime2.html" title="Daytime.2 - A synchronous TCP daytime server">Daytime.2 - A synchronous
TCP daytime server</a>
</p>
<p>
Next: <a class="link" href="tutdaytime4.html" title="Daytime.4 - A synchronous UDP daytime client">Daytime.4 - A synchronous
UDP daytime client</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>)
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