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| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_asio.tutorial.tutdaytime6"></a><a class="link" href="tutdaytime6.html" title="Daytime.6 - An asynchronous UDP daytime server">Daytime.6 - An asynchronous |
| UDP daytime server</a> |
| </h3></div></div></div> |
| <a name="boost_asio.tutorial.tutdaytime6.the_main___function"></a><h5> |
| <a name="id804751"></a> |
| <a class="link" href="tutdaytime6.html#boost_asio.tutorial.tutdaytime6.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> |
| Create a server object to accept incoming client requests, and run the <a class="link" href="../reference/io_service.html" title="io_service">io_service</a> object. |
| </p> |
| <pre class="programlisting"> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span> <span class="identifier">io_service</span><span class="special">;</span> |
| <span class="identifier">udp_server</span> <span class="identifier">server</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span> |
| <span class="identifier">io_service</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">&</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"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</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> |
| <a name="boost_asio.tutorial.tutdaytime6.the_udp_server_class"></a><h5> |
| <a name="id805041"></a> |
| <a class="link" href="tutdaytime6.html#boost_asio.tutorial.tutdaytime6.the_udp_server_class">The |
| udp_server class</a> |
| </h5> |
| <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">udp_server</span> |
| <span class="special">{</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| </pre> |
| <p> |
| The constructor initialises a socket to listen on UDP port 13. |
| </p> |
| <pre class="programlisting"> <span class="identifier">udp_server</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">&</span> <span class="identifier">io_service</span><span class="special">)</span> |
| <span class="special">:</span> <span class="identifier">socket_</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">,</span> <span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</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">13</span><span class="special">))</span> |
| <span class="special">{</span> |
| <span class="identifier">start_receive</span><span class="special">();</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">private</span><span class="special">:</span> |
| <span class="keyword">void</span> <span class="identifier">start_receive</span><span class="special">()</span> |
| <span class="special">{</span> |
| </pre> |
| <p> |
| The function <a class="link" href="../reference/basic_datagram_socket/async_receive_from.html" title="basic_datagram_socket::async_receive_from">ip::udp::socket::async_receive_from()</a> |
| will cause the application to listen in the background for a new request. |
| When such a request is received, the <a class="link" href="../reference/io_service.html" title="io_service">io_service</a> |
| object will invoke the <code class="computeroutput"><span class="identifier">handle_receive</span><span class="special">()</span></code> function with two arguments: a value of |
| type boost::system::error_code indicating whether the operation succeeded |
| or failed, and a <code class="computeroutput"><span class="identifier">size_t</span></code> value |
| <code class="computeroutput"><span class="identifier">bytes_transferred</span></code> specifying |
| the number of bytes received. |
| </p> |
| <pre class="programlisting"> <span class="identifier">socket_</span><span class="special">.</span><span class="identifier">async_receive_from</span><span class="special">(</span> |
| <span class="identifier">boost</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">recv_buffer_</span><span class="special">),</span> <span class="identifier">remote_endpoint_</span><span class="special">,</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&</span><span class="identifier">udp_server</span><span class="special">::</span><span class="identifier">handle_receive</span><span class="special">,</span> <span class="keyword">this</span><span class="special">,</span> |
| <span class="identifier">boost</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">boost</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> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| The function <code class="computeroutput"><span class="identifier">handle_receive</span><span class="special">()</span></code> will service the client request. |
| </p> |
| <pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">handle_receive</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span> |
| <span class="identifier">std</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> |
| </pre> |
| <p> |
| The <code class="computeroutput"><span class="identifier">error</span></code> parameter contains |
| the result of the asynchronous operation. Since we only provide the 1-byte |
| <code class="computeroutput"><span class="identifier">recv_buffer_</span></code> to contain the |
| client's request, the <a class="link" href="../reference/io_service.html" title="io_service">io_service</a> |
| object would return an error if the client sent anything larger. We can ignore |
| such an error if it comes up. |
| </p> |
| <pre class="programlisting"> <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">error</span> <span class="special">||</span> <span class="identifier">error</span> <span class="special">==</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">message_size</span><span class="special">)</span> |
| <span class="special">{</span> |
| </pre> |
| <p> |
| Determine what we are going to send. |
| </p> |
| <pre class="programlisting"> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">message</span><span class="special">(</span> |
| <span class="keyword">new</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">(</span><span class="identifier">make_daytime_string</span><span class="special">()));</span> |
| </pre> |
| <p> |
| We now call <a class="link" href="../reference/basic_datagram_socket/async_send_to.html" title="basic_datagram_socket::async_send_to">ip::udp::socket::async_send_to()</a> |
| to serve the data to the client. |
| </p> |
| <pre class="programlisting"> <span class="identifier">socket_</span><span class="special">.</span><span class="identifier">async_send_to</span><span class="special">(</span><span class="identifier">boost</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">remote_endpoint_</span><span class="special">,</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(&</span><span class="identifier">udp_server</span><span class="special">::</span><span class="identifier">handle_send</span><span class="special">,</span> <span class="keyword">this</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">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">boost</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> |
| When initiating the asynchronous operation, and if using boost::bind(), you |
| must specify only the arguments that match the handler's parameter list. |
| In this program, both of the argument placeholders (boost::asio::placeholders::error |
| and boost::asio::placeholders::bytes_transferred) could potentially have |
| been removed. |
| </p> |
| <p> |
| Start listening for the next client request. |
| </p> |
| <pre class="programlisting"> <span class="identifier">start_receive</span><span class="special">();</span> |
| </pre> |
| <p> |
| Any further actions for this client request are now the responsibility of |
| <code class="computeroutput"><span class="identifier">handle_send</span><span class="special">()</span></code>. |
| </p> |
| <pre class="programlisting"> <span class="special">}</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| The function <code class="computeroutput"><span class="identifier">handle_send</span><span class="special">()</span></code> is invoked after the service request has |
| been completed. |
| </p> |
| <pre class="programlisting"> <span class="keyword">void</span> <span class="identifier">handle_send</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="comment">/*message*/</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&</span> <span class="comment">/*error*/</span><span class="special">,</span> |
| <span class="identifier">std</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">udp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">socket_</span><span class="special">;</span> |
| <span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="identifier">remote_endpoint_</span><span class="special">;</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="number">1</span><span class="special">></span> <span class="identifier">recv_buffer_</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| See the <a class="link" href="tutdaytime6/src.html" title="Source listing for Daytime.6">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="tutdaytime5.html" title="Daytime.5 - A synchronous UDP daytime server">Daytime.5 - A synchronous |
| UDP daytime server</a> |
| </p> |
| <p> |
| Next: <a class="link" href="tutdaytime7.html" title="Daytime.7 - A combined TCP/UDP asynchronous server">Daytime.7 - A combined |
| TCP/UDP asynchronous server</a> |
| </p> |
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| <td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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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