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<title>Daytime.6 - An asynchronous UDP daytime server</title>
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<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>
<h5>
<a name="boost_asio.tutorial.tutdaytime6.h0"></a>
<span class="phrase"><a name="boost_asio.tutorial.tutdaytime6.the_main___function"></a></span><a class="link" href="tutdaytime6.html#boost_asio.tutorial.tutdaytime6.the_main___function">The
main() function</a>
</h5>
<pre class="programlisting">int main()
{
try
{
</pre>
<p>
Create a server object to accept incoming client requests, and run the <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> object.
</p>
<pre class="programlisting"> boost::asio::io_context io_context;
udp_server server(io_context);
io_context.run();
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}
</pre>
<h5>
<a name="boost_asio.tutorial.tutdaytime6.h1"></a>
<span class="phrase"><a name="boost_asio.tutorial.tutdaytime6.the_udp_server_class"></a></span><a class="link" href="tutdaytime6.html#boost_asio.tutorial.tutdaytime6.the_udp_server_class">The udp_server
class</a>
</h5>
<pre class="programlisting">class udp_server
{
public:
</pre>
<p>
The constructor initialises a socket to listen on UDP port 13.
</p>
<pre class="programlisting"> udp_server(boost::asio::io_context& io_context)
: socket_(io_context, udp::endpoint(udp::v4(), 13))
{
start_receive();
}
private:
void start_receive()
{
</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_context.html" title="io_context">io_context</a>
object will invoke the <code class="computeroutput">handle_receive()</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">size_t</code> value <code class="computeroutput">bytes_transferred</code>
specifying the number of bytes received.
</p>
<pre class="programlisting"> socket_.async_receive_from(
boost::asio::buffer(recv_buffer_), remote_endpoint_,
boost::bind(&udp_server::handle_receive, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
</pre>
<p>
The function <code class="computeroutput">handle_receive()</code> will service the client request.
</p>
<pre class="programlisting"> void handle_receive(const boost::system::error_code& error,
std::size_t /*bytes_transferred*/)
{
</pre>
<p>
The <code class="computeroutput">error</code> parameter contains the result of the asynchronous
operation. Since we only provide the 1-byte <code class="computeroutput">recv_buffer_</code> to
contain the client's request, the <a class="link" href="../reference/io_context.html" title="io_context">io_context</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"> if (!error)
{
</pre>
<p>
Determine what we are going to send.
</p>
<pre class="programlisting"> boost::shared_ptr<std::string> message(
new std::string(make_daytime_string()));
</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"> socket_.async_send_to(boost::asio::buffer(*message), remote_endpoint_,
boost::bind(&udp_server::handle_send, this, message,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
</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"> start_receive();
</pre>
<p>
Any further actions for this client request are now the responsibility of
<code class="computeroutput">handle_send()</code>.
</p>
<pre class="programlisting"> }
}
</pre>
<p>
The function <code class="computeroutput">handle_send()</code> is invoked after the service request
has been completed.
</p>
<pre class="programlisting"> void handle_send(boost::shared_ptr<std::string> /*message*/,
const boost::system::error_code& /*error*/,
std::size_t /*bytes_transferred*/)
{
}
udp::socket socket_;
udp::endpoint remote_endpoint_;
boost::array<char, 1> recv_buffer_;
};
</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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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2018 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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