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< title > Daytime.6 - An asynchronous UDP daytime server< / title >
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< a name = "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 >
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< h5 >
< a name = "asio.tutorial.tutdaytime6.h0" > < / a >
< span > < a name = "asio.tutorial.tutdaytime6.the_main___function" > < / a > < / span > < a class = "link" href = "tutdaytime6.html#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_context.html" title = "io_context" > io_context< / a > object.
< / 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" > udp_server< / span > < span class = "identifier" > server< / 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" > 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 >
< h5 >
< a name = "asio.tutorial.tutdaytime6.h1" > < / a >
< span > < a name = "asio.tutorial.tutdaytime6.the_udp_server_class" > < / a > < / span > < a class = "link" href = "tutdaytime6.html#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" > asio< / 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 >
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< span class = "special" > :< / span > < span class = "identifier" > local_socket< / span > < span class = "special" > (< / span > < span class = "identifier" > io_context< / 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 >
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< 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_context.html" title = "io_context" > io_context< / 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 < a class = "link" href = "../reference/error_code.html" title = "error_code" > error_code< / a > 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 >
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< pre class = "programlisting" > < span class = "identifier" > local_socket< / span > < span class = "special" > .< / span > < span class = "identifier" > async_receive_from< / 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_connection< / span > < span class = "special" > ,< / span >
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< 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" > 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 >
< 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" > asio< / 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_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" > < span class = "keyword" > if< / span > < span class = "special" > (!< / span > < span class = "identifier" > error< / 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 >
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< pre class = "programlisting" > < span class = "identifier" > local_socket< / span > < span class = "special" > .< / span > < span class = "identifier" > async_send_to< / 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_connection< / span > < span class = "special" > ,< / span >
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< 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" > 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 >
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.
< / 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" > asio< / 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 >
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< span class = "identifier" > udp< / span > < span class = "special" > ::< / span > < span class = "identifier" > socket< / span > < span class = "identifier" > local_socket< / span > < span class = "special" > ;< / span >
< span class = "identifier" > udp< / span > < span class = "special" > ::< / span > < span class = "identifier" > endpoint< / span > < span class = "identifier" > remote_connection< / span > < span class = "special" > ;< / span >
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< 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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< 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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