2023-10-24 21:59:30 -04:00
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< 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 >
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< 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" > & < / 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.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" > & < / 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" > -> < / 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" > (& < / 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" > & < / 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" > -> < / 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" > < < / span > < span class = "identifier" > tcp_connection< / span > < span class = "special" > > < / 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" > < < / span > < span class = "identifier" > tcp_connection< / span > < span class = "special" > > < / 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" > & < / 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" > & < / span > < span class = "identifier" > socket< / span > < span class = "special" > ()< / span >
< span class = "special" > {< / span >
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< span class = "keyword" > return< / span > < span class = "identifier" > local_socket< / span > < span class = "special" > ;< / span >
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< 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 >
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< 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" > local_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 >
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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" > 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" > & < / 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 >
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< 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" > & < / 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 >
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< span class = "identifier" > tcp< / span > < span class = "special" > ::< / span > < span class = "identifier" > socket< / span > < span class = "identifier" > local_socket< / span > < span class = "special" > ;< / span >
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< 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 >
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< 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" > local_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 >
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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" > 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 > )
< / p >
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< div class = "spirit-nav" >
< a accesskey = "p" href = "tutdaytime2/src.html" > < img src = "../../prev.png" alt = "Prev" > < / a > < a accesskey = "u" href = "../tutorial.html" > < img src = "../../up.png" alt = "Up" > < / a > < a accesskey = "h" href = "../../index.html" > < img src = "../../home.png" alt = "Home" > < / a > < a accesskey = "n" href = "tutdaytime3/src.html" > < img src = "../../next.png" alt = "Next" > < / a >
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