tutorial.qbk

来自「Boost provides free peer-reviewed portab」· QBK 代码 · 共 2,067 行 · 第 1/5 页

  ``''''''``}

Return to [link boost_asio.tutorial.tutdaytime4 Daytime.4 - A synchronous UDP daytime client]

[endsect]

[endsect]

[section:tutdaytime5 Daytime.5 - A synchronous UDP daytime server]

This tutorial program shows how to use asio to implement a server application with UDP.


  ``''''''``int main()
  ``''''''``{
  ``''''''``  try
  ``''''''``  {
  ``''''''``    boost::asio::io_service io_service;



Create an [link boost_asio.reference.ip__udp.socket ip::udp::socket] object to receive requests on UDP port 13.



  ``''''''``    udp::socket socket(io_service, udp::endpoint(udp::v4(), 13));



Wait for a client to initiate contact with us. The remote\_endpoint object will be populated by [link boost_asio.reference.basic_datagram_socket.receive_from ip::udp::socket::receive_from()].



  ``''''''``    for (;;)
  ``''''''``    {
  ``''''''``      boost::array<char, 1> recv_buf;
  ``''''''``      udp::endpoint remote_endpoint;
  ``''''''``      boost::system::error_code error;
  ``''''''``      socket.receive_from(boost::asio::buffer(recv_buf),
  ``''''''``          remote_endpoint, 0, error);

  ``''''''``      if (error && error != boost::asio::error::message_size)
  ``''''''``        throw boost::system::system_error(error);



Determine what we are going to send back to the client.



  ``''''''``      std::string message = make_daytime_string();



Send the response to the remote\_endpoint.



  ``''''''``      boost::system::error_code ignored_error;
  ``''''''``      socket.send_to(boost::asio::buffer(message),
  ``''''''``          remote_endpoint, 0, ignored_error);
  ``''''''``    }
  ``''''''``  }



Finally, handle any exceptions.


  ``''''''``  catch (std::exception& e)
  ``''''''``  {
  ``''''''``    std::cerr << e.what() << std::endl;
  ``''''''``  }

  ``''''''``  return 0;
  ``''''''``}



See the [link boost_asio.tutorial.tutdaytime5.src full source listing]

Return to the [link boost_asio.tutorial tutorial index]

Previous: [link boost_asio.tutorial.tutdaytime4 Daytime.4 - A synchronous UDP daytime client]

Next: [link boost_asio.tutorial.tutdaytime6 Daytime.6 - An asynchronous UDP daytime server]



[section:src Source listing for Daytime.5]


  ``''''''``//
  ``''''''``// server.cpp
  ``''''''``// ~~~~~~~~~~
  ``''''''``//
  ``''''''``// Copyright (c) 2003-2008 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  ``''''''``//
  ``''''''``// Distributed under the Boost Software License, Version 1.0. (See accompanying
  ``''''''``// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  ``''''''``//

  ``''''''``#include <ctime>
  ``''''''``#include <iostream>
  ``''''''``#include <string>
  ``''''''``#include <boost/array.hpp>
  ``''''''``#include <boost/asio.hpp>

  ``''''''``using boost::asio::ip::udp;

  ``''''''``std::string make_daytime_string()
  ``''''''``{
  ``''''''``  using namespace std; // For time_t, time and ctime;
  ``''''''``  time_t now = time(0);
  ``''''''``  return ctime(&now);
  ``''''''``}

  ``''''''``int main()
  ``''''''``{
  ``''''''``  try
  ``''''''``  {
  ``''''''``    boost::asio::io_service io_service;

  ``''''''``    udp::socket socket(io_service, udp::endpoint(udp::v4(), 13));

  ``''''''``    for (;;)
  ``''''''``    {
  ``''''''``      boost::array<char, 1> recv_buf;
  ``''''''``      udp::endpoint remote_endpoint;
  ``''''''``      boost::system::error_code error;
  ``''''''``      socket.receive_from(boost::asio::buffer(recv_buf),
  ``''''''``          remote_endpoint, 0, error);

  ``''''''``      if (error && error != boost::asio::error::message_size)
  ``''''''``        throw boost::system::system_error(error);

  ``''''''``      std::string message = make_daytime_string();

  ``''''''``      boost::system::error_code ignored_error;
  ``''''''``      socket.send_to(boost::asio::buffer(message),
  ``''''''``          remote_endpoint, 0, ignored_error);
  ``''''''``    }
  ``''''''``  }
  ``''''''``  catch (std::exception& e)
  ``''''''``  {
  ``''''''``    std::cerr << e.what() << std::endl;
  ``''''''``  }

  ``''''''``  return 0;
  ``''''''``}

Return to [link boost_asio.tutorial.tutdaytime5 Daytime.5 - A synchronous UDP daytime server]

[endsect]

[endsect]

[section:tutdaytime6 Daytime.6 - An asynchronous UDP daytime server]

[heading The main() function]


  ``''''''``int main()
  ``''''''``{
  ``''''''``  try
  ``''''''``  {



Create a server object to accept incoming client requests, and run the 
[link boost_asio.reference.io_service io_service] object.


  ``''''''``    boost::asio::io_service io_service;
  ``''''''``    udp_server server(io_service);
  ``''''''``    io_service.run();
  ``''''''``  }
  ``''''''``  catch (std::exception& e)
  ``''''''``  {
  ``''''''``    std::cerr << e.what() << std::endl;
  ``''''''``  }

  ``''''''``  return 0;
  ``''''''``}



[heading The udp_server class]


  ``''''''``class udp_server
  ``''''''``{
  ``''''''``public:



The constructor initialises a socket to listen on UDP port 13.


  ``''''''``  udp_server(boost::asio::io_service& io_service)
  ``''''''``    : socket_(io_service, udp::endpoint(udp::v4(), 13))
  ``''''''``  {
  ``''''''``    start_receive();
  ``''''''``  }

  ``''''''``private:
  ``''''''``  void start_receive()
  ``''''''``  {



The function [link boost_asio.reference.basic_datagram_socket.async_receive_from ip::udp::socket::async_receive_from()] will cause the application to listen in the background for a new request. When such a request is received, the 
[link boost_asio.reference.io_service io_service] object will invoke the `handle_receive()` function with two arguments: a value of type boost::system::error\_code indicating whether the operation succeeded or failed, and a `size_t` value `bytes_transferred` specifying the number of bytes received.


  ``''''''``    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));
  ``''''''``  }



The function `handle_receive()` will service the client request.



  ``''''''``  void handle_receive(const boost::system::error_code& error,
  ``''''''``      std::size_t /*bytes_transferred*/)
  ``''''''``  {



The `error` parameter contains the result of the asynchronous operation. Since we only provide the 1-byte `recv_buffer_` to contain the client's request, the 
[link boost_asio.reference.io_service io_service] object would return an error if the client sent anything larger. We can ignore such an error if it comes up.


  ``''''''``    if (!error || error == boost::asio::error::message_size)
  ``''''''``    {



Determine what we are going to send.


  ``''''''``      boost::shared_ptr<std::string> message(
  ``''''''``          new std::string(make_daytime_string()));



We now call [link boost_asio.reference.basic_datagram_socket.async_send_to ip::udp::socket::async_send_to()] to serve the data to the client.



  ``''''''``      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));



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.

Start listening for the next client request.



  ``''''''``      start_receive();



Any further actions for this client request are now the responsibility of `handle_send()`.


  ``''''''``    }
  ``''''''``  }



The function `handle_send()` is invoked after the service request has been completed.



  ``''''''``  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_;
  ``''''''``};



See the [link boost_asio.tutorial.tutdaytime6.src full source listing]

Return to the [link boost_asio.tutorial tutorial index]

Previous: [link boost_asio.tutorial.tutdaytime5 Daytime.5 - A synchronous UDP daytime server]

Next: [link boost_asio.tutorial.tutdaytime7 Daytime.7 - A combined TCP/UDP asynchronous server]



[section:src Source listing for Daytime.6]


  ``''''''``//
  ``''''''``// server.cpp
  ``''''''``// ~~~~~~~~~~
  ``''''''``//
  ``''''''``// Copyright (c) 2003-2008 Christopher M. Kohlhoff (chris at kohlhoff dot com)
  ``''''''``//
  ``''''''``// Distributed under the Boost Software License, Version 1.0. (See accompanying
  ``''''''``// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  ``''''''``//

  ``''''''``#include <ctime>
  ``''''''``#include <iostream>
  ``''''''``#include <string>
  ``''''''``#include <boost/array.hpp>
  ``''''''``#include <boost/bind.hpp>
  ``''''''``#include <boost/shared_ptr.hpp>
  ``''''''``#include <boost/asio.hpp>

  ``''''''``using boost::asio::ip::udp;

  ``''''''``std::string make_daytime_string()
  ``''''''``{
  ``''''''``  using namespace std; // For time_t, time and ctime;
  ``''''''``  time_t now = time(0);
  ``''''''``  return ctime(&now);
  ``''''''``}

  ``''''''``class udp_server
  ``''''''``{
  ``''''''``public:
  ``''''''``  udp_server(boost::asio::io_service& io_service)
  ``''''''``    : socket_(io_service, udp::endpoint(udp::v4(), 13))
  ``''''''``  {
  ``''''''``    start_receive();
  ``''''''``  }

  ``''''''``private:
  ``''''''``  void start_receive()
  ``''''''``  {
  ``''''''``    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));
  ``''''''``  }

  ``''''''``  void handle_receive(const boost::system::error_code& error,
  ``''''''``      std::size_t /*bytes_transferred*/)
  ``''''''``  {
  ``''''''``    if (!error || error == boost::asio::error::message_size)
  ``''''''``    {
  ``''''''``      boost::shared_ptr<std::string> message(
  ``''''''``          new std::string(make_daytime_string()));

  ``''''''``      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));

  ``''''''``      start_receive();
  ``''''''``    }
  ``''''''``  }

  ``''''''``  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_;
  ``''''''``};

  ``''''''``int main()
  ``''''''``{
  ``''''''``  try
  ``''''''``  {
  ``''''''``    boost::asio::io_service io_service;
  ``''''''``    udp_server server(io_service);
  ``''''''``    io_service.run();
  ``''''''``  }
  ``''''''``  catch (std::exception& e)
  ``''''''``  {
  ``''''''``    std::cerr << e.what() << std::endl;
  ``''''''``  }

  ``''''''``  return 0;
  ``''''''``}

Return to [link boost_asio.tutorial.tutdaytime6 Daytime.6 - An asynchronous UDP daytime server]

[endsect]

[endsect]

[section:tutdaytime7 Daytime.7 - A combined TCP/UDP asynchronous server]

This tutorial program shows how to combine the two asynchronous servers that we have just written, into a single server application.

[head