tutorial.qbk

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  ``''''''``  {
  ``''''''``    start_accept();
  ``''''''``  }

  ``''''''``private:



The function `start_accept()` creates a socket and initiates an asynchronous accept operation to wait for a new connection.


  ``''''''``  void start_accept()
  ``''''''``  {
  ``''''''``    tcp_connection::pointer new_connection =
  ``''''''``      tcp_connection::create(acceptor_.io_service());

  ``''''''``    acceptor_.async_accept(new_connection->socket(),
  ``''''''``        boost::bind(&tcp_server::handle_accept, this, new_connection,
  ``''''''``          boost::asio::placeholders::error));
  ``''''''``  }



The function `handle_accept()` is called when the asynchronous accept operation initiated by `start_accept()` finishes. It services the client request, and then calls `start_accept()` to initiate the next accept operation.



  ``''''''``  void handle_accept(tcp_connection::pointer new_connection,
  ``''''''``      const boost::system::error_code& error)
  ``''''''``  {
  ``''''''``    if (!error)
  ``''''''``    {
  ``''''''``      new_connection->start();
  ``''''''``      start_accept();
  ``''''''``    }
  ``''''''``  }



[heading The tcp_connection class]

We will use `shared_ptr` and `enable_shared_from_this` because we want to keep the `tcp_connection` object alive as long as there is an operation that refers to it.


  ``''''''``class tcp_connection
  ``''''''``  : public boost::enable_shared_from_this<tcp_connection>
  ``''''''``{
  ``''''''``public:
  ``''''''``  typedef boost::shared_ptr<tcp_connection> pointer;

  ``''''''``  static pointer create(boost::asio::io_service& io_service)
  ``''''''``  {
  ``''''''``    return pointer(new tcp_connection(io_service));
  ``''''''``  }

  ``''''''``  tcp::socket& socket()
  ``''''''``  {
  ``''''''``    return socket_;
  ``''''''``  }



In the function `start()`, we call boost::asio::async\_write() to serve the data to the client. Note that we are using boost::asio::async\_write(), rather than [link boost_asio.reference.basic_stream_socket.async_write_some ip::tcp::socket::async_write_some()], to ensure that the entire block of data is sent.



  ``''''''``  void start()
  ``''''''``  {



The data to be sent is stored in the class member `message_` as we need to keep the data valid until the asynchronous operation is complete.


  ``''''''``    message_ = make_daytime_string();



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, since they are not being used in `handle_write()`.



  ``''''''``    boost::asio::async_write(socket_, boost::asio::buffer(message_),
  ``''''''``        boost::bind(&tcp_connection::handle_write, shared_from_this(),
  ``''''''``          boost::asio::placeholders::error,
  ``''''''``          boost::asio::placeholders::bytes_transferred));



Any further actions for this client connection are now the responsibility of `handle_write()`.


  ``''''''``  }

  ``''''''``private:
  ``''''''``  tcp_connection(boost::asio::io_service& io_service)
  ``''''''``    : socket_(io_service)
  ``''''''``  {
  ``''''''``  }

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

  ``''''''``  tcp::socket socket_;
  ``''''''``  std::string message_;
  ``''''''``};



[heading Removing unused handler parameters]

You may have noticed that the `error`, and `bytes_transferred` parameters are not used in the body of the `handle_write()` function. If parameters are not needed, it is possible to remove them from the function so that it looks like:


  ``''''''``  void handle_write()
  ``''''''``  {
  ``''''''``  }



The boost::asio::async\_write() call used to initiate the call can then be changed to just:


  ``''''''``  boost::asio::async_write(socket_, boost::asio::buffer(message_),
  ``''''''``      boost::bind(&tcp_connection::handle_write, shared_from_this()));



See the [link boost_asio.tutorial.tutdaytime3.src full source listing]

Return to the [link boost_asio.tutorial tutorial index]

Previous: [link boost_asio.tutorial.tutdaytime2 Daytime.2 - A synchronous TCP daytime server]

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



[section:src Source listing for Daytime.3]


  ``''''''``//
  ``''''''``// 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/bind.hpp>
  ``''''''``#include <boost/shared_ptr.hpp>
  ``''''''``#include <boost/enable_shared_from_this.hpp>
  ``''''''``#include <boost/asio.hpp>

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

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

  ``''''''``class tcp_connection
  ``''''''``  : public boost::enable_shared_from_this<tcp_connection>
  ``''''''``{
  ``''''''``public:
  ``''''''``  typedef boost::shared_ptr<tcp_connection> pointer;

  ``''''''``  static pointer create(boost::asio::io_service& io_service)
  ``''''''``  {
  ``''''''``    return pointer(new tcp_connection(io_service));
  ``''''''``  }

  ``''''''``  tcp::socket& socket()
  ``''''''``  {
  ``''''''``    return socket_;
  ``''''''``  }

  ``''''''``  void start()
  ``''''''``  {
  ``''''''``    message_ = make_daytime_string();

  ``''''''``    boost::asio::async_write(socket_, boost::asio::buffer(message_),
  ``''''''``        boost::bind(&tcp_connection::handle_write, shared_from_this(),
  ``''''''``          boost::asio::placeholders::error,
  ``''''''``          boost::asio::placeholders::bytes_transferred));
  ``''''''``  }

  ``''''''``private:
  ``''''''``  tcp_connection(boost::asio::io_service& io_service)
  ``''''''``    : socket_(io_service)
  ``''''''``  {
  ``''''''``  }

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

  ``''''''``  tcp::socket socket_;
  ``''''''``  std::string message_;
  ``''''''``};

  ``''''''``class tcp_server
  ``''''''``{
  ``''''''``public:
  ``''''''``  tcp_server(boost::asio::io_service& io_service)
  ``''''''``    : acceptor_(io_service, tcp::endpoint(tcp::v4(), 13))
  ``''''''``  {
  ``''''''``    start_accept();
  ``''''''``  }

  ``''''''``private:
  ``''''''``  void start_accept()
  ``''''''``  {
  ``''''''``    tcp_connection::pointer new_connection =
  ``''''''``      tcp_connection::create(acceptor_.io_service());

  ``''''''``    acceptor_.async_accept(new_connection->socket(),
  ``''''''``        boost::bind(&tcp_server::handle_accept, this, new_connection,
  ``''''''``          boost::asio::placeholders::error));
  ``''''''``  }

  ``''''''``  void handle_accept(tcp_connection::pointer new_connection,
  ``''''''``      const boost::system::error_code& error)
  ``''''''``  {
  ``''''''``    if (!error)
  ``''''''``    {
  ``''''''``      new_connection->start();
  ``''''''``      start_accept();
  ``''''''``    }
  ``''''''``  }

  ``''''''``  tcp::acceptor acceptor_;
  ``''''''``};

  ``''''''``int main()
  ``''''''``{
  ``''''''``  try
  ``''''''``  {
  ``''''''``    boost::asio::io_service io_service;
  ``''''''``    tcp_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.tutdaytime3 Daytime.3 - An asynchronous TCP daytime server]

[endsect]

[endsect]

[section:tutdaytime4 Daytime.4 - A synchronous UDP daytime client]

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


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

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



The start of the application is essentially the same as for the TCP daytime client.



  ``''''''``int main(int argc, char* argv[])
  ``''''''``{
  ``''''''``  try
  ``''''''``  {
  ``''''''``    if (argc != 2)
  ``''''''``    {
  ``''''''``      std::cerr << "Usage: client <host>" << std::endl;
  ``''''''``      return 1;
  ``''''''``    }

  ``''''''``    boost::asio::io_service io_service;



We use an [link boost_asio.reference.ip__udp.resolver ip::udp::resolver] object to find the correct remote endpoint to use based on the host and service names. The query is restricted to return only IPv4 endpoints by the [link boost_asio.reference.ip__udp.v4 ip::udp::v4()] argument.



  ``''''''``    udp::resolver resolver(io_service);
  ``''''''``    udp::resolver::query query(udp::v4(), argv[1], "daytime");



The [link boost_asio.reference.ip__basic_resolver.resolve ip::udp::resolver::resolve()] function is guaranteed to return at least one endpoint in the list if it does not fail. This means it is safe to dereference the return value directly.


  ``''''''``    udp::endpoint receiver_endpoint = *resolver.resolve(query);



Since UDP is datagram-oriented, we will not be using a stream socket. Create an [link boost_asio.reference.ip__udp.socket ip::udp::socket] and initiate contact with the remote endpoint.



  ``''''''``    udp::socket socket(io_service);
  ``''''''``    socket.open(udp::v4());

  ``''''''``    boost::array<char, 1> send_buf  = { 0 };
  ``''''''``    socket.send_to(boost::asio::buffer(send_buf), receiver_endpoint);



Now we need to be ready to accept whatever the server sends back to us. The endpoint on our side that receives the server's response will be initialised by [link boost_asio.reference.basic_datagram_socket.receive_from ip::udp::socket::receive_from()].



  ``''''''``    boost::array<char, 128> recv_buf;
  ``''''''``    udp::endpoint sender_endpoint;
  ``''''''``    size_t len = socket.receive_from(
  ``''''''``        boost::asio::buffer(recv_buf), sender_endpoint);

  ``''''''``    std::cout.write(recv_buf.data(), len);
  ``''''''``  }



Finally, handle any exceptions that may have been thrown.


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

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

See the [link boost_asio.tutorial.tutdaytime4.src full source listing]

Return to the [link boost_asio.tutorial tutorial index]

Previous: [link boost_asio.tutorial.tutdaytime3 Daytime.3 - An asynchronous TCP daytime server]

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



[section:src Source listing for Daytime.4]


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

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

  ``''''''``int main(int argc, char* argv[])
  ``''''''``{
  ``''''''``  try
  ``''''''``  {
  ``''''''``    if (argc != 2)
  ``''''''``    {
  ``''''''``      std::cerr << "Usage: client <host>" << std::endl;
  ``''''''``      return 1;
  ``''''''``    }

  ``''''''``    boost::asio::io_service io_service;

  ``''''''``    udp::resolver resolver(io_service);
  ``''''''``    udp::resolver::query query(udp::v4(), argv[1], "daytime");
  ``''''''``    udp::endpoint receiver_endpoint = *resolver.resolve(query);

  ``''''''``    udp::socket socket(io_service);
  ``''''''``    socket.open(udp::v4());

  ``''''''``    boost::array<char, 1> send_buf  = { 0 };
  ``''''''``    socket.send_to(boost::asio::buffer(send_buf), receiver_endpoint);

  ``''''''``    boost::array<char, 128> recv_buf;
  ``''''''``    udp::endpoint sender_endpoint;
  ``''''''``    size_t len = socket.receive_from(
  ``''''''``        boost::asio::buffer(recv_buf), sender_endpoint);

  ``''''''``    std::cout.write(recv_buf.data(), len);
  ``''''''``  }
  ``''''''``  catch (std::exception& e)
  ``''''''``  {
  ``''''''``    std::cerr << e.what() << std::endl;
  ``''''''``  }

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