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# echo/async_udp_echo_server.cpp

    #include <cstdlib>
    #include <iostream>
    #include <boost/bind.hpp>
    #include <boost/asio.hpp>

    using boost::asio::ip::udp;

    class server
    {
    public:
      server(boost::asio::io_service& io_service, short port)
        : io_service_(io_service),
          socket_(io_service, udp::endpoint(udp::v4(), port))
      {
        socket_.async_receive_from(
            boost::asio::buffer(data_, max_length), sender_endpoint_,
            boost::bind(&server::handle_receive_from, this,
              boost::asio::placeholders::error,
              boost::asio::placeholders::bytes_transferred));
      }

      void handle_receive_from(const boost::asio::error& error, size_t bytes_recvd)
      {
        if (!error && bytes_recvd > 0)
        {
          socket_.async_send_to(
              boost::asio::buffer(data_, bytes_recvd), sender_endpoint_,
              boost::bind(&server::handle_send_to, this,
                boost::asio::placeholders::error,
                boost::asio::placeholders::bytes_transferred));
        }
        else
        {
          socket_.async_receive_from(
              boost::asio::buffer(data_, max_length), sender_endpoint_,
              boost::bind(&server::handle_receive_from, this,
                boost::asio::placeholders::error,
                boost::asio::placeholders::bytes_transferred));
        }
      }

      void handle_send_to(const boost::asio::error& error, size_t bytes_sent)
      {
        socket_.async_receive_from(
            boost::asio::buffer(data_, max_length), sender_endpoint_,
            boost::bind(&server::handle_receive_from, this,
              boost::asio::placeholders::error,
              boost::asio::placeholders::bytes_transferred));
      }

    private:
      boost::asio::io_service& io_service_;
      udp::socket socket_;
      udp::endpoint sender_endpoint_;
      enum { max_length = 1024 };
      char data_[max_length];
    };

    int main(int argc, char* argv[])
    {
      try
      {
        if (argc != 2)
        {
          std::cerr << "Usage: async_udp_echo_server <port>\n";
          return 1;
        }

        boost::asio::io_service io_service;

        using namespace std; // For atoi.
        server s(io_service, atoi(argv[1]));

        io_service.run();
      }
      catch (boost::asio::error& e)
      {
        std::cerr << e << "\n";
      }
      catch (std::exception& e)
      {
        std::cerr << "Exception: " << e.what() << "\n";
      }

      return 0;
    }

| Copyright © 2003 - 2006 Christopher M. Kohlhoff