#### Source listing for Daytime.6

    //
    // server.cpp
    // ~~~~~~~~~~
    //
    // Copyright (c) 2003-2020 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/bind.hpp>
    #include <boost/shared_ptr.hpp>
    #include <asio.hpp>

    using 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(asio::io_context& io_context)
        : socket_(io_context, udp::endpoint(udp::v4(), 13))
      {
        start_receive();
      }

    private:
      void start_receive()
      {
        socket_.async_receive_from(
            asio::buffer(recv_buffer_), remote_endpoint_,
            boost::bind(&udp_server::handle_receive, this,
              asio::placeholders::error,
              asio::placeholders::bytes_transferred));
      }

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

          socket_.async_send_to(asio::buffer(*message), remote_endpoint_,
              boost::bind(&udp_server::handle_send, this, message,
                asio::placeholders::error,
                asio::placeholders::bytes_transferred));

          start_receive();
        }
      }

      void handle_send(boost::shared_ptr<std::string> /*message*/,
          const asio::error_code& /*error*/,
          std::size_t /*bytes_transferred*/)
      {
      }

      udp::socket socket_;
      udp::endpoint remote_endpoint_;
      boost::array<char, 1> recv_buffer_;
    };

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

      return 0;
    }

Return to Daytime.6 - An asynchronous UDP daytime server