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# chat/chat_server.cpp

    #include <algorithm>
    #include <cstdlib>
    #include <deque>
    #include <iostream>
    #include <list>
    #include <set>
    #include <boost/bind.hpp>
    #include <boost/shared_ptr.hpp>
    #include <boost/enable_shared_from_this.hpp>
    #include <boost/asio.hpp>
    #include "chat_message.hpp"

    using boost::asio::ip::tcp;

    //----------------------------------------------------------------------

    typedef std::deque<chat_message> chat_message_queue;

    //----------------------------------------------------------------------

    class chat_participant
    {
    public:
      virtual ~chat_participant() {}
      virtual void deliver(const chat_message& msg) = 0;
    };

    typedef boost::shared_ptr<chat_participant> chat_participant_ptr;

    //----------------------------------------------------------------------

    class chat_room
    {
    public:
      void join(chat_participant_ptr participant)
      {
        participants_.insert(participant);
        std::for_each(recent_msgs_.begin(), recent_msgs_.end(),
            boost::bind(&chat_participant::deliver, participant, _1));
      }

      void leave(chat_participant_ptr participant)
      {
        participants_.erase(participant);
      }

      void deliver(const chat_message& msg)
      {
        recent_msgs_.push_back(msg);
        while (recent_msgs_.size() > max_recent_msgs)
          recent_msgs_.pop_front();

        std::for_each(participants_.begin(), participants_.end(),
            boost::bind(&chat_participant::deliver, _1, boost::ref(msg)));
      }

    private:
      std::set<chat_participant_ptr> participants_;
      enum { max_recent_msgs = 100 };
      chat_message_queue recent_msgs_;
    };

    //----------------------------------------------------------------------

    class chat_session
      : public chat_participant,
        public boost::enable_shared_from_this<chat_session>
    {
    public:
      chat_session(boost::asio::io_service& io_service, chat_room& room)
        : socket_(io_service),
          room_(room)
      {
      }

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

      void start()
      {
        room_.join(shared_from_this());
        boost::asio::async_read(socket_,
            boost::asio::buffer(read_msg_.data(), chat_message::header_length),
            boost::bind(
              &chat_session::handle_read_header, shared_from_this(),
              boost::asio::placeholders::error));
      }

      void deliver(const chat_message& msg)
      {
        bool write_in_progress = !write_msgs_.empty();
        write_msgs_.push_back(msg);
        if (!write_in_progress)
        {
          boost::asio::async_write(socket_,
              boost::asio::buffer(write_msgs_.front().data(),
                write_msgs_.front().length()),
              boost::bind(&chat_session::handle_write, shared_from_this(),
                boost::asio::placeholders::error));
        }
      }

      void handle_read_header(const boost::asio::error& error)
      {
        if (!error && read_msg_.decode_header())
        {
          boost::asio::async_read(socket_,
              boost::asio::buffer(read_msg_.body(), read_msg_.body_length()),
              boost::bind(&chat_session::handle_read_body, shared_from_this(),
                boost::asio::placeholders::error));
        }
        else
        {
          room_.leave(shared_from_this());
        }
      }

      void handle_read_body(const boost::asio::error& error)
      {
        if (!error)
        {
          room_.deliver(read_msg_);
          boost::asio::async_read(socket_,
              boost::asio::buffer(read_msg_.data(), chat_message::header_length),
              boost::bind(&chat_session::handle_read_header, shared_from_this(),
                boost::asio::placeholders::error));
        }
        else
        {
          room_.leave(shared_from_this());
        }
      }

      void handle_write(const boost::asio::error& error)
      {
        if (!error)
        {
          write_msgs_.pop_front();
          if (!write_msgs_.empty())
          {
            boost::asio::async_write(socket_,
                boost::asio::buffer(write_msgs_.front().data(),
                  write_msgs_.front().length()),
                boost::bind(&chat_session::handle_write, shared_from_this(),
                  boost::asio::placeholders::error));
          }
        }
        else
        {
          room_.leave(shared_from_this());
        }
      }

    private:
      tcp::socket socket_;
      chat_room& room_;
      chat_message read_msg_;
      chat_message_queue write_msgs_;
    };

    typedef boost::shared_ptr<chat_session> chat_session_ptr;

    //----------------------------------------------------------------------

    class chat_server
    {
    public:
      chat_server(boost::asio::io_service& io_service,
          const tcp::endpoint& endpoint)
        : io_service_(io_service),
          acceptor_(io_service, endpoint)
      {
        chat_session_ptr new_session(new chat_session(io_service_, room_));
        acceptor_.async_accept(new_session->socket(),
            boost::bind(&chat_server::handle_accept, this, new_session,
              boost::asio::placeholders::error));
      }

      void handle_accept(chat_session_ptr session, const boost::asio::error& error)
      {
        if (!error)
        {
          session->start();
          chat_session_ptr new_session(new chat_session(io_service_, room_));
          acceptor_.async_accept(new_session->socket(),
              boost::bind(&chat_server::handle_accept, this, new_session,
                boost::asio::placeholders::error));
        }
      }

    private:
      boost::asio::io_service& io_service_;
      tcp::acceptor acceptor_;
      chat_room room_;
    };

    typedef boost::shared_ptr<chat_server> chat_server_ptr;
    typedef std::list<chat_server_ptr> chat_server_list;

    //----------------------------------------------------------------------

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

        boost::asio::io_service io_service;

        chat_server_list servers;
        for (int i = 1; i < argc; ++i)
        {
          using namespace std; // For atoi.
          tcp::endpoint endpoint(tcp::v4(), atoi(argv[i]));
          chat_server_ptr server(new chat_server(io_service, endpoint));
          servers.push_back(server);
        }

        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