boost asio异步读写网络聊天程序client 实例具体解释

boost官方文档中聊天程序实例解说

数据包格式chat_message.hpp

<pre name="code" class="cpp"><h3>数据包chat_message.hpp</h3>
// chat_message.hpp
// ~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2013 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)
//实例源于http://www.boost.org/doc/libs/1_55_0/doc/html/boost_asio/examples/cpp03_examples.html 文档中没有凝视，自己在///開始看的时候也走了点弯路，本文对该源代码写了具体的凝视，希望能让后来者们少走些弯路。
//首先看看数据包的结构：
//数据包分为两个部分。首先是报头占4bytes，每一byte表示一个数字。也就是最多能表示的出9999，不足在前填0；
// 数据包头的数字表示数据部分的长度大小。
 

#ifndef CHAT_MESSAGE_HPP
#define CHAT_MESSAGE_HPP

#include <cstdio>
#include <cstdlib>
#include <cstring>

class chat_message
{
public:
  enum { header_length = 4 };
  enum { max_body_length = 512 };

  chat_message()
    : body_length_(0)
  {
  }

  const char* data() const
  {
    return data_;
  }

  char* data()
  {
    return data_;
  }

  size_t length() const
  {
    return header_length + body_length_;
  }

  const char* body() const
  {
    return data_ + header_length;
  }

  char* body()
  {
    return data_ + header_length;
  }

  size_t body_length() const
  {
    return body_length_;
  }

  void body_length(size_t new_length)
  {
    body_length_ = new_length;
    if (body_length_ > max_body_length)
      body_length_ = max_body_length;
  }

  bool decode_header()//将报头的4字节字符串转换成数字
  {
    using namespace std; // For strncat and atoi.
    char header[header_length + 1] = "";
    strncat(header, data_, header_length);
    body_length_ = atoi(header);
    if (body_length_ > max_body_length)
    {
      body_length_ = 0;
      return false;
    }
    return true;
  }

  void encode_header()//把数据部分大小编码成字符串
  {
    using namespace std; // For sprintf and memcpy.
    char header[header_length + 1] = "";
    sprintf(header, "%4d", body_length_);
    memcpy(data_, header, header_length);
  }

private:
  char data_[header_length + max_body_length];
  size_t body_length_;
};

#endif // CHAT_MESSAGE_HPP

聊天客户端chat_client.cpp

///////////////////////////////////////////////////////////////////////////////////////////////////////

<h3>
</h3><h3>
	<span style="white-space:pre-wrap">聊天客户端chat_client.cpp</span>
</h3>
<pre>

///////////////////////////////////////////////////////////////////////////////////////////////////////

//
// chat_client.cpp
// ~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2013 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)
//
//boost开发文档中实时聊天程序的客户端
//实现的大致思路是：在创建的客户端实例中初始化socket、连接server端，而且不断的进行着异步读操作（从server端读数据）
//在主线程中，从console中不断读取要被发送的消息，而且把这些消息post至io_service，然后进行异步写操作
//读写socket都是用异步操作
//这样的方法不同于分别开一个读线程，一个写线程， 它的优势是线程不会一直等待读写数据，在并发数大的情况下通过异步读写能提高资源利用率


#include <cstdlib>
#include <deque>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/thread/thread.hpp>
#include "chat_message.hpp"

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

typedef std::deque<chat_message> chat_message_queue;

class chat_client
{
public:
  chat_client(boost::asio::io_service& io_service,
      tcp::resolver::iterator endpoint_iterator)
    : io_service_(io_service),
      socket_(io_service) //使得成员函数能直接使用这些变量
  {
    boost::asio::async_connect(socket_, endpoint_iterator,
        boost::bind(&chat_client::handle_connect, this,
          boost::asio::placeholders::error)); //全部的操作都採用异步的方式
  }

  void write(const chat_message& msg)
  {
    io_service_.post(boost::bind(&chat_client::do_write, this, msg)); //将消息主动投递给io_service
  }

  void close()
  {
    io_service_.post(boost::bind(&chat_client::do_close, this)); //这个close函数是客户端要主动终止时调用  do_close函数是从server端
                                                                //读数据失败时调用
  }

private:

  void handle_connect(const boost::system::error_code& error)
  {
    if (!error)
    {
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.data(), chat_message::header_length), //读取数据报头
          boost::bind(&chat_client::handle_read_header, this,
            boost::asio::placeholders::error));
    }
  }

  void handle_read_header(const boost::system::error_code& error)
  {
    if (!error && read_msg_.decode_header()) //分别处理数据报头和数据部分
    {
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.body(), read_msg_.body_length()),//读取数据包数据部分
          boost::bind(&chat_client::handle_read_body, this,
            boost::asio::placeholders::error));
    }
    else
    {
      do_close();
    }
  }

  void handle_read_body(const boost::system::error_code& error)
  {
    if (!error)
    {
      std::cout.write(read_msg_.body(), read_msg_.body_length()); //输出消息
      std::cout << "\n";
      boost::asio::async_read(socket_, 
          boost::asio::buffer(read_msg_.data(), chat_message::header_length), //在这里读取下一个数据包头
          boost::bind(&chat_client::handle_read_header, this,  
            boost::asio::placeholders::error)); //完毕一次读操作（处理完一个数据包）  进行下一次读操作
    }
    else
    {
      do_close();
    }
  }

  void do_write(chat_message msg)
  {
    bool write_in_progress = !write_msgs_.empty(); //空的话变量为false
    write_msgs_.push_back(msg); //把要写的数据push至写队列
    if (!write_in_progress)//队列初始为空 push一个msg后就有一个元素了
    {
      boost::asio::async_write(socket_,
          boost::asio::buffer(write_msgs_.front().data(),
            write_msgs_.front().length()),
          boost::bind(&chat_client::handle_write, this, 
            boost::asio::placeholders::error));
    }
  }

  void handle_write(const boost::system::error_code& error)//第一个消息单独处理，剩下的才更好操作
  {
    if (!error)
    {
      write_msgs_.pop_front();//刚才处理完一个数据 所以要pop一个
      if (!write_msgs_.empty())  
      {
        boost::asio::async_write(socket_,
            boost::asio::buffer(write_msgs_.front().data(),
              write_msgs_.front().length()),
            boost::bind(&chat_client::handle_write, this,
              boost::asio::placeholders::error)); //循环处理剩余的消息
      }
    }
    else
    {
      do_close();
    }
  }

  void do_close()
  {
    socket_.close();
  }

private:
  boost::asio::io_service& io_service_;
  tcp::socket socket_;
  chat_message read_msg_;
  chat_message_queue write_msgs_;
};

int main(int argc, char* argv[])
{
  try
  {
    if (argc != 3)
    {
      std::cerr << "Usage: chat_client <host> <port>\n";
      return 1;
    }

    boost::asio::io_service io_service;

    tcp::resolver resolver(io_service);
    tcp::resolver::query query(argv[1], argv[2]); //输入ip（或域名）和端口号
    tcp::resolver::iterator iterator = resolver.resolve(query);

    chat_client c(io_service, iterator);

    boost::thread t(boost::bind(&boost::asio::io_service::run, &io_service));

    char line[chat_message::max_body_length + 1];
    while (std::cin.getline(line, chat_message::max_body_length + 1))
    {
      using namespace std; // For strlen and memcpy.
      chat_message msg;
      msg.body_length(strlen(line));
      memcpy(msg.body(), line, msg.body_length());
      msg.encode_header();
      c.write(msg);
    }

    c.close();
    t.join();
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}

聊天服务器端chat_server.cpp

//
// chat_server.cpp
// ~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2013 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)
//
//服务器端程序，首先开启一个chat_server，用来初始话io_service和chat_room;  服务器每次仅仅开启一个chat_room，chat_room的作用是 1//.保存用户信息  2.实现用户的join和leave  3.保存从每个client接收到的信息  4.将接收到的消息挂到每个clientwrite_msgs队尾
//每连接上一个client（socket）就开启一个新的chat_session 并增加唯一的chat_room   chat_session中实现分别对每个client的异步读写//操作

#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; //后面须要重载
};

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);
  }


//将从某个client收到的消息挂到 每个client的write_msgs队尾 详细见chat_participant::deliver

  void deliver(const chat_message& msg)

  {
    recent_msgs_.push_back(msg);
    while (recent_msgs_.size() > max_recent_msgs)
      recent_msgs_.pop_front(); //room中保存的消息数有限

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

private:
  std::set<chat_participant_ptr> participants_;//用set来保存用户信息
  enum { max_recent_msgs = 100 };
  chat_message_queue recent_msgs_;//用来保存从某个client接收到的信息
};

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

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()//每生成一个新的chat_session都会调用
  {
    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)); //异步读client发来的消息
  }

  void deliver(const chat_message& msg)
  {
    bool write_in_progress = !write_msgs_.empty();
    write_msgs_.push_back(msg); //把room中保存的消息挂到write_msgs队尾
    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::system::error_code& 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::system::error_code& 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::system::error_code& 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)); //服务器端将收到的消息送给全部的client（广播的方式）
      }
    }
    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) //全局仅仅有一个io_service和一个acceptor
  {
    start_accept();
  }

  void start_accept()
  {
    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::system::error_code& error)
  {
    if (!error)
    {
      session->start();
    }

    start_accept(); //每连接上一个socket都会调用
  }

private:
  boost::asio::io_service& io_service_;
  tcp::acceptor acceptor_;
  chat_room room_; //chat_room中没有重载构造函数 所以会直接调用默认构造函数
};

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 (std::exception& e)
  {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}