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falsewrite_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::delivervoid 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;}