CPP网络编程-异步sever

代码：

// AsyncServer.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//#include <iostream>
#include<boost/asio.hpp>
#include"Session.h"int main()
{try {boost::asio::io_context ioc;using namespace std;Server s(ioc, 10086);ioc.run();}catch(std::exception& e) {std::cout << e.what() << std::endl;}
}

//Session.h
#pragma once
#include<iostream>
#include<boost/asio.hpp>using boost::asio::ip::tcp;
class Session
{
public:Session(boost::asio::io_context& ioc):_socket(ioc) {}tcp::socket& Socket() {return _socket;}void Start();private:void handle_read(const boost::system::error_code& error, size_t bytes_transferred);void handle_write(const boost::system::error_code& error);//异步发送，发送完tcp::socket _socket;enum { max_length = 1024 };char _data[max_length];
};//建立连接
class Server {
public:Server(boost::asio::io_context& ioc, short port);
private:void start_accept();void handle_accept(Session* new_session, const boost::system::error_code& error);boost::asio::io_context& _ioc;tcp::acceptor _acceptor;
};

//Session.cpp
#include "Session.h"
#include<iostream>
using namespace std;void Session::Start() {memset(_data, 0, max_length);//置0初始化_socket.async_read_some(boost::asio::buffer(_data, max_length),std::bind(&Session::handle_read, this,placeholders::_1, placeholders::_2));//_socket——>异步读，读到的数据放在_data中，当读完后，调用handle_read
}void Session::handle_read(const boost::system::error_code& error,size_t bytes_transferred ){if (!error) {cout << "server receive data is " << _data << endl;boost::asio::async_write(_socket, boost::asio::buffer(_data, bytes_transferred),std::bind(&Session::handle_write, this, placeholders::_1));}else {cout<<"read error"<<endl;delete this;}
}void Session::handle_write(const boost::system::error_code& error) {if (!error) {memset(_data,0, max_length);_socket.async_read_some(boost::asio::buffer(_data, max_length),std::bind(&Session::handle_read, this, placeholders::_1, placeholders::_2));}else {cout << "write error" << error.value()<<endl;delete this;}
}Server::Server(boost::asio::io_context& ioc, short port):_ioc(ioc),_acceptor(ioc,tcp::endpoint(tcp::v4(),port)) {cout << "server start,port:" <<port<< endl;start_accept();
}
void Server::start_accept() {/*先创建一个new_session，然后调用async_accept，当有新的连接时，会调用handle_accept，*/Session* new_session = new Session(_ioc);_acceptor.async_accept(new_session->Socket(),std::bind(&Server::handle_accept,this,new_session,placeholders::_1));
}
void Server::handle_accept(Session* new_session, const boost::system::error_code& error) {if (!error) {new_session->Start();}else {delete new_session;}start_accept();
}

Session.h

Session 类

Server 类

Session.cpp

void Session::Start() {memset(_data, 0, max_length);_socket.async_read_some(boost::asio::buffer(_data, max_length),std::bind(&Session::handle_read, this, placeholders::_1, placeholders::_2));
}

启动对当前socket的异步读取，等待客户端发送数据
async_read_some非阻塞读，只要有数据就触发回调，_data缓冲区，然后绑定回调函数handle_read

此函数只调用一次（在连接建立后），之后通过 handle_read → handle_write → 再次 async_read_some 形成循环。

void Session::handle_read(const boost::system::error_code& error, size_t bytes_transferred) {if (!error) {cout << "server receive data is " << _data << endl;boost::asio::async_write(_socket, boost::asio::buffer(_data, bytes_transferred),std::bind(&Session::handle_write, this, placeholders::_1));} else {cout << "read error" << endl;delete this;}
}

如果读取成功打印数据，使用async_write将数据完整回传给客户端，发送完调用handle_write

void Session::handle_write(const boost::system::error_code& error) {if (!error) {memset(_data, 0, max_length);_socket.async_read_some(boost::asio::buffer(_data, max_length),std::bind(&Session::handle_read, this, placeholders::_1, placeholders::_2));} else {cout << "write error" << error.value() << endl;delete this;}
}

• 写操作完成后的回调。
• 若成功：清空缓冲区，重新开始 async_read_some，等待下一条消息

Server::Server(boost::asio::io_context& ioc, short port): _ioc(ioc), _acceptor(ioc, tcp::endpoint(tcp::v4(), port)) {cout << "server start,port:" << port << endl;start_accept();
}

初始化 _acceptor，绑定到 IPv4

void Server::start_accept() {Session* new_session = new Session(_ioc);_acceptor.async_accept(new_session->Socket(),std::bind(&Server::handle_accept, this, new_session, placeholders::_1));
}

• 每次调用都 new 一个 Session；
• 将 Session 的 _socket 作为参数传给 async_accept；
• 设置回调为 handle_accept，并把 new_session 指针传进去

void Server::handle_accept(Session* new_session, const boost::system::error_code& error) {if (!error) {new_session->Start();  // 启动会话} else {delete new_session;    // 接受失败，清理}start_accept();  // 无论成功与否，继续监听下一个连接
}

• 如果接受连接成功 → 启动 Session::Start() 开始读取；
• 如果失败（如监听关闭）→ 删除刚创建的 Session

                     +------------------+|   Server启动     |+--------+---------+|v创建_acceptor，绑定端口10086|v调用 start_accept()|vnew Session(_ioc)     ← 堆上创建|v_acceptor.async_accept(socket, handle_accept)|| (等待客户端连接)↓[客户端连接到来]|v触发 handle_accept()|+-------+--------+| 是否出错？     |+-------+--------+|是 /        \ 否v          vdelete session   new_session->Start()|v_socket.async_read_some(...)|| (等待客户端发数据)↓[客户端发送数据]|v触发 handle_read(...)|v打印数据 → async_write(...)|| (等待发送完成)↓触发 handle_write(...)|v清空缓冲 → 再次 async_read_some(...)|(循环往复)