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断线重连机制，它成为确保应用在网络不稳定情况下仍能持续提供服务的关键技术之一。本文旨在深入探讨TCP（传输控制协议）连接中的断线重连机制，解析其工作原理、设计原则、实现策略以及在实际应用中的挑战与解决方案。试着写一个客户端重连的代码，模拟并理解一些客户端行为，比如游戏客户端等。

断线重连代码

#include <iostream>
#include <string>
#include <memory>
#include <cstring>
#include <cstdlib>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>enum Status
{NEW,          // 新建状态，就是单纯的连接CONNECTING,   // 正在连接，仅仅方便查询 conn 状态CONNECTED,    // 连接或者重连成功DISCONNECTED, // 重连失败CLOSED        // 连接失败，经历重连，无法连接
};const static int defaultretryinterval = 1;  // 重试时间间隔
const static int defaultmaxretries = 5;     // 最大重试次数
const static int defaultsockfd = -1;        // 默认的sockfdclass ConnectClient
{
public:ConnectClient(std::string &serverip, uint16_t serverport)   : _serverip(serverip),_serverport(serverport),_sockfd(defaultsockfd),_retry_interval(defaultretryinterval),_max_retries(defaultmaxretries),_status(Status::NEW){}void Connect() // 建立连接{// 创建 流式socket_sockfd = ::socket(AF_INET, SOCK_STREAM, 0);if (_sockfd < 0){std::cout << "socket create fail..." << std::endl;exit(2);}// 连接struct sockaddr_in serveraddr;memset(&serveraddr, 0, sizeof(serveraddr));serveraddr.sin_family = AF_INET;serveraddr.sin_port = _serverport;serveraddr.sin_addr.s_addr = inet_addr(_serverip.c_str());int n = connect(_sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));if (n < 0) // 连接失败{Disconnect(); // 重置_sockfd_status = Status::DISCONNECTED;return;}// 连接成功_status = Status::CONNECTED;std::cout << "connect success..." << std::endl;}void Reconnect() // 重新连接{_status = Status::CONNECTING;int cnt = 1;while (true){Connect();if (_status == Status::CONNECTED){return;}std::cout << "重连次数: " << cnt << ", 最大上限: " << _max_retries << std::endl;cnt++;if (cnt > _max_retries)   //超过连接设置的最大次数，直接连接失败，关闭client{_status = Status::CLOSED;return;}sleep(defaultretryinterval);}}void process()  //客服端连接成功执行的业务{while (true){std::string str = "Hello world!";ssize_t n = ::send(_sockfd, str.c_str(), str.size(), 0);if (n > 0) // 发送成功{char buffer[1024]; // 接收bufferssize_t m = ::recv(_sockfd, buffer, sizeof(buffer) - 1, 0);if (m > 0) // 接收成功{buffer[m] = 0;std::cout << "server echo#" << buffer << std::endl;}else // 接收失败{_status = Status::DISCONNECTED; // 接受失败，说明连接断开了 ，设置状态，重新连接break;}}else // 发送失败{_status = Status::CLOSED; // 连接成功，但是发送失败，说明服务器异常，直接将Client关闭break;}}}void Disconnect()   //关闭Client{if (_sockfd > defaultsockfd){::close(_sockfd);_status = Status::CLOSED;_sockfd = defaultsockfd;}}Status GetStatus() // 获取当前状态{return _status;}~ConnectClient(){}private:int _sockfd;uint16_t _serverport;     // server port 端口号std::string _serverip;    // server ip 地址int _retry_interval;      // 重试时间间隔int _max_retries;         // 重试次数Status _status;           // 连接状态
};class TcpClinet
{
public:TcpClinet(std::string &serverip, uint16_t serverport): _connect(serverip, serverport){}void Excute()     // 执行client{while (true){switch (_connect.GetStatus()){case Status::NEW:          //如果状态是新创建，则连接_connect.Connect();break;case Status::CONNECTED:    //已经建立连接了_connect.process();    //进行通信break;case Status::DISCONNECTED:  //断开连接了_connect.Reconnect();   //进行重连break;case Status::CLOSED:        //关闭_connect.Disconnect();  //则关闭文件描述符return;default:break;}}}~TcpClinet(){}private:ConnectClient _connect;
};void Usage(std::string args)
{std::cout << "Usage:\n\t" << args << " serverip serverport" << std::endl;
}
// ./Tcp_Client serverip serverport
int main(int argc, char *argv[])
{if (argc != 3){Usage(argv[0]);exit(1);}std::string serverip = argv[1];int serverport = std::stoi(argv[2]);std::shared_ptr<TcpClinet> TcpClientptr = std::make_shared<TcpClinet>(serverip, serverport);TcpClientptr->Excute();return 0;
}

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