客户端会面临服务器崩溃的情况，我们可以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。
TcpClient.cc
- 采用状态机，实现一个简单的 tcp client 可以实现重连效果
#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>using namespace std;void Usage(const std::string &process)
{std::cout << "Usage: " << process << " server_ip server_port"
<< std::endl;
}enum class Status // C++11 强类型枚举
{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
};class ClientConnection
{
public:ClientConnection(uint16_t serverport, const std::string &serverip): _sockfd(-1),_serverport(serverport),_serverip(serverip),_retry_interval(1),_max_retries(5),_status(Status::NEW){}void Connect(){// 1. 创建 socket_sockfd = socket(AF_INET, SOCK_STREAM, 0);if (_sockfd < 0){cerr << "socket error" << endl;exit(1);}// 2. 要不要 bind？必须要有 Ip 和 Port, 需要 bind，但是不需要用户显示的 bind，client 系统随机端口// 发起连接的时候，client 会被 OS 自动进行本地绑定// 2. connectstruct sockaddr_in server;memset(&server, 0, sizeof(server));server.sin_family = AF_INET;server.sin_port = htons(_serverport);// p:process(进程), n(网络) -- 不太准确，但是好记忆inet_pton(AF_INET, _serverip.c_str(), &server.sin_addr);// 1. 字符串 ip->4 字节 IP 2. 网络序列int n = connect(_sockfd, (struct sockaddr *)&server,sizeof(server)); // 自动进行 bind 哦！if (n < 0){Disconnect(); // 恢复_sockfd 的默认值，是连接没有成功，不代表 sockfd 创建没有成功_status = Status::DISCONNECTED; // 没有连接成功return;}_status = Status::CONNECTED; // 连接成功}int SocketFd(){return _sockfd;}void Reconnect(){_status = Status::CONNECTING; // 正在重连int count = 0;while (count < _max_retries){Connect(); // 重连if (_status == Status::CONNECTED){return;}sleep(_retry_interval);count++;std::cout << "重连次数: " << count << ", 最大上限: " <<_max_retries << std::endl;}_status = Status::CLOSED; // 重连失败，可以关闭了}void Disconnect(){if (_sockfd != -1){close(_sockfd);_status = Status::CLOSED;_sockfd = -1;}}Status GetStatus(){return _status;}void Process(){// 简单的 IO 即可while (true){string inbuffer;cout << "Please Enter# ";getline(cin, inbuffer);if(inbuffer.empty()) continue;ssize_t n = write(_sockfd, inbuffer.c_str(),inbuffer.size());if (n > 0){char buffer[1024];ssize_t m = read(_sockfd, buffer, sizeof(buffer) -1);if (m > 0){buffer[m] = 0;cout << "echo messsge -> " << buffer << endl;}else if (m == 0) // 这里证明 server 端掉线了{_status = Status::DISCONNECTED;break;}else{std::cout << "read m : " << m << "errno: " <<errno << "errno string: " << strerror(errno) << std::endl;_status = Status::CLOSED;break;}}else{std::cout << "write n : " << n << "errno: " <<errno << "errno string: " << strerror(errno) << std::endl;_status = Status::CLOSED;break;}}}~ClientConnection(){Disconnect();}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 TcpClient
{
public:TcpClient(uint16_t serverport, const std::string &serverip) :_conn(serverport, serverip){}void Execute(){while (true){switch (_conn.GetStatus()){case Status::NEW:_conn.Connect();break;case Status::CONNECTED:std::cout << "连接成功, 开始进行通信." << std::endl;_conn.Process();break;case Status::DISCONNECTED:std::cout << "连接失败或者对方掉线，开始重连." << std::endl;_conn.Reconnect();break;case Status::CLOSED:_conn.Disconnect();std::cout << "重连失败, 退出." << std::endl;return; // 退出default:break;}}}~TcpClient(){}private:ClientConnection _conn; // 简单组合起来即可
};// class Tcp
// ./tcp_client serverip serverport
int main(int argc, char *argv[])
{if (argc != 3){Usage(argv[0]);return 1;}std::string serverip = argv[1];uint16_t serverport = stoi(argv[2]);TcpClient client(serverport, serverip);client.Execute();return 0;
}测试重连