【Linux】客户端 connect 断线重连

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。

一. 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 <unistd.h>
#include <cstring>#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netinet/in.h>enum class Status
{NEW,          // 初始连接状态RECONNECTING, // 正在重连CONNECTED,    // 连接成功DISCONNECTED, // 连接失败CLOSED        // 关闭连接
};static const int default_sockfd = -1;
static const int default_retry_interval = 1;
static const int default_retries = 5;class ClientConnection
{
public:ClientConnection(const std::string &serverip, uint16_t serverport): _sockfd(default_sockfd), _server_ip(serverip), _server_port(serverport), _status(Status::NEW), _retry_interval(default_retry_interval), _retries(default_retries){}~ClientConnection() {}Status ConnectionStatus() { return _status; }void Connect(){_sockfd = ::socket(AF_INET, SOCK_STREAM, 0);if (_sockfd < 0){std::cerr << "socket create error" << std::endl;exit(1);}struct sockaddr_in server;memset(&server, 0, sizeof(server));server.sin_family = AF_INET;server.sin_port = ::htons(_server_port);::inet_pton(AF_INET, _server_ip.c_str(), &server.sin_addr);int n = ::connect(_sockfd, (struct sockaddr *)&server, sizeof(server));if (n < 0){Disconnect();_status = Status::DISCONNECTED;return;}std::cout << "连接成功..." << std::endl;_status = Status::CONNECTED;}// 重连void Reconnect(){_status = Status::RECONNECTING;int cnt = 0;while (true){Connect();if (_status == Status::CONNECTED)break;cnt++;if (cnt > _retries){_status = Status::CLOSED;std::cout << "重连失败, 请检查你的网络..." << std::endl;break;}std::cout << "断线重连中, 重连次数: " << cnt << std::endl;sleep(_retry_interval);}}// 连接失败时: 关闭_sockfdvoid Disconnect(){if (_sockfd != default_sockfd){::close(_sockfd);_status = Status::CLOSED;_sockfd = default_sockfd;}}// 连接成功时: 进行通信void Process(){while (true){std::string message = "hello server";ssize_t n = send(_sockfd, message.c_str(), message.size(), 0);if (n > 0){char buffer[1024];int m = ::recv(_sockfd, buffer, sizeof(buffer) - 1, 0);if (m > 0){buffer[m] = 0;std::cout << "server echo# " << buffer << std::endl;}else if (m == 0){_status = Status::DISCONNECTED;std::cout << "服务器端掉线..." << std::endl;break;}else {std::cerr << "recv error" << std::endl;_status = Status::CLOSED;break;}}else{std::cerr << "send error" << std::endl;_status = Status::CLOSED;break;}sleep(1);}}private:int _sockfd;std::string _server_ip;uint16_t _server_port;Status _status;      // 连接状态int _retry_interval; // 重连的时间间隔int _retries;        // 重连的次数
};class TcpClient
{
public:TcpClient(const std::string &serverip, uint16_t serverport): _conn(serverip, serverport){}~TcpClient() {}void Execute(){while (true){switch (_conn.ConnectionStatus()){case Status::NEW:_conn.Connect(); // 连接到来时: 进行连接break;case Status::CONNECTED:_conn.Process(); // 连接成功时: 进行通信break;case Status::DISCONNECTED:_conn.Reconnect(); // 连接失败时: 进行重连break;case Status::CLOSED:_conn.Disconnect(); // 连接关闭时: 关闭_sockfdreturn;default:// Do Nothingbreak;}}}private:ClientConnection _conn;
};void Usage(std::string process)
{std::cout << "Usage: " << process << " server_ip server_port" << std::endl;
}// ./tcp_client server_ip server_port
int main(int argc, char *argv[])
{if (argc != 3){Usage(argv[0]);exit(0);}std::string server_ip = argv[1];uint16_t server_port = std::stoi(argv[2]);TcpClient client(server_ip, server_port);client.Execute();return 0;
}

二. TcpServer.cc

#include <iostream>
#include <string>
#include <cerrno>
#include <cstring>
#include <cstdlib>
#include <memory>
#include <unistd.h>#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>enum
{Usage_Err = 1,Socket_Err,Bind_Err,Listen_Err
};const static int default_backlog = 6;class TcpServer
{
public:TcpServer(uint16_t port): _port(port), _isrunning(false){}~TcpServer() {}// 都是固定套路void Init(){// 1. 创建socket, file fd, 本质是文件_listensock = socket(AF_INET, SOCK_STREAM, 0);if (_listensock < 0){exit(0);}int opt = 1;setsockopt(_listensock, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt));// 2. 填充本地网络信息并bindstruct sockaddr_in local;memset(&local, 0, sizeof(local));local.sin_family = AF_INET;local.sin_port = htons(_port);local.sin_addr.s_addr = htonl(INADDR_ANY);// 2.1 bindif (bind(_listensock, (struct sockaddr *)&local, sizeof(local)) != 0){exit(Bind_Err);}// 3. 设置socket为监听状态，tcp特有的if (listen(_listensock, default_backlog) != 0){exit(Listen_Err);}}void ProcessConnection(int sockfd, struct sockaddr_in &peer){uint16_t clientport = ntohs(peer.sin_port);std::string clientip = inet_ntoa(peer.sin_addr);std::string prefix = clientip + ":" + std::to_string(clientport);std::cout << "get a new connection, info is : " << prefix << std::endl;while (true){char inbuffer[1024];ssize_t s = ::read(sockfd, inbuffer, sizeof(inbuffer) - 1);if (s > 0){inbuffer[s] = 0;std::cout << prefix << "# " << inbuffer << std::endl;std::string echo = inbuffer;echo += "[tcp server echo message]";write(sockfd, echo.c_str(), echo.size());}else{std::cout << prefix << " client quit" << std::endl;break;}}}void Start(){_isrunning = true;while (_isrunning){// 4. 获取连接struct sockaddr_in peer;socklen_t len = sizeof(peer);int sockfd = accept(_listensock, (struct sockaddr *)&peer, &len);if (sockfd < 0){continue;}ProcessConnection(sockfd, peer);}}private:uint16_t _port;int _listensock;bool _isrunning;
};using namespace std;void Usage(std::string proc)
{std::cout << "Usage : \n\t" << proc << " local_port\n"<< std::endl;
}// ./tcp_server 8888
int main(int argc, char *argv[])
{if (argc != 2){Usage(argv[0]);return Usage_Err;}uint16_t port = stoi(argv[1]);std::unique_ptr<TcpServer> tsvr = make_unique<TcpServer>(port);tsvr->Init();tsvr->Start();return 0;
}

三. 运行效果