介绍

本文将通过一个简单的例子，介绍如何使用C++实现一个基本的TCP服务器和客户端。这个例子展示了如何创建服务器端接收客户端的连接，如何处理接收到的数据，并如何将数据发送回客户端。

我们会分两部分来介绍：

1. TCP服务器的实现：包括如何创建服务器、监听端口、接收客户端请求等。
2. TCP客户端的实现：客户端如何连接到服务器、发送数据并接收服务器返回的数据。

准备工作

首先，确保你的开发环境中已经安装了C++编译器（如GCC或Clang）以及支持的标准库。在Linux或类Unix系统上进行开发是最常见的，下面的代码也适用于这种环境。

1. TCP服务器实现

代码结构

首先，来看下TCP服务器的代码实现：

#include <arpa/inet.h>
#include <cstring>
#include <sys/socket.h>
#include <unistd.h>
#include <iostream>
#include <thread>

#define SERVER_PORT 12345
#define BUFFER_SIZE 1024

class TcpServer {
public:
    TcpServer(int port);
    ~TcpServer();
    void Start();
    void Stop();

private:
    void ListenThreadFunc();
    void ReceiveThreadFunc(int clientSocket);
    void CloseListenSocket();
    void CloseDataSocket();

    int mListenSocket;
    int mDataSocket;
    int mPort;
    std::unique_ptr<std::thread> mListenThread;
    bool mRunning;
};

TcpServer::TcpServer(int port) : mListenSocket(-1), mDataSocket(-1), mPort(port), mListenThread(nullptr), mRunning(false) {}

TcpServer::~TcpServer() {
    Stop();
}

void TcpServer::Start() {
    if (mRunning) {
        std::cerr << "Server is already running!" << std::endl;
        return;
    }

    mRunning = true;

    mListenSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (mListenSocket == -1) {
        std::cerr << "Failed to create listen socket!" << std::endl;
        return;
    }

    sockaddr_in serverAddr{};
    memset(&serverAddr, 0, sizeof(serverAddr));
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(mPort);
    serverAddr.sin_addr.s_addr = INADDR_ANY;

    if (bind(mListenSocket, reinterpret_cast<const sockaddr*>(&serverAddr), sizeof(serverAddr)) == -1) {
        std::cerr << "Failed to bind socket!" << std::endl;
        CloseListenSocket();
        return;
    }

    if (listen(mListenSocket, 5) == -1) {
        std::cerr << "Failed to listen on socket!" << std::endl;
        CloseListenSocket();
        return;
    }

    mListenThread = std::make_unique<std::thread>([this] { ListenThreadFunc(); });
}

void TcpServer::Stop() {
    if (!mRunning) return;

    mRunning = false;
    CloseListenSocket();
    CloseDataSocket();

    if (mListenThread && mListenThread->joinable()) {
        mListenThread->join();
    }
}

void TcpServer::ListenThreadFunc() {
    while (mRunning) {
        sockaddr_in clientAddr{};
        socklen_t len = sizeof(clientAddr);

        int clientSocket = accept(mListenSocket, reinterpret_cast<sockaddr*>(&clientAddr), &len);
        if (clientSocket == -1) {
            std::cerr << "Accept failed!" << std::endl;
            continue;
        }

        std::cout << "Client connected!" << std::endl;

        std::thread receiveThread([this, clientSocket] { ReceiveThreadFunc(clientSocket); });
        receiveThread.detach();
    }
}

void TcpServer::ReceiveThreadFunc(int clientSocket) {
    char buffer[BUFFER_SIZE];
    while (mRunning) {
        memset(buffer, 0, BUFFER_SIZE);
        int res = recv(clientSocket, buffer, sizeof(buffer) - 1, 0);
        if (res <= 0) {
            std::cerr << "Receive failed or client disconnected!" << std::endl;
            break;
        }

        std::cout << "Received from client: " << buffer << std::endl;
        send(clientSocket, "Message received", 17, 0);  // Send acknowledgment back
    }

    CloseDataSocket();
}

void TcpServer::CloseListenSocket() {
    if (mListenSocket != -1) {
        close(mListenSocket);
        mListenSocket = -1;
    }
}

void TcpServer::CloseDataSocket() {
    if (mDataSocket != -1) {
        close(mDataSocket);
        mDataSocket = -1;
    }
}

int main() {
    TcpServer server(SERVER_PORT);
    server.Start();

    std::this_thread::sleep_for(std::chrono::minutes(10)); // Server will run for 10 minutes
    server.Stop();

    return 0;
}

解释

• TcpServer 类：定义了一个 TcpServer 类来处理服务器的启动、停止以及接收客户端请求。
• Start() 方法：创建一个监听套接字，绑定端口并开始监听。
• ListenThreadFunc() 方法：负责监听来自客户端的连接请求。
• ReceiveThreadFunc() 方法：每个客户端连接都会创建一个新的线程来处理数据接收。

2. TCP客户端实现

代码结构

接下来是客户端的实现。客户端需要连接到服务器，发送请求并接收响应。

#include <iostream>
#include <string>
#include <unistd.h>
#include <arpa/inet.h>
#include <cstring>
#include <sys/socket.h>

#define SERVER_PORT 12345
#define SERVER_IP "127.0.0.1"
#define BUFFER_SIZE 1024

int main() {
    int clientSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (clientSocket == -1) {
        std::cerr << "Create socket failed!" << std::endl;
        return -1;
    }

    sockaddr_in serverAddr{};
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(SERVER_PORT);
    serverAddr.sin_addr.s_addr = inet_addr(SERVER_IP);

    if (connect(clientSocket, reinterpret_cast<sockaddr*>(&serverAddr), sizeof(serverAddr)) == -1) {
        std::cerr << "Connect to server failed!" << std::endl;
        close(clientSocket);
        return -1;
    }

    std::cout << "Connected to server!" << std::endl;

    // Send message
    std::string message = "Hello from client!";
    send(clientSocket, message.c_str(), message.size(), 0);

    // Receive response
    char buffer[BUFFER_SIZE];
    ssize_t receivedBytes = recv(clientSocket, buffer, sizeof(buffer) - 1, 0);
    if (receivedBytes == -1) {
        std::cerr << "Receive failed!" << std::endl;
    } else if (receivedBytes == 0) {
        std::cerr << "Server closed connection!" << std::endl;
    } else {
        buffer[receivedBytes] = '\0';
        std::cout << "Received from server: " << buffer << std::endl;
    }

    close(clientSocket);
    return 0;
}

解释

• TcpClient：客户端通过 connect() 与服务器建立连接，使用 send() 发送数据，并通过 recv() 接收服务器的响应。

3. 测试

1.编译：

• 编译服务器：

g++ TcpServer.cpp -o TcpServer -std=c++17 -lpthread

• 编译客户端

g++ TcpClient.cpp -o TcpClient -std=c++17

2.运行

• 启动服务器：

./TcpServer

• 启动客户端

./TcpClient

结语

通过这篇文章，我们实现了一个简单的 TCP 服务器和客户端示例，学习了如何使用 C++ 来进行网络编程。在实际项目中，你可以根据需求进一步扩展这些功能，比如加入多线程处理、客户端消息队列、认证机制等。