如何在Ubuntu上使用C++进行网络编程 - 问答

在Ubuntu上使用C++进行网络编程，你可以使用套接字（socket）API。以下是一个简单的例子，展示了如何创建一个TCP服务器和客户端。

1. 安装必要的库

首先，确保你已经安装了g++编译器和libssl-dev库（用于SSL/TLS支持，可选）。

sudo apt update
sudo apt install g++ libssl-dev

2. 创建TCP服务器

创建一个名为tcp_server.cpp的文件，并添加以下代码：

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    const char* hello = "Hello from server";

    // Creating socket file descriptor
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // Forcefully attaching socket to the port 8080
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(8080);

    // Bind the socket to the address
    if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // Listen for connections
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    // Accept a connection
    if ((new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen)) < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    // Read data from the client
    read(new_socket, buffer, 1024);
    std::cout << "Message from client: " << buffer << std::endl;

    // Send a response back to the client
    send(new_socket, hello, strlen(hello), 0);
    std::cout << "Hello message sent" << std::endl;

    // Close the socket
    close(new_socket);
    close(server_fd);

    return 0;
}

3. 创建TCP客户端

创建一个名为tcp_client.cpp的文件，并添加以下代码：

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

int main() {
    int sock = 0;
    struct sockaddr_in serv_addr;
    const char* hello = "Hello from client";
    char buffer[1024] = {0};

    // Create a socket
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        std::cout << "
 Socket creation error 
";
        return -1;
    }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(8080);

    // Convert IPv4 and IPv6 addresses from text to binary form
    if(inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        std::cout << "
Invalid address/ Address not supported 
";
        return -1;
    }

    // Connect to the server
    if (connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0) {
        std::cout << "
Connection Failed 
";
        return -1;
    }

    // Send a message to the server
    send(sock, hello, strlen(hello), 0);
    std::cout << "Hello message sent" << std::endl;

    // Read the response from the server
    read(sock, buffer, 1024);
    std::cout << "Message from server: " << buffer << std::endl;

    // Close the socket
    close(sock);

    return 0;
}

4. 编译和运行

编译服务器和客户端：

g++ -o tcp_server tcp_server.cpp
g++ -o tcp_client tcp_client.cpp

运行服务器：

./tcp_server

在另一个终端运行客户端：

./tcp_client

你应该会看到服务器和客户端之间的通信。

5. 使用SSL/TLS（可选）

如果你需要使用SSL/TLS进行加密通信，可以使用OpenSSL库。首先安装OpenSSL开发库：

sudo apt install libssl-dev

然后修改服务器和客户端的代码以使用SSL/TLS。

服务器端（使用SSL/TLS）

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

void init_openssl() {
    SSL_load_error_strings();
    OpenSSL_add_ssl_algorithms();
}

void cleanup_openssl() {
    EVP_cleanup();
}

SSL_CTX* create_context() {
    const SSL_METHOD* method;
    SSL_CTX* ctx;

    method = TLS_server_method();

    ctx = SSL_CTX_new(method);
    if (!ctx) {
        perror("Unable to create SSL context");
        ERR_print_errors_fp(stderr);
        exit(EXIT_FAILURE);
    }

    return ctx;
}

void configure_context(SSL_CTX* ctx) {
    SSL_CTX_set_ecdh_auto(ctx, 1);

    // Set the key and cert
    if (SSL_CTX_use_certificate_file(ctx, "server.crt", SSL_FILETYPE_PEM) <= 0) {
        ERR_print_errors_fp(stderr);
        exit(EXIT_FAILURE);
    }

    if (SSL_CTX_use_PrivateKey_file(ctx, "server.key", SSL_FILETYPE_PEM) <= 0 ) {
        ERR_print_errors_fp(stderr);
        exit(EXIT_FAILURE);
    }
}

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    const char* hello = "Hello from server";

    init_openssl();
    SSL_CTX* ctx = create_context();
    configure_context(ctx);

    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(8080);

    if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    if ((new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen)) < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    SSL* ssl;
    SSL_set_fd(ssl, new_socket);
    if (SSL_accept(ssl) <= 0) {
        ERR_print_errors_fp(stderr);
    } else {
        SSL_write(ssl, hello, strlen(hello));
        std::cout << "Hello message sent" << std::endl;
    }

    SSL_shutdown(ssl);
    SSL_free(ssl);
    close(new_socket);
    close(server_fd);
    SSL_CTX_free(ctx);
    cleanup_openssl();

    return 0;
}

客户端（使用SSL/TLS）

#include <iostream>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

void init_openssl() {
    SSL_load_error_strings();
    OpenSSL_add_ssl_algorithms();
}

void cleanup_openssl() {
    EVP_cleanup();
}

SSL_CTX* create_context() {
    const SSL_METHOD* method;
    SSL_CTX* ctx;

    method = TLS_client_method();

    ctx = SSL_CTX_new(method);
    if (!ctx) {
        perror("Unable to create SSL context");
        ERR_print_errors_fp(stderr);
        exit(EXIT_FAILURE);
    }

    return ctx;
}

void configure_context(SSL_CTX* ctx) {
    SSL_CTX_set_default_verify_paths(ctx);
}

int main() {
    int sock = 0;
    struct sockaddr_in serv_addr;
    const char* hello = "Hello from client";
    char buffer[1024] = {0};

    init_openssl();
    SSL_CTX* ctx = create_context();
    configure_context(ctx);

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        std::cout << "
 Socket creation error 
";
        return -1;
    }

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(8080);

    if(inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        std::cout << "
Invalid address/ Address not supported 
";
        return -1;
    }

    if (connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0) {
        std::cout << "
Connection Failed 
";
        return -1;
    }

    SSL* ssl;
    ssl = SSL_new(ctx);
    SSL_set_fd(ssl, sock);

    if (SSL_connect(ssl) <= 0) {
        ERR_print_errors_fp(stderr);
    } else {
        SSL_write(ssl, hello, strlen(hello));
        std::cout << "Hello message sent" << std::endl;
    }

    SSL_shutdown(ssl);
    SSL_free(ssl);
    close(sock);
    SSL_CTX_free(ctx);
    cleanup_openssl();

    return 0;
}

6. 生成SSL证书和密钥

你可以使用OpenSSL生成自签名证书和密钥：

openssl req -x509 -newkey rsa:4096 -keyout server.key -out server.crt -days 365 -nodes

按照提示输入相关信息。

7. 编译和运行（使用SSL/TLS）

编译服务器和客户端：

g++ -o tcp_server ssl_server.cpp -lssl -lcrypto
g++ -o tcp_client ssl_client.cpp -lssl -lcrypto

运行服务器：

./tcp_server

在另一个终端运行客户端：

./tcp_client

你应该会看到服务器和客户端之间的加密通信。

通过这些步骤，你可以在Ubuntu上使用C++进行基本的网络编程，并且可以选择性地使用SSL/TLS进行加密通信。

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