c语言 实现正向代理

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

#define BUFFER_SIZE 1024

void error(const char *msg) {
    perror(msg);
    exit(1);
}

void forward_data(int client_socket, const char *target_address, int target_port) {
    struct sockaddr_in target_addr;
    int target_socket, n;
    char buffer[BUFFER_SIZE];

    // 创建与目标服务器的套接字
    if ((target_socket = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        error("Error opening target socket");

    memset(&target_addr, 0, sizeof(target_addr));
    target_addr.sin_family = AF_INET;
    target_addr.sin_port = htons(target_port);

    if (inet_pton(AF_INET, target_address, &target_addr.sin_addr) <= 0)
        error("Invalid target address");

    // 连接到目标服务器
    if (connect(target_socket, (struct sockaddr*)&target_addr, sizeof(target_addr)) < 0)
        error("Error connecting to target server");

    // 从客户端读取数据并将其转发到目标服务器
    while ((n = read(client_socket, buffer, sizeof(buffer))) > 0) {
        write(target_socket, buffer, n);
    }

    // 从目标服务器读取数据并将其转发到客户端
    while ((n = read(target_socket, buffer, sizeof(buffer))) > 0) {
        write(client_socket, buffer, n);
    }

    // 关闭与目标服务器的连接
    close(target_socket);
}

void proxy(int port, const char *target_address, int target_port) {
    struct sockaddr_in proxy_addr, client_addr;
    int proxy_socket, client_socket, client_addr_len;

    // 创建代理服务器套接字
    if ((proxy_socket = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        error("Error opening proxy socket");

    memset(&proxy_addr, 0, sizeof(proxy_addr));
    proxy_addr.sin_family = AF_INET;
    proxy_addr.sin_addr.s_addr = INADDR_ANY;
    proxy_addr.sin_port = htons(port);

    // 将代理服务器绑定到指定端口
    if (bind(proxy_socket, (struct sockaddr*)&proxy_addr, sizeof(proxy_addr)) < 0)
        error("Error binding proxy socket");

    // 开始监听客户端连接
    listen(proxy_socket, 5);

    printf("Proxy server is running on port %d\n", port);

    while (1) {
        // 接受客户端连接
        client_addr_len = sizeof(client_addr);
        client_socket = accept(proxy_socket, (struct sockaddr*)&client_addr, (socklen_t*)&client_addr_len);
        if (client_socket < 0)
            error("Error accepting client connection");

        printf("Accepted connection from %s:%d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

        // 创建子进程处理代理
        if (fork() == 0) {
            close(proxy_socket); // 子进程不需要监听代理套接字
            forward_data(client_socket, target_address, target_port);
            close(client_socket);
            exit(0);
        } else {
            close(client_socket); // 父进程不需要客户端套接字
        }
    }

    // 关闭代理服务器套接字
    close(proxy_socket);
}

int main(int argc, char *argv[]) {
    if (argc != 4) {
        fprintf(stderr, "Usage: %s <port> <target_address> <target_port>\n", argv[0]);
        exit(1);
    }

    int port = atoi(argv[1]);
    const char *target_address = argv[2];
    int target_port = atoi(argv[3]);

    proxy(port, target_address, target_port);

    return 0;
}

这个正向代理服务器会监听指定的端口，当有客户端连接时，它会创建一个子进程来处理代理。代理将客户端的请求转发到指定的目标服务器，并将目标服务器的响应返回给客户端。请注意，这只是一个基本的例子，可能需要根据你的实际需求进行修改和改进。