C 实现 镜子反射 服务器，将服务器反射的信息客户端的端口号，即：服务器将客户端的端口号反弹回去。同时客户端要获取自己 的端口号，并与服务器反射回来的对比看是否一致

服务器端实现：

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

#define BUF_SIZE 1024

void error_handling(char *message);

int main(int argc, char *argv[]) {
    int serv_sock;
    struct sockaddr_in serv_addr, clnt_addr;
    socklen_t clnt_addr_size;
    char message[BUF_SIZE];
    int str_len;

    if (argc != 2) {
        printf("Usage: %s <port>\n", argv[0]);
        exit(1);
    }

    serv_sock = socket(PF_INET, SOCK_DGRAM, 0);
    if (serv_sock == -1) {
        error_handling("socket() error");
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));

    if (bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1) {
        error_handling("bind() error");
    }

    while (1) {
        clnt_addr_size = sizeof(clnt_addr);
        str_len = recvfrom(serv_sock, message, BUF_SIZE, 0, (struct sockaddr*)&clnt_addr, &clnt_addr_size);
        if (str_len < 0) {
            error_handling("recvfrom() error");
        }
        printf("Received message: %s\n", message);

        // 将客户端的端口号反弹回去
        sendto(serv_sock, &clnt_addr.sin_port, sizeof(clnt_addr.sin_port), 0, (struct sockaddr*)&clnt_addr, clnt_addr_size);
    }

    close(serv_sock);
    return 0;
}

void error_handling(char *message) {
    perror(message);
    exit(1);
}

客户端实现：

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

void error_handling(char *message);

int main(int argc, char *argv[]) {
    int sock;
    struct sockaddr_in serv_addr;
    socklen_t serv_addr_size;
    char message[] = "Hello, server!";
    int str_len;
    int port;

    if (argc != 3) {
        printf("Usage: %s <IP> <port>\n", argv[0]);
        exit(1);
    }

    sock = socket(PF_INET, SOCK_DGRAM, 0);
    if (sock == -1) {
        error_handling("socket() error");
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_addr.sin_port = htons(atoi(argv[2]));

    // 发送消息到服务器
    str_len = sendto(sock, message, strlen(message), 0, (struct sockaddr*)&serv_addr, sizeof(serv_addr));
    if (str_len < 0) {
        error_handling("sendto() error");
    }

    // 接收服务器反弹回来的消息，即客户端的端口号
    serv_addr_size = sizeof(serv_addr);
    str_len = recvfrom(sock, &port, sizeof(port), 0, (struct sockaddr*)&serv_addr, &serv_addr_size);
    if (str_len < 0) {
        error_handling("recvfrom() error");
    }
    printf("My port: %d. Server port: %d.\n", ntohs(serv_addr.sin_port), ntohs(port));

    if (ntohs(serv_addr.sin_port) == ntohs(port)) {
        printf("Port numbers match!\n");
    } else {
        printf("Port numbers do not match!\n");
    }

    close(sock);
    return 0;
}

void error_handling(char *message) {
    perror(message);
    exit(1);
}