如何在C中获取发件人的UDP端口？

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

#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    int sockfd;
    struct sockaddr_in serv_addr, cli_addr;
    socklen_t cli_addr_size;
    char buf[BUF_SIZE];
    int n;

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

    sockfd = socket(PF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    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(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        perror("bind");
        exit(1);
    }

    while (1) {
        cli_addr_size = sizeof(cli_addr);
        n = recvfrom(sockfd, buf, BUF_SIZE, 0, (struct sockaddr *)&cli_addr, &cli_addr_size);
        if (n < 0) {
            perror("recvfrom");
            exit(1);
        }

        printf("Received %d bytes from %s:%d\n", n, inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port));
    }

    close(sockfd);

    return 0;
}