Linux的udp报文解析

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

#define BUFLEN 512
#define PORT 8888

void die(char *s) {
    perror(s);
    exit(1);
}

int main(void) {
    struct sockaddr_in si_me, si_other;
    int s, slen = sizeof(si_other);
    char buf[BUFLEN];

    if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
        die("socket");
    }

    memset((char *)&si_me, 0, sizeof(si_me));
    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(PORT);
    si_me.sin_addr.s_addr = htonl(INADDR_ANY);

    if (bind(s, (struct sockaddr*)&si_me, sizeof(si_me)) == -1) {
        die("bind");
    }

    while (1) {
        printf("Waiting for data...\n");
        memset(buf, 0, BUFLEN);
        if (recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *)&si_other, &slen) == -1) {
            die("recvfrom()");
        }

        // 解析UDP头部
        struct udphdr *udp_header = (struct udphdr *)buf;
        printf("Received packet from %s:%d\n", inet_ntoa(si_other.sin_addr), ntohs(udp_header->source));
        printf("Destination port: %d\n", ntohs(udp_header->dest));
        printf("UDP Length: %d\n", ntohs(udp_header->len));
        printf("UDP Checksum: %d\n", ntohs(udp_header->check));

        // 处理数据部分
        char *data = buf + sizeof(struct udphdr);
        printf("Data: %s\n", data);
    }

    close(s);
    return 0;
}