用linux c写dns报文查询代码

下面是一个简单的 DNS 查询代码，使用 C 语言在 Linux 上编写：

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

#define DNS_QUERY_PORT 53
#define DNS_SERVER_IP "8.8.8.8"
#define DNS_QUERY_NAME "www.google.com"

struct DNS_HEADER
{
    unsigned short id;
    unsigned char rd :1;
    unsigned char tc :1;
    unsigned char aa :1;
    unsigned char opcode :4;
    unsigned char qr :1;

    unsigned char rcode :4;
    unsigned char cd :1;
    unsigned char ad :1;
    unsigned char z :1;
    unsigned char ra :1;

    unsigned short q_count;
    unsigned short ans_count;
    unsigned short auth_count;
    unsigned short add_count;
};

struct QUESTION
{
    unsigned short qtype;
    unsigned short qclass;
};

int main(int argc, char *argv[])
{
    int sockfd;
    struct sockaddr_in serv_addr;
    char send_buf[1024];
    char recv_buf[1024];
    int send_len;
    int recv_len;

    // 创建套接字
    if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
    {
        perror("socket error");
        exit(EXIT_FAILURE);
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(DNS_QUERY_PORT);
    serv_addr.sin_addr.s_addr = inet_addr(DNS_SERVER_IP);

    struct DNS_HEADER *dns = (struct DNS_HEADER *)send_buf;
    struct QUESTION *qinfo = (struct QUESTION *)(send_buf + sizeof(struct DNS_HEADER));

    dns->id = (unsigned short)htons(getpid());
    dns->qr = 0;
    dns->opcode = 0;
    dns->aa = 0;
    dns->tc = 0;
    dns->rd = 1;
    dns->ra = 0;
    dns->z = 0;
    dns->ad = 0;
    dns->cd = 0;
    dns->rcode = 0;
    dns->q_count = htons(1);
    dns->ans_count = 0;
    dns->auth_count = 0;
    dns->add_count = 0;

    qinfo->qtype = htons(1);