用c语言写一个ntp服务端的代码

以下是一个基本的NTP服务器端代码，它使用C语言编写：

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

#define PORT 123
#define NTP_TIMESTAMP_DELTA 2208988800ull

typedef struct {
    uint8_t li_vn_mode;
    uint8_t stratum;
    uint8_t poll;
    uint8_t precision;
    uint32_t rootDelay;
    uint32_t rootDispersion;
    uint32_t refId;
    uint32_t refTm_s;
    uint32_t refTm_f;
    uint32_t origTm_s;
    uint32_t origTm_f;
    uint32_t rxTm_s;
    uint32_t rxTm_f;
    uint32_t txTm_s;
    uint32_t txTm_f;
} ntp_packet;

int main(int argc, char *argv[]) {
    int sockfd, n;
    struct sockaddr_in servaddr, cliaddr;
    socklen_t len;
    char buffer[1024];
    time_t rawtime;
    ntp_packet packet;

    sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (sockfd < 0) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }

    memset(&servaddr, 0, sizeof(servaddr));
    memset(&cliaddr, 0, sizeof(cliaddr));

    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = INADDR_ANY;
    servaddr.sin_port = htons(PORT);

    if (bind(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    while (1) {
        len = sizeof(cliaddr);
        n = recvfrom(sockfd, buffer, sizeof(buffer), MSG_WAITALL,
                     (struct sockaddr *)&cliaddr, &len);
        if (n < 0) {
            perror("recvfrom failed");
            continue;
        }

        memset(&packet, 0, sizeof(packet));
        packet.li_vn_mode = (0x3 << 6) | (0x4 << 3) | 0x3;
        packet.stratum = 0;
        packet.poll = 4;
        packet.precision = -20;

        packet.txTm_s = htonl((uint32_t)(time(NULL) + NTP_TIMESTAMP_DELTA));
        packet.txTm_f = htonl(0x12345678);

        sendto(sockfd, &packet, sizeof(packet), MSG_CONFIRM,
               (const struct sockaddr *)&cliaddr, len);
    }

    return 0;
}

当客户端向服务器发送NTP请求时，服务器将返回一个包含当前时间戳的NTP响应。在此示例中，服务器使用系统时间来生成时间戳。请注意，此代码仅用于演示目的，实际的NTP服务器需要更多的逻辑来确保时间戳的准确性。