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ntp客户端从授时中心更新本地时间

时间:2013-05-24 15:48来源:www.chengxuyuans.com 点击:

代码简介

从授时中心更新本地时间,简易的TCP/IP 应用层协议开发示例。

代码片段

#include <sys/socket.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/un.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <netinet/in.h>
#include <string.h>
#include <netdb.h>
 
#define NTP_PORT               123               /*NTP专 用端口号字符串*/
#define TIME_PORT              37               /* TIME/UDP端 口号 */
#define NTP_SERVER_IP       "202.120.2.101" /*上海授时中心 IP*/
#define NTP_PORT_STR        "123"          /*NTP专用端口号字 符串*/
#define NTPV1                "NTP/V1"      /*协议及其版本号*/
#define NTPV2                "NTP/V2"
#define NTPV3                "NTP/V3"
#define NTPV4                "NTP/V4"
#define TIME                "TIME/UDP"
 
#define NTP_PCK_LEN 48
#define LI 0
#define VN 3
#define MODE 3
#define STRATUM 0
#define POLL 4
#define PREC -6
 
#define JAN_1970 0x83aa7e80 /* 1900年~1970年之间的时间秒数 */
#define NTPFRAC(x)     (4294 * (x) + ((1981 * (x)) >> 11))
#define USEC(x)         (((x) >> 12) - 759 * ((((x) >> 10) + 32768) >> 16))

 
typedef struct _ntp_time
{
    unsigned int coarse;

    unsigned int fine;

} ntp_time;
 
struct ntp_packet
{
     unsigned char leap_ver_mode;

     unsigned char startum;

     char poll;

     char precision;

     int root_delay;
     int root_dispersion;
     int reference_identifier;

     ntp_time reference_timestamp;

     ntp_time originage_timestamp;

     ntp_time receive_timestamp;

     ntp_time transmit_timestamp;

};
 
char protocol[32];
/*构建NTP协议包*/
int construct_packet(char *packet)
{
     char version = 1;

     long tmp_wrd;

     int port;
     time_t timer;
     strcpy(protocol, NTPV4);
     /*判断协议版本*/
     if(!strcmp(protocol, NTPV1)||!strcmp(protocol, NTPV2)

           ||!strcmp(protocol, NTPV3)||!strcmp(protocol, NTPV4))

     {
          memset(packet, 0, NTP_PCK_LEN);
          port = NTP_PORT;
          /*设置16字节的包头*/
          version = protocol[5]-0x30;
          tmp_wrd = htonl((LI << 30)|(version << 27)

                |(MODE << 24)|(STRATUM << 16)|(POLL << 8)|(PREC & 0xff));

          memcpy(packet, &tmp_wrd, sizeof(tmp_wrd));

         
          /*设置Root Delay、Root Dispersion和Reference Indentifier */
          tmp_wrd = htonl(1<<16);

          memcpy(&packet[4], &tmp_wrd, sizeof(tmp_wrd));

          memcpy(&packet[8], &tmp_wrd, sizeof(tmp_wrd));

          /*设置Timestamp部分*/
          time(&timer);
          /*设置Transmit Timestamp coarse*/
          tmp_wrd = htonl(JAN_1970 + (long)timer);

          memcpy(&packet[40], &tmp_wrd, sizeof(tmp_wrd));

          /*设置Transmit Timestamp fine*/
          tmp_wrd = htonl((long)NTPFRAC(timer));

          memcpy(&packet[44], &tmp_wrd, sizeof(tmp_wrd));

          return NTP_PCK_LEN;

     }
     else if (!strcmp(protocol, TIME))/* "TIME/UDP" */

     {
          port = TIME_PORT;
          memset(packet, 0, 4);
          return 4;
     }
     return 0;
}
 
/*获取NTP时间*/
int get_ntp_time(int sk, struct addrinfo *addr, struct ntp_packet *ret_time)

{
     fd_set pending_data;
     struct timeval block_time;

     char data[NTP_PCK_LEN * 8];

     int packet_len, data_len = addr->ai_addrlen, count = 0, result, i, re;

 
     if (!(packet_len = construct_packet(data)))

     {
          return 0;

     }
     /*客户端给服务器端发送NTP协议数据包*/
     if ((result = sendto(sk, data,

             packet_len, 0, addr->ai_addr, data_len)) < 0)

     {
          perror("sendto");
          return 0;

     }
    
     /*调用select()函数,并设定超时时间为1s*/
     FD_ZERO(&pending_data);
     FD_SET(sk, &pending_data);

     block_time.tv_sec=10;
     block_time.tv_usec=0;
     if (select(sk + 1, &pending_data, NULL, NULL, &block_time) > 0)

     {
          /*接收服务器端的信息*/
          if ((count = recvfrom(sk, data,

                        NTP_PCK_LEN * 8, 0, addr->ai_addr, &data_len)) < 0)

          {
               perror("recvfrom");

               return 0;

          }
         
          if (protocol == TIME)

          {
               memcpy(&ret_time->transmit_timestamp, data, 4);

               return 1;

          }
          else if (count < NTP_PCK_LEN)

          {
               return 0;

          }
/* 设置接收NTP包的数据结构 */
          ret_time->leap_ver_mode = ntohl(data[0]);

          ret_time->startum = ntohl(data[1]);
          ret_time->poll = ntohl(data[2]);

          ret_time->precision = ntohl(data[3]);

          ret_time->root_delay = ntohl(*(int*)&(data[4]));

          ret_time->root_dispersion = ntohl(*(int*)&(data[8]));

         ret_time->reference_identifier = ntohl(*(int*)&(data[12]));

          ret_time->reference_timestamp.coarse = ntohl(*(int*)&(data[16]));

          ret_time->reference_timestamp.fine = ntohl(*(int*)&(data[20]));

          ret_time->originage_timestamp.coarse = ntohl(*(int*)&(data[24]));

          ret_time->originage_timestamp.fine = ntohl(*(int*)&(data[28]));

          ret_time->receive_timestamp.coarse = ntohl(*(int*)&(data[32]));

          ret_time->receive_timestamp.fine = ntohl(*(int*)&(data[36]));

          ret_time->transmit_timestamp.coarse = ntohl(*(int*)&(data[40]));

          ret_time->transmit_timestamp.fine = ntohl(*(int*)&(data[44]));

          return 1;

     } /* end of if select */

     return 0;

}
 
/* 修改本地时间 */
int set_local_time(struct ntp_packet * pnew_time_packet)

{
     struct timeval tv;

     tv.tv_sec = pnew_time_packet->transmit_timestamp.coarse - JAN_1970;

     tv.tv_usec = USEC(pnew_time_packet->transmit_timestamp.fine);

     return settimeofday(&tv, NULL);

}
 
int main()
{
     int sockfd, rc;

     struct addrinfo hints, *res = NULL;

     struct ntp_packet new_time_packet;

 
     memset(&hints, 0, sizeof(hints));

     hints.ai_family = AF_UNSPEC;
     hints.ai_socktype = SOCK_DGRAM;

     hints.ai_protocol = IPPROTO_UDP;
     /*调用getaddrinfo()函数,获取地址信息*/
     rc = getaddrinfo(NTP_SERVER_IP, NTP_PORT_STR, &hints, &res);

     if (rc != 0)
     {
          perror("getaddrinfo");
          return 1;
     }
     /* 创建套接字 */
     sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);

     if (sockfd <0 )
     {
          perror("socket");
          return 1;
     }         

/*调用取得NTP时间的函数*/
     if (get_ntp_time(sockfd, res, &new_time_packet))

     {
          /*调整本地时间*/
          if (!set_local_time(&new_time_packet))
          {
               printf("NTP client success!\n");

          }
     }    
     close(sockfd);
     return 0;

}

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