Linux之通过NTP协议实现服务器时间同步的源码

Linux下通过NTP协议实现服务器时间同步（C实现）

  (2009-12-09 20:59:41)

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标签：  ntp   linux   时间同步   杂谈

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

#define   int8           char
#define   uint8         unsigned char
#define   uint32       unsigned int
#define   ulong32     unsigned long
#define   long32       long
#define   int32         int
#define   long64       long long

#define   debug

//3600s*24h*(365days*70years+17days)
#define   From00to70 0x83aa7e80U

#define   NTPSVR1   "132.163.4.102"               //USA
#define   NTPSVR2   "132.163.135.132"           //USA
#define   NTPSVR3   "192.53.103.103"             //Germany

#define   NTPPORT   123
typedef struct NTPPACKET
{
   uint8         li_vn_mode;
   uint8         stratum;
   uint8         poll;
   uint8         precision;
   ulong32     root_delay;
   ulong32     root_dispersion;
   int8           ref_id[4];
   ulong32     reftimestamphigh;
   ulong32     reftimestamplow;
   ulong32     oritimestamphigh;
   ulong32     oritimestamplow;
   ulong32     recvtimestamphigh;
   ulong32     recvtimestamplow;
   ulong32     trantimestamphigh;   
   ulong32     trantimestamplow;
}NTPPacket;

NTPPacket   ntppack,newpack;

//定义为long64,解决32位数的符号位问题
long64     firsttimestamp,finaltimestamp;
long64     diftime,delaytime;

void NTP_Init()
{
   bzero(&ntppack,sizeof(ntppack));
   ntppack.li_vn_mode=0x1b;//0|(3<<2)|(3<<5);
   //获取初始时间戳T1
   firsttimestamp="From00to70"+time(NULL);//-8*3600;
   ntppack.oritimestamphigh=htonl(firsttimestamp);
}
int main()
{

//   ulong32 clienttime;
//   ulong32 diftime,firsttimestamp,finaltimestamp;
   fd_set   inset1;
   int32   sockfd;
   struct tim tv,tv1;
   struct timezone tz;
   struct sockaddr_in addr;
// printf("%d,%d,%d\n",&ntppack.li_vn_mode,&ntppack.stratum,&ntppack.poll);
// printf("%d   %ld\n",sizeof(NTPPacket),sizeof(ntppack));
 
//   printf("%ld\n",time(NULL));
 
   if((sockfd=socket(AF_INET,SOCK_DGRAM,0))<0)
       {
           perror("create socket error!\n");
           exit(1);
       }
 
   addr.sin_family=AF_INET;     //IPV4协议
   addr.sin_port =htons(NTPPORT);     //NTP专用的123端口
   addr.sin_addr.s_addr=inet_addr(NTPSVR1);     //校时服务器
   bzero(&(addr.sin_zero),8);     //清零
 
   //wait 5s
   tv.tv_sec=10;       //select等待时间为10S
   tv.tv_usec=0;
 
   FD_ZERO(&inset1);
   FD_SET(sockfd,&inset1);
 
   NTP_Init();
   //发送数据请求包
   sendto(sockfd,&ntppack,sizeof(ntppack),0,(struct sockaddr *)&addr,sizeof(struct sockaddr));
   //select巡视
   if(select(sockfd+1,&inset1,NULL,NULL,&tv)<0)
   {
       perror("select error!\n");
       exit(1);
   }
   else
   {
   //printf("OK\n");
       if(FD_ISSET(sockfd,&inset1))
       {
   // printf("OK\n");
         if(recv(sockfd,&newpack,sizeof(newpack),0)<0)               //接收数据在newpack中。
         {
           perror("recv error!\n");
           exit(1);
         }
       }
   }
   //到达客户机时间戳T4
   finaltimestamp=time(NULL)+From00to70;//-8*3600;
 
   //将网络上传送的大端数据改为小端形式。
  newpack.root_delay= ntohl(newpack.root_delay);
  newpack.root_dispersion= ntohl(newpack.root_dispersion);
  newpack.reftimestamphigh=ntohl(newpack.reftimestamphigh);
  newpack.reftimestamplow= ntohl(newpack.reftimestamplow);
  newpack.oritimestamphigh= ntohl(newpack.oritimestamphigh);
  newpack.oritimestamplow= ntohl(newpack.oritimestamplow);
  newpack.recvtimestamphigh= ntohl(newpack.recvtimestamphigh);
  newpack.recvtimestamplow= ntohl(newpack.recvtimestamplow);
  newpack.trantimestamphigh= ntohl(newpack.trantimestamphigh);
  newpack.trantimestamplow= ntohl(newpack.trantimestamplow);
 
  //求出客户机跟服务器的时间差=((T2-T1)+(T3-T4))/2
  diftime=((newpack.recvtimestamphigh-firsttimestamp)+(newpack.trantimestamphigh-finaltimestamp))>>1;
  //求出延时
  delaytime=((newpack.recvtimestamphigh-firsttimestamp)-(newpack.trantimestamphigh-finaltimestamp))>>1;
  //diftime=(5-9)>>1;

  //求出真正时间的时间戳
  tv1.tv_sec=time(NULL)+diftime+delaytime;
  tv1.tv_usec=0;
  //tz.

  #ifdef debug
   printf("\n\ndebug information ...\n\n");
   printf("time(NULL) is %ld\n",time(NULL));
   printf("different time is %ld\n",diftime);
   printf("delaytime is %ld\n",delaytime);
   printf("time(NULL)+diftime+delaytime=%ld\n",time(NULL)+diftime+delaytime);
   printf("tv1.tv_sec is %ld\n\n", tv1.tv_sec);
  #endif
 
   settimeofday(&tv1,NULL);
//diftime=diftime-From00to70;

  #ifdef debug
   //printf("different time is %ld\n",diftime);
   printf("delay   time is %ld\n",delaytime);
   //printf("firsttimestamp is %x\n",time(NULL));
   printf("newpack.tran is %ld\n",newpack.trantimestamphigh);
   printf("newpack.recv is %ld\n",newpack.recvtimestamphigh);
   printf("firsttimestamp is %ld\n",firsttimestamp);
   printf("finaltimestamp is %ld\n",finaltimestamp);
   printf("newpack.recv-firsttimestamp is %ld\n",newpack.recvtimestamphigh-firsttimestamp);
   printf("newpack.tran-finaltimestamp is %ld\n",newpack.trantimestamphigh-finaltimestamp);
   printf("(recv-first)+(ftran-final) is %ld\n",(newpack.recvtimestamphigh-firsttimestamp)+(newpack.trantimestamphigh-finaltimestamp));
   printf("((recv-first)+(ftran-final))>>1 is %ld\n",((newpack.recvtimestamphigh-firsttimestamp)+(newpack.trantimestamphigh-finaltimestamp))>>1);
   printf("different time is %ld\n\n",diftime);
   printf("sizeof(long long)   is:%d\n",sizeof(long long));
   printf("Current time is...\n");
   system("date");
  #endif
}