linux下ntp实现

#include <sys/types.h> #include <sys/socket.h> #include <netdb.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <time.h> #define NTP_SERVER "clock.via.net" #define NTP_PORT 123 // //rfc1305 defined from 1900 so also 2208988800 (1900 - 1970 ) seconds left // //timeval.tv_sec + JAN_1970 = timestamp.coarse #define JAN_1970 0x83aa7e80 //timeval.tv_usec=>timestamp.fine #define NTPFRAC(x) (4294 * (x) + ((1981 * (x))>>11)) //timeval.tv_usec<=timestamp.fine #define USEC(x) (((x) >> 12) - 759 * ((((x) >> 10) + 32768) >> 16)) #define Data(i) ntohl(((unsigned int *)data)[i]) #define LI 0 #define VN 3 #define MODE 3 #define STRATUM 0 #define POLL 4 #define PREC -6 struct ntptime { unsigned int coarse; unsigned int fine; }; void send_packet(int fd) { unsigned int data[12]; struct timeval now; int ret; if (sizeof(data) != 48) { fprintf(stderr,"size error/n"); return; } memset((char*)data, 0, sizeof(data)); data[0] = htonl((LI << 30) | (VN << 27) | (MODE << 24) | (STRATUM << 16) | (POLL << 8) | (PREC & 0xff)); data[1] = htonl(1<<16); /* Root Delay (seconds) */ data[2] = htonl(1<<16); /* Root Dispersion (seconds) */ gettimeofday(&now, NULL); data[10] = htonl(now.tv_sec + JAN_1970); /* Transmit Timestamp coarse */ data[11] = htonl(NTPFRAC(now.tv_usec)); /* Transmit Timestamp fine */ send(fd, data, 48, 0); } void get_udp_arrival_local_timestamp(struct ntptime *udp_arrival_local_timestamp) { struct timeval udp_arrival_local_time; gettimeofday(&udp_arrival_local_time, NULL); //print just precise to second printf("local time=>%s/n",ctime(&(udp_arrival_local_time.tv_sec))); } void get_new_time(unsigned int *data,struct timeval* new_time) { //int li, vn, mode, stratum, poll, prec; //int delay, disp, refid; //struct ntptime reftime, orgtime, rectime; struct ntptime trantime; /*li = Data(0) >> 30 & 0x03; vn = Data(0) >> 27 & 0x07; mode = Data(0) >> 24 & 0x07; stratum = Data(0) >> 16 & 0xff; poll = Data(0) >> 8 & 0xff; prec = Data(0) & 0xff; if (prec & 0x80) prec|=0xffffff00; delay = Data(1); disp = Data(2); refid = Data(3); reftime.coarse = Data(4); reftime.fine = Data(5); orgtime.coarse = Data(6); orgtime.fine = Data(7); rectime.coarse = Data(8); rectime.fine = Data(9);*/ trantime.coarse = Data(10); trantime.fine = Data(11); new_time->tv_sec = trantime.coarse - JAN_1970; new_time->tv_usec = USEC(trantime.fine); //print just precise to second printf("server time=>%s/n",ctime(&(new_time->tv_sec))); } void set_local_time(struct timeval new_time) { /* need root user. */ if (0 != getuid() && 0 != geteuid()) { printf("must be root user!:0)/n"); return; } settimeofday(&new_time, NULL); } int main(void) { int sockfd; struct sockaddr_in addr_src,addr_dst; fd_set fds_read; int ret; int receivebytes; unsigned int buf[12]; int addr_len; struct timeval timeout,new_time; struct ntptime udp_arrival_local_timestamp; struct hostent* host; addr_len = sizeof(struct sockaddr_in); memset(&addr_src, 0, addr_len); addr_src.sin_family = AF_INET; addr_src.sin_addr.s_addr = htonl(INADDR_ANY); addr_src.sin_port = htons(0); memset(&addr_dst, 0, addr_len); addr_dst.sin_family = AF_INET; host = gethostbyname(NTP_SERVER); memcpy(&(addr_dst.sin_addr.s_addr), host->h_addr_list[0], 4); addr_dst.sin_port = htons(NTP_PORT); /* create socket. */ if(-1==(sockfd = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))) { printf("create socket error!/n"); exit(1); } /* bind local address. */ ret = bind(sockfd, (struct sockaddr*)&addr_src, addr_len); if(-1==ret) { printf("bind error!/n"); close(sockfd); } /* connect to ntp server. */ ret = connect(sockfd, (struct sockaddr*)&addr_dst, addr_len); if(-1==ret) { printf("connect error!/n"); close(sockfd); } /*get and set time*/ while (1) { FD_ZERO(&fds_read); FD_SET(sockfd, &fds_read); timeout.tv_sec = 6; timeout.tv_usec = 0; ret = select(sockfd + 1, &fds_read, NULL, NULL, &timeout); if (0 == ret || !FD_ISSET(sockfd, &fds_read)) { /* send ntp protocol packet. */ send_packet(sockfd); continue; } /* recv ntp server's response. */ receivebytes = recvfrom(sockfd, buf, sizeof(buf), 0, (struct sockaddr *)&addr_dst, &addr_len); if(-1==receivebytes) { printf("recvfrom error/n"); close(sockfd); exit(1); } /* get local timestamp. */ get_udp_arrival_local_timestamp(&udp_arrival_local_timestamp); /* get server's time and print it. */ get_new_time(buf, &new_time); /* set local time to the server's time, if you're a root user. */ set_local_time(new_time); } close(sockfd); return 0; }