[Linux网络编程]应用实例--获取网络时间
#include#include #include #include #include #include #include #include #include #include #include #include #include #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 "61.135.250.78" /*国家授时中心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, NTPV3); /*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[6] - 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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