#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;
}
网站题目：[Linux网络编程]应用实例--获取网络时间
网页URL：
http://kswsj.cn/article/gegopd.html
