ntpc.c

/* forgotfun.org forgotfun(佐须之男) */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <time.h>
#include <unistd.h>
#include <sys/time.h>
#include <signal.h>
#include <syslog.h>

#define I_MISC		0
#define I_ORTIME	6
#define	I_TXTIME	10

#define TIMEFIX		2208988800UL

#ifdef DEBUG_NOISY
#define _dprintf                cprintf
#else
#define _dprintf(args...)       do { } while(0)
#endif


// 0 = ok, 1 = failed, 2 = permanent failure
static int ntpc(struct in_addr addr)
{
	uint32_t packet[12];
	struct timeval txtime;
	struct timeval rxtime;
	struct timeval tv;
	uint32_t u;
	uint32_t txn;
	int fd;
	fd_set fds;
	int len;
	struct sockaddr_in sa;
	char s[64], q[128];
	time_t t;
	time_t ntpt;
	time_t diff;

	memset(&sa, 0, sizeof(sa));
	sa.sin_addr = addr;
	sa.sin_port = htons(123);
	sa.sin_family = AF_INET;

	if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
		printf("Unable to create a socket\n");
		return 1;
	}

	if (connect(fd, (struct sockaddr*)&sa, sizeof(sa)) == -1) {
		printf("Unable to connect\n");
	}
	else {
		memset(&packet, 0, sizeof(packet));
		packet[I_MISC] = htonl((4 << 27) | (3 << 24));	// VN=v4 | mode=3 (client)
//		packet[I_MISC] = htonl((3 << 27) | (3 << 24));	// VN=v3 | mode=3 (client)
		gettimeofday(&txtime, NULL);
		packet[I_TXTIME] = txn = htonl(txtime.tv_sec + TIMEFIX);
		send(fd, packet, sizeof(packet), 0);

		FD_ZERO(&fds);
		FD_SET(fd, &fds);
		tv.tv_sec = 3;	// no more than 3 seconds
		tv.tv_usec = 0;
		if (select(fd + 1, &fds, NULL, NULL, &tv) != 1) {
			printf("Timeout\n");
		}
		else {
			len = recv(fd, packet, sizeof(packet), 0);
			if (len != sizeof(packet)) {
				printf("Invalid packet size\n");
			}
			else {
				gettimeofday(&rxtime, NULL);

				u = ntohl(packet[0]);

				_dprintf("u = 0x%08x\n", u);
				_dprintf("LI = %u\n", u >> 30);
				_dprintf("VN = %u\n", (u >> 27) & 0x07);
				_dprintf("mode = %u\n", (u >> 24) & 0x07);
				_dprintf("stratum = %u\n", (u >> 16) & 0xFF);
				_dprintf("poll interval = %u\n", (u >> 8) & 0xFF);
				_dprintf("precision = %u\n", u & 0xFF);

				if ((u & 0x07000000) != 0x04000000) {	// mode != 4 (server)
					printf("Invalid response\n");
				}
				else {
					close(fd);

					// notes:
					//	- Windows' ntpd returns vn=3, stratum=0

					if ((u & 0x00FF0000) == 0) {			// stratum == 0
						printf("Received stratum=0\n");
#if 0
						if (!nvram_match("ntp_kiss_ignore", "1")) {
							return 2;
						}
#endif
					}

					ntpt = ntohl(packet[I_TXTIME]) - TIMEFIX;
					t = (rxtime.tv_sec - txtime.tv_sec) >> 1;
					diff = (ntpt - rxtime.tv_sec) + t;

					_dprintf("txtime = %ld\n", txtime.tv_sec);
					_dprintf("rxtime = %ld\n", rxtime.tv_sec);
					_dprintf("ntpt   = %ld\n", ntpt);
					_dprintf("rtt/2  = %ld\n", t);
					_dprintf("diff   = %ld\n", diff);

					if (diff != 0) {
						gettimeofday(&tv, NULL);
						tv.tv_sec  += diff;
//						tv.tv_usec = 0;// sorry, I'm not a time geek :P
						settimeofday(&tv, NULL);

						_dprintf("new    = %lu\n", tv.tv_sec);

						strftime(s, sizeof(s), "%a, %d %b %Y %H:%M:%S %z", localtime(&tv.tv_sec));
						sprintf(q, "Time Updated: %s [%s%lds]", s, diff > 0 ? "+" : "", diff);
					}
					else {
						t = time(0);
						strftime(s, sizeof(s), "%a, %d %b %Y %H:%M:%S %z", localtime(&t));
						sprintf(q, "Time: %s, no change was needed.", s);
					}
					printf("\n\n%s\n", q);
					syslog(LOG_INFO, q);
					return 0;
				}
			}
		}
	}

	close(fd);
	return 1;
}


// -----------------------------------------------------------------------------


int main(int argc, char **argv)
{
	struct hostent *he;
	struct in_addr ia;
	const char *s;
	int i;

	for (i = 1; i < argc; ++i) {
		if ((he = gethostbyname(argv[i])) != NULL) {
			memcpy(&ia, he->h_addr_list[0], sizeof(ia));
			s = inet_ntoa(ia);
			if (strcmp(s, argv[i]) == 0) printf("Trying %s: ", s);
				else printf("Trying %s [%s]:", argv[i], s);
			if (ntpc(ia) == 0) return 0;
		}
		else {
			printf("Unable to resolve: %s\n", argv[i]);
		}
	}

	if (argc < 2) {
		printf("Usage: ntpc <server>\n");
		printf("Example: ntpc 0.asia.pool.ntp.org 1.asia.pool.ntp.org 2.asia.pool.ntp.org\n");
	}

	return 1;
}

/*

                       1                   2                    3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9  0 1
  +---+-----+-----+---------------+---------------+----------------+
  |LI | VN  |Mode |    Stratum    |     Poll      |   Precision    | 0
  +---+-----+-----+---------------+---------------+----------------+
  |                          Root  Delay                           | 1
  +----------------------------------------------------------------+
  |                       Root  Dispersion                         | 2
  +----------------------------------------------------------------+
  |                     Reference Identifier                       | 3
  +----------------------------------------------------------------+
  |                    Reference Timestamp (64)                    | 4
  +----------------------------------------------------------------+
  |                    Originate Timestamp (64)                    | 6
  +----------------------------------------------------------------+
  |                     Receive Timestamp (64)                     | 8
  +----------------------------------------------------------------+
  |                     Transmit Timestamp (64)                    | 10
  +----------------------------------------------------------------+
  |                 Key Identifier (optional) (32)                 | 12
  +----------------------------------------------------------------+
  |                 Message Digest (optional) (128)                | 13+
  +----------------------------------------------------------------+

timestamp:
	since 1900

1970-1900:
	25,567 days can be converted to one of these units:
		* 2,208,988,800 seconds
		* 36,816,480 minutes
		* 613,608 hours
		* 3652 weeks (rounded down)

refs:
	http://www.faqs.org/rfcs/rfc2030.html
	http://www.ntp.org/ntpfaq/NTP-s-algo.htm

*/