/* sntp.c - sntp client and server * * Copyright 2019 Rob Landley * * See https://www.ietf.org/rfc/rfc4330.txt modes: oneshot display, oneshot set, persist, serve, multi USE_SNTP(NEWTOY(sntp, "m:Sp:asdDqr#<4>17=10[!as]", TOYFLAG_USR|TOYFLAG_BIN)) config SNTP bool "sntp" default y help usage: sntp [-saSdDqm] [-r SHIFT] [-m ADDRESS] [-p PORT] [SERVER] Simple Network Time Protocol client. Query SERVER and display time. -p Use PORT (default 123) -s Set system clock suddenly -a Adjust system clock gradually -S Serve time instead of querying (bind to SERVER address if specified) -m Wait for updates from multicast ADDRESS (RFC 4330 says use 224.0.1.1) -d Daemonize (run in background re-querying ) -D Daemonize but stay in foreground: re-query time every 1000 seconds -r Retry shift (every 1<= 0) { struct pollfd pfd; pfd.fd = fd; pfd.events = POLLIN; if (!xpoll(&pfd, 1, timeout)) return 0; } len = recvfrom(fd, buf, len, 0, (void *)sa, &sl); if (len<0) perror_exit("recvfrom"); return len; } // Adjust timespec by nanosecond offset static void nanomove(struct timespec *ts, long long offset) { long long nano = ts->tv_nsec + offset, secs = nano/1000000000; ts->tv_sec += secs; nano %= 1000000000; if (nano<0) { ts->tv_sec--; nano += 1000000000; } ts->tv_nsec = nano; } // Get time and return ntptime (saving timespec in pointer if not null) // NTP time is high 32 bits = seconds since 1970 (blame RFC 868), low 32 bits // fraction of a second. // diff is how far off we think our clock is from reality (in nanoseconds) static unsigned long long lunchtime(struct timespec *television, long long diff) { struct timespec tv; clock_gettime(CLOCK_REALTIME, &tv); if (diff) nanomove(&tv, diff); if (television) *television = tv; // Unix time is 1970 but RFCs 868 and 958 said 1900 so add seconds 1900->1970 // If they'd done a 34/30 bit split the Y2036 problem would be centuries // from now and still give us nanosecond accuracy, but no... return ((tv.tv_sec+SEVENTIES)<<32)+(((long long)tv.tv_nsec)<<32)/1000000000; } // convert ntptime back to struct timespec. static void doublyso(unsigned long long now, struct timespec *tv) { // Y2036 fixup: if time wrapped, it's in the future tv->tv_sec = (now>>32) + (1LL<<32)*!(now&(1LL<<63)); tv->tv_sec -= SEVENTIES; // Force signed math for Y2038 fixup tv->tv_nsec = ((now&0xFFFFFFFF)*1000000000)>>32; } // return difference between two timespecs in nanosecs static long long nanodiff(struct timespec *old, struct timespec *new) { return (new->tv_sec - old->tv_sec)*1000000000LL+(new->tv_nsec - old->tv_nsec); } void sntp_main(void) { struct timespec tv, tv2; unsigned long long *pktime = (void *)toybuf, now, then, before = before; long long diff = 0; struct addrinfo *ai; union socksaddr sa; int fd, tries = 0; if (!(FLAG(S)||FLAG(m)) && !*toys.optargs) error_exit("Need -Sm or SERVER address"); // Lookup address and open server or client UDP socket if (!TT.p || !*TT.p) TT.p = "123"; ai = xgetaddrinfo(*toys.optargs, TT.p, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, AI_PASSIVE*!*toys.optargs); if (FLAG(d) && daemon(0, 0)) perror_exit("daemonize"); // Act as server if necessary if (FLAG(S)|FLAG(m)) { fd = xbind(ai); if (TT.m) { struct ip_mreq group; // subscribe to multicast group memset(&group, 0, sizeof(group)); group.imr_multiaddr.s_addr = inet_addr(TT.m); xsetsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &group, sizeof(group)); } } else fd = xsocket(ai->ai_family, SOCK_DGRAM, IPPROTO_UDP); // -Sm = loop waiting for input // -Dd = loop polling time and waiting until next poll period // Otherwise poll up to 3 times to get 2 responses, then exit // loop sending/receiving packets for (;;) { now = millitime(); // Figure out if we're in server and multicast modes don't poll if (FLAG(m) || FLAG(S)) then = -1; // daemon and oneshot modes send a packet each time through outer loop else { then = now + 3000; if (FLAG(d) || FLAG(D)) then = now + (1<ai_addr); } // Loop receiving packets until it's time to send the next one. for (;;) { int strike; // Wait to receive a packet if (then>0 && then<(now = millitime())) break;; strike = xrecvwait(fd, toybuf, sizeof(toybuf), &sa, then-now); if (strike<1) { if (!(FLAG(S)||FLAG(m)||FLAG(D)||FLAG(d)) && ++tries == 3) error_exit("no reply from %s", *toys.optargs); break; } if (strike<48) continue; // Validate packet if (!FLAG(S) || FLAG(m)) { char buf[128]; int mode = 7&*toybuf; // Is source address what we expect? xstrncpy(buf, ntop(ai->ai_addr), 128); strike = strcmp(buf, ntop((void *)&sa)); // Does this reply's originate timestamp match the packet we sent? if (!FLAG(S) && !FLAG(m) && before != SWAP_BE64(pktime[3])) continue; // Ignore packets from wrong address or with wrong mode if (strike && !FLAG(S)) continue; if (!((FLAG(m) && mode==5) || (FLAG(S) && mode==3) || (!FLAG(m) && !FLAG(S) && mode==4))) continue; } // If received a -S request packet, send server packet if (strike) { char *buf = toybuf+48; *buf = 0x24; // LI 0 VN 4 mode 4. buf[1] = 3; // stratum 3 buf[2] = 10; // recommended retry every 1<<10=1024 seconds buf[3] = 250; // precision -6, minimum allowed strcpy(buf+12, "LOCL"); pktime[6+3] = pktime[5]; // send back reference time they sent us // everything else is current time pktime[6+2] = pktime[6+4] = pktime[6+5] = SWAP_BE64(lunchtime(0, 0)); xsendto(fd, buf, 48, (void *)&sa); // Got a time packet from a recognized server } else { int unset = !diff; // First packet: figure out how far off our clock is from what server // said and try again. Don't set clock, just record offset to use // generating second reuest. (We know this time is in the past // because transmission took time, but it's a start. And if time is // miraculously exact, don't loop.) lunchtime(&tv2, diff); diff = nanodiff(&tv, &tv2); if (unset && diff) break; // Second packet: determine midpoint of packet transit time according // to local clock, assuming each direction took same time so midpoint // is time server reported. The first television was the adjusted time // we sent the packet at, tv2 is what server replied, so now diff // is round trip time. // What time did the server say and how far off are we? nanomove(&tv, diff/2); doublyso(SWAP_BE64(pktime[5]), &tv2); diff = nanodiff(&tv, &tv2); if (FLAG(s)) { // Do read/adjust/set to lose as little time as possible. clock_gettime(CLOCK_REALTIME, &tv2); nanomove(&tv2, diff); if (clock_settime(CLOCK_REALTIME, &tv2)) perror_exit("clock_settime"); } else if (FLAG(a)) { struct timeval why; // call adjtime() to move the clock gradually, copying nanoseconds // into gratuitous microseconds structure for sad historical reasons memset(&tv2, 0, sizeof(tv2)); nanomove(&tv2, diff); why.tv_sec = tv2.tv_sec; why.tv_usec = tv2.tv_nsec/1000; if (adjtime(&why, 0)) perror_exit("adjtime"); } // Display the time and offset if (!FLAG(q)) { format_iso_time(toybuf, sizeof(toybuf)-1, &tv2); printf("%s offset %c%lld.%09lld secs\n", toybuf, (diff<0) ? '-' : '+', llabs(diff/1000000000), llabs(diff%1000000000)); } // If we're not in daemon mode, we're done. (Can't get here for -S.) if (!FLAG(d) && !FLAG(D)) return; } } } }