1 /* sntp.c - sntp client and server 2 * 3 * Copyright 2019 Rob Landley <rob (at) landley.net> 4 * 5 * See https://www.ietf.org/rfc/rfc4330.txt 6 7 modes: oneshot display, oneshot set, persist, serve, multi 8 9 USE_SNTP(NEWTOY(sntp, "M:m:Sp:asdDqr#<4>17=10[!as]", TOYFLAG_USR|TOYFLAG_BIN)) 10 11 config SNTP 12 bool "sntp" 13 default y 14 help 15 usage: sntp [-saSdDqm] [-r SHIFT] [-m ADDRESS] [-p PORT] [SERVER] 16 17 Simple Network Time Protocol client. Query SERVER and display time. 18 19 -p Use PORT (default 123) 20 -s Set system clock suddenly 21 -a Adjust system clock gradually 22 -S Serve time instead of querying (bind to SERVER address if specified) 23 -m Wait for updates from multicast ADDRESS (RFC 4330 says use 224.0.1.1) 24 -M Multicast server on ADDRESS 25 -d Daemonize (run in background re-querying ) 26 -D Daemonize but stay in foreground: re-query time every 1000 seconds 27 -r Retry shift (every 1<<SHIFT seconds) 28 -q Quiet (don't display time) 29 */ 30 31 #define FOR_sntp 32 #include "toys.h" 33 34 GLOBALS( 35 long r; 36 char *p, *m, *M; 37 ) 38 39 // Seconds from 1900 to 1970, including appropriate leap days 40 #define SEVENTIES 2208988800L 41 42 // Get time and return ntptime (saving timespec in pointer if not null) 43 // NTP time is high 32 bits = seconds since 1970 (blame RFC 868), low 32 bits 44 // fraction of a second. 45 // diff is how far off we think our clock is from reality (in nanoseconds) 46 static unsigned long long lunchtime(struct timespec *television, long long diff) 47 { 48 struct timespec tv; 49 50 clock_gettime(CLOCK_REALTIME, &tv); 51 if (diff) nanomove(&tv, diff); 52 53 if (television) *television = tv; 54 55 // Unix time is 1970 but RFCs 868 and 958 said 1900 so add seconds 1900->1970 56 // If they'd done a 34/30 bit split the Y2036 problem would be centuries 57 // from now and still give us nanosecond accuracy, but no... 58 return ((tv.tv_sec+SEVENTIES)<<32)+(((long long)tv.tv_nsec)<<32)/1000000000; 59 } 60 61 // convert ntptime back to struct timespec. 62 static void doublyso(unsigned long long now, struct timespec *tv) 63 { 64 // Y2036 fixup: if time wrapped, it's in the future 65 tv->tv_sec = (now>>32) + (1LL<<32)*!(now&(1LL<<63)); 66 tv->tv_sec -= SEVENTIES; // Force signed math for Y2038 fixup 67 tv->tv_nsec = ((now&0xFFFFFFFF)*1000000000)>>32; 68 } 69 70 void sntp_main(void) 71 { 72 struct timespec tv, tv2; 73 unsigned long long *pktime = (void *)toybuf, now, then, before = before; 74 long long diff = 0; 75 struct addrinfo *ai; 76 union socksaddr sa; 77 int fd, tries = 0; 78 79 if (!(FLAG(S)||FLAG(m)) && !*toys.optargs) 80 error_exit("Need -Sm or SERVER address"); 81 82 // Lookup address and open server or client UDP socket 83 if (!TT.p || !*TT.p) TT.p = "123"; 84 ai = xgetaddrinfo(*toys.optargs, TT.p, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, 85 AI_PASSIVE*!*toys.optargs); 86 87 if (FLAG(d) && daemon(0, 0)) perror_exit("daemonize"); 88 89 // Act as server if necessary 90 if (FLAG(S)|FLAG(m)) { 91 fd = xbind(ai); 92 if (TT.m) { 93 struct ip_mreq group; 94 95 // subscribe to multicast group 96 memset(&group, 0, sizeof(group)); 97 group.imr_multiaddr.s_addr = inet_addr(TT.m); 98 xsetsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &group, sizeof(group)); 99 } 100 } else fd = xsocket(ai->ai_family, SOCK_DGRAM, IPPROTO_UDP); 101 102 // -Sm = loop waiting for input 103 // -Dd = loop polling time and waiting until next poll period 104 // Otherwise poll up to 3 times to get 2 responses, then exit 105 106 // loop sending/receiving packets 107 for (;;) { 108 now = millitime(); 109 110 // Figure out if we're in server and multicast modes don't poll 111 if (FLAG(m) || FLAG(S)) then = -1; 112 113 // daemon and oneshot modes send a packet each time through outer loop 114 else { 115 then = now + 3000; 116 if (FLAG(d) || FLAG(D)) then = now + (1<<TT.r)*1000; 117 118 // Send NTP query packet 119 memset(toybuf, 0, 48); 120 *toybuf = 0xe3; // li = 3 (unsynchronized), version = 4, mode = 3 (client) 121 toybuf[2] = 8; // poll frequency 1<<8 = 256 seconds 122 pktime[5] = SWAP_BE64(before = lunchtime(&tv, diff)); 123 xsendto(fd, toybuf, 48, ai->ai_addr); 124 } 125 126 // Loop receiving packets until it's time to send the next one. 127 for (;;) { 128 int strike; 129 130 // Wait to receive a packet 131 132 if (then>0 && then<(now = millitime())) break;; 133 strike = xrecvwait(fd, toybuf, sizeof(toybuf), &sa, then-now); 134 if (strike<1) { 135 if (!(FLAG(S)||FLAG(m)||FLAG(D)||FLAG(d)) && ++tries == 3) 136 error_exit("no reply from %s", *toys.optargs); 137 break; 138 } 139 if (strike<48) continue; 140 141 // Validate packet 142 if (!FLAG(S) || FLAG(m)) { 143 char buf[128]; 144 int mode = 7&*toybuf; 145 146 // Is source address what we expect? 147 xstrncpy(buf, ntop(ai->ai_addr), 128); 148 strike = strcmp(buf, ntop((void *)&sa)); 149 // Does this reply's originate timestamp match the packet we sent? 150 if (!FLAG(S) && !FLAG(m) && before != SWAP_BE64(pktime[3])) continue; 151 // Ignore packets from wrong address or with wrong mode 152 if (strike && !FLAG(S)) continue; 153 if (!((FLAG(m) && mode==5) || (FLAG(S) && mode==3) || 154 (!FLAG(m) && !FLAG(S) && mode==4))) continue; 155 } 156 157 // If received a -S request packet, send server packet 158 if (strike) { 159 char *buf = toybuf+48; 160 161 *buf = 0x24; // LI 0 VN 4 mode 4. 162 buf[1] = 3; // stratum 3 163 buf[2] = 10; // recommended retry every 1<<10=1024 seconds 164 buf[3] = 250; // precision -6, minimum allowed 165 strcpy(buf+12, "LOCL"); 166 pktime[6+3] = pktime[5]; // send back reference time they sent us 167 // everything else is current time 168 pktime[6+2] = pktime[6+4] = pktime[6+5] = SWAP_BE64(lunchtime(0, 0)); 169 xsendto(fd, buf, 48, (void *)&sa); 170 171 // Got a time packet from a recognized server 172 } else { 173 int unset = !diff; 174 175 // First packet: figure out how far off our clock is from what server 176 // said and try again. Don't set clock, just record offset to use 177 // generating second reuest. (We know this time is in the past 178 // because transmission took time, but it's a start. And if time is 179 // miraculously exact, don't loop.) 180 181 lunchtime(&tv2, diff); 182 diff = nanodiff(&tv, &tv2); 183 if (unset && diff) break; 184 185 // Second packet: determine midpoint of packet transit time according 186 // to local clock, assuming each direction took same time so midpoint 187 // is time server reported. The first television was the adjusted time 188 // we sent the packet at, tv2 is what server replied, so now diff 189 // is round trip time. 190 191 // What time did the server say and how far off are we? 192 nanomove(&tv, diff/2); 193 doublyso(SWAP_BE64(pktime[5]), &tv2); 194 diff = nanodiff(&tv, &tv2); 195 196 if (FLAG(s)) { 197 // Do read/adjust/set to lose as little time as possible. 198 clock_gettime(CLOCK_REALTIME, &tv2); 199 nanomove(&tv2, diff); 200 if (clock_settime(CLOCK_REALTIME, &tv2)) 201 perror_exit("clock_settime"); 202 } else if (FLAG(a)) { 203 struct timeval why; 204 205 // call adjtime() to move the clock gradually, copying nanoseconds 206 // into gratuitous microseconds structure for sad historical reasons 207 memset(&tv2, 0, sizeof(tv2)); 208 nanomove(&tv2, diff); 209 why.tv_sec = tv2.tv_sec; 210 why.tv_usec = tv2.tv_nsec/1000; 211 if (adjtime(&why, 0)) perror_exit("adjtime"); 212 } 213 214 // Display the time and offset 215 if (!FLAG(q)) { 216 format_iso_time(toybuf, sizeof(toybuf)-1, &tv2); 217 printf("%s offset %c%lld.%09lld secs\n", toybuf, (diff<0) ? '-' : '+', 218 llabs(diff/1000000000), llabs(diff%1000000000)); 219 } 220 221 // If we're not in daemon mode, we're done. (Can't get here for -S.) 222 if (!FLAG(d) && !FLAG(D)) return; 223 } 224 } 225 } 226 } 227
