From 208163ac89cfc14db46cd089110517761b69dc76 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Tue, 22 Jan 2019 07:43:13 -0600
Subject: Actually calculating/displaying a reasonable time.

Not yet setting, no server/multicast, should validate source address...
---
 toys/pending/sntp.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 120 insertions(+), 11 deletions(-)

diff --git a/toys/pending/sntp.c b/toys/pending/sntp.c
index f34c3da2..446e3f75 100644
--- a/toys/pending/sntp.c
+++ b/toys/pending/sntp.c
@@ -4,24 +4,30 @@
  *
  * See https://www.ietf.org/rfc/rfc4330.txt
 
-USE_SNTP(NEWTOY(sntp, "<1", TOYFLAG_USR|TOYFLAG_BIN))
+USE_SNTP(NEWTOY(sntp, "sp:", TOYFLAG_USR|TOYFLAG_BIN))
 
 config SNTP
   bool "sntp"
   default n
   help
-    usage: sntp SERVER...
+    usage: sntp [-sm] [-p PORT] SERVER...
 
     Simple Network Time Protocol client, set system clock from a server.
+
+    -p	Use PORT (default 123)
+    -s	Serer
 */
 
 #define FOR_sntp
 #include "toys.h"
 
 GLOBALS(
-  int unused;
+  char *p, *m;
 )
 
+// Seconds from 1900 to 1970, including appropriate leap days
+#define SEVENTIES 2208988800L
+
 union socksaddr {
   struct sockaddr_in in;
   struct sockaddr_in6 in6;
@@ -46,20 +52,123 @@ int xrecvwait(int fd, char *buf, int len, union socksaddr *sa, int timeout)
   return len;
 }
 
+/// hardwired getaddrinfo() variant for what we want here.
+static struct addrinfo *gai(char *server)
+{
+  return xgetaddrinfo(server, TT.p, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, 0);
+}
+
+// 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.
+static unsigned long long lunchtime(struct timespec *television)
+{
+  struct timespec tv;
+
+  clock_gettime(CLOCK_REALTIME, &tv);
+
+  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) + (1L<<32)*!(now&(1L<<63));
+  tv->tv_sec -= SEVENTIES; // Force signed math for Y2038 fixup
+  tv->tv_nsec = ((now&((1L<<32)-1))*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);
+}
+
+// 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;
+}
+
+int multicast = 0;
+
 void sntp_main(void)
 {
+  struct timespec tv, tv2;
+  unsigned long long *pktime = (void *)toybuf, now, then, before;
+  long long diff;
   struct addrinfo *ai;
   union socksaddr sa;
-  int fd, len;
+  int fd, attempts;
+
+  if (!FLAG(s) && !*toys.optargs) error_exit("Need -s or SERVER");
 
-  ai = xgetaddrinfo(*toys.optargs, 0, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, 0);
+  // Lookup address and open server or client UDP socket
+  if (!TT.p || !*TT.p) TT.p = "123";
+  ai = gai(*toys.optargs);
   // When root, bind to local server address
-  if (!getuid())
-    fd = xbind(xgetaddrinfo("", "123", AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, 0));
+  if (!getuid()) fd = xbind(gai(""));
   else fd = xsocket(ai->ai_family, SOCK_DGRAM, IPPROTO_UDP);
 
-  xsendto(fd, toybuf, 48, ai->ai_addr);
-  len = xrecvwait(fd, toybuf, sizeof(toybuf), &sa, 5000);
-  printf("%d\n", len);
-  if (len>0) write(1, toybuf, len);
+  // Try 3 times
+  for (attempts = 0; attempts < 3; attempts++) {
+    // Prepare outgoing NTP packet
+    memset(toybuf, 0, 48);
+    *toybuf = 0xe3; // li = 3 (unsynchronized), version = 4, mode = 3 (client)
+    toybuf[2] = 8;  // poll frequency 1<<8 = 256 seconds
+    pktime[5] = SWAP_BE64(before = lunchtime(&tv));
+
+    // Send and ye shall receive
+    xsendto(fd, toybuf, 48, ai->ai_addr);
+    then = (now = millitime())+4000;
+    while (now<then) {
+      // TODO: confirm sa matches
+      if (48 == xrecvwait(fd, toybuf, sizeof(toybuf), &sa, then-now)) {
+        if (multicast || pktime[3] == SWAP_BE64(before)) break;
+      }
+      now = millitime();
+    }
+    if (now < then) break;
+  }
+  lunchtime(&tv2);
+
+//printf("before) %ld %ld\n", (long)tv.tv_sec, (long)tv.tv_nsec);
+//printf("after) %ld %ld\n", (long)tv2.tv_sec, (long)tv2.tv_nsec);
+
+  // determine midpoint of packet transit time according to local clock
+  // (simple calculation: assume each direction took same time so midpoint
+  // is time reported by other clock)
+  diff = nanodiff(&tv, &tv2)/2;
+//printf("halfoff = %lld %llx\n", diff, diff);
+  nanomove(&tv, diff);
+//printf("midpoint) %ld %ld\n", (long)tv.tv_sec, (long)tv.tv_nsec);
+
+  doublyso(SWAP_BE64(pktime[5]), &tv2);
+  diff = nanodiff(&tv2, &tv);
+//printf("server) %ld %ld\n", (long)tv2.tv_sec, (long)tv2.tv_nsec);
+//printf("offby = %lld\n", diff);
+
+//int i;
+//for (i=0; i<48; ) {
+//  printf("%02x", toybuf[i]);
+//  if (!(++i&15)) printf("\n");
+//}
+
+  format_iso_time(toybuf, sizeof(toybuf)-1, &tv);
+  printf("%s offset %c%d.%09d secs\n", toybuf, (diff<0) ? '-' : '+',
+    abs(diff/1000000000), abs(diff%1000000000));
 }
-- 
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