Detect week-counter overruns using the leap second.

1 files changed, 30 insertions, 6 deletions

diff --git a/libgpsd_core.c b/libgpsd_core.c
index 73e12bdd..a4e45521 100644
--- a/libgpsd_core.c
+++ b/libgpsd_core.c
@@ -835,19 +835,43 @@ char /*@observer@*/ *gpsd_id( /*@in@ */ struct gps_device_t *session)
     return (buf);
 }
 
-void gpsd_rollover_check(/*@in@ */ struct gps_device_t *session, const double unixtime)
+void gpsd_rollover_check(/*@in@*/struct gps_device_t *session, 
+			 const double unixtime)
 {
     /*
+     * If the system clock is zero or has a small-integer value,
+     * no sanity-checking is possible.
+     */
+    if (session->context->start_time < GPS_EPOCH)
+	return;
+
+    /*
+     * Check the time passed in against the leap-second offset the satellites
+     * are reporting.  After a rollover, the receiver will probably report a
+     * time far enough in the past that it won't be consistent with the
+     * leap-second value.
+     */
+    if (gpsd_check_leapsecond(session->context->leap_seconds, unixtime) == 0) {
+	char scr[128];
+	(void)unix_to_iso8601(unixtime, scr, sizeof(scr));
+	gpsd_report(LOG_WARN, "leap-second %d is impossible at time %s (%f)\n", 
+		    session->context->leap_seconds, scr, unixtime);
+    }
+
+    /*
+     * If the GPS is reporting a time from before the daemon started, we've
+     * had a rollover event while the daemon was running.
+     *
      * The reason for the 12-hour slop is that our recorded start time is local,
      * but GPSes deliver time as though in UTC.  This test could be exact if we
      * counted on knowing our timezone at startup, but since we can't count on
      * knowing location...
      */
-    if (session->context->start_time >= GPS_EPOCH && unixtime + (12*60*60) < (double)session->context->start_time) {
-    char scr[128];
-    (void)unix_to_iso8601(unixtime, scr, sizeof(scr));
-    gpsd_report(LOG_WARN, "GPS week rollover makes time %s (%f) invalid\n", 
-		scr, unixtime);
+    if (unixtime + (12*60*60) < (double)session->context->start_time) {
+	char scr[128];
+	(void)unix_to_iso8601(unixtime, scr, sizeof(scr));
+	gpsd_report(LOG_WARN, "GPS week rollover makes time %s (%f) invalid\n", 
+		    scr, unixtime);
     }
 }