fix: lost notify message during zone transfer

closes #344

src/knot/zone/events/events.c

@@ -279,8 +279,11 @@ void zone_events_schedule_at(zone_t *zone, zone_event_type_t type, time_t time)
 	zone_events_t *events = &zone->events;
 
 	pthread_mutex_lock(&events->mx);
-	event_set_time(events, type, time);
-	reschedule(events);
+	time_t current = event_get_time(events, type);
+	if (time == 0 || current == 0 || time < current) {
+		event_set_time(events, type, time);
+		reschedule(events);
+	}
 	pthread_mutex_unlock(&events->mx);
 }
 

src/knot/zone/events/events.h

@@ -104,6 +104,10 @@ void zone_events_enqueue(struct zone *zone, zone_event_type_t type);
 /*!
  * \brief Schedule new zone event to absolute time.
  *
+ * If the event is already scheduled, the new time will be set only if the
+ * new time is earlier than the currently scheduled one. An exception is
+ * a zero time, which causes event cancellation.
+ *
  * \param zone  Zone to schedule new event for.
  * \param type  Type of event.
  * \param time  Absolute time.
@@ -113,6 +117,8 @@ void zone_events_schedule_at(struct zone *zone, zone_event_type_t type, time_t t
 /*!
  * \brief Schedule new zone event using relative time to current time.
  *
+ * The function internally uses \ref zone_events_schedule_at.
+ *
  * \param zone  Zone to schedule new event for.
  * \param type  Type of event.
  * \param dt    Relative time.