syncer: Add syncing fallback

Author: lukechampine

syncer/syncer.go

@@ -686,6 +686,15 @@ func (s *Syncer) syncLoop(ctx context.Context) error {
 				return err // generally fatal
 			}
 			p.setSynced(true)
+			// as a fallback to ensure we never stop syncing prematurely, reset
+			// the sync status after 60-120 seconds
+			//
+			// NOTE: the AfterFuncs will be garbage collected after syncLoop
+			// returns. If we instead called defer Stop() on each of them, we
+			// would constantly accumulate defers, leaking memory until syncLoop
+			// returns.
+			resyncDelay := time.Duration(60+frand.Intn(60)) * time.Second
+			time.AfterFunc(resyncDelay, func() { p.setSynced(false) })
 			s.log.Debug("syncing with peer", zap.Stringer("peer", p))
 			oldTip := s.cm.Tip()
 			oldTime := time.Now()