discovery/gossiper: require explict gossip syncer init

This commit removes the fallback in fetchGossipSyncer
that creates a gossip syncer if one is not registered
w/in the gossiper. Now that we register gossip syncers
explicitly before reading any gossip query messages,
this should not longer be required. The fallback also
did not honor the cfg.NoChanUpdates flag, which may
have led to inconsistencies between configuration and
actual behavior.

discovery/gossiper.go

@@ -35,6 +35,11 @@ var (
 	// ErrGossiperShuttingDown is an error that is returned if the gossiper
 	// is in the process of being shut down.
 	ErrGossiperShuttingDown = errors.New("gossiper is shutting down")
+
+	// ErrGossipSyncerNotFound signals that we were unable to find an active
+	// gossip syncer corresponding to a gossip query message received from
+	// the remote peer.
+	ErrGossipSyncerNotFound = errors.New("gossip syncer not found")
 )
 
 // networkMsg couples a routing related wire message with the peer that
@@ -919,45 +924,7 @@ func (d *AuthenticatedGossiper) findGossipSyncer(pub *btcec.PublicKey) (
 		return syncer, nil
 	}
 
-	// A known gossip syncer doesn't exist, so we may have to create one
-	// from scratch. To do so, we'll query for a reference directly to the
-	// active peer.
-	syncPeer, err := d.cfg.FindPeer(pub)
-	if err != nil {
-		log.Debugf("unable to find gossip peer %v: %v",
-			pub.SerializeCompressed(), err)
-		return nil, err
-	}
-
-	// Finally, we'll obtain the exclusive mutex, then check again if a
-	// gossiper was added after we dropped the read mutex.
-	d.syncerMtx.Lock()
-	syncer, ok = d.peerSyncers[target]
-	if ok {
-		d.syncerMtx.Unlock()
-		return syncer, nil
-	}
-
-	// At this point, a syncer doesn't yet exist, so we'll create a new one
-	// for the peer and return it to the caller.
-	encoding := lnwire.EncodingSortedPlain
-	syncer = newGossiperSyncer(gossipSyncerCfg{
-		chainHash:       d.cfg.ChainHash,
-		syncChanUpdates: true,
-		channelSeries:   d.cfg.ChanSeries,
-		encodingType:    encoding,
-		chunkSize:       encodingTypeToChunkSize[encoding],
-		sendToPeer: func(msgs ...lnwire.Message) error {
-			return syncPeer.SendMessage(false, msgs...)
-		},
-	})
-	copy(syncer.peerPub[:], pub.SerializeCompressed())
-	d.peerSyncers[target] = syncer
-	syncer.Start()
-
-	d.syncerMtx.Unlock()
-
-	return syncer, nil
+	return nil, ErrGossipSyncerNotFound
 }
 
 // networkHandler is the primary goroutine that drives this service. The roles
@@ -1041,6 +1008,9 @@ func (d *AuthenticatedGossiper) networkHandler() {
 					announcement.source,
 				)
 				if err != nil {
+					log.Warnf("Unable to find gossip "+
+						"syncer for peer=%x: %v",
+						announcement.peer.PubKey(), err)
 					continue
 				}
 
@@ -1066,6 +1036,9 @@ func (d *AuthenticatedGossiper) networkHandler() {
 					announcement.source,
 				)
 				if err != nil {
+					log.Warnf("Unable to find gossip "+
+						"syncer for peer=%x: %v",
+						announcement.source, err)
 					continue
 				}