Merge pull request #5138 from Roasbeef/strict-zombie

channeldb+discovery: implement strict zombie pruning

channeldb/graph.go

@@ -188,6 +188,7 @@ type ChannelGraph struct {
 // returned instance has its own unique reject cache and channel cache.
 func newChannelGraph(db *DB, rejectCacheSize, chanCacheSize int,
 	batchCommitInterval time.Duration) *ChannelGraph {
+
 	g := &ChannelGraph{
 		db:          db,
 		rejectCache: newRejectCache(rejectCacheSize),
@@ -199,6 +200,7 @@ func newChannelGraph(db *DB, rejectCacheSize, chanCacheSize int,
 	g.nodeScheduler = batch.NewTimeScheduler(
 		db.Backend, nil, batchCommitInterval,
 	)
+
 	return g
 }
 
@@ -953,7 +955,7 @@ func (c *ChannelGraph) PruneGraph(spentOutputs []*wire.OutPoint,
 			// was successfully pruned.
 			err = delChannelEdge(
 				edges, edgeIndex, chanIndex, zombieIndex, nodes,
-				chanID, false,
+				chanID, false, false,
 			)
 			if err != nil && err != ErrEdgeNotFound {
 				return err
@@ -1202,7 +1204,7 @@ func (c *ChannelGraph) DisconnectBlockAtHeight(height uint32) ([]*ChannelEdgeInf
 		for _, k := range keys {
 			err = delChannelEdge(
 				edges, edgeIndex, chanIndex, zombieIndex, nodes,
-				k, false,
+				k, false, false,
 			)
 			if err != nil && err != ErrEdgeNotFound {
 				return err
@@ -1301,11 +1303,14 @@ func (c *ChannelGraph) PruneTip() (*chainhash.Hash, uint32, error) {
 	return &tipHash, tipHeight, nil
 }
 
-// DeleteChannelEdges removes edges with the given channel IDs from the database
+// DeleteChannelEdges removes edges with the given channel IDs from the
-// and marks them as zombies. This ensures that we're unable to re-add it to our
+// database and marks them as zombies. This ensures that we're unable to re-add
-// database once again. If an edge does not exist within the database, then
+// it to our database once again. If an edge does not exist within the
-// ErrEdgeNotFound will be returned.
+// database, then ErrEdgeNotFound will be returned. If strictZombiePruning is
-func (c *ChannelGraph) DeleteChannelEdges(chanIDs ...uint64) error {
+// true, then when we mark these edges as zombies, we'll set up the keys such
+// that we require the node that failed to send the fresh update to be the one
+// that resurrects the channel from its zombie state.
+func (c *ChannelGraph) DeleteChannelEdges(strictZombiePruning bool, chanIDs ...uint64) error {
 	// TODO(roasbeef): possibly delete from node bucket if node has no more
 	// channels
 	// TODO(roasbeef): don't delete both edges?
@@ -1340,7 +1345,7 @@ func (c *ChannelGraph) DeleteChannelEdges(chanIDs ...uint64) error {
 			byteOrder.PutUint64(rawChanID[:], chanID)
 			err := delChannelEdge(
 				edges, edgeIndex, chanIndex, zombieIndex, nodes,
-				rawChanID[:], true,
+				rawChanID[:], true, strictZombiePruning,
 			)
 			if err != nil {
 				return err
@@ -1929,7 +1934,7 @@ func delEdgeUpdateIndexEntry(edgesBucket kvdb.RwBucket, chanID uint64,
 }
 
 func delChannelEdge(edges, edgeIndex, chanIndex, zombieIndex,
-	nodes kvdb.RwBucket, chanID []byte, isZombie bool) error {
+	nodes kvdb.RwBucket, chanID []byte, isZombie, strictZombie bool) error {
 
 	edgeInfo, err := fetchChanEdgeInfo(edgeIndex, chanID)
 	if err != nil {
@@ -1997,12 +2002,57 @@ func delChannelEdge(edges, edgeIndex, chanIndex, zombieIndex,
 		return nil
 	}
 
+	nodeKey1, nodeKey2 := edgeInfo.NodeKey1Bytes, edgeInfo.NodeKey2Bytes
+	if strictZombie {
+		nodeKey1, nodeKey2 = makeZombiePubkeys(&edgeInfo, edge1, edge2)
+	}
+
 	return markEdgeZombie(
-		zombieIndex, byteOrder.Uint64(chanID), edgeInfo.NodeKey1Bytes,
+		zombieIndex, byteOrder.Uint64(chanID), nodeKey1, nodeKey2,
-		edgeInfo.NodeKey2Bytes,
 	)
 }
 
+// makeZombiePubkeys derives the node pubkeys to store in the zombie index for a
+// particular pair of channel policies. The return values are one of:
+//  1. (pubkey1, pubkey2)
+//  2. (pubkey1, blank)
+//  3. (blank, pubkey2)
+//
+// A blank pubkey means that corresponding node will be unable to resurrect a
+// channel on its own. For example, node1 may continue to publish recent
+// updates, but node2 has fallen way behind. After marking an edge as a zombie,
+// we don't want another fresh update from node1 to resurrect, as the edge can
+// only become live once node2 finally sends something recent.
+//
+// In the case where we have neither update, we allow either party to resurrect
+// the channel. If the channel were to be marked zombie again, it would be
+// marked with the correct lagging channel since we received an update from only
+// one side.
+func makeZombiePubkeys(info *ChannelEdgeInfo,
+	e1, e2 *ChannelEdgePolicy) ([33]byte, [33]byte) {
+
+	switch {
+
+	// If we don't have either edge policy, we'll return both pubkeys so
+	// that the channel can be resurrected by either party.
+	case e1 == nil && e2 == nil:
+		return info.NodeKey1Bytes, info.NodeKey2Bytes
+
+	// If we're missing edge1, or if both edges are present but edge1 is
+	// older, we'll return edge1's pubkey and a blank pubkey for edge2. This
+	// means that only an update from edge1 will be able to resurrect the
+	// channel.
+	case e1 == nil || (e2 != nil && e1.LastUpdate.Before(e2.LastUpdate)):
+		return info.NodeKey1Bytes, [33]byte{}
+
+	// Otherwise, we're missing edge2 or edge2 is the older side, so we
+	// return a blank pubkey for edge1. In this case, only an update from
+	// edge2 can resurect the channel.
+	default:
+		return [33]byte{}, info.NodeKey2Bytes
+	}
+}
+
 // UpdateEdgePolicy updates the edge routing policy for a single directed edge
 // within the database for the referenced channel. The `flags` attribute within
 // the ChannelEdgePolicy determines which of the directed edges are being

channeldb/graph_test.go

@@ -368,7 +368,7 @@ func TestEdgeInsertionDeletion(t *testing.T) {
 
 	// Next, attempt to delete the edge from the database, again this
 	// should proceed without any issues.
-	if err := graph.DeleteChannelEdges(chanID); err != nil {
+	if err := graph.DeleteChannelEdges(false, chanID); err != nil {
 		t.Fatalf("unable to delete edge: %v", err)
 	}
 
@@ -387,7 +387,7 @@ func TestEdgeInsertionDeletion(t *testing.T) {
 
 	// Finally, attempt to delete a (now) non-existent edge within the
 	// database, this should result in an error.
-	err = graph.DeleteChannelEdges(chanID)
+	err = graph.DeleteChannelEdges(false, chanID)
 	if err != ErrEdgeNotFound {
 		t.Fatalf("deleting a non-existent edge should fail!")
 	}
@@ -1756,7 +1756,7 @@ func TestFilterKnownChanIDs(t *testing.T) {
 		if err := graph.AddChannelEdge(&channel); err != nil {
 			t.Fatalf("unable to create channel edge: %v", err)
 		}
-		err := graph.DeleteChannelEdges(channel.ChannelID)
+		err := graph.DeleteChannelEdges(false, channel.ChannelID)
 		if err != nil {
 			t.Fatalf("unable to mark edge zombie: %v", err)
 		}
@@ -2038,7 +2038,7 @@ func TestFetchChanInfos(t *testing.T) {
 	if err := graph.AddChannelEdge(&zombieChan); err != nil {
 		t.Fatalf("unable to create channel edge: %v", err)
 	}
-	err = graph.DeleteChannelEdges(zombieChan.ChannelID)
+	err = graph.DeleteChannelEdges(false, zombieChan.ChannelID)
 	if err != nil {
 		t.Fatalf("unable to delete and mark edge zombie: %v", err)
 	}
@@ -2654,7 +2654,7 @@ func TestNodeIsPublic(t *testing.T) {
 	// graph. This will make Alice be seen as a private node as it no longer
 	// has any advertised edges.
 	for _, graph := range graphs {
-		err := graph.DeleteChannelEdges(aliceBobEdge.ChannelID)
+		err := graph.DeleteChannelEdges(false, aliceBobEdge.ChannelID)
 		if err != nil {
 			t.Fatalf("unable to remove edge: %v", err)
 		}
@@ -2671,7 +2671,7 @@ func TestNodeIsPublic(t *testing.T) {
 	// completely remove the edge as it is not possible for her to know of
 	// it without it being advertised.
 	for i, graph := range graphs {
-		err := graph.DeleteChannelEdges(bobCarolEdge.ChannelID)
+		err := graph.DeleteChannelEdges(false, bobCarolEdge.ChannelID)
 		if err != nil {
 			t.Fatalf("unable to remove edge: %v", err)
 		}
@@ -2779,7 +2779,7 @@ func TestDisabledChannelIDs(t *testing.T) {
 	}
 
 	// Delete the channel edge and ensure it is removed from the disabled list.
-	if err = graph.DeleteChannelEdges(edgeInfo.ChannelID); err != nil {
+	if err = graph.DeleteChannelEdges(false, edgeInfo.ChannelID); err != nil {
 		t.Fatalf("unable to delete channel edge: %v", err)
 	}
 	disabledChanIds, err = graph.DisabledChannelIDs()
@@ -3017,7 +3017,7 @@ func TestGraphZombieIndex(t *testing.T) {
 
 	// If we delete the edge and mark it as a zombie, then we should expect
 	// to see it within the index.
-	err = graph.DeleteChannelEdges(edge.ChannelID)
+	err = graph.DeleteChannelEdges(false, edge.ChannelID)
 	if err != nil {
 		t.Fatalf("unable to mark edge as zombie: %v", err)
 	}

discovery/gossiper.go

@@ -47,6 +47,10 @@ var (
 	// gossip syncer corresponding to a gossip query message received from
 	// the remote peer.
 	ErrGossipSyncerNotFound = errors.New("gossip syncer not found")
+
+	// emptyPubkey is used to compare compressed pubkeys against an empty
+	// byte array.
+	emptyPubkey [33]byte
 )
 
 // optionalMsgFields is a set of optional message fields that external callers
@@ -1881,44 +1885,13 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 			break
 
 		case channeldb.ErrZombieEdge:
-			// Since we've deemed the update as not stale above,
+			err = d.processZombieUpdate(chanInfo, msg)
-			// before marking it live, we'll make sure it has been
-			// signed by the correct party. The least-significant
-			// bit in the flag on the channel update tells us which
-			// edge is being updated.
-			var pubKey *btcec.PublicKey
-			switch {
-			case msg.ChannelFlags&lnwire.ChanUpdateDirection == 0:
-				pubKey, _ = chanInfo.NodeKey1()
-			case msg.ChannelFlags&lnwire.ChanUpdateDirection == 1:
-				pubKey, _ = chanInfo.NodeKey2()
-			}
-
-			err := routing.VerifyChannelUpdateSignature(msg, pubKey)
 			if err != nil {
-				err := fmt.Errorf("unable to verify channel "+
+				log.Warn(err)
-					"update signature: %v", err)
-				log.Error(err)
 				nMsg.err <- err
 				return nil, false
 			}
 
-			// With the signature valid, we'll proceed to mark the
-			// edge as live and wait for the channel announcement to
-			// come through again.
-			err = d.cfg.Router.MarkEdgeLive(msg.ShortChannelID)
-			if err != nil {
-				err := fmt.Errorf("unable to remove edge with "+
-					"chan_id=%v from zombie index: %v",
-					msg.ShortChannelID, err)
-				log.Error(err)
-				nMsg.err <- err
-				return nil, false
-			}
-
-			log.Debugf("Removed edge with chan_id=%v from zombie "+
-				"index", msg.ShortChannelID)
-
 			// We'll fallthrough to ensure we stash the update until
 			// we receive its corresponding ChannelAnnouncement.
 			// This is needed to ensure the edge exists in the graph
@@ -2447,6 +2420,54 @@ func (d *AuthenticatedGossiper) processNetworkAnnouncement(
 	}
 }
 
+// processZombieUpdate determines whether the provided channel update should
+// resurrect a given zombie edge.
+func (d *AuthenticatedGossiper) processZombieUpdate(
+	chanInfo *channeldb.ChannelEdgeInfo, msg *lnwire.ChannelUpdate) error {
+
+	// The least-significant bit in the flag on the channel update tells us
+	// which edge is being updated.
+	isNode1 := msg.ChannelFlags&lnwire.ChanUpdateDirection == 0
+
+	// Since we've deemed the update as not stale above, before marking it
+	// live, we'll make sure it has been signed by the correct party. If we
+	// have both pubkeys, either party can resurect the channel. If we've
+	// already marked this with the stricter, single-sided resurrection we
+	// will only have the pubkey of the node with the oldest timestamp.
+	var pubKey *btcec.PublicKey
+	switch {
+	case isNode1 && chanInfo.NodeKey1Bytes != emptyPubkey:
+		pubKey, _ = chanInfo.NodeKey1()
+	case !isNode1 && chanInfo.NodeKey2Bytes != emptyPubkey:
+		pubKey, _ = chanInfo.NodeKey2()
+	}
+	if pubKey == nil {
+		return fmt.Errorf("incorrect pubkey to resurrect zombie "+
+			"with chan_id=%v", msg.ShortChannelID)
+	}
+
+	err := routing.VerifyChannelUpdateSignature(msg, pubKey)
+	if err != nil {
+		return fmt.Errorf("unable to verify channel "+
+			"update signature: %v", err)
+	}
+
+	// With the signature valid, we'll proceed to mark the
+	// edge as live and wait for the channel announcement to
+	// come through again.
+	err = d.cfg.Router.MarkEdgeLive(msg.ShortChannelID)
+	if err != nil {
+		return fmt.Errorf("unable to remove edge with "+
+			"chan_id=%v from zombie index: %v",
+			msg.ShortChannelID, err)
+	}
+
+	log.Debugf("Removed edge with chan_id=%v from zombie "+
+		"index", msg.ShortChannelID)
+
+	return nil
+}
+
 // fetchNodeAnn fetches the latest signed node announcement from our point of
 // view for the node with the given public key.
 func (d *AuthenticatedGossiper) fetchNodeAnn(

discovery/gossiper_test.go

@@ -397,7 +397,9 @@ func (r *mockGraphSource) MarkEdgeZombie(chanID lnwire.ShortChannelID, pubKey1,
 
 	r.mu.Lock()
 	defer r.mu.Unlock()
+
 	r.zombies[chanID.ToUint64()] = [][33]byte{pubKey1, pubKey2}
+
 	return nil
 }
 
@@ -2317,15 +2319,34 @@ func TestProcessZombieEdgeNowLive(t *testing.T) {
 		t.Fatalf("unable to sign update with new timestamp: %v", err)
 	}
 
-	// We'll also add the edge to our zombie index.
+	// We'll also add the edge to our zombie index, provide a blank pubkey
+	// for the first node as we're simulating the sitaution where the first
+	// ndoe is updating but the second node isn't. In this case we only
+	// want to allow a new update from the second node to allow the entire
+	// edge to be resurrected.
 	chanID := batch.chanAnn.ShortChannelID
 	err = ctx.router.MarkEdgeZombie(
-		chanID, batch.chanAnn.NodeID1, batch.chanAnn.NodeID2,
+		chanID, [33]byte{}, batch.chanAnn.NodeID2,
 	)
 	if err != nil {
 		t.Fatalf("unable mark channel %v as zombie: %v", chanID, err)
 	}
 
+	// If we send a new update but for the other direction of the channel,
+	// then it should still be rejected as we want a fresh update from the
+	// one that was considered stale.
+	batch.chanUpdAnn1.Timestamp = uint32(time.Now().Unix())
+	if err := signUpdate(remoteKeyPriv1, batch.chanUpdAnn1); err != nil {
+		t.Fatalf("unable to sign update with new timestamp: %v", err)
+	}
+	processAnnouncement(batch.chanUpdAnn1, true, true)
+
+	// At this point, the channel should still be consiered a zombie.
+	_, _, _, err = ctx.router.GetChannelByID(chanID)
+	if err != channeldb.ErrZombieEdge {
+		t.Fatalf("channel should still be a zombie")
+	}
+
 	// Attempting to process the current channel update should fail due to
 	// its edge being considered a zombie and its timestamp not being within
 	// the live horizon. We should not expect an error here since it is just

lncfg/routing.go

@@ -2,5 +2,7 @@ package lncfg
 
 // Routing holds the configuration options for routing.
 type Routing struct {
-	AssumeChannelValid bool `long:"assumechanvalid" description:"DEPRECATED: This is now turned on by default for Neutrino (use neutrino.validatechannels=true to turn off) and shouldn't be used for any other backend! (default: false)"`
+	AssumeChannelValid bool `long:"assumechanvalid" description:"Skip checking channel spentness during graph validation. This speedup comes at the risk of using an unvalidated view of the network for routing. (default: false)"`
+
+	StrictZombiePruning bool `long:"strictgraphpruning" description:"If true, then the graph will be pruned more aggressively for zombies. In practice this means that edges with a single stale edge will be considered a zombie."`
 }

routing/router.go

@@ -342,6 +342,13 @@ type Config struct {
 
 	// Clock is mockable time provider.
 	Clock clock.Clock
+
+	// StrictZombiePruning determines if we attempt to prune zombie
+	// channels according to a stricter criteria. If true, then we'll prune
+	// a channel if only *one* of the edges is considered a zombie.
+	// Otherwise, we'll only prune the channel when both edges have a very
+	// dated last update.
+	StrictZombiePruning bool
 }
 
 // EdgeLocator is a struct used to identify a specific edge.
@@ -824,30 +831,39 @@ func (r *ChannelRouter) pruneZombieChans() error {
 			return nil
 		}
 
-		// If *both* edges haven't been updated for a period of
+		// If either edge hasn't been updated for a period of
 		// chanExpiry, then we'll mark the channel itself as eligible
 		// for graph pruning.
-		var e1Zombie, e2Zombie bool
+		e1Zombie := e1 == nil || time.Since(e1.LastUpdate) >= chanExpiry
-		if e1 != nil {
+		e2Zombie := e2 == nil || time.Since(e2.LastUpdate) >= chanExpiry
-			e1Zombie = time.Since(e1.LastUpdate) >= chanExpiry
+
-			if e1Zombie {
+		if e1Zombie {
-				log.Tracef("Edge #1 of ChannelID(%v) last "+
+			log.Tracef("Node1 pubkey=%x of chan_id=%v is zombie",
-					"update: %v", info.ChannelID,
+				info.NodeKey1Bytes, info.ChannelID)
-					e1.LastUpdate)
-			}
 		}
-		if e2 != nil {
+		if e2Zombie {
-			e2Zombie = time.Since(e2.LastUpdate) >= chanExpiry
+			log.Tracef("Node2 pubkey=%x of chan_id=%v is zombie",
-			if e2Zombie {
+				info.NodeKey2Bytes, info.ChannelID)
-				log.Tracef("Edge #2 of ChannelID(%v) last "+
-					"update: %v", info.ChannelID,
-					e2.LastUpdate)
-			}
 		}
 
-		// If the channel is not considered zombie, we can move on to
+		// If we're using strict zombie pruning, then a channel is only
-		// the next.
+		// considered live if both edges have a recent update we know
-		if !e1Zombie || !e2Zombie {
+		// of.
+		var channelIsLive bool
+		switch {
+		case r.cfg.StrictZombiePruning:
+			channelIsLive = !e1Zombie && !e2Zombie
+
+		// Otherwise, if we're using the less strict variant, then a
+		// channel is considered live if either of the edges have a
+		// recent update.
+		default:
+			channelIsLive = !e1Zombie || !e2Zombie
+		}
+
+		// Return early if the channel is still considered to be live
+		// with the current set of configuration parameters.
+		if channelIsLive {
 			return nil
 		}
 
@@ -908,7 +924,8 @@ func (r *ChannelRouter) pruneZombieChans() error {
 		toPrune = append(toPrune, chanID)
 		log.Tracef("Pruning zombie channel with ChannelID(%v)", chanID)
 	}
-	if err := r.cfg.Graph.DeleteChannelEdges(toPrune...); err != nil {
+	err = r.cfg.Graph.DeleteChannelEdges(r.cfg.StrictZombiePruning, toPrune...)
+	if err != nil {
 		return fmt.Errorf("unable to delete zombie channels: %v", err)
 	}
 

routing/router_test.go

@@ -69,16 +69,17 @@ func (c *testCtx) RestartRouter() error {
 	return nil
 }
 
-func createTestCtxFromGraphInstance(startingHeight uint32, graphInstance *testGraphInstance) (
+func createTestCtxFromGraphInstance(startingHeight uint32, graphInstance *testGraphInstance,
-	*testCtx, func(), error) {
+	strictPruning bool) (*testCtx, func(), error) {
 
 	return createTestCtxFromGraphInstanceAssumeValid(
-		startingHeight, graphInstance, false,
+		startingHeight, graphInstance, false, strictPruning,
 	)
 }
 
 func createTestCtxFromGraphInstanceAssumeValid(startingHeight uint32,
-	graphInstance *testGraphInstance, assumeValid bool) (*testCtx, func(), error) {
+	graphInstance *testGraphInstance, assumeValid bool,
+	strictPruning bool) (*testCtx, func(), error) {
 
 	// We'll initialize an instance of the channel router with mock
 	// versions of the chain and channel notifier. As we don't need to test
@@ -134,9 +135,10 @@ func createTestCtxFromGraphInstanceAssumeValid(startingHeight uint32,
 			next := atomic.AddUint64(&uniquePaymentID, 1)
 			return next, nil
 		},
-		PathFindingConfig:  pathFindingConfig,
+		PathFindingConfig:   pathFindingConfig,
-		Clock:              clock.NewTestClock(time.Unix(1, 0)),
+		Clock:               clock.NewTestClock(time.Unix(1, 0)),
-		AssumeChannelValid: assumeValid,
+		AssumeChannelValid:  assumeValid,
+		StrictZombiePruning: strictPruning,
 	})
 	if err != nil {
 		return nil, nil, fmt.Errorf("unable to create router %v", err)
@@ -187,7 +189,7 @@ func createTestCtxSingleNode(startingHeight uint32) (*testCtx, func(), error) {
 		cleanUp: cleanup,
 	}
 
-	return createTestCtxFromGraphInstance(startingHeight, graphInstance)
+	return createTestCtxFromGraphInstance(startingHeight, graphInstance, false)
 }
 
 func createTestCtxFromFile(startingHeight uint32, testGraph string) (*testCtx, func(), error) {
@@ -198,7 +200,7 @@ func createTestCtxFromFile(startingHeight uint32, testGraph string) (*testCtx, f
 		return nil, nil, fmt.Errorf("unable to create test graph: %v", err)
 	}
 
-	return createTestCtxFromGraphInstance(startingHeight, graphInstance)
+	return createTestCtxFromGraphInstance(startingHeight, graphInstance, false)
 }
 
 // TestFindRoutesWithFeeLimit asserts that routes found by the FindRoutes method
@@ -365,9 +367,9 @@ func TestChannelUpdateValidation(t *testing.T) {
 
 	const startingBlockHeight = 101
 
-	ctx, cleanUp, err := createTestCtxFromGraphInstance(startingBlockHeight,
+	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		testGraph)
+		startingBlockHeight, testGraph, true,
-
+	)
 	defer cleanUp()
 	if err != nil {
 		t.Fatalf("unable to create router: %v", err)
@@ -1028,7 +1030,7 @@ func TestIgnoreChannelEdgePolicyForUnknownChannel(t *testing.T) {
 	defer testGraph.cleanUp()
 
 	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		startingBlockHeight, testGraph,
+		startingBlockHeight, testGraph, false,
 	)
 	if err != nil {
 		t.Fatalf("unable to create router: %v", err)
@@ -1946,8 +1948,8 @@ func TestPruneChannelGraphStaleEdges(t *testing.T) {
 	freshTimestamp := time.Now()
 	staleTimestamp := time.Unix(0, 0)
 
-	// We'll create the following test graph so that only the last channel
+	// We'll create the following test graph so that two of the channels
-	// is pruned.
+	// are pruned.
 	testChannels := []*testChannel{
 		// No edges.
 		{
@@ -1960,7 +1962,7 @@ func TestPruneChannelGraphStaleEdges(t *testing.T) {
 		// Only one edge with a stale timestamp.
 		{
 			Node1: &testChannelEnd{
-				Alias: "a",
+				Alias: "d",
 				testChannelPolicy: &testChannelPolicy{
 					LastUpdate: staleTimestamp,
 				},
@@ -1970,6 +1972,20 @@ func TestPruneChannelGraphStaleEdges(t *testing.T) {
 			ChannelID: 2,
 		},
 
+		// Only one edge with a stale timestamp, but it's the source
+		// node so it won't get pruned.
+		{
+			Node1: &testChannelEnd{
+				Alias: "a",
+				testChannelPolicy: &testChannelPolicy{
+					LastUpdate: staleTimestamp,
+				},
+			},
+			Node2:     &testChannelEnd{Alias: "b"},
+			Capacity:  100000,
+			ChannelID: 3,
+		},
+
 		// Only one edge with a fresh timestamp.
 		{
 			Node1: &testChannelEnd{
@@ -1980,10 +1996,11 @@ func TestPruneChannelGraphStaleEdges(t *testing.T) {
 			},
 			Node2:     &testChannelEnd{Alias: "b"},
 			Capacity:  100000,
-			ChannelID: 3,
+			ChannelID: 4,
 		},
 
-		// One edge fresh, one edge stale.
+		// One edge fresh, one edge stale. This will be pruned with
+		// strict pruning activated.
 		{
 			Node1: &testChannelEnd{
 				Alias: "c",
@@ -1998,47 +2015,57 @@ func TestPruneChannelGraphStaleEdges(t *testing.T) {
 				},
 			},
 			Capacity:  100000,
-			ChannelID: 4,
+			ChannelID: 5,
 		},
 
 		// Both edges fresh.
 		symmetricTestChannel("g", "h", 100000, &testChannelPolicy{
 			LastUpdate: freshTimestamp,
-		}, 5),
+		}, 6),
 
-		// Both edges stale, only one pruned.
+		// Both edges stale, only one pruned. This should be pruned for
+		// both normal and strict pruning.
 		symmetricTestChannel("e", "f", 100000, &testChannelPolicy{
 			LastUpdate: staleTimestamp,
-		}, 6),
+		}, 7),
 	}
 
-	// We'll create our test graph and router backed with these test
+	for _, strictPruning := range []bool{true, false} {
-	// channels we've created.
+		// We'll create our test graph and router backed with these test
-	testGraph, err := createTestGraphFromChannels(testChannels, "a")
+		// channels we've created.
-	if err != nil {
+		testGraph, err := createTestGraphFromChannels(testChannels, "a")
-		t.Fatalf("unable to create test graph: %v", err)
+		if err != nil {
+			t.Fatalf("unable to create test graph: %v", err)
+		}
+		defer testGraph.cleanUp()
+
+		const startingHeight = 100
+		ctx, cleanUp, err := createTestCtxFromGraphInstance(
+			startingHeight, testGraph, strictPruning,
+		)
+		if err != nil {
+			t.Fatalf("unable to create test context: %v", err)
+		}
+		defer cleanUp()
+
+		// All of the channels should exist before pruning them.
+		assertChannelsPruned(t, ctx.graph, testChannels)
+
+		// Proceed to prune the channels - only the last one should be pruned.
+		if err := ctx.router.pruneZombieChans(); err != nil {
+			t.Fatalf("unable to prune zombie channels: %v", err)
+		}
+
+		// We expect channels that have either both edges stale, or one edge
+		// stale with both known.
+		var prunedChannels []uint64
+		if strictPruning {
+			prunedChannels = []uint64{2, 5, 7}
+		} else {
+			prunedChannels = []uint64{2, 7}
+		}
+		assertChannelsPruned(t, ctx.graph, testChannels, prunedChannels...)
 	}
-	defer testGraph.cleanUp()
-
-	const startingHeight = 100
-	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		startingHeight, testGraph,
-	)
-	if err != nil {
-		t.Fatalf("unable to create test context: %v", err)
-	}
-	defer cleanUp()
-
-	// All of the channels should exist before pruning them.
-	assertChannelsPruned(t, ctx.graph, testChannels)
-
-	// Proceed to prune the channels - only the last one should be pruned.
-	if err := ctx.router.pruneZombieChans(); err != nil {
-		t.Fatalf("unable to prune zombie channels: %v", err)
-	}
-
-	prunedChannel := testChannels[len(testChannels)-1].ChannelID
-	assertChannelsPruned(t, ctx.graph, testChannels, prunedChannel)
 }
 
 // TestPruneChannelGraphDoubleDisabled test that we can properly prune channels
@@ -2147,7 +2174,7 @@ func testPruneChannelGraphDoubleDisabled(t *testing.T, assumeValid bool) {
 
 	const startingHeight = 100
 	ctx, cleanUp, err := createTestCtxFromGraphInstanceAssumeValid(
-		startingHeight, testGraph, assumeValid,
+		startingHeight, testGraph, assumeValid, false,
 	)
 	if err != nil {
 		t.Fatalf("unable to create test context: %v", err)
@@ -2529,9 +2556,9 @@ func TestUnknownErrorSource(t *testing.T) {
 
 	const startingBlockHeight = 101
 
-	ctx, cleanUp, err := createTestCtxFromGraphInstance(startingBlockHeight,
+	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		testGraph)
+		startingBlockHeight, testGraph, false,
-
+	)
 	defer cleanUp()
 	if err != nil {
 		t.Fatalf("unable to create router: %v", err)
@@ -2668,7 +2695,7 @@ func TestSendToRouteStructuredError(t *testing.T) {
 	const startingBlockHeight = 101
 
 	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		startingBlockHeight, testGraph,
+		startingBlockHeight, testGraph, false,
 	)
 	if err != nil {
 		t.Fatalf("unable to create router: %v", err)
@@ -2904,7 +2931,7 @@ func TestSendToRouteMaxHops(t *testing.T) {
 	const startingBlockHeight = 101
 
 	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		startingBlockHeight, testGraph,
+		startingBlockHeight, testGraph, false,
 	)
 	if err != nil {
 		t.Fatalf("unable to create router: %v", err)
@@ -3018,7 +3045,7 @@ func TestBuildRoute(t *testing.T) {
 	const startingBlockHeight = 101
 
 	ctx, cleanUp, err := createTestCtxFromGraphInstance(
-		startingBlockHeight, testGraph,
+		startingBlockHeight, testGraph, false,
 	)
 	if err != nil {
 		t.Fatalf("unable to create router: %v", err)

rpcserver.go

@@ -2344,7 +2344,7 @@ func abandonChanFromGraph(chanGraph *channeldb.ChannelGraph,
 
 	// If the channel ID is still in the graph, then that means the channel
 	// is still open, so we'll now move to purge it from the graph.
-	return chanGraph.DeleteChannelEdges(chanID)
+	return chanGraph.DeleteChannelEdges(false, chanID)
 }
 
 // AbandonChannel removes all channel state from the database except for a

sample-lnd.conf

@@ -489,6 +489,12 @@ bitcoin.node=btcd
 ; other backend!
 ; --routing.assumechanvalid=true
 
+; If set to true, then we'll prune a channel if only a single edge is seen as
+; being stale. This results in a more compact channel graph, and also is helpful
+; for neutrino nodes as it means they'll only maintain edges where both nodes are
+; seen as being live from it's PoV.
+; --routing.strictgraphpruning=true
+
 [Btcd]
 
 ; The base directory that contains the node's data, logs, configuration file,

server.go

@@ -768,6 +768,8 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 
 	s.controlTower = routing.NewControlTower(paymentControl)
 
+	strictPruning := (cfg.Bitcoin.Node == "neutrino" ||
+		cfg.Routing.StrictZombiePruning)
 	s.chanRouter, err = routing.New(routing.Config{
 		Graph:               chanGraph,
 		Chain:               cc.ChainIO,
@@ -784,6 +786,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		NextPaymentID:       sequencer.NextID,
 		PathFindingConfig:   pathFindingConfig,
 		Clock:               clock.NewDefaultClock(),
+		StrictZombiePruning: strictPruning,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("can't create router: %v", err)