graph: add IsZombieEdge method

This is in preparation for the commit where we move across all the
funding tx validation so that we can test that we are correctly updating
the zombie index.

discovery/gossiper_test.go

@@ -113,6 +113,17 @@ func (r *mockGraphSource) MarkZombieEdge(scid uint64) error {
 	)
 }
 
+func (r *mockGraphSource) IsZombieEdge(chanID lnwire.ShortChannelID) (bool,
+	error) {
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	_, ok := r.zombies[chanID.ToUint64()]
+
+	return ok, nil
+}
+
 func (r *mockGraphSource) AddEdge(info *models.ChannelEdgeInfo,
 	_ ...batch.SchedulerOption) error {
 

graph/builder.go

@@ -1630,6 +1630,16 @@ func (b *Builder) IsKnownEdge(chanID lnwire.ShortChannelID) bool {
 	return exists || isZombie
 }
 
+// IsZombieEdge returns true if the graph source has marked the given channel ID
+// as a zombie edge.
+//
+// NOTE: This method is part of the ChannelGraphSource interface.
+func (b *Builder) IsZombieEdge(chanID lnwire.ShortChannelID) (bool, error) {
+	_, _, _, isZombie, err := b.cfg.Graph.HasChannelEdge(chanID.ToUint64())
+
+	return isZombie, err
+}
+
 // IsStaleEdgePolicy returns true if the graph source has a channel edge for
 // the passed channel ID (and flags) that have a more recent timestamp.
 //

graph/interfaces.go

@@ -88,6 +88,10 @@ type ChannelGraphSource interface {
 
 	// MarkZombieEdge marks the channel with the given ID as a zombie edge.
 	MarkZombieEdge(chanID uint64) error
+
+	// IsZombieEdge returns true if the edge with the given channel ID is
+	// currently marked as a zombie edge.
+	IsZombieEdge(chanID lnwire.ShortChannelID) (bool, error)
 }
 
 // DB is an interface describing a persisted Lightning Network graph.