channeldb: add ErrEdgeAlreadyExist error

channeldb/error.go

@@ -69,7 +69,11 @@ var (
 
 	// ErrEdgeNotFound is returned when an edge for the target chanID
 	// can't be found.
-	ErrEdgeNotFound = fmt.Errorf("edge for chanID not found")
+	ErrEdgeNotFound = fmt.Errorf("edge not found")
+
+	// ErrEdgeAlreadyExist is returned when edge with specific
+	// channel id can't be added because it already exist.
+	ErrEdgeAlreadyExist = fmt.Errorf("edge already exist")
 
 	// ErrNodeAliasNotFound is returned when alias for node can't be found.
 	ErrNodeAliasNotFound = fmt.Errorf("alias for node not found")

channeldb/graph.go

@@ -424,7 +424,7 @@ func (c *ChannelGraph) AddChannelEdge(edge *ChannelEdgeInfo) error {
 		// created. If so, then we can exit early as this method is
 		// meant to be idempotent.
 		if edgeInfo := edgeIndex.Get(chanKey[:]); edgeInfo != nil {
-			return nil
+			return ErrEdgeAlreadyExist
 		}
 
 		// If the edge hasn't been created yet, then we'll first add it