lnrpc: extract hop unmarshall code

rpcserver.go

@@ -3516,50 +3516,71 @@ func (r *rpcServer) marshallRoute(route *routing.Route) *lnrpc.Route {
 	return resp
 }
 
+// unmarshallHopByChannelLookup unmarshalls an rpc hop for which the pub key is
+// not known. This function will query the channel graph with channel id to
+// retrieve both endpoints and determine the hop pubkey using the previous hop
+// pubkey. If the channel is unknown, an error is returned.
+func unmarshallHopByChannelLookup(graph *channeldb.ChannelGraph, hop *lnrpc.Hop,
+	prevPubKeyBytes []byte) (*routing.Hop, error) {
+
+	// Discard edge policies, because they may be nil.
+	edgeInfo, _, _, err := graph.FetchChannelEdgesByID(hop.ChanId)
+	if err != nil {
+		return nil, fmt.Errorf("unable to fetch channel edges by "+
+			"channel ID %d: %v", hop.ChanId, err)
+	}
+
+	var pubKeyBytes [33]byte
+	switch {
+	case bytes.Equal(prevPubKeyBytes, edgeInfo.NodeKey1Bytes[:]):
+		pubKeyBytes = edgeInfo.NodeKey2Bytes
+	case bytes.Equal(prevPubKeyBytes, edgeInfo.NodeKey2Bytes[:]):
+		pubKeyBytes = edgeInfo.NodeKey1Bytes
+	default:
+		return nil, fmt.Errorf("channel edge does not match expected node")
+	}
+
+	return &routing.Hop{
+		OutgoingTimeLock: hop.Expiry,
+		AmtToForward:     lnwire.MilliSatoshi(hop.AmtToForwardMsat),
+		PubKeyBytes:      pubKeyBytes,
+		ChannelID:        edgeInfo.ChannelID,
+	}, nil
+}
+
+// unmarshallRoute unmarshalls an rpc route. For hops that don't specify a
+// pubkey, the channel graph is queried.
 func (r *rpcServer) unmarshallRoute(rpcroute *lnrpc.Route,
 	graph *channeldb.ChannelGraph) (*routing.Route, error) {
 
-	node, err := graph.SourceNode()
+	sourceNode, err := graph.SourceNode()
 	if err != nil {
 		return nil, fmt.Errorf("unable to fetch source node from graph "+
 			"while unmarshaling route. %v", err)
 	}
 
-	nodePubKeyBytes := node.PubKeyBytes[:]
+	prevNodePubKey := sourceNode.PubKeyBytes[:]
 
 	hops := make([]*routing.Hop, len(rpcroute.Hops))
 	for i, hop := range rpcroute.Hops {
-		// Discard edge policies, because they may be nil.
+		// No hop pub key is given, so the local channel graph needs to
-		edgeInfo, _, _, err := graph.FetchChannelEdgesByID(hop.ChanId)
+		// be queried to complete the information necessary for routing.
+		routeHop, err := unmarshallHopByChannelLookup(graph,
+			hop, prevNodePubKey)
+
 		if err != nil {
-			return nil, fmt.Errorf("unable to fetch channel edges by "+
+			return nil, err
-				"channel ID for hop (%d): %v", i, err)
 		}
 
-		var pubKeyBytes [33]byte
+		hops[i] = routeHop
-		switch {
-		case bytes.Equal(nodePubKeyBytes[:], edgeInfo.NodeKey1Bytes[:]):
-			pubKeyBytes = edgeInfo.NodeKey2Bytes
-		case bytes.Equal(nodePubKeyBytes[:], edgeInfo.NodeKey2Bytes[:]):
-			pubKeyBytes = edgeInfo.NodeKey1Bytes
-		default:
-			return nil, fmt.Errorf("channel edge does not match expected node")
-		}
 
-		hops[i] = &routing.Hop{
+		prevNodePubKey = routeHop.PubKeyBytes[:]
-			OutgoingTimeLock: hop.Expiry,
-			AmtToForward:     lnwire.MilliSatoshi(hop.AmtToForwardMsat),
-			PubKeyBytes:      pubKeyBytes,
-			ChannelID:        edgeInfo.ChannelID,
-		}
-
-		nodePubKeyBytes = pubKeyBytes[:]
 	}
 
 	route := routing.NewRouteFromHops(
 		lnwire.MilliSatoshi(rpcroute.TotalAmtMsat),
 		rpcroute.TotalTimeLock,
-		node.PubKeyBytes,
+		sourceNode.PubKeyBytes,
 		hops,
 	)