routing: add new param to FindRoutes for CLTV expiry for final hop

In this commit, we modify the FindRoutes method to pass in the CLTV
expiry for the final hop. If the value isn’t passed in, then we’ll use
the current global default value in place.

routing/router.go

@@ -25,6 +25,12 @@ import (
 	"github.com/lightningnetwork/lightning-onion"
 )
 
+const (
+	// DefaultFinalCLTVDelta is the default value to be used as the final
+	// CLTV delta for a route if one is unspecified.
+	DefaultFinalCLTVDelta = 9
+)
+
 // ChannelGraphSource represent the source of information about the topology of
 // lightning network, it responsible for addition of nodes, edges
 // and applying edges updates, return the current block with with out
@@ -948,7 +954,14 @@ func pruneChannelFromRoutes(routes []*Route, skipChan uint64) []*Route {
 // route that will be ranked the highest is the one with the lowest cumulative
 // fee along the route.
 func (r *ChannelRouter) FindRoutes(target *btcec.PublicKey,
-	amt lnwire.MilliSatoshi) ([]*Route, error) {
+	amt lnwire.MilliSatoshi, finalExpiry ...uint16) ([]*Route, error) {
+
+	var finalCLTVDelta uint16
+	if len(finalExpiry) == 0 {
+		finalCLTVDelta = DefaultFinalCLTVDelta
+	} else {
+		finalCLTVDelta = finalExpiry[0]
+	}
 
 	// TODO(roasbeef): make num routes a param
 
@@ -1024,7 +1037,7 @@ func (r *ChannelRouter) FindRoutes(target *btcec.PublicKey,
 		// hop in the path as it contains a "self-hop" that is inserted
 		// by our KSP algorithm.
 		route, err := newRoute(amt, sourceVertex, path[1:],
-			uint32(currentHeight))
+			uint32(currentHeight), finalCLTVDelta)
 		if err != nil {
 			continue
 		}