routing: use distinct probability estimation for local channels

Previously we used the a priori probability also for our own untried
channels. This led to local channels that had seen a success already
being prioritized over untried local channels. In some cases, depending
on the configured payment attempt cost, this could lead to the payment
taking a two hop route while a direct payment was also possible.

routing/missioncontrol.go

@@ -118,6 +118,9 @@ type MissionControlConfig struct {
 	// probability completely and only base the probability on historical
 	// results, unless there are none available.
 	AprioriWeight float64
+
+	// SelfNode is our own pubkey.
+	SelfNode route.Vertex
 }
 
 // TimedPairResult describes a timestamped pair result.
@@ -261,6 +264,11 @@ func (m *MissionControl) GetProbability(fromNode, toNode route.Vertex,
 	now := m.now()
 	results := m.lastPairResult[fromNode]
 
+	// Use a distinct probability estimation function for local channels.
+	if fromNode == m.cfg.SelfNode {
+		return m.estimator.getLocalPairProbability(now, results, toNode)
+	}
+
 	return m.estimator.getPairProbability(now, results, toNode, amt)
 }
 

routing/missioncontrol_test.go

@@ -13,7 +13,7 @@ import (
 
 var (
 	mcTestRoute = &route.Route{
-		SourcePubKey: route.Vertex{10},
+		SourcePubKey: mcTestSelf,
 		Hops: []*route.Hop{
 			{
 				ChannelID:     1,
@@ -30,6 +30,7 @@ var (
 	}
 
 	mcTestTime  = time.Date(2018, time.January, 9, 14, 00, 00, 0, time.UTC)
+	mcTestSelf  = route.Vertex{10}
 	mcTestNode1 = mcTestRoute.Hops[0].PubKeyBytes
 	mcTestNode2 = mcTestRoute.Hops[1].PubKeyBytes
 
@@ -80,6 +81,7 @@ func (ctx *mcTestContext) restartMc() {
 			PenaltyHalfLife:       testPenaltyHalfLife,
 			AprioriHopProbability: testAprioriHopProbability,
 			AprioriWeight:         testAprioriWeight,
+			SelfNode:              mcTestSelf,
 		},
 	)
 	if err != nil {
@@ -98,7 +100,6 @@ func (ctx *mcTestContext) cleanup() {
 
 // Assert that mission control returns a probability for an edge.
 func (ctx *mcTestContext) expectP(amt lnwire.MilliSatoshi, expected float64) {
-
 	ctx.t.Helper()
 
 	p := ctx.mc.GetProbability(mcTestNode1, mcTestNode2, amt)
@@ -138,6 +139,13 @@ func TestMissionControl(t *testing.T) {
 
 	testTime := time.Date(2018, time.January, 9, 14, 00, 00, 0, time.UTC)
 
+	// For local channels, we expect a higher probability than our a prior
+	// test probability.
+	selfP := ctx.mc.GetProbability(mcTestSelf, mcTestNode1, 100)
+	if selfP != prevSuccessProbability {
+		t.Fatalf("expected prev success prob for untried local chans")
+	}
+
 	// Initial probability is expected to be the a priori.
 	ctx.expectP(1000, testAprioriHopProbability)
 

routing/probability_estimator.go

@@ -123,6 +123,22 @@ func (p *probabilityEstimator) getPairProbability(
 	)
 }
 
+// getLocalPairProbability estimates the probability of successfully traversing
+// our own local channels to toNode.
+func (p *probabilityEstimator) getLocalPairProbability(
+	now time.Time, results NodeResults, toNode route.Vertex) float64 {
+
+	// For local channels that have never been tried before, we assume them
+	// to be successful. We have accurate balance and online status
+	// information on our own channels, so when we select them in a route it
+	// is close to certain that those channels will work.
+	nodeProbability := p.prevSuccessProbability
+
+	return p.calculateProbability(
+		now, results, nodeProbability, toNode, lnwire.MaxMilliSatoshi,
+	)
+}
+
 // calculateProbability estimates the probability of successfully traversing to
 // toNode based on historical payment outcomes and a fall-back node probability.
 func (p *probabilityEstimator) calculateProbability(

server.go

@@ -672,6 +672,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 			PenaltyHalfLife:       routingConfig.PenaltyHalfLife,
 			MaxMcHistory:          routingConfig.MaxMcHistory,
 			AprioriWeight:         routingConfig.AprioriWeight,
+			SelfNode:              selfNode.PubKeyBytes,
 		},
 	)
 	if err != nil {