routing: stricter mission control state failure updates

This commit puts a mechanism in place to prevent a failure for a low
amount from being overwritten very soon after by a higher amount
failure.

routing/missioncontrol.go

@@ -50,6 +50,11 @@ const (
 	// DefaultAprioriWeight is the default a priori weight. See
 	// MissionControlConfig for further explanation.
 	DefaultAprioriWeight = 0.5
+
+	// DefaultMinFailureRelaxInterval is the default minimum time that must
+	// have passed since the previously recorded failure before the failure
+	// amount may be raised.
+	DefaultMinFailureRelaxInterval = time.Minute
 )
 
 // NodeResults contains previous results from a node to its peers.
@@ -113,6 +118,11 @@ type MissionControlConfig struct {
 	// results, unless there are none available.
 	AprioriWeight float64
 
+	// MinFailureRelaxInterval is the minimum time that must have passed
+	// since the previously recorded failure before the failure amount may
+	// be raised.
+	MinFailureRelaxInterval time.Duration
+
 	// SelfNode is our own pubkey.
 	SelfNode route.Vertex
 }
@@ -188,7 +198,7 @@ func NewMissionControl(db kvdb.Backend, cfg *MissionControlConfig) (
 	}
 
 	mc := &MissionControl{
-		state:     newMissionControlState(),
+		state:     newMissionControlState(cfg.MinFailureRelaxInterval),
 		now:       time.Now,
 		cfg:       cfg,
 		store:     store,

routing/missioncontrol_state.go

@@ -19,13 +19,21 @@ type missionControlState struct {
 	// lastSecondChance tracks the last time a second chance was granted for
 	// a directed node pair.
 	lastSecondChance map[DirectedNodePair]time.Time
+
+	// minFailureRelaxInterval is the minimum time that must have passed
+	// since the previously recorded failure before the failure amount may
+	// be raised.
+	minFailureRelaxInterval time.Duration
 }
 
 // newMissionControlState instantiates a new mission control state object.
-func newMissionControlState() *missionControlState {
+func newMissionControlState(
+	minFailureRelaxInterval time.Duration) *missionControlState {
+
 	return &missionControlState{
 		lastPairResult:          make(map[route.Vertex]NodeResults),
 		lastSecondChance:        make(map[DirectedNodePair]time.Time),
+		minFailureRelaxInterval: minFailureRelaxInterval,
 	}
 }
 
@@ -87,6 +95,22 @@ func (m *missionControlState) setLastPairResult(fromNode, toNode route.Vertex,
 		// condition) to be revived as if it just happened.
 		failAmt := result.amt
 
+		// Drop result if it would increase the failure amount too soon
+		// after a previous failure. This can happen if htlc results
+		// come in out of order. This check makes it easier for payment
+		// processes to converge to a final state.
+		failInterval := timestamp.Sub(current.FailTime)
+		if failAmt > current.FailAmt &&
+			failInterval < m.minFailureRelaxInterval {
+
+			log.Debugf("Ignoring higher amount failure within min "+
+				"failure relaxation interval: prev_fail_amt=%v, "+
+				"fail_amt=%v, interval=%v",
+				current.FailAmt, failAmt, failInterval)
+
+			return
+		}
+
 		current.FailTime = timestamp
 		current.FailAmt = failAmt
 

routing/missioncontrol_state_test.go

@@ -0,0 +1,47 @@
+package routing
+
+import (
+	"testing"
+	"time"
+
+	"github.com/lightningnetwork/lnd/routing/route"
+)
+
+// TestMissionControlStateFailureResult tests setting failure results on the
+// mission control state.
+func TestMissionControlStateFailureResult(t *testing.T) {
+	const minFailureRelaxInterval = time.Minute
+	state := newMissionControlState(minFailureRelaxInterval)
+
+	var (
+		from      = route.Vertex{1}
+		to        = route.Vertex{2}
+		timestamp = testTime
+	)
+
+	// Report a 1000 sat failure.
+	state.setLastPairResult(from, to, timestamp, &pairResult{amt: 1000})
+	result, _ := state.getLastPairResult(from)
+	if result[to].FailAmt != 1000 {
+		t.Fatalf("unexpected fail amount %v", result[to].FailAmt)
+	}
+
+	// Report an 1100 sat failure one hour later. It is expected to
+	// overwrite the previous failure.
+	timestamp = timestamp.Add(time.Hour)
+	state.setLastPairResult(from, to, timestamp, &pairResult{amt: 1100})
+	result, _ = state.getLastPairResult(from)
+	if result[to].FailAmt != 1100 {
+		t.Fatalf("unexpected fail amount %v", result[to].FailAmt)
+	}
+
+	// Report a 1200 sat failure one second later. Because this increase of
+	// the failure amount is too soon after the previous failure, the result
+	// is not applied.
+	timestamp = timestamp.Add(time.Second)
+	state.setLastPairResult(from, to, timestamp, &pairResult{amt: 1200})
+	result, _ = state.getLastPairResult(from)
+	if result[to].FailAmt != 1100 {
+		t.Fatalf("unexpected fail amount %v", result[to].FailAmt)
+	}
+}

server.go

@@ -715,6 +715,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 			MaxMcHistory:            routingConfig.MaxMcHistory,
 			AprioriWeight:           routingConfig.AprioriWeight,
 			SelfNode:                selfNode.PubKeyBytes,
+			MinFailureRelaxInterval: routing.DefaultMinFailureRelaxInterval,
 		},
 	)
 	if err != nil {