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_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)
+	}
+}