channeldb+routing: apply method Terminated to decide a payment's terminal state

This commit applies the new method `Terminated`. A side effect from
using this method is, we can now save one query `fetchPayment` inside
`FetchInFlightPayments`.

routing/control_tower.go

@@ -280,7 +280,7 @@ func (p *controlTower) SubscribePayment(paymentHash lntypes.Hash) (
 	// updates. Otherwise this update is the final update and the incoming
 	// channel can be closed. This will close the queue's outgoing channel
 	// when all updates have been written.
-	if payment.Status == channeldb.StatusInFlight {
+	if !payment.Terminated() {
 		p.subscribersMtx.Lock()
 		p.subscribers[paymentHash] = append(
 			p.subscribers[paymentHash], subscriber,
@@ -344,7 +344,7 @@ func (p *controlTower) notifySubscribers(paymentHash lntypes.Hash,
 
 	// If the payment reached a terminal state, the subscriber list can be
 	// cleared. There won't be any more updates.
-	terminal := event.Status != channeldb.StatusInFlight
+	terminal := event.Terminated()
 	if terminal {
 		delete(p.subscribers, paymentHash)
 	}

routing/control_tower_test.go

@@ -119,9 +119,9 @@ func TestControlTowerSubscribeSuccess(t *testing.T) {
 		subscriber1, subscriber2, subscriber3,
 	}
 
-	for _, s := range subscribers {
+	for i, s := range subscribers {
 		var result *channeldb.MPPayment
-		for result == nil || result.Status == channeldb.StatusInFlight {
+		for result == nil || !result.Terminated() {
 			select {
 			case item := <-s.Updates():
 				result = item.(*channeldb.MPPayment)
@@ -130,9 +130,10 @@ func TestControlTowerSubscribeSuccess(t *testing.T) {
 			}
 		}
 
-		if result.Status != channeldb.StatusSucceeded {
-			t.Fatal("unexpected payment state")
-		}
+		require.Equalf(t, channeldb.StatusSucceeded, result.Status,
+			"subscriber %v failed, want %s, got %s", i,
+			channeldb.StatusSucceeded, result.Status)
+
 		settle, _ := result.TerminalInfo()
 		if settle.Preimage != preimg {
 			t.Fatal("unexpected preimage")
@@ -474,9 +475,9 @@ func testPaymentControlSubscribeFail(t *testing.T, registerAttempt,
 		subscriber1, subscriber2,
 	}
 
-	for _, s := range subscribers {
+	for i, s := range subscribers {
 		var result *channeldb.MPPayment
-		for result == nil || result.Status == channeldb.StatusInFlight {
+		for result == nil || !result.Terminated() {
 			select {
 			case item := <-s.Updates():
 				result = item.(*channeldb.MPPayment)
@@ -510,6 +511,10 @@ func testPaymentControlSubscribeFail(t *testing.T, registerAttempt,
 				len(result.HTLCs))
 		}
 
+		require.Equalf(t, channeldb.StatusFailed, result.Status,
+			"subscriber %v failed, want %s, got %s", i,
+			channeldb.StatusFailed, result.Status)
+
 		if *result.FailureReason != channeldb.FailureReasonTimeout {
 			t.Fatal("unexpected failure reason")
 		}