routing: map insufficient local bandwidth error to no path

With mpp it isn't possible anymore for findPath to determine that there
isn't enough local bandwidth. The full payment amount isn't known at
that point.

In a follow-up, this payment outcome can be reintroduced on a higher
level (payment lifecycle).

channeldb/payments.go

@@ -116,6 +116,9 @@ const (
 
 	// FailureReasonInsufficientBalance indicates that we didn't have enough
 	// balance to complete the payment.
+	//
+	// This reason isn't assigned anymore, but may still exist for older
+	// payments.
 	FailureReasonInsufficientBalance FailureReason = 4
 
 	// TODO(halseth): cancel state.

routing/pathfind.go

@@ -478,7 +478,7 @@ func findPathInternal(
 			return nil, err
 		}
 		if max < amt {
-			return nil, errInsufficientBalance
+			return nil, errNoPathFound
 		}
 	}
 

routing/pathfind_test.go

@@ -2809,37 +2809,6 @@ func TestRouteToSelf(t *testing.T) {
 	ctx.assertPath(path, []uint64{1, 3, 2})
 }
 
-// TestInsufficientBalance tests that a dedicated error is returned for
-// insufficient local balance.
-func TestInsufficientBalance(t *testing.T) {
-	t.Parallel()
-
-	testChannels := []*testChannel{
-		symmetricTestChannel("source", "target", 100000, &testChannelPolicy{
-			Expiry:      144,
-			FeeBaseMsat: 500,
-		}, 1),
-	}
-
-	ctx := newPathFindingTestContext(t, testChannels, "source")
-	defer ctx.cleanup()
-
-	paymentAmt := lnwire.NewMSatFromSatoshis(100)
-	target := ctx.keyFromAlias("target")
-
-	ctx.graphParams.bandwidthHints = map[uint64]lnwire.MilliSatoshi{
-		1: lnwire.NewMSatFromSatoshis(50),
-	}
-
-	// Find the best path to self. We expect this to be source->a->source,
-	// because a charges the lowest forwarding fee.
-	_, err := ctx.findPath(target, paymentAmt)
-	if err != errInsufficientBalance {
-		t.Fatalf("expected insufficient balance error, but got: %v",
-			err)
-	}
-}
-
 type pathFindingTestContext struct {
 	t                 *testing.T
 	graphParams       graphParams

routing/payment_session.go

@@ -26,10 +26,6 @@ const (
 	// not exist in the graph.
 	errNoPathFound
 
-	// errInsufficientLocalBalance is returned when none of the local
-	// channels have enough balance for the payment.
-	errInsufficientBalance
-
 	// errEmptyPaySession is returned when the empty payment session is
 	// queried for a route.
 	errEmptyPaySession
@@ -50,9 +46,6 @@ func (e noRouteError) Error() string {
 	case errEmptyPaySession:
 		return "empty payment session"
 
-	case errInsufficientBalance:
-		return "insufficient local balance"
-
 	default:
 		return "unknown no-route error"
 	}
@@ -69,9 +62,6 @@ func (e noRouteError) FailureReason() channeldb.FailureReason {
 
 		return channeldb.FailureReasonNoRoute
 
-	case errInsufficientBalance:
-		return channeldb.FailureReasonInsufficientBalance
-
 	default:
 		return channeldb.FailureReasonError
 	}