routing: local balance check

routing/pathfind.go

@@ -76,6 +76,10 @@ var (
 	// errMaxHopsExceeded is returned when a candidate path is found, but
 	// the length of that path exceeds HopLimit.
 	errMaxHopsExceeded = errors.New("potential path has too many hops")
+
+	// errInsufficientLocalBalance is returned when none of the local
+	// channels have enough balance for the payment.
+	errInsufficientBalance = errors.New("insufficient local balance")
 )
 
 // edgePolicyWithSource is a helper struct to keep track of the source node
@@ -305,6 +309,50 @@ type PathFindingConfig struct {
 	MinProbability float64
 }
 
+// getMaxOutgoingAmt returns the maximum available balance in any of the
+// channels of the given node.
+func getMaxOutgoingAmt(node route.Vertex, outgoingChan *uint64,
+	g *graphParams, tx *bbolt.Tx) (lnwire.MilliSatoshi, error) {
+
+	var max lnwire.MilliSatoshi
+	cb := func(_ *bbolt.Tx, edgeInfo *channeldb.ChannelEdgeInfo, outEdge,
+		_ *channeldb.ChannelEdgePolicy) error {
+
+		if outEdge == nil {
+			return nil
+		}
+
+		chanID := outEdge.ChannelID
+
+		// Enforce outgoing channel restriction.
+		if outgoingChan != nil && chanID != *outgoingChan {
+			return nil
+		}
+
+		bandwidth, ok := g.bandwidthHints[chanID]
+
+		// If the bandwidth is not available for whatever reason, don't
+		// fail the pathfinding early.
+		if !ok {
+			max = lnwire.MaxMilliSatoshi
+			return nil
+		}
+
+		if bandwidth > max {
+			max = bandwidth
+		}
+
+		return nil
+	}
+
+	// Iterate over all channels of the to node.
+	err := g.graph.ForEachNodeChannel(tx, node[:], cb)
+	if err != nil {
+		return 0, err
+	}
+	return max, err
+}
+
 // findPath attempts to find a path from the source node within the
 // ChannelGraph to the target node that's capable of supporting a payment of
 // `amt` value. The current approach implemented is modified version of
@@ -332,7 +380,13 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 			"time=%v", nodesVisited, edgesExpanded, timeElapsed)
 	}()
 
-	var err error
+	// Get source node outside of the pathfinding tx, to prevent a deadlock.
+	selfNode, err := g.graph.SourceNode()
+	if err != nil {
+		return nil, err
+	}
+	self := selfNode.PubKeyBytes
+
 	tx := g.tx
 	if tx == nil {
 		tx, err = g.graph.Database().Begin(false)
@@ -365,6 +419,18 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 		}
 	}
 
+	// If we are routing from ourselves, check that we have enough local
+	// balance available.
+	if source == self {
+		max, err := getMaxOutgoingAmt(self, r.OutgoingChannelID, g, tx)
+		if err != nil {
+			return nil, err
+		}
+		if max < amt {
+			return nil, errInsufficientBalance
+		}
+	}
+
 	// First we'll initialize an empty heap which'll help us to quickly
 	// locate the next edge we should visit next during our graph
 	// traversal.
@@ -375,7 +441,6 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 
 	additionalEdgesWithSrc := make(map[route.Vertex][]*edgePolicyWithSource)
 	for vertex, outgoingEdgePolicies := range g.additionalEdges {
-
 		// Build reverse lookup to find incoming edges. Needed because
 		// search is taken place from target to source.
 		for _, outgoingEdgePolicy := range outgoingEdgePolicies {

routing/pathfind_test.go

@@ -2271,6 +2271,37 @@ 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_lifecycle.go

@@ -194,6 +194,9 @@ func errorToPaymentFailure(err error) channeldb.FailureReason {
 		errPrebuiltRouteTried:
 
 		return channeldb.FailureReasonNoRoute
+
+	case errInsufficientBalance:
+		return channeldb.FailureReasonInsufficientBalance
 	}
 
 	return channeldb.FailureReasonError