Merge pull request #2640 from joostjager/cltv-limit

routing: add cltv limit

cmd/lncli/commands.go

@@ -1954,6 +1954,12 @@ func closedChannels(ctx *cli.Context) error {
 	return nil
 }
 
+var cltvLimitFlag = cli.UintFlag{
+	Name: "cltv_limit",
+	Usage: "the maximum time lock that may be used for " +
+		"this payment",
+}
+
 var sendPaymentCommand = cli.Command{
 	Name:     "sendpayment",
 	Category: "Payments",
@@ -2000,6 +2006,7 @@ var sendPaymentCommand = cli.Command{
 			Usage: "percentage of the payment's amount used as the" +
 				"maximum fee allowed when sending the payment",
 		},
+		cltvLimitFlag,
 		cli.StringFlag{
 			Name:  "payment_hash, r",
 			Usage: "the hash to use within the payment's HTLC",
@@ -2119,6 +2126,7 @@ func sendPayment(ctx *cli.Context) error {
 			Amt:            ctx.Int64("amt"),
 			FeeLimit:       feeLimit,
 			OutgoingChanId: ctx.Uint64("outgoing_chan_id"),
+			CltvLimit:      uint32(ctx.Int(cltvLimitFlag.Name)),
 		}
 
 		return sendPaymentRequest(client, req)
@@ -2266,6 +2274,7 @@ var payInvoiceCommand = cli.Command{
 			Usage: "percentage of the payment's amount used as the" +
 				"maximum fee allowed when sending the payment",
 		},
+		cltvLimitFlag,
 		cli.Uint64Flag{
 			Name: "outgoing_chan_id",
 			Usage: "short channel id of the outgoing channel to " +
@@ -2312,7 +2321,9 @@ func payInvoice(ctx *cli.Context) error {
 		Amt:            ctx.Int64("amt"),
 		FeeLimit:       feeLimit,
 		OutgoingChanId: ctx.Uint64("outgoing_chan_id"),
+		CltvLimit:      uint32(ctx.Int(cltvLimitFlag.Name)),
 	}
+
 	return sendPaymentRequest(client, req)
 }
 

lnrpc/rpc.proto

@@ -790,7 +790,14 @@ message SendRequest {
     any channel may be used.
     */
     uint64 outgoing_chan_id = 9;
+
+    /** 
+    An optional maximum total time lock for the route. If zero, there is no
+    maximum enforced.
+    */
+    uint32 cltv_limit = 10;
 }
+
 message SendResponse {
     string payment_error = 1 [json_name = "payment_error"];
     bytes payment_preimage = 2 [json_name = "payment_preimage"];

lnrpc/rpc.swagger.json

@@ -2977,6 +2977,11 @@
           "type": "string",
           "format": "uint64",
           "description": "*\nThe channel id of the channel that must be taken to the first hop. If zero,\nany channel may be used."
+        },
+        "cltv_limit": {
+          "type": "integer",
+          "format": "int64",
+          "description": "* \nAn optional maximum total time lock for the route. If zero, there is no\nmaximum enforced."
         }
       }
     },

routing/heap.go

@@ -21,6 +21,10 @@ type nodeWithDist struct {
 	// amount that includes also the fees for subsequent hops.
 	amountToReceive lnwire.MilliSatoshi
 
+	// incomingCltv is the expected cltv value for the incoming htlc of this
+	// node. This value does not include the final cltv.
+	incomingCltv uint32
+
 	// fee is the fee that this node is charging for forwarding.
 	fee lnwire.MilliSatoshi
 }

routing/missioncontrol.go

@@ -226,6 +226,7 @@ func (m *missionControl) NewPaymentSession(routeHints [][]zpay32.HopHint,
 		bandwidthHints:       bandwidthHints,
 		errFailedPolicyChans: make(map[EdgeLocator]struct{}),
 		mc:                   m,
+		pathFinder:           findPath,
 	}, nil
 }
 
@@ -240,6 +241,7 @@ func (m *missionControl) NewPaymentSessionFromRoutes(routes []*Route) *paymentSe
 		preBuiltRoutes:       routes,
 		errFailedPolicyChans: make(map[EdgeLocator]struct{}),
 		mc:                   m,
+		pathFinder:           findPath,
 	}
 }
 

routing/pathfind.go

@@ -39,6 +39,11 @@ const (
 	RiskFactorBillionths = 15
 )
 
+// pathFinder defines the interface of a path finding algorithm.
+type pathFinder = func(g *graphParams, r *RestrictParams,
+	source, target Vertex, amt lnwire.MilliSatoshi) (
+	[]*channeldb.ChannelEdgePolicy, error)
+
 // Hop represents an intermediate or final node of the route. This naming
 // is in line with the definition given in BOLT #4: Onion Routing Protocol.
 // The struct houses the channel along which this hop can be reached and
@@ -393,6 +398,11 @@ type RestrictParams struct {
 	// OutgoingChannelID is the channel that needs to be taken to the first
 	// hop. If nil, any channel may be used.
 	OutgoingChannelID *uint64
+
+	// CltvLimit is the maximum time lock of the route excluding the final
+	// ctlv. After path finding is complete, the caller needs to increase
+	// all cltv expiry heights with the required final cltv delta.
+	CltvLimit *uint32
 }
 
 // findPath attempts to find a path from the source node within the
@@ -479,6 +489,7 @@ func findPath(g *graphParams, r *RestrictParams, source, target Vertex,
 		node:            targetNode,
 		amountToReceive: amt,
 		fee:             0,
+		incomingCltv:    0,
 	}
 
 	// We'll use this map as a series of "next" hop pointers. So to get
@@ -575,6 +586,14 @@ func findPath(g *graphParams, r *RestrictParams, source, target Vertex,
 			timeLockDelta = edge.TimeLockDelta
 		}
 
+		incomingCltv := toNodeDist.incomingCltv +
+			uint32(timeLockDelta)
+
+		// Check that we have cltv limit and that we are within it.
+		if r.CltvLimit != nil && incomingCltv > *r.CltvLimit {
+			return
+		}
+
 		// amountToReceive is the amount that the node that is added to
 		// the distance map needs to receive from a (to be found)
 		// previous node in the route. That previous node will need to
@@ -606,14 +625,11 @@ func findPath(g *graphParams, r *RestrictParams, source, target Vertex,
 			return
 		}
 
-		// If the edge has no time lock delta, the payment will always
-		// fail, so return.
-		//
-		// TODO(joostjager): Is this really true? Can't it be that
-		// nodes take this risk in exchange for a extraordinary high
-		// fee?
+		// Every edge should have a positive time lock delta. If we
+		// encounter a zero delta, log a warning line.
 		if edge.TimeLockDelta == 0 {
-			return
+			log.Warnf("Channel %v has zero cltv delta",
+				edge.ChannelID)
 		}
 
 		// All conditions are met and this new tentative distance is
@@ -625,6 +641,7 @@ func findPath(g *graphParams, r *RestrictParams, source, target Vertex,
 			node:            fromNode,
 			amountToReceive: amountToReceive,
 			fee:             fee,
+			incomingCltv:    incomingCltv,
 		}
 
 		next[fromVertex] = edge

routing/pathfind_test.go

@@ -2021,3 +2021,111 @@ func TestRestrictOutgoingChannel(t *testing.T) {
 			"but channel %v was selected instead", route.Hops[0].ChannelID)
 	}
 }
+
+// TestCltvLimit asserts that a cltv limit is obeyed by the path finding
+// algorithm.
+func TestCltvLimit(t *testing.T) {
+	t.Run("no limit", func(t *testing.T) { testCltvLimit(t, 0, 1) })
+	t.Run("no path", func(t *testing.T) { testCltvLimit(t, 50, 0) })
+	t.Run("force high cost", func(t *testing.T) { testCltvLimit(t, 80, 3) })
+}
+
+func testCltvLimit(t *testing.T, limit uint32, expectedChannel uint64) {
+	t.Parallel()
+
+	// Set up a test graph with three possible paths to the target. The path
+	// through a is the lowest cost with a high time lock (144). The path
+	// through b has a higher cost but a lower time lock (100). That path
+	// through c and d (two hops) has the same case as the path through b,
+	// but the total time lock is lower (60).
+	testChannels := []*testChannel{
+		symmetricTestChannel("roasbeef", "a", 100000, &testChannelPolicy{}, 1),
+		symmetricTestChannel("a", "target", 100000, &testChannelPolicy{
+			Expiry:      144,
+			FeeBaseMsat: 10000,
+			MinHTLC:     1,
+		}),
+		symmetricTestChannel("roasbeef", "b", 100000, &testChannelPolicy{}, 2),
+		symmetricTestChannel("b", "target", 100000, &testChannelPolicy{
+			Expiry:      100,
+			FeeBaseMsat: 20000,
+			MinHTLC:     1,
+		}),
+		symmetricTestChannel("roasbeef", "c", 100000, &testChannelPolicy{}, 3),
+		symmetricTestChannel("c", "d", 100000, &testChannelPolicy{
+			Expiry:      30,
+			FeeBaseMsat: 10000,
+			MinHTLC:     1,
+		}),
+		symmetricTestChannel("d", "target", 100000, &testChannelPolicy{
+			Expiry:      30,
+			FeeBaseMsat: 10000,
+			MinHTLC:     1,
+		}),
+	}
+
+	testGraphInstance, err := createTestGraphFromChannels(testChannels)
+	if err != nil {
+		t.Fatalf("unable to create graph: %v", err)
+	}
+	defer testGraphInstance.cleanUp()
+
+	sourceNode, err := testGraphInstance.graph.SourceNode()
+	if err != nil {
+		t.Fatalf("unable to fetch source node: %v", err)
+	}
+	sourceVertex := Vertex(sourceNode.PubKeyBytes)
+
+	ignoredEdges := make(map[EdgeLocator]struct{})
+	ignoredVertexes := make(map[Vertex]struct{})
+
+	paymentAmt := lnwire.NewMSatFromSatoshis(100)
+	target := testGraphInstance.aliasMap["target"]
+
+	// Find the best path given the cltv limit.
+	var cltvLimit *uint32
+	if limit != 0 {
+		cltvLimit = &limit
+	}
+
+	path, err := findPath(
+		&graphParams{
+			graph: testGraphInstance.graph,
+		},
+		&RestrictParams{
+			IgnoredNodes: ignoredVertexes,
+			IgnoredEdges: ignoredEdges,
+			FeeLimit:     noFeeLimit,
+			CltvLimit:    cltvLimit,
+		},
+		sourceVertex, target, paymentAmt,
+	)
+	if expectedChannel == 0 {
+		// Finish test if we expect no route.
+		if IsError(err, ErrNoPathFound) {
+			return
+		}
+		t.Fatal("expected no path to be found")
+	}
+	if err != nil {
+		t.Fatalf("unable to find path: %v", err)
+	}
+
+	const (
+		startingHeight = 100
+		finalHopCLTV   = 1
+	)
+	route, err := newRoute(
+		paymentAmt, sourceVertex, path, startingHeight, finalHopCLTV,
+	)
+	if err != nil {
+		t.Fatalf("unable to create path: %v", err)
+	}
+
+	// Assert that the route starts with the expected channel.
+	if route.Hops[0].ChannelID != expectedChannel {
+		t.Fatalf("expected route to pass through channel %v, "+
+			"but channel %v was selected instead", expectedChannel,
+			route.Hops[0].ChannelID)
+	}
+}

routing/payment_session.go

@@ -33,6 +33,8 @@ type paymentSession struct {
 
 	haveRoutes     bool
 	preBuiltRoutes []*Route
+
+	pathFinder pathFinder
 }
 
 // ReportVertexFailure adds a vertex to the graph prune view after a client
@@ -136,12 +138,22 @@ func (p *paymentSession) RequestRoute(payment *LightningPayment,
 		"edges, %v vertexes", len(pruneView.edges),
 		len(pruneView.vertexes))
 
+	// If a route cltv limit was specified, we need to subtract the final
+	// delta before passing it into path finding. The optimal path is
+	// independent of the final cltv delta and the path finding algorithm is
+	// unaware of this value.
+	var cltvLimit *uint32
+	if payment.CltvLimit != nil {
+		limit := *payment.CltvLimit - uint32(finalCltvDelta)
+		cltvLimit = &limit
+	}
+
 	// TODO(roasbeef): sync logic amongst dist sys
 
 	// Taking into account this prune view, we'll attempt to locate a path
 	// to our destination, respecting the recommendations from
 	// missionControl.
-	path, err := findPath(
+	path, err := p.pathFinder(
 		&graphParams{
 			graph:           p.mc.graph,
 			additionalEdges: p.additionalEdges,
@@ -152,6 +164,7 @@ func (p *paymentSession) RequestRoute(payment *LightningPayment,
 			IgnoredEdges:      pruneView.edges,
 			FeeLimit:          payment.FeeLimit,
 			OutgoingChannelID: payment.OutgoingChannelID,
+			CltvLimit:         cltvLimit,
 		},
 		p.mc.selfNode.PubKeyBytes, payment.Target,
 		payment.Amount,

routing/payment_session_test.go

@@ -0,0 +1,60 @@
+package routing
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+func TestRequestRoute(t *testing.T) {
+	const (
+		height = 10
+	)
+
+	findPath := func(g *graphParams, r *RestrictParams,
+		source, target Vertex, amt lnwire.MilliSatoshi) (
+		[]*channeldb.ChannelEdgePolicy, error) {
+
+		// We expect find path to receive a cltv limit excluding the
+		// final cltv delta.
+		if *r.CltvLimit != 22 {
+			t.Fatal("wrong cltv limit")
+		}
+
+		path := []*channeldb.ChannelEdgePolicy{
+			{
+				Node: &channeldb.LightningNode{},
+			},
+		}
+
+		return path, nil
+	}
+
+	session := &paymentSession{
+		mc: &missionControl{
+			selfNode: &channeldb.LightningNode{},
+		},
+		pruneViewSnapshot: graphPruneView{},
+		pathFinder:        findPath,
+	}
+
+	cltvLimit := uint32(30)
+	finalCltvDelta := uint16(8)
+
+	payment := &LightningPayment{
+		CltvLimit:      &cltvLimit,
+		FinalCLTVDelta: &finalCltvDelta,
+	}
+
+	route, err := session.RequestRoute(payment, height, finalCltvDelta)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We expect an absolute route lock value of height + finalCltvDelta
+	if route.TotalTimeLock != 18 {
+		t.Fatalf("unexpected total time lock of %v",
+			route.TotalTimeLock)
+	}
+}

routing/router.go

@@ -1523,6 +1523,10 @@ type LightningPayment struct {
 	// if there isn't a route with lower fees than this limit.
 	FeeLimit lnwire.MilliSatoshi
 
+	// CltvLimit is the maximum time lock that is allowed for attempts to
+	// complete this payment.
+	CltvLimit *uint32
+
 	// PaymentHash is the r-hash value to use within the HTLC extended to
 	// the first hop.
 	PaymentHash [32]byte