Merge pull request #9925 from ellemouton/rbIncomingFollowup

routing: clean-up & fix blinded path incoming chained channel logic

docs/release-notes/release-notes-0.20.0.md

@@ -37,7 +37,8 @@ circuit. The indices are only available for forwarding events saved after v0.20.
 
 
 * The `lncli addinvoice --blind` command now has the option to include a
-  [chained channels](https://github.com/lightningnetwork/lnd/pull/9127)
+  chained channels [1](https://github.com/lightningnetwork/lnd/pull/9127)
+  [2](https://github.com/lightningnetwork/lnd/pull/9925)
   incoming list `--blinded_path_incoming_channel_list` which gives users the 
   control of specifying the channels they prefer to receive the payment on. With
   the option to specify multiple channels this control can be extended to

itest/lnd_route_blinding_test.go

@@ -1428,25 +1428,55 @@ func testBlindedPaymentHTLCReForward(ht *lntest.HarnessTest) {
 //     pre-specified.
 func testPartiallySpecifiedBlindedPath(ht *lntest.HarnessTest) {
 	// Create a six hop network:
-	// Alice -> Bob -> Carol -> Dave -> Eve -> Frank.
-	chanAmt := btcutil.Amount(100000)
-	cfgs := [][]string{nil, nil, nil, nil, nil, nil}
+	// 	Alice -> Bob -> Carol -> Dave -> Eve -> Frank.
+	// Carol will be the node generating invoices containing blinded paths.
 	chanPoints, nodes := ht.CreateSimpleNetwork(
-		cfgs, lntest.OpenChannelParams{Amt: chanAmt},
+		[][]string{nil, nil, nil, nil, nil, nil},
+		lntest.OpenChannelParams{
+			Amt:     chanAmt,
+			PushAmt: chanAmt / 2,
+		},
 	)
 
-	alice, bob, carol, dave, eve := nodes[0], nodes[1], nodes[2], nodes[3],
-		nodes[4]
-
-	chanPointAliceBob, chanPointBobCarol, chanPointCarolDave :=
-		chanPoints[0], chanPoints[1], chanPoints[2]
+	var (
+		alice = nodes[0]
+		bob   = nodes[1]
+		carol = nodes[2]
+		dave  = nodes[3]
+		eve   = nodes[4]
+		frank = nodes[5]
+	)
 
 	// Lookup full channel info so that we have channel ids for our route.
-	aliceBobChan := ht.GetChannelByChanPoint(alice, chanPointAliceBob)
-	bobCarolChan := ht.GetChannelByChanPoint(bob, chanPointBobCarol)
-	carolDaveChan := ht.GetChannelByChanPoint(carol, chanPointCarolDave)
+	aliceBobChan := ht.GetChannelByChanPoint(alice, chanPoints[0])
+	bobCarolChan := ht.GetChannelByChanPoint(bob, chanPoints[1])
+	carolDaveChan := ht.GetChannelByChanPoint(carol, chanPoints[2])
 
-	// Let carol set no incoming channel restrictions.
+	// assertPathDetails is a helper function that asserts the details of
+	// the blinded paths returned in the invoice.
+	assertPathDetails := func(invoice *lnrpc.AddInvoiceResponse,
+		expPathLengths int, expIntroNodes ...[]byte) {
+
+		payReq := carol.RPC.DecodePayReq(invoice.PaymentRequest)
+		paths := payReq.BlindedPaths
+
+		introNodes := make([][]byte, 0, len(paths))
+		for _, p := range paths {
+			require.Len(
+				ht, p.BlindedPath.BlindedHops, expPathLengths,
+			)
+
+			introNodes = append(
+				introNodes, p.BlindedPath.IntroductionNode,
+			)
+		}
+		require.ElementsMatch(ht, introNodes, expIntroNodes)
+	}
+
+	// Let carol set no incoming channel restrictions. With a min of 1 hop,
+	// we expect the following blinded paths to be included:
+	//  1) Bob->Carol
+	//  2) Dave->Carol
 	var (
 		minNumRealHops uint32 = 1
 		numHops        uint32 = 1
@@ -1460,122 +1490,94 @@ func testPartiallySpecifiedBlindedPath(ht *lntest.HarnessTest) {
 			NumHops:        &numHops,
 		},
 	})
+	assertPathDetails(invoice, 2, bob.PubKey[:], dave.PubKey[:])
 
-	introNodesFound := make([][]byte, 0)
-	introNodesExpected := [][]byte{bob.PubKey[:], dave.PubKey[:]}
-
-	// Assert that it contains two blinded path with only 2 hops each one.
-	payReq := carol.RPC.DecodePayReq(invoice.PaymentRequest)
-	require.Len(ht, payReq.BlindedPaths, 2)
-	path := payReq.BlindedPaths[0].BlindedPath
-	require.Len(ht, path.BlindedHops, 2)
-	introNodesFound = append(introNodesFound, path.IntroductionNode)
-	path = payReq.BlindedPaths[1].BlindedPath
-	require.Len(ht, path.BlindedHops, 2)
-	introNodesFound = append(introNodesFound, path.IntroductionNode)
-
-	// Assert the introduction nodes without caring about the routes order.
-	require.ElementsMatch(ht, introNodesExpected, introNodesFound)
-
-	// Let carol choose the wrong incoming channel.
-	var (
-		incomingChannelList = []uint64{aliceBobChan.ChanId}
-	)
-
-	err := fmt.Sprintf("incoming channel %v is not seen as owned by node",
-		aliceBobChan.ChanId)
-
+	// Let carol choose an invalid incoming channel list for the blinded
+	// path. It is invalid since it does not connect to her node.
+	// Assert that the expected error is returned.
 	carol.RPC.AddInvoiceAssertErr(
 		&lnrpc.Invoice{
 			Memo:      "test",
 			ValueMsat: 10_000_000,
 			IsBlinded: true,
 			BlindedPathConfig: &lnrpc.BlindedPathConfig{
-				MinNumRealHops:      &minNumRealHops,
-				NumHops:             &numHops,
-				IncomingChannelList: incomingChannelList,
+				MinNumRealHops: &minNumRealHops,
+				NumHops:        &numHops,
+				IncomingChannelList: []uint64{
+					aliceBobChan.ChanId,
+				},
 			},
 		},
-		err,
+		fmt.Sprintf("incoming channel %v is not seen as owned by node",
+			aliceBobChan.ChanId),
 	)
 
 	// Let Carol set the incoming channel list greater than minimum number
 	// of real hops.
-	incomingChannelList = []uint64{aliceBobChan.ChanId, bobCarolChan.ChanId}
-	err = fmt.Sprintf("minimum number of blinded path hops (%d) must be "+
-		"greater than or equal to the number of hops specified on "+
-		"the chained channels (%d)", minNumRealHops,
-		len(incomingChannelList),
-	)
-
+	// Assert that the expected error is returned.
 	carol.RPC.AddInvoiceAssertErr(
 		&lnrpc.Invoice{
 			Memo:      "test",
 			ValueMsat: 10_000_000,
 			IsBlinded: true,
 			BlindedPathConfig: &lnrpc.BlindedPathConfig{
-				MinNumRealHops:      &minNumRealHops,
-				NumHops:             &numHops,
-				IncomingChannelList: incomingChannelList,
+				MinNumRealHops: &minNumRealHops,
+				NumHops:        &numHops,
+				IncomingChannelList: []uint64{
+					aliceBobChan.ChanId,
+					bobCarolChan.ChanId,
+				},
 			},
 		},
-		err,
+		"must be greater than or equal to the number of hops "+
+			"specified on the chained channels",
 	)
 
 	// Let Carol choose an incoming channel that points to a node in the
 	// omission set.
-	incomingChannelList = []uint64{bobCarolChan.ChanId}
-	var nodeOmissionList [][]byte
-	nodeOmissionList = append(nodeOmissionList, bob.PubKey[:])
-
-	err = fmt.Sprintf("cannot simultaneously be included in the omission " +
-		"set and in the partially specified path",
-	)
-
 	carol.RPC.AddInvoiceAssertErr(
 		&lnrpc.Invoice{
 			Memo:      "test",
 			ValueMsat: 10_000_000,
 			IsBlinded: true,
 			BlindedPathConfig: &lnrpc.BlindedPathConfig{
-				MinNumRealHops:      &minNumRealHops,
-				NumHops:             &numHops,
-				IncomingChannelList: incomingChannelList,
-				NodeOmissionList:    nodeOmissionList,
+				MinNumRealHops: &minNumRealHops,
+				NumHops:        &numHops,
+				IncomingChannelList: []uint64{
+					bobCarolChan.ChanId,
+				},
+				NodeOmissionList: [][]byte{
+					bob.PubKey[:],
+				},
 			},
 		},
-		err,
+		"cannot simultaneously be included in the omission set and "+
+			"in the partially specified path",
 	)
 
 	// Let carol restrict bob as incoming channel.
-	incomingChannelList = []uint64{bobCarolChan.ChanId}
-
 	invoice = carol.RPC.AddInvoice(&lnrpc.Invoice{
 		Memo:      "test",
 		ValueMsat: 10_000_000,
 		IsBlinded: true,
 		BlindedPathConfig: &lnrpc.BlindedPathConfig{
-			MinNumRealHops:      &minNumRealHops,
-			NumHops:             &numHops,
-			IncomingChannelList: incomingChannelList,
+			MinNumRealHops: &minNumRealHops,
+			NumHops:        &numHops,
+			IncomingChannelList: []uint64{
+				bobCarolChan.ChanId,
+			},
 		},
 	})
 
 	// Assert that it contains a single blinded path with only
 	// 2 hops, with bob as the introduction node.
-	payReq = carol.RPC.DecodePayReq(invoice.PaymentRequest)
-	require.Len(ht, payReq.BlindedPaths, 1)
-	path = payReq.BlindedPaths[0].BlindedPath
-	require.Len(ht, path.BlindedHops, 2)
-	require.EqualValues(ht, path.IntroductionNode, bob.PubKey[:])
+	assertPathDetails(invoice, 2, bob.PubKey[:])
 
-	// Now let alice pay the invoice.
+	// Check that Alice can pay the invoice.
 	ht.CompletePaymentRequests(alice, []string{invoice.PaymentRequest})
 
-	// Let carol restrict dave as incoming channel and max Hops as 2
+	// Let carol restrict dave as incoming channel and max hops as 2.
 	numHops = 2
-	incomingChannelList = []uint64{carolDaveChan.ChanId}
-
 	invoice = carol.RPC.AddInvoice(&lnrpc.Invoice{
 		Memo:      "test",
 		ValueMsat: 10_000_000,
@@ -1583,16 +1585,15 @@ func testPartiallySpecifiedBlindedPath(ht *lntest.HarnessTest) {
 		BlindedPathConfig: &lnrpc.BlindedPathConfig{
 			MinNumRealHops:      &minNumRealHops,
 			NumHops:             &numHops,
-			IncomingChannelList: incomingChannelList,
+			IncomingChannelList: []uint64{carolDaveChan.ChanId},
 		},
 	})
 
-	// Assert that it contains one path with 3 hops, with dave as the
-	// introduction node. The path alice -> bob -> carol is discarded
-	// because alice is a dead-end.
-	payReq = carol.RPC.DecodePayReq(invoice.PaymentRequest)
-	require.Len(ht, payReq.BlindedPaths, 1)
-	path = payReq.BlindedPaths[0].BlindedPath
-	require.Len(ht, path.BlindedHops, 3)
-	require.EqualValues(ht, path.IntroductionNode, eve.PubKey[:])
+	// Assert that it contains two paths: one 3 hop one starting at Eve and
+	// a 3 hop one starting at Dave (this one will be padded with a dummy
+	// hop) in order to keep all the paths equidistant.
+	assertPathDetails(invoice, 3, eve.PubKey[:], dave.PubKey[:])
+
+	// Check that Frank can pay the invoice.
+	ht.CompletePaymentRequests(frank, []string{invoice.PaymentRequest})
 }

routing/pathfind.go

@@ -1227,24 +1227,46 @@ func findBlindedPaths(g Graph, target route.Vertex,
 	}
 
 	var (
-		// The target node is always the last hop in the path.
-		incomingPath     = []blindedHop{{vertex: target}}
-		whiteListedNodes = map[route.Vertex]bool{target: true}
+		// The target node is always the last hop in the path, and so
+		// we add it to the incoming path from the get-go. Any additions
+		// to the slice should be prepended.
+		incomingPath = []blindedHop{{
+			vertex: target,
+		}}
+
+		// supportsRouteBlinding is a list of nodes that we can assume
+		// support route blinding without needing to rely on the feature
+		// bits announced in their node announcement. Since we are
+		// finding a path to the target node, we can assume it supports
+		// route blinding.
+		supportsRouteBlinding = map[route.Vertex]bool{
+			target: true,
+		}
+
 		visited          = make(map[route.Vertex]bool)
-		errChanFound     = errors.New("found incoming channel")
 		nextTarget       = target
+		haveIncomingPath = len(restrictions.incomingChainedChannels) > 0
+
+		// errChanFound is an error variable we return from the DB
+		// iteration call below when we have found the channel we are
+		// looking for. This lets us exit the iteration early.
+		errChanFound = errors.New("found incoming channel")
 	)
 	for _, chanID := range restrictions.incomingChainedChannels {
+		// Mark that we have visited this node so that we don't revisit
+		// it later on when we call "processNodeForBlindedPath".
 		visited[nextTarget] = true
 
 		err := g.ForEachNodeDirectedChannel(nextTarget,
 			func(channel *graphdb.DirectedChannel) error {
-				// Not the right channel, continue to the node's
-				// other channels.
+				// This is not the right channel, continue to
+				// the node's other channels.
 				if channel.ChannelID != chanID {
 					return nil
 				}
 
+				// We found the channel in question. Prepend it
+				// to the incoming path.
 				incomingPath = append([]blindedHop{
 					{
 						vertex:       channel.OtherNode,
@@ -1259,39 +1281,37 @@ func findBlindedPaths(g Graph, target route.Vertex,
 				return errChanFound
 			},
 		)
-		if err == nil {
+		// We expect errChanFound to be returned if the channel in
+		// question was found.
+		if !errors.Is(err, errChanFound) && err != nil {
+			return nil, err
+		} else if err == nil {
 			return nil, fmt.Errorf("incoming channel %d is not "+
 				"seen as owned by node %v", chanID, nextTarget)
 		}
-		if !errors.Is(err, errChanFound) {
-			return nil, err
-		}
 
 		// Check that the user didn't accidentally add a channel that
-		// is owned by a node in the node omission set
+		// is owned by a node in the node omission set.
 		if restrictions.nodeOmissionSet.Contains(nextTarget) {
 			return nil, fmt.Errorf("node %v cannot simultaneously "+
 				"be included in the omission set and in the "+
 				"partially specified path", nextTarget)
 		}
 
-		if whiteListedNodes[nextTarget] {
+		// Check that we have not already visited the next target node
+		// since this would mean a circular incoming path.
+		if visited[nextTarget] {
 			return nil, fmt.Errorf("a circular route cannot be " +
 				"specified for the incoming blinded path")
 		}
-		whiteListedNodes[nextTarget] = true
+
+		supportsRouteBlinding[nextTarget] = true
 	}
 
-	// If the node is not the destination node, then it is required that the
-	// node advertise the route blinding feature-bit in order for it to be
-	// chosen as a node on the blinded path.
-	// We skip checking the target node, as accepting blinded payments
-	// (via invoice) doesn't imply support for routing them (via node
-	// announcement).
-	// We skip checking incomingChainedChannels nodes, as we might not yet
-	// have an updated node announcement for them.
-	supportsRouteBlinding := func(node route.Vertex) (bool, error) {
-		if whiteListedNodes[node] {
+	// A helper closure which checks if the node in question has advertised
+	// that it supports route blinding.
+	nodeSupportsRouteBlinding := func(node route.Vertex) (bool, error) {
+		if supportsRouteBlinding[node] {
 			return true, nil
 		}
 
@@ -1308,39 +1328,46 @@ func findBlindedPaths(g Graph, target route.Vertex,
 	// conditions such as: The maxHops number being reached or reaching
 	// a node that doesn't have any other edges - in that final case, the
 	// whole path should be ignored.
+	//
+	// NOTE: any paths returned will end at the "nextTarget" node meaning
+	// that if we have a fixed list of incoming chained channels, then this
+	// fixed list must be appended to any of the returned paths.
 	paths, _, err := processNodeForBlindedPath(
-		g, nextTarget, supportsRouteBlinding, visited, restrictions,
+		g, nextTarget, nodeSupportsRouteBlinding, visited, restrictions,
 	)
 	if err != nil {
 		return nil, err
 	}
 
-	orderedPaths := make([][]blindedHop, len(paths))
+	// Reverse each path so that the order is correct (from introduction
+	// node to last hop node) and then append the incoming path (if any was
+	// specified) to the end of the path.
+	orderedPaths := make([][]blindedHop, 0, len(paths))
+	for _, path := range paths {
+		sort.Slice(path, func(i, j int) bool {
+			return j < i
+		})
 
-	// When there is no path to add, but incomingChainedChannels can be
-	// used.
-	lenChainedChannels := int8(len(restrictions.incomingChainedChannels))
-	if len(paths) == 0 && lenChainedChannels > 0 {
-		orderedPaths = [][]blindedHop{incomingPath}
-	} else {
-		// Reverse each path so that the order is correct (from
-		// introduction node to last hop node) and then append this node
-		// on as the destination of each path.
-		for i, path := range paths {
-			sort.Slice(path, func(i, j int) bool {
-				return j < i
-			})
+		orderedPaths = append(
+			orderedPaths, append(path, incomingPath...),
+		)
+	}
 
-			orderedPaths[i] = append(path, incomingPath...)
-		}
+	// There is a chance we have an incoming path that by itself satisfies
+	// the minimum hop restriction. In that case, we add it as its own path.
+	if haveIncomingPath &&
+		len(incomingPath) > int(restrictions.minNumHops) {
+
+		orderedPaths = append(orderedPaths, incomingPath)
 	}
 
 	// Handle the special case that allows a blinded path with the
-	// introduction node as the destination node.
-	if restrictions.minNumHops == 0 && lenChainedChannels == 0 {
+	// introduction node as the destination node. This only applies if no
+	// incoming path was specified since in that case, by definition, the
+	// caller wants a non-zero length blinded path.
+	if restrictions.minNumHops == 0 && !haveIncomingPath {
 		singleHopPath := [][]blindedHop{{{vertex: target}}}
 
-		//nolint:makezero
 		orderedPaths = append(
 			orderedPaths, singleHopPath...,
 		)

routing/pathfind_test.go

@@ -538,6 +538,7 @@ func createTestGraphFromChannels(t *testing.T, useCache bool,
 
 	aliasMap := make(map[string]route.Vertex)
 	privKeyMap := make(map[string]*btcec.PrivateKey)
+	channelIDs := make(map[route.Vertex]map[route.Vertex]uint64)
 
 	nodeIndex := byte(0)
 	addNodeWithAlias := func(alias string, features *lnwire.FeatureVector) (
@@ -652,6 +653,16 @@ func createTestGraphFromChannels(t *testing.T, useCache bool,
 			node1Vertex, node2Vertex = node2Vertex, node1Vertex
 		}
 
+		if _, ok := channelIDs[node1Vertex]; !ok {
+			channelIDs[node1Vertex] = map[route.Vertex]uint64{}
+		}
+		channelIDs[node1Vertex][node2Vertex] = channelID
+
+		if _, ok := channelIDs[node2Vertex]; !ok {
+			channelIDs[node2Vertex] = map[route.Vertex]uint64{}
+		}
+		channelIDs[node2Vertex][node1Vertex] = channelID
+
 		// We first insert the existence of the edge between the two
 		// nodes.
 		edgeInfo := models.ChannelEdgeInfo{
@@ -765,6 +776,7 @@ func createTestGraphFromChannels(t *testing.T, useCache bool,
 		mcBackend:  graphBackend,
 		aliasMap:   aliasMap,
 		privKeyMap: privKeyMap,
+		channelIDs: channelIDs,
 		links:      links,
 	}, nil
 }
@@ -3192,6 +3204,16 @@ func newPathFindingTestContext(t *testing.T, useCache bool,
 	return ctx
 }
 
+func (c *pathFindingTestContext) nodePairChannel(alias1, alias2 string) uint64 {
+	node1 := c.keyFromAlias(alias1)
+	node2 := c.keyFromAlias(alias2)
+
+	channel, ok := c.testGraphInstance.channelIDs[node1][node2]
+	require.True(c.t, ok)
+
+	return channel
+}
+
 func (c *pathFindingTestContext) keyFromAlias(alias string) route.Vertex {
 	return c.testGraphInstance.aliasMap[alias]
 }
@@ -3876,7 +3898,7 @@ func TestFindBlindedPaths(t *testing.T) {
 		"eve,bob,dave",
 	})
 
-	// 5) Finally, we will test the special case where the destination node
+	// 5) We will also test the special case where the destination node
 	// is also the recipient.
 	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
 		minNumHops: 0,
@@ -3888,93 +3910,138 @@ func TestFindBlindedPaths(t *testing.T) {
 		"dave",
 	})
 
-	// 6) Restrict the min & max path length such that we only include paths
-	// with one being only the intro-node and the others with one hop other
-	// than the destination hop.
+	// 6) Now, we will test some cases where the user manually specifies
+	// the first few incoming channels of a route.
+	//
+	// 6.1) Let the user specify the B-D channel as the last hop with a
+	// max of 1 hop.
 	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
-		minNumHops: 0,
+		minNumHops: 1,
 		maxNumHops: 1,
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("bob", "dave"),
+		},
+	})
+	require.NoError(t, err)
+
+	// If the max number of hops is 1, then only the B->D path is chosen
+	assertPaths(paths, []string{
+		"bob,dave",
+	})
+
+	// 6.2) Extend the search to include 2 hops along with the B-D channel
+	// restriction.
+	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
+		minNumHops: 1,
+		maxNumHops: 2,
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("bob", "dave"),
+		},
 	})
 	require.NoError(t, err)
 
 	// We expect the following paths:
-	//	- D
 	//	- B, D
-	// 	- C, D
-	// The (A, D) path is not chosen since A does not advertise the route
-	// blinding feature bit. The (G, D) path is not chosen since G does not
-	// have any other known channels.
-	assertPaths(paths, []string{
-		"dave",
-		"bob,dave",
-		"charlie,dave",
-	})
-
-	// 7) Restrict the min & max path length such that we only include paths
-	// with one hop other than the destination hop. Now with bob-dave as the
-	// incoming channel.
-	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
-		minNumHops:              1,
-		maxNumHops:              1,
-		incomingChainedChannels: []uint64{2},
-	})
-	require.NoError(t, err)
-
-	// Expect only B->D path.
-	assertPaths(paths, []string{
-		"bob,dave",
-	})
-
-	// 8) Extend the search to include 2 hops other than the destination,
-	// with bob-dave as the incoming channel.
-	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
-		minNumHops:              1,
-		maxNumHops:              2,
-		incomingChainedChannels: []uint64{2},
-	})
-	require.NoError(t, err)
-
-	// We expect the following paths:
 	//	- F, B, D
 	// 	- E, B, D
 	assertPaths(paths, []string{
+		"bob,dave",
 		"frank,bob,dave",
 		"eve,bob,dave",
 	})
 
-	// 9) Extend the search even further and also increase the minimum path
-	// length, but this time with charlie-dave as the incoming channel.
-	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
-		minNumHops:              2,
-		maxNumHops:              3,
-		incomingChainedChannels: []uint64{3},
-	})
-	require.NoError(t, err)
-
-	// We expect the following paths:
-	//	- E, C, D
-	// 	- B, E, C, D
-	assertPaths(paths, []string{
-		"eve,charlie,dave",
-		"bob,eve,charlie,dave",
-	})
-
-	// 10) Repeat the above test but instruct the function to never use
-	// charlie.
+	// 6.3) Repeat the above test but instruct the function to never use
+	// bob. This should fail since bob owns one of the channels in the
+	// partially specified path.
 	_, err = ctx.findBlindedPaths(&blindedPathRestrictions{
-		minNumHops:              2,
-		maxNumHops:              3,
-		nodeOmissionSet:         fn.NewSet(ctx.keyFromAlias("charlie")),
-		incomingChainedChannels: []uint64{3},
+		minNumHops:      1,
+		maxNumHops:      2,
+		nodeOmissionSet: fn.NewSet(ctx.keyFromAlias("bob")),
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("bob", "dave"),
+		},
 	})
 	require.ErrorContains(t, err, "cannot simultaneously be included in "+
 		"the omission set and in the partially specified path")
 
-	// 11) Test the circular route error.
-	_, err = ctx.findBlindedPaths(&blindedPathRestrictions{
-		minNumHops:              2,
-		maxNumHops:              3,
-		incomingChainedChannels: []uint64{2, 7, 6, 3},
+	// 6.4) Repeat it again but this time omit frank and demonstrate that
+	// the resulting set contains all the results from 6.2 except for the
+	// frank path.
+	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
+		minNumHops:      1,
+		maxNumHops:      2,
+		nodeOmissionSet: fn.NewSet(ctx.keyFromAlias("frank")),
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("bob", "dave"),
+		},
+	})
+	require.NoError(t, err)
+
+	// We expect the following paths:
+	//	- B, D
+	// 	- E, B, D
+	assertPaths(paths, []string{
+		"bob,dave",
+		"eve,bob,dave",
+	})
+
+	// 6.5) Users may specify channels to nodes that do not signal route
+	// blinding (like A). So if we specify the A-D channel, we should get
+	// valid paths.
+	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
+		minNumHops: 1,
+		maxNumHops: 4,
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("dave", "alice"),
+		},
+	})
+	require.NoError(t, err)
+
+	// We expect the following paths:
+	// 	- A, D
+	// 	- F, A, D
+	// 	- B, F, A, D
+	// 	- E, B, F, A, D
+	assertPaths(paths, []string{
+		"alice,dave",
+		"frank,alice,dave",
+		"bob,frank,alice,dave",
+		"eve,bob,frank,alice,dave",
+	})
+
+	// 6.6) Assert that an error is returned if a user accidentally tries
+	// to force a circular path.
+	_, err = ctx.findBlindedPaths(&blindedPathRestrictions{
+		minNumHops: 2,
+		maxNumHops: 3,
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("dave", "alice"),
+			ctx.nodePairChannel("alice", "frank"),
+			ctx.nodePairChannel("frank", "bob"),
+			ctx.nodePairChannel("bob", "dave"),
+		},
+	})
+	require.ErrorContains(t, err, "circular route")
+
+	// 6.7) Test specifying a chain of incoming channels. We specify
+	// the following incoming list: [A->D, F->A].
+	paths, err = ctx.findBlindedPaths(&blindedPathRestrictions{
+		minNumHops: 1,
+		maxNumHops: 4,
+		incomingChainedChannels: []uint64{
+			ctx.nodePairChannel("dave", "alice"),
+			ctx.nodePairChannel("alice", "frank"),
+		},
+	})
+	require.NoError(t, err)
+
+	// We expect the following paths:
+	// 	- F, A, D
+	// 	- B, F, A, D
+	// 	- E, B, F, A, D
+	assertPaths(paths, []string{
+		"frank,alice,dave",
+		"bob,frank,alice,dave",
+		"eve,bob,frank,alice,dave",
 	})
-	require.ErrorContains(t, err, "a circular route cannot be specified")
 }

routing/router.go

@@ -699,8 +699,8 @@ func (r *ChannelRouter) FindBlindedPaths(destination route.Vertex,
 				"path since it resulted in an low "+
 				"probability path(%.3f)",
 				route.ChanIDString(routeWithProbability.route),
-				routeWithProbability.probability,
-			)
+				routeWithProbability.probability)
+
 			continue
 		}