[3/4] Route Blinding: send MPP over multiple blinded paths

docs/release-notes/release-notes-0.18.1.md

@@ -40,6 +40,9 @@
 
 * [Generate and send to](https://github.com/lightningnetwork/lnd/pull/8735) an 
   invoice with blinded paths.
+
+* Add the ability to [send to use multiple blinded payment 
+  paths](https://github.com/lightningnetwork/lnd/pull/8764) in an MP payment.
 
 ## Testing
 ## Database

itest/list_on_test.go

@@ -590,6 +590,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "mpp to single blinded path",
 		TestFunc: testMPPToSingleBlindedPath,
 	},
+	{
+		Name:     "mpp to multiple blinded paths",
+		TestFunc: testMPPToMultipleBlindedPaths,
+	},
 	{
 		Name:     "removetx",
 		TestFunc: testRemoveTx,

itest/lnd_route_blinding_test.go

@@ -1042,3 +1042,166 @@ func testMPPToSingleBlindedPath(ht *lntest.HarnessTest) {
 		ht.AssertNumWaitingClose(hn, 0)
 	}
 }
+
+// testMPPToMultipleBlindedPaths tests that a two-shard MPP payment can be sent
+// over a multiple blinded paths. The following network is created where Dave
+// is the recipient and Alice the sender. Dave will create an invoice containing
+// two blinded paths: one with Bob at the intro node and one with Carol as the
+// intro node. Channel liquidity will be set up in such a way that Alice will be
+// forced to send one shared via the Bob->Dave route and one over the
+// Carol->Dave route.
+//
+//		   --- Bob ---
+//	          /            \
+//	      Alice           Dave
+//		  \	       /
+//		   --- Carol ---
+func testMPPToMultipleBlindedPaths(ht *lntest.HarnessTest) {
+	alice, bob := ht.Alice, ht.Bob
+
+	// Create a four-node context consisting of Alice, Bob and three new
+	// nodes.
+	dave := ht.NewNode("dave", []string{
+		"--invoices.blinding.min-num-hops=1",
+		"--invoices.blinding.max-num-hops=1",
+	})
+	carol := ht.NewNode("carol", nil)
+
+	// Connect nodes to ensure propagation of channels.
+	ht.EnsureConnected(alice, carol)
+	ht.EnsureConnected(alice, carol)
+	ht.EnsureConnected(carol, dave)
+	ht.EnsureConnected(bob, dave)
+
+	// Fund the new nodes.
+	ht.FundCoinsUnconfirmed(btcutil.SatoshiPerBitcoin, carol)
+	ht.FundCoinsUnconfirmed(btcutil.SatoshiPerBitcoin, dave)
+	ht.MineBlocks(1)
+
+	const paymentAmt = btcutil.Amount(300000)
+
+	nodes := []*node.HarnessNode{alice, bob, carol, dave}
+
+	reqs := []*lntest.OpenChannelRequest{
+		{
+			Local:  alice,
+			Remote: bob,
+			Param: lntest.OpenChannelParams{
+				Amt: paymentAmt * 2 / 3,
+			},
+		},
+		{
+			Local:  alice,
+			Remote: carol,
+			Param: lntest.OpenChannelParams{
+				Amt: paymentAmt * 2 / 3,
+			},
+		},
+		{
+			Local:  bob,
+			Remote: dave,
+			Param:  lntest.OpenChannelParams{Amt: paymentAmt * 2},
+		},
+		{
+			Local:  carol,
+			Remote: dave,
+			Param:  lntest.OpenChannelParams{Amt: paymentAmt * 2},
+		},
+	}
+
+	channelPoints := ht.OpenMultiChannelsAsync(reqs)
+
+	// Make sure every node has heard every channel.
+	for _, hn := range nodes {
+		for _, cp := range channelPoints {
+			ht.AssertTopologyChannelOpen(hn, cp)
+		}
+
+		// Each node should have exactly 5 edges.
+		ht.AssertNumEdges(hn, len(channelPoints), false)
+	}
+
+	// Ok now make a payment that must be slit to succeed.
+
+	// Make Dave create an invoice for Alice to pay
+	invoice := &lnrpc.Invoice{
+		Memo:  "test",
+		Value: int64(paymentAmt),
+		Blind: true,
+	}
+	invoiceResp := dave.RPC.AddInvoice(invoice)
+
+	// Assert that two blinded paths are included in the invoice.
+	payReq := dave.RPC.DecodePayReq(invoiceResp.PaymentRequest)
+	require.Len(ht, payReq.BlindedPaths, 2)
+
+	sendReq := &routerrpc.SendPaymentRequest{
+		PaymentRequest: invoiceResp.PaymentRequest,
+		MaxParts:       10,
+		TimeoutSeconds: 60,
+		FeeLimitMsat:   noFeeLimitMsat,
+	}
+	payment := ht.SendPaymentAssertSettled(alice, sendReq)
+
+	preimageBytes, err := hex.DecodeString(payment.PaymentPreimage)
+	require.NoError(ht, err)
+
+	preimage, err := lntypes.MakePreimage(preimageBytes)
+	require.NoError(ht, err)
+
+	hash, err := lntypes.MakeHash(invoiceResp.RHash)
+	require.NoError(ht, err)
+
+	// Make sure we got the preimage.
+	require.True(ht, preimage.Matches(hash), "preimage doesn't match")
+
+	// Check that Alice split the payment in at least two shards. Because
+	// the hand-off of the htlc to the link is asynchronous (via a mailbox),
+	// there is some non-determinism in the process. Depending on whether
+	// the new pathfinding round is started before or after the htlc is
+	// locked into the channel, different sharding may occur. Therefore we
+	// can only check if the number of shards isn't below the theoretical
+	// minimum.
+	succeeded := 0
+	for _, htlc := range payment.Htlcs {
+		if htlc.Status == lnrpc.HTLCAttempt_SUCCEEDED {
+			succeeded++
+		}
+	}
+
+	const minExpectedShards = 2
+	require.GreaterOrEqual(ht, succeeded, minExpectedShards,
+		"expected shards not reached")
+
+	// Make sure Dave show the invoice as settled for the full amount.
+	inv := dave.RPC.LookupInvoice(invoiceResp.RHash)
+
+	require.EqualValues(ht, paymentAmt, inv.AmtPaidSat,
+		"incorrect payment amt")
+
+	require.Equal(ht, lnrpc.Invoice_SETTLED, inv.State,
+		"Invoice not settled")
+
+	settled := 0
+	for _, htlc := range inv.Htlcs {
+		if htlc.State == lnrpc.InvoiceHTLCState_SETTLED {
+			settled++
+		}
+	}
+	require.Equal(ht, succeeded, settled, "num of HTLCs wrong")
+
+	// Close all channels without mining the closing transactions.
+	ht.CloseChannelAssertPending(alice, channelPoints[0], false)
+	ht.CloseChannelAssertPending(alice, channelPoints[1], false)
+	ht.CloseChannelAssertPending(bob, channelPoints[2], false)
+	ht.CloseChannelAssertPending(carol, channelPoints[3], false)
+
+	// Now mine a block to include all the closing transactions. (first
+	// iteration: no blinded paths)
+	ht.MineBlocks(1)
+
+	// Assert that the channels are closed.
+	for _, hn := range nodes {
+		ht.AssertNumWaitingClose(hn, 0)
+	}
+}

lnrpc/routerrpc/router_backend.go

@@ -280,7 +280,7 @@ func (r *RouterBackend) parseQueryRoutesRequest(in *lnrpc.QueryRoutesRequest) (
 	var (
 		targetPubKey   *route.Vertex
 		routeHintEdges map[route.Vertex][]routing.AdditionalEdge
-		blindedPmt     *routing.BlindedPayment
+		blindedPathSet *routing.BlindedPaymentPathSet
 
 		// finalCLTVDelta varies depending on whether we're sending to
 		// a blinded route or an unblinded node. For blinded paths,
@@ -297,13 +297,14 @@ func (r *RouterBackend) parseQueryRoutesRequest(in *lnrpc.QueryRoutesRequest) (
 	// Validate that the fields provided in the request are sane depending
 	// on whether it is using a blinded path or not.
 	if len(in.BlindedPaymentPaths) > 0 {
-		blindedPmt, err = parseBlindedPayment(in)
+		blindedPathSet, err = parseBlindedPaymentPaths(in)
 		if err != nil {
 			return nil, err
 		}
 
-		if blindedPmt.Features != nil {
-			destinationFeatures = blindedPmt.Features.Clone()
+		pathFeatures := blindedPathSet.Features()
+		if pathFeatures != nil {
+			destinationFeatures = pathFeatures.Clone()
 		}
 	} else {
 		// If we do not have a blinded path, a target pubkey must be
@@ -387,10 +388,10 @@ func (r *RouterBackend) parseQueryRoutesRequest(in *lnrpc.QueryRoutesRequest) (
 				fromNode, toNode, amt, capacity,
 			)
 		},
-		DestCustomRecords: record.CustomSet(in.DestCustomRecords),
-		CltvLimit:         cltvLimit,
-		DestFeatures:      destinationFeatures,
-		BlindedPayment:    blindedPmt,
+		DestCustomRecords:     record.CustomSet(in.DestCustomRecords),
+		CltvLimit:             cltvLimit,
+		DestFeatures:          destinationFeatures,
+		BlindedPaymentPathSet: blindedPathSet,
 	}
 
 	// Pass along an outgoing channel restriction if specified.
@@ -419,39 +420,24 @@ func (r *RouterBackend) parseQueryRoutesRequest(in *lnrpc.QueryRoutesRequest) (
 
 	return routing.NewRouteRequest(
 		sourcePubKey, targetPubKey, amt, in.TimePref, restrictions,
-		customRecords, routeHintEdges, blindedPmt, finalCLTVDelta,
+		customRecords, routeHintEdges, blindedPathSet,
+		finalCLTVDelta,
 	)
 }
 
-func parseBlindedPayment(in *lnrpc.QueryRoutesRequest) (
-	*routing.BlindedPayment, error) {
+func parseBlindedPaymentPaths(in *lnrpc.QueryRoutesRequest) (
+	*routing.BlindedPaymentPathSet, error) {
 
 	if len(in.PubKey) != 0 {
 		return nil, fmt.Errorf("target pubkey: %x should not be set "+
 			"when blinded path is provided", in.PubKey)
 	}
 
-	if len(in.BlindedPaymentPaths) != 1 {
-		return nil, errors.New("query routes only supports a single " +
-			"blinded path")
-	}
-
-	blindedPath := in.BlindedPaymentPaths[0]
-
 	if len(in.RouteHints) > 0 {
 		return nil, errors.New("route hints and blinded path can't " +
 			"both be set")
 	}
 
-	blindedPmt, err := unmarshalBlindedPayment(blindedPath)
-	if err != nil {
-		return nil, fmt.Errorf("parse blinded payment: %w", err)
-	}
-
-	if err := blindedPmt.Validate(); err != nil {
-		return nil, fmt.Errorf("invalid blinded path: %w", err)
-	}
-
 	if in.FinalCltvDelta != 0 {
 		return nil, errors.New("final cltv delta should be " +
 			"zero for blinded paths")
@@ -466,7 +452,21 @@ func parseBlindedPayment(in *lnrpc.QueryRoutesRequest) (
 			"be populated in blinded path")
 	}
 
-	return blindedPmt, nil
+	paths := make([]*routing.BlindedPayment, len(in.BlindedPaymentPaths))
+	for i, paymentPath := range in.BlindedPaymentPaths {
+		blindedPmt, err := unmarshalBlindedPayment(paymentPath)
+		if err != nil {
+			return nil, fmt.Errorf("parse blinded payment: %w", err)
+		}
+
+		if err := blindedPmt.Validate(); err != nil {
+			return nil, fmt.Errorf("invalid blinded path: %w", err)
+		}
+
+		paths[i] = blindedPmt
+	}
+
+	return routing.NewBlindedPaymentPathSet(paths)
 }
 
 func unmarshalBlindedPayment(rpcPayment *lnrpc.BlindedPaymentPath) (
@@ -1001,28 +1001,24 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 		payIntent.Metadata = payReq.Metadata
 
 		if len(payReq.BlindedPaymentPaths) > 0 {
-			// NOTE: Currently we only choose a single payment path.
-			// This will be updated in a future PR to handle
-			// multiple blinded payment paths.
-			path := payReq.BlindedPaymentPaths[0]
-			if len(path.Hops) == 0 {
-				return nil, fmt.Errorf("a blinded payment " +
-					"must have at least 1 hop")
+			pathSet, err := BuildBlindedPathSet(
+				payReq.BlindedPaymentPaths,
+			)
+			if err != nil {
+				return nil, err
 			}
+			payIntent.BlindedPathSet = pathSet
 
-			finalHop := path.Hops[len(path.Hops)-1]
-
-			payIntent.BlindedPayment = MarshalBlindedPayment(path)
-
-			// Replace the target node with the blinded public key
-			// of the blinded path's final node.
+			// Replace the target node with the target public key
+			// of the blinded path set.
 			copy(
 				payIntent.Target[:],
-				finalHop.BlindedNodePub.SerializeCompressed(),
+				pathSet.TargetPubKey().SerializeCompressed(),
 			)
 
-			if !path.Features.IsEmpty() {
-				payIntent.DestFeatures = path.Features.Clone()
+			pathFeatures := pathSet.Features()
+			if !pathFeatures.IsEmpty() {
+				payIntent.DestFeatures = pathFeatures.Clone()
 			}
 		}
 	} else {
@@ -1163,9 +1159,29 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 	return payIntent, nil
 }
 
-// MarshalBlindedPayment marshals a zpay32.BLindedPaymentPath into a
+// BuildBlindedPathSet marshals a set of zpay32.BlindedPaymentPath and uses
+// the result to build a new routing.BlindedPaymentPathSet.
+func BuildBlindedPathSet(paths []*zpay32.BlindedPaymentPath) (
+	*routing.BlindedPaymentPathSet, error) {
+
+	marshalledPaths := make([]*routing.BlindedPayment, len(paths))
+	for i, path := range paths {
+		paymentPath := marshalBlindedPayment(path)
+
+		err := paymentPath.Validate()
+		if err != nil {
+			return nil, err
+		}
+
+		marshalledPaths[i] = paymentPath
+	}
+
+	return routing.NewBlindedPaymentPathSet(marshalledPaths)
+}
+
+// marshalBlindedPayment marshals a zpay32.BLindedPaymentPath into a
 // routing.BlindedPayment.
-func MarshalBlindedPayment(
+func marshalBlindedPayment(
 	path *zpay32.BlindedPaymentPath) *routing.BlindedPayment {
 
 	return &routing.BlindedPayment{