routing+channeldb: send payment metadata from invoice

channeldb/payments.go

@@ -1141,6 +1141,10 @@ func serializeHop(w io.Writer, h *route.Hop) error {
 		records = append(records, h.MPP.Record())
 	}
 
+	if h.Metadata != nil {
+		records = append(records, record.NewMetadataRecord(&h.Metadata))
+	}
+
 	// Final sanity check to absolutely rule out custom records that are not
 	// custom and write into the standard range.
 	if err := h.CustomRecords.Validate(); err != nil {
@@ -1255,6 +1259,13 @@ func deserializeHop(r io.Reader) (*route.Hop, error) {
 		h.MPP = mpp
 	}
 
+	metadataType := uint64(record.MetadataOnionType)
+	if metadata, ok := tlvMap[metadataType]; ok {
+		delete(tlvMap, metadataType)
+
+		h.Metadata = metadata
+	}
+
 	h.CustomRecords = tlvMap
 
 	return h, nil

channeldb/payments_test.go

@@ -31,7 +31,8 @@ var (
 			65536: []byte{},
 			80001: []byte{},
 		},
-		MPP: record.NewMPP(32, [32]byte{0x42}),
+		MPP:      record.NewMPP(32, [32]byte{0x42}),
+		Metadata: []byte{1, 2, 3},
 	}
 
 	testHop2 = &route.Hop{

docs/release-notes/release-notes-0.15.0.md

@@ -1,5 +1,16 @@
 # Release Notes
 
+## Payments
+
+Support according to the
+[spec](https://github.com/lightningnetwork/lightning-rfc/pull/912) has been
+added for [payment metadata in
+invoices](https://github.com/lightningnetwork/lnd/pull/5810). If metadata is
+present in the invoice, it is encoded as a tlv record for the receiver.
+
+This functionality unlocks future features such as [stateless
+invoices](https://lists.linuxfoundation.org/pipermail/lightning-dev/2021-September/003236.html).
+
 ## Security
 
 * [Misconfigured ZMQ

lnrpc/lightning.proto

@@ -2792,6 +2792,9 @@ message Hop {
     to drop off at each hop within the onion.
     */
     map<uint64, bytes> custom_records = 11;
+
+    // The payment metadata to send along with the payment to the payee.
+    bytes metadata = 13;
 }
 
 message MPPRecord {

lnrpc/lightning.swagger.json

@@ -4616,6 +4616,11 @@
             "format": "byte"
           },
           "description": "An optional set of key-value TLV records. This is useful within the context\nof the SendToRoute call as it allows callers to specify arbitrary K-V pairs\nto drop off at each hop within the onion."
+        },
+        "metadata": {
+          "type": "string",
+          "format": "byte",
+          "description": "The payment metadata to send along with the payment to the payee."
         }
       }
     },

lnrpc/routerrpc/router.swagger.json

@@ -819,6 +819,11 @@
             "format": "byte"
           },
           "description": "An optional set of key-value TLV records. This is useful within the context\nof the SendToRoute call as it allows callers to specify arbitrary K-V pairs\nto drop off at each hop within the onion."
+        },
+        "metadata": {
+          "type": "string",
+          "format": "byte",
+          "description": "The payment metadata to send along with the payment to the payee."
         }
       }
     },

lnrpc/routerrpc/router_backend.go

@@ -444,6 +444,7 @@ func (r *RouterBackend) MarshallRoute(route *route.Route) (*lnrpc.Route, error)
 			CustomRecords: hop.CustomRecords,
 			TlvPayload:    !hop.LegacyPayload,
 			MppRecord:     mpp,
+			Metadata:      hop.Metadata,
 		}
 		incomingAmt = hop.AmtToForward
 	}
@@ -766,6 +767,7 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 		payIntent.DestFeatures = payReq.Features
 		payIntent.PaymentAddr = payAddr
 		payIntent.PaymentRequest = []byte(rpcPayReq.PaymentRequest)
+		payIntent.Metadata = payReq.Metadata
 	} else {
 		// Otherwise, If the payment request field was not specified
 		// (and a custom route wasn't specified), construct the payment

lnwire/features.go

@@ -155,6 +155,16 @@ const (
 	// TODO: Decide on actual feature bit value.
 	ExplicitChannelTypeOptional = 45
 
+	// PaymentMetadataRequired is a required bit that denotes that if an
+	// invoice contains metadata, it must be passed along with the payment
+	// htlc(s).
+	PaymentMetadataRequired = 48
+
+	// PaymentMetadataOptional is an optional bit that denotes that if an
+	// invoice contains metadata, it may be passed along with the payment
+	// htlc(s).
+	PaymentMetadataOptional = 49
+
 	// ScriptEnforcedLeaseOptional is an optional feature bit that signals
 	// that the node requires channels having zero-fee second-level HTLC
 	// transactions, which also imply anchor commitments, along with an
@@ -218,6 +228,8 @@ var Features = map[FeatureBit]string{
 	WumboChannelsOptional:         "wumbo-channels",
 	AMPRequired:                   "amp",
 	AMPOptional:                   "amp",
+	PaymentMetadataOptional:       "payment-metadata",
+	PaymentMetadataRequired:       "payment-metadata",
 	ExplicitChannelTypeOptional:   "explicit-commitment-type",
 	ExplicitChannelTypeRequired:   "explicit-commitment-type",
 	ScriptEnforcedLeaseRequired:   "script-enforced-lease",

record/hop.go

@@ -16,6 +16,10 @@ const (
 	// NextHopOnionType is the type used in the onion to reference the ID
 	// of the next hop.
 	NextHopOnionType tlv.Type = 6
+
+	// MetadataOnionType is the type used in the onion for the payment
+	// metadata.
+	MetadataOnionType tlv.Type = 16
 )
 
 // NewAmtToFwdRecord creates a tlv.Record that encodes the amount_to_forward
@@ -45,3 +49,15 @@ func NewLockTimeRecord(lockTime *uint32) tlv.Record {
 func NewNextHopIDRecord(cid *uint64) tlv.Record {
 	return tlv.MakePrimitiveRecord(NextHopOnionType, cid)
 }
+
+// NewMetadataRecord creates a tlv.Record that encodes the metadata (type 10)
+// for an onion payload.
+func NewMetadataRecord(metadata *[]byte) tlv.Record {
+	return tlv.MakeDynamicRecord(
+		MetadataOnionType, metadata,
+		func() uint64 {
+			return uint64(len(*metadata))
+		},
+		tlv.EVarBytes, tlv.DVarBytes,
+	)
+}

routing/pathfind.go

@@ -89,6 +89,10 @@ type finalHopParams struct {
 	cltvDelta   uint16
 	records     record.CustomSet
 	paymentAddr *[32]byte
+
+	// metadata is additional data that is sent along with the payment to
+	// the payee.
+	metadata []byte
 }
 
 // newRoute constructs a route using the provided path and final hop constraints.
@@ -138,6 +142,7 @@ func newRoute(sourceVertex route.Vertex,
 			tlvPayload       bool
 			customRecords    record.CustomSet
 			mpp              *record.MPP
+			metadata         []byte
 		)
 
 		// Define a helper function that checks this edge's feature
@@ -202,6 +207,8 @@ func newRoute(sourceVertex route.Vertex,
 					*finalHop.paymentAddr,
 				)
 			}
+
+			metadata = finalHop.metadata
 		} else {
 			// The amount that the current hop needs to forward is
 			// equal to the incoming amount of the next hop.
@@ -232,6 +239,7 @@ func newRoute(sourceVertex route.Vertex,
 			LegacyPayload:    !tlvPayload,
 			CustomRecords:    customRecords,
 			MPP:              mpp,
+			Metadata:         metadata,
 		}
 
 		hops = append([]*route.Hop{currentHop}, hops...)
@@ -330,6 +338,10 @@ type RestrictParams struct {
 	// mitigate probing vectors and payment sniping attacks on overpaid
 	// invoices.
 	PaymentAddr *[32]byte
+
+	// Metadata is additional data that is sent along with the payment to
+	// the payee.
+	Metadata []byte
 }
 
 // PathFindingConfig defines global parameters that control the trade-off in
@@ -474,6 +486,14 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 		return nil, errNoPaymentAddr
 	}
 
+	// If the caller needs to send custom records, check that our
+	// destination feature vector supports TLV.
+	if r.Metadata != nil &&
+		!features.HasFeature(lnwire.TLVOnionPayloadOptional) {
+
+		return nil, errNoTlvPayload
+	}
+
 	// Set up outgoing channel map for quicker access.
 	var outgoingChanMap map[uint64]struct{}
 	if len(r.OutgoingChannelIDs) > 0 {
@@ -547,7 +567,8 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 		LegacyPayload: !features.HasFeature(
 			lnwire.TLVOnionPayloadOptional,
 		),
-		MPP: mpp,
+		MPP:      mpp,
+		Metadata: r.Metadata,
 	}
 
 	// We can't always assume that the end destination is publicly

routing/pathfind_test.go

@@ -28,6 +28,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/stretchr/testify/require"
 )
 
 const (
@@ -840,6 +841,9 @@ func TestPathFinding(t *testing.T) {
 	}, {
 		name: "route to self",
 		fn:   runRouteToSelf,
+	}, {
+		name: "with metadata",
+		fn:   runFindPathWithMetadata,
 	}}
 
 	// Run with graph cache enabled.
@@ -866,6 +870,46 @@ func TestPathFinding(t *testing.T) {
 	}
 }
 
+// runFindPathWithMetadata tests that metadata is taken into account during
+// pathfinding.
+func runFindPathWithMetadata(t *testing.T, useCache bool) {
+	testChannels := []*testChannel{
+		symmetricTestChannel("alice", "bob", 100000, &testChannelPolicy{
+			Expiry:  144,
+			FeeRate: 400,
+			MinHTLC: 1,
+			MaxHTLC: 100000000,
+		}),
+	}
+
+	ctx := newPathFindingTestContext(t, useCache, testChannels, "alice")
+	defer ctx.cleanup()
+
+	paymentAmt := lnwire.NewMSatFromSatoshis(100)
+	target := ctx.keyFromAlias("bob")
+
+	// Assert that a path is found when metadata is specified.
+	ctx.restrictParams.Metadata = []byte{1, 2, 3}
+	ctx.restrictParams.DestFeatures = tlvFeatures
+
+	path, err := ctx.findPath(target, paymentAmt)
+	require.NoError(t, err)
+	require.Len(t, path, 1)
+
+	// Assert that no path is found when metadata is too large.
+	ctx.restrictParams.Metadata = make([]byte, 2000)
+
+	_, err = ctx.findPath(target, paymentAmt)
+	require.ErrorIs(t, errNoPathFound, err)
+
+	// Assert that tlv payload support takes precedence over metadata
+	// issues.
+	ctx.restrictParams.DestFeatures = lnwire.EmptyFeatureVector()
+
+	_, err = ctx.findPath(target, paymentAmt)
+	require.ErrorIs(t, errNoTlvPayload, err)
+}
+
 // runFindLowestFeePath tests that out of two routes with identical total
 // time lock values, the route with the lowest total fee should be returned.
 // The fee rates are chosen such that the test failed on the previous edge
@@ -1340,6 +1384,9 @@ func TestNewRoute(t *testing.T) {
 
 		paymentAddr *[32]byte
 
+		// metadata is the payment metadata to attach to the route.
+		metadata []byte
+
 		// expectedFees is a list of fees that every hop is expected
 		// to charge for forwarding.
 		expectedFees []lnwire.MilliSatoshi
@@ -1380,6 +1427,7 @@ func TestNewRoute(t *testing.T) {
 			hops: []*channeldb.CachedEdgePolicy{
 				createHop(100, 1000, 1000000, 10),
 			},
+			metadata:              []byte{1, 2, 3},
 			expectedFees:          []lnwire.MilliSatoshi{0},
 			expectedTimeLocks:     []uint32{1},
 			expectedTotalAmount:   100000,
@@ -1561,6 +1609,12 @@ func TestNewRoute(t *testing.T) {
 					" but got: %v instead",
 					testCase.expectedMPP, finalHop.MPP)
 			}
+
+			if !bytes.Equal(finalHop.Metadata, testCase.metadata) {
+				t.Errorf("Expected final metadata field: %v, "+
+					" but got: %v instead",
+					testCase.metadata, finalHop.Metadata)
+			}
 		}
 
 		t.Run(testCase.name, func(t *testing.T) {
@@ -1572,6 +1626,7 @@ func TestNewRoute(t *testing.T) {
 					cltvDelta:   finalHopCLTV,
 					records:     nil,
 					paymentAddr: testCase.paymentAddr,
+					metadata:    testCase.metadata,
 				},
 			)
 

routing/payment_session.go

@@ -257,6 +257,7 @@ func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi,
 		DestCustomRecords:  p.payment.DestCustomRecords,
 		DestFeatures:       p.payment.DestFeatures,
 		PaymentAddr:        p.payment.PaymentAddr,
+		Metadata:           p.payment.Metadata,
 	}
 
 	finalHtlcExpiry := int32(height) + int32(finalCltvDelta)
@@ -388,6 +389,7 @@ func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi,
 				cltvDelta:   finalCltvDelta,
 				records:     p.payment.DestCustomRecords,
 				paymentAddr: p.payment.PaymentAddr,
+				metadata:    p.payment.Metadata,
 			},
 		)
 		if err != nil {

routing/route/route.go

@@ -127,6 +127,10 @@ type Hop struct {
 	// understand the new TLV payload, so we must instead use the legacy
 	// payload.
 	LegacyPayload bool
+
+	// Metadata is additional data that is sent along with the payment to
+	// the payee.
+	Metadata []byte
 }
 
 // Copy returns a deep copy of the Hop.
@@ -205,6 +209,13 @@ func (h *Hop) PackHopPayload(w io.Writer, nextChanID uint64) error {
 		}
 	}
 
+	// If metadata is specified, generate a tlv record for it.
+	if h.Metadata != nil {
+		records = append(records,
+			record.NewMetadataRecord(&h.Metadata),
+		)
+	}
+
 	// Append any custom types destined for this hop.
 	tlvRecords := tlv.MapToRecords(h.CustomRecords)
 	records = append(records, tlvRecords...)
@@ -259,6 +270,11 @@ func (h *Hop) PayloadSize(nextChanID uint64) uint64 {
 		addRecord(record.AMPOnionType, h.AMP.PayloadSize())
 	}
 
+	// Add metadata if present.
+	if h.Metadata != nil {
+		addRecord(record.MetadataOnionType, uint64(len(h.Metadata)))
+	}
+
 	// Add custom records.
 	for k, v := range h.CustomRecords {
 		addRecord(tlv.Type(k), uint64(len(v)))

routing/route/route_test.go

@@ -186,6 +186,7 @@ func TestPayloadSize(t *testing.T) {
 				100000:  {1, 2, 3},
 				1000000: {4, 5},
 			},
+			Metadata: []byte{10, 11},
 		},
 	}