Merge pull request #3442 from cfromknecht/router-registry

single-shot, sender-side mpp via sendtoroute

channeldb/payments.go

@@ -14,6 +14,7 @@ import (
 	"github.com/coreos/bbolt"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/tlv"
 )
@@ -508,7 +509,9 @@ func deserializePaymentAttemptInfo(r io.Reader) (*PaymentAttemptInfo, error) {
 
 func serializeHop(w io.Writer, h *route.Hop) error {
 	if err := WriteElements(w,
-		h.PubKeyBytes[:], h.ChannelID, h.OutgoingTimeLock,
+		h.PubKeyBytes[:],
+		h.ChannelID,
+		h.OutgoingTimeLock,
 		h.AmtToForward,
 	); err != nil {
 		return err
@@ -525,10 +528,23 @@ func serializeHop(w io.Writer, h *route.Hop) error {
 		return WriteElements(w, uint32(0))
 	}
 
+	// Gather all non-primitive TLV records so that they can be serialized
+	// as a single blob.
+	//
+	// TODO(conner): add migration to unify all fields in a single TLV
+	// blobs. The split approach will cause headaches down the road as more
+	// fields are added, which we can avoid by having a single TLV stream
+	// for all payload fields.
+	var records []tlv.Record
+	if h.MPP != nil {
+		records = append(records, h.MPP.Record())
+	}
+	records = append(records, h.TLVRecords...)
+
 	// Otherwise, we'll transform our slice of records into a map of the
 	// raw bytes, then serialize them in-line with a length (number of
 	// elements) prefix.
-	mapRecords, err := tlv.RecordsToMap(h.TLVRecords)
+	mapRecords, err := tlv.RecordsToMap(records)
 	if err != nil {
 		return err
 	}
@@ -604,6 +620,29 @@ func deserializeHop(r io.Reader) (*route.Hop, error) {
 		tlvMap[tlvType] = rawRecordBytes
 	}
 
+	// If the MPP type is present, remove it from the generic TLV map and
+	// parse it back into a proper MPP struct.
+	//
+	// TODO(conner): add migration to unify all fields in a single TLV
+	// blobs. The split approach will cause headaches down the road as more
+	// fields are added, which we can avoid by having a single TLV stream
+	// for all payload fields.
+	mppType := uint64(record.MPPOnionType)
+	if mppBytes, ok := tlvMap[mppType]; ok {
+		delete(tlvMap, mppType)
+
+		var (
+			mpp    = &record.MPP{}
+			mppRec = mpp.Record()
+			r      = bytes.NewReader(mppBytes)
+		)
+		err := mppRec.Decode(r, uint64(len(mppBytes)))
+		if err != nil {
+			return nil, err
+		}
+		h.MPP = mpp
+	}
+
 	tlvRecords, err := tlv.MapToRecords(tlvMap)
 	if err != nil {
 		return nil, err

channeldb/payments_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/tlv"
 )
@@ -31,6 +32,7 @@ var (
 			tlv.MakeStaticRecord(1, nil, 3, tlvEncoder, nil),
 			tlv.MakeStaticRecord(2, nil, 3, tlvEncoder, nil),
 		},
+		MPP: record.NewMPP(32, [32]byte{0x42}),
 	}
 
 	testHop2 = &route.Hop{
@@ -46,8 +48,8 @@ var (
 		TotalAmount:   1234567,
 		SourcePubKey:  route.NewVertex(pub),
 		Hops: []*route.Hop{
-			testHop1,
 			testHop2,
+			testHop1,
 		},
 	}
 )

contractcourt/interfaces.go

@@ -21,7 +21,7 @@ type Registry interface {
 	NotifyExitHopHtlc(payHash lntypes.Hash, paidAmount lnwire.MilliSatoshi,
 		expiry uint32, currentHeight int32,
 		circuitKey channeldb.CircuitKey, hodlChan chan<- interface{},
-		eob []byte) (*invoices.HodlEvent, error)
+		payload invoices.Payload) (*invoices.HodlEvent, error)
 
 	// HodlUnsubscribeAll unsubscribes from all hodl events.
 	HodlUnsubscribeAll(subscriber chan<- interface{})

contractcourt/mock_registry_test.go

@@ -24,7 +24,7 @@ type mockRegistry struct {
 func (r *mockRegistry) NotifyExitHopHtlc(payHash lntypes.Hash,
 	paidAmount lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
 	circuitKey channeldb.CircuitKey, hodlChan chan<- interface{},
-	eob []byte) (*invoices.HodlEvent, error) {
+	payload invoices.Payload) (*invoices.HodlEvent, error) {
 
 	r.notifyChan <- notifyExitHopData{
 		hodlChan:      hodlChan,

htlcswitch/hop/iterator.go

@@ -16,15 +16,13 @@ import (
 // interpret the forwarding information encoded within the HTLC packet, and hop
 // to encode the forwarding information for the _next_ hop.
 type Iterator interface {
-	// ForwardingInstructions returns the set of fields that detail exactly
+	// HopPayload returns the set of fields that detail exactly _how_ this
-	// _how_ this hop should forward the HTLC to the next hop.
+	// hop should forward the HTLC to the next hop.  Additionally, the
-	// Additionally, the information encoded within the returned
+	// information encoded within the returned ForwardingInfo is to be used
-	// ForwardingInfo is to be used by each hop to authenticate the
+	// by each hop to authenticate the information given to it by the prior
-	// information given to it by the prior hop.
+	// hop. The payload will also contain any additional TLV fields provided
-	ForwardingInstructions() (ForwardingInfo, error)
+	// by the sender.
-
+	HopPayload() (*Payload, error)
-	// ExtraOnionBlob returns the additional EOB data (if available).
-	ExtraOnionBlob() []byte
 
 	// EncodeNextHop encodes the onion packet destined for the next hop
 	// into the passed io.Writer.
@@ -72,50 +70,35 @@ func (r *sphinxHopIterator) EncodeNextHop(w io.Writer) error {
 	return r.processedPacket.NextPacket.Encode(w)
 }
 
-// ForwardingInstructions returns the set of fields that detail exactly _how_
+// HopPayload returns the set of fields that detail exactly _how_ this hop
-// this hop should forward the HTLC to the next hop.  Additionally, the
+// should forward the HTLC to the next hop.  Additionally, the information
-// information encoded within the returned ForwardingInfo is to be used by each
+// encoded within the returned ForwardingInfo is to be used by each hop to
-// hop to authenticate the information given to it by the prior hop.
+// authenticate the information given to it by the prior hop. The payload will
+// also contain any additional TLV fields provided by the sender.
 //
 // NOTE: Part of the HopIterator interface.
-func (r *sphinxHopIterator) ForwardingInstructions() (ForwardingInfo, error) {
+func (r *sphinxHopIterator) HopPayload() (*Payload, error) {
 	switch r.processedPacket.Payload.Type {
+
 	// If this is the legacy payload, then we'll extract the information
 	// directly from the pre-populated ForwardingInstructions field.
 	case sphinx.PayloadLegacy:
 		fwdInst := r.processedPacket.ForwardingInstructions
-		p := NewLegacyPayload(fwdInst)
+		return NewLegacyPayload(fwdInst), nil
-
-		return p.ForwardingInfo(), nil
 
 	// Otherwise, if this is the TLV payload, then we'll make a new stream
 	// to decode only what we need to make routing decisions.
 	case sphinx.PayloadTLV:
-		p, err := NewPayloadFromReader(bytes.NewReader(
+		return NewPayloadFromReader(bytes.NewReader(
 			r.processedPacket.Payload.Payload,
 		))
-		if err != nil {
-			return ForwardingInfo{}, err
-		}
-
-		return p.ForwardingInfo(), nil
 
 	default:
-		return ForwardingInfo{}, fmt.Errorf("unknown "+
+		return nil, fmt.Errorf("unknown sphinx payload type: %v",
-			"sphinx payload type: %v",
 			r.processedPacket.Payload.Type)
 	}
 }
 
-// ExtraOnionBlob returns the additional EOB data (if available).
-func (r *sphinxHopIterator) ExtraOnionBlob() []byte {
-	if r.processedPacket.Payload.Type == sphinx.PayloadLegacy {
-		return nil
-	}
-
-	return r.processedPacket.Payload.Payload
-}
-
 // ExtractErrorEncrypter decodes and returns the ErrorEncrypter for this hop,
 // along with a failure code to signal if the decoding was successful. The
 // ErrorEncrypter is used to encrypt errors back to the sender in the event that

htlcswitch/hop/iterator_test.go

@@ -85,12 +85,13 @@ func TestSphinxHopIteratorForwardingInstructions(t *testing.T) {
 	for i, testCase := range testCases {
 		iterator.processedPacket = testCase.sphinxPacket
 
-		fwdInfo, err := iterator.ForwardingInstructions()
+		pld, err := iterator.HopPayload()
 		if err != nil {
 			t.Fatalf("#%v: unable to extract forwarding "+
 				"instructions: %v", i, err)
 		}
 
+		fwdInfo := pld.ForwardingInfo()
 		if fwdInfo != testCase.expectedFwdInfo {
 			t.Fatalf("#%v: wrong fwding info: expected %v, got %v",
 				i, spew.Sdump(testCase.expectedFwdInfo),

htlcswitch/hop/payload.go

@@ -81,6 +81,10 @@ type Payload struct {
 	// FwdInfo holds the basic parameters required for HTLC forwarding, e.g.
 	// amount, cltv, and next hop.
 	FwdInfo ForwardingInfo
+
+	// MPP holds the info provided in an option_mpp record when parsed from
+	// a TLV onion payload.
+	MPP *record.MPP
 }
 
 // NewLegacyPayload builds a Payload from the amount, cltv, and next hop
@@ -105,12 +109,14 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		cid  uint64
 		amt  uint64
 		cltv uint32
+		mpp  = &record.MPP{}
 	)
 
 	tlvStream, err := tlv.NewStream(
 		record.NewAmtToFwdRecord(&amt),
 		record.NewLockTimeRecord(&cltv),
 		record.NewNextHopIDRecord(&cid),
+		mpp.Record(),
 	)
 	if err != nil {
 		return nil, err
@@ -151,6 +157,12 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		return nil, err
 	}
 
+	// If no MPP field was parsed, set the MPP field on the resulting
+	// payload to nil.
+	if _, ok := parsedTypes[record.MPPOnionType]; !ok {
+		mpp = nil
+	}
+
 	return &Payload{
 		FwdInfo: ForwardingInfo{
 			Network:         BitcoinNetwork,
@@ -158,6 +170,7 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 			AmountToForward: lnwire.MilliSatoshi(amt),
 			OutgoingCTLV:    cltv,
 		},
+		MPP: mpp,
 	}, nil
 }
 
@@ -179,6 +192,7 @@ func ValidateParsedPayloadTypes(parsedTypes tlv.TypeSet,
 	_, hasAmt := parsedTypes[record.AmtOnionType]
 	_, hasLockTime := parsedTypes[record.LockTimeOnionType]
 	_, hasNextHop := parsedTypes[record.NextHopOnionType]
+	_, hasMPP := parsedTypes[record.MPPOnionType]
 
 	switch {
 
@@ -207,7 +221,21 @@ func ValidateParsedPayloadTypes(parsedTypes tlv.TypeSet,
 			Violation: IncludedViolation,
 			FinalHop:  true,
 		}
+
+	// Intermediate nodes should never receive MPP fields.
+	case !isFinalHop && hasMPP:
+		return ErrInvalidPayload{
+			Type:      record.MPPOnionType,
+			Violation: IncludedViolation,
+			FinalHop:  isFinalHop,
+		}
 	}
 
 	return nil
 }
+
+// MultiPath returns the record corresponding the option_mpp parsed from the
+// onion payload.
+func (h *Payload) MultiPath() *record.MPP {
+	return h.MPP
+}

htlcswitch/hop/payload_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
 )
 
@@ -13,6 +14,7 @@ type decodePayloadTest struct {
 	name          string
 	payload       []byte
 	expErr        error
+	shouldHaveMPP bool
 }
 
 var decodePayloadTests = []decodePayloadTest{
@@ -79,9 +81,9 @@ var decodePayloadTests = []decodePayloadTest{
 	},
 	{
 		name:    "required type after omitted hop id",
-		payload: []byte{0x02, 0x00, 0x04, 0x00, 0x08, 0x00},
+		payload: []byte{0x02, 0x00, 0x04, 0x00, 0x0a, 0x00},
 		expErr: hop.ErrInvalidPayload{
-			Type:      8,
+			Type:      10,
 			Violation: hop.RequiredViolation,
 			FinalHop:  true,
 		},
@@ -89,10 +91,10 @@ var decodePayloadTests = []decodePayloadTest{
 	{
 		name: "required type after included hop id",
 		payload: []byte{0x02, 0x00, 0x04, 0x00, 0x06, 0x08, 0x01, 0x00,
-			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0a, 0x00,
 		},
 		expErr: hop.ErrInvalidPayload{
-			Type:      8,
+			Type:      10,
 			Violation: hop.RequiredViolation,
 			FinalHop:  false,
 		},
@@ -112,7 +114,7 @@ var decodePayloadTests = []decodePayloadTest{
 			0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
 		},
 		expErr: hop.ErrInvalidPayload{
-			Type:      6,
+			Type:      record.NextHopOnionType,
 			Violation: hop.IncludedViolation,
 			FinalHop:  true,
 		},
@@ -128,6 +130,60 @@ var decodePayloadTests = []decodePayloadTest{
 			FinalHop:  false,
 		},
 	},
+	{
+		name: "valid intermediate hop",
+		payload: []byte{0x02, 0x00, 0x04, 0x00, 0x06, 0x08, 0x01, 0x00,
+			0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		},
+		expErr: nil,
+	},
+	{
+		name:    "valid final hop",
+		payload: []byte{0x02, 0x00, 0x04, 0x00},
+		expErr:  nil,
+	},
+	{
+		name: "intermediate hop with mpp",
+		payload: []byte{
+			// amount
+			0x02, 0x00,
+			// cltv
+			0x04, 0x00,
+			// next hop id
+			0x06, 0x08,
+			0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+			// mpp
+			0x08, 0x21,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x08,
+		},
+		expErr: hop.ErrInvalidPayload{
+			Type:      record.MPPOnionType,
+			Violation: hop.IncludedViolation,
+			FinalHop:  false,
+		},
+	},
+	{
+		name: "final hop with mpp",
+		payload: []byte{
+			// amount
+			0x02, 0x00,
+			// cltv
+			0x04, 0x00,
+			// mpp
+			0x08, 0x21,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x08,
+		},
+		expErr:        nil,
+		shouldHaveMPP: true,
+	},
 }
 
 // TestDecodeHopPayloadRecordValidation asserts that parsing the payloads in the
@@ -142,9 +198,37 @@ func TestDecodeHopPayloadRecordValidation(t *testing.T) {
 }
 
 func testDecodeHopPayloadValidation(t *testing.T, test decodePayloadTest) {
-	_, err := hop.NewPayloadFromReader(bytes.NewReader(test.payload))
+	var (
+		testTotalMsat = lnwire.MilliSatoshi(8)
+		testAddr      = [32]byte{
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+			0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11,
+		}
+	)
+
+	p, err := hop.NewPayloadFromReader(bytes.NewReader(test.payload))
 	if !reflect.DeepEqual(test.expErr, err) {
 		t.Fatalf("expected error mismatch, want: %v, got: %v",
 			test.expErr, err)
 	}
+	if err != nil {
+		return
+	}
+
+	// Assert MPP fields if we expect them.
+	if test.shouldHaveMPP {
+		if p.MPP == nil {
+			t.Fatalf("payload should have MPP record")
+		}
+		if p.MPP.TotalMsat() != testTotalMsat {
+			t.Fatalf("invalid total msat")
+		}
+		if p.MPP.PaymentAddr() != testAddr {
+			t.Fatalf("invalid payment addr")
+		}
+	} else if p.MPP != nil {
+		t.Fatalf("unexpected MPP payload")
+	}
 }

htlcswitch/interfaces.go

@@ -27,7 +27,7 @@ type InvoiceDatabase interface {
 	NotifyExitHopHtlc(payHash lntypes.Hash, paidAmount lnwire.MilliSatoshi,
 		expiry uint32, currentHeight int32,
 		circuitKey channeldb.CircuitKey, hodlChan chan<- interface{},
-		eob []byte) (*invoices.HodlEvent, error)
+		payload invoices.Payload) (*invoices.HodlEvent, error)
 
 	// CancelInvoice attempts to cancel the invoice corresponding to the
 	// passed payment hash.

htlcswitch/link.go

@@ -2642,7 +2642,7 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 
 		heightNow := l.cfg.Switch.BestHeight()
 
-		fwdInfo, err := chanIterator.ForwardingInstructions()
+		pld, err := chanIterator.HopPayload()
 		if err != nil {
 			// If we're unable to process the onion payload, or we
 			// received invalid onion payload failure, then we
@@ -2671,11 +2671,12 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			continue
 		}
 
+		fwdInfo := pld.ForwardingInfo()
+
 		switch fwdInfo.NextHop {
 		case hop.Exit:
 			updated, err := l.processExitHop(
-				pd, obfuscator, fwdInfo, heightNow,
+				pd, obfuscator, fwdInfo, heightNow, pld,
-				chanIterator.ExtraOnionBlob(),
 			)
 			if err != nil {
 				l.fail(LinkFailureError{code: ErrInternalError},
@@ -2844,7 +2845,7 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 // returns a boolean indicating whether the commitment tx needs an update.
 func (l *channelLink) processExitHop(pd *lnwallet.PaymentDescriptor,
 	obfuscator hop.ErrorEncrypter, fwdInfo hop.ForwardingInfo,
-	heightNow uint32, eob []byte) (bool, error) {
+	heightNow uint32, payload invoices.Payload) (bool, error) {
 
 	// If hodl.ExitSettle is requested, we will not validate the final hop's
 	// ADD, nor will we settle the corresponding invoice or respond with the
@@ -2895,7 +2896,7 @@ func (l *channelLink) processExitHop(pd *lnwallet.PaymentDescriptor,
 
 	event, err := l.cfg.Registry.NotifyExitHopHtlc(
 		invoiceHash, pd.Amount, pd.Timeout, int32(heightNow),
-		circuitKey, l.hodlQueue.ChanIn(), eob,
+		circuitKey, l.hodlQueue.ChanIn(), payload,
 	)
 
 	switch err {

htlcswitch/link_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/coreos/bbolt"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/go-errors/errors"
+	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/build"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/contractcourt"
@@ -563,7 +564,7 @@ func TestExitNodeTimelockPayloadMismatch(t *testing.T) {
 	// per-hop payload for outgoing time lock to be the incorrect value.
 	// The proper value of the outgoing CLTV should be the policy set by
 	// the receiving node, instead we set it to be a random value.
-	hops[0].OutgoingCTLV = 500
+	hops[0].FwdInfo.OutgoingCTLV = 500
 	firstHop := n.firstBobChannelLink.ShortChanID()
 	_, err = makePayment(
 		n.aliceServer, n.bobServer, firstHop, hops, amount, htlcAmt,
@@ -616,7 +617,7 @@ func TestExitNodeAmountPayloadMismatch(t *testing.T) {
 	// per-hop payload for amount to be the incorrect value.  The proper
 	// value of the amount to forward should be the amount that the
 	// receiving node expects to receive.
-	hops[0].AmountToForward = 1
+	hops[0].FwdInfo.AmountToForward = 1
 	firstHop := n.firstBobChannelLink.ShortChanID()
 	_, err = makePayment(
 		n.aliceServer, n.bobServer, firstHop, hops, amount, htlcAmt,
@@ -4354,13 +4355,13 @@ func generateHtlcAndInvoice(t *testing.T,
 
 	htlcAmt := lnwire.NewMSatFromSatoshis(10000)
 	htlcExpiry := testStartingHeight + testInvoiceCltvExpiry
-	hops := []hop.ForwardingInfo{
+	hops := []*hop.Payload{
-		{
+		hop.NewLegacyPayload(&sphinx.HopData{
-			Network:         hop.BitcoinNetwork,
+			Realm:         [1]byte{}, // hop.BitcoinNetwork
-			NextHop:         hop.Exit,
+			NextAddress:   [8]byte{}, // hop.Exit,
-			AmountToForward: htlcAmt,
+			ForwardAmount: uint64(htlcAmt),
-			OutgoingCTLV:    uint32(htlcExpiry),
+			OutgoingCltv:  uint32(htlcExpiry),
-		},
+		}),
 	}
 	blob, err := generateRoute(hops...)
 	if err != nil {

htlcswitch/mock.go

@@ -265,16 +265,14 @@ func (s *mockServer) QuitSignal() <-chan struct{} {
 // mockHopIterator represents the test version of hop iterator which instead
 // of encrypting the path in onion blob just stores the path as a list of hops.
 type mockHopIterator struct {
-	hops []hop.ForwardingInfo
+	hops []*hop.Payload
 }
 
-func newMockHopIterator(hops ...hop.ForwardingInfo) hop.Iterator {
+func newMockHopIterator(hops ...*hop.Payload) hop.Iterator {
 	return &mockHopIterator{hops: hops}
 }
 
-func (r *mockHopIterator) ForwardingInstructions() (
+func (r *mockHopIterator) HopPayload() (*hop.Payload, error) {
-	hop.ForwardingInfo, error) {
-
 	h := r.hops[0]
 	r.hops = r.hops[1:]
 	return h, nil
@@ -300,7 +298,8 @@ func (r *mockHopIterator) EncodeNextHop(w io.Writer) error {
 	}
 
 	for _, hop := range r.hops {
-		if err := encodeFwdInfo(w, &hop); err != nil {
+		fwdInfo := hop.ForwardingInfo()
+		if err := encodeFwdInfo(w, &fwdInfo); err != nil {
 			return err
 		}
 	}
@@ -434,14 +433,22 @@ func (p *mockIteratorDecoder) DecodeHopIterator(r io.Reader, rHash []byte,
 	}
 	hopLength := binary.BigEndian.Uint32(b[:])
 
-	hops := make([]hop.ForwardingInfo, hopLength)
+	hops := make([]*hop.Payload, hopLength)
 	for i := uint32(0); i < hopLength; i++ {
-		f := &hop.ForwardingInfo{}
+		var f hop.ForwardingInfo
-		if err := decodeFwdInfo(r, f); err != nil {
+		if err := decodeFwdInfo(r, &f); err != nil {
 			return nil, lnwire.CodeTemporaryChannelFailure
 		}
 
-		hops[i] = *f
+		var nextHopBytes [8]byte
+		binary.BigEndian.PutUint64(nextHopBytes[:], f.NextHop.ToUint64())
+
+		hops[i] = hop.NewLegacyPayload(&sphinx.HopData{
+			Realm:         [1]byte{}, // hop.BitcoinNetwork
+			NextAddress:   nextHopBytes,
+			ForwardAmount: uint64(f.AmountToForward),
+			OutgoingCltv:  f.OutgoingCTLV,
+		})
 	}
 
 	return newMockHopIterator(hops...), lnwire.CodeNone
@@ -807,10 +814,11 @@ func (i *mockInvoiceRegistry) SettleHodlInvoice(preimage lntypes.Preimage) error
 func (i *mockInvoiceRegistry) NotifyExitHopHtlc(rhash lntypes.Hash,
 	amt lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
 	circuitKey channeldb.CircuitKey, hodlChan chan<- interface{},
-	eob []byte) (*invoices.HodlEvent, error) {
+	payload invoices.Payload) (*invoices.HodlEvent, error) {
 
 	event, err := i.registry.NotifyExitHopHtlc(
-		rhash, amt, expiry, currentHeight, circuitKey, hodlChan, eob,
+		rhash, amt, expiry, currentHeight, circuitKey, hodlChan,
+		payload,
 	)
 	if err != nil {
 		return nil, err

htlcswitch/test_utils.go

@@ -23,6 +23,7 @@ import (
 	"github.com/btcsuite/fastsha256"
 	"github.com/coreos/bbolt"
 	"github.com/go-errors/errors"
+	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/contractcourt"
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
@@ -601,7 +602,7 @@ func generatePayment(invoiceAmt, htlcAmt lnwire.MilliSatoshi, timelock uint32,
 }
 
 // generateRoute generates the path blob by given array of peers.
-func generateRoute(hops ...hop.ForwardingInfo) (
+func generateRoute(hops ...*hop.Payload) (
 	[lnwire.OnionPacketSize]byte, error) {
 
 	var blob [lnwire.OnionPacketSize]byte
@@ -642,13 +643,12 @@ type threeHopNetwork struct {
 // also the time lock value needed to route an HTLC with the target amount over
 // the specified path.
 func generateHops(payAmt lnwire.MilliSatoshi, startingHeight uint32,
-	path ...*channelLink) (lnwire.MilliSatoshi, uint32,
+	path ...*channelLink) (lnwire.MilliSatoshi, uint32, []*hop.Payload) {
-	[]hop.ForwardingInfo) {
 
 	totalTimelock := startingHeight
 	runningAmt := payAmt
 
-	hops := make([]hop.ForwardingInfo, len(path))
+	hops := make([]*hop.Payload, len(path))
 	for i := len(path) - 1; i >= 0; i-- {
 		// If this is the last hop, then the next hop is the special
 		// "exit node". Otherwise, we look to the "prior" hop.
@@ -676,7 +676,7 @@ func generateHops(payAmt lnwire.MilliSatoshi, startingHeight uint32,
 		amount := payAmt
 		if i != len(path)-1 {
 			prevHop := hops[i+1]
-			prevAmount := prevHop.AmountToForward
+			prevAmount := prevHop.ForwardingInfo().AmountToForward
 
 			fee := ExpectedFee(path[i].cfg.FwrdingPolicy, prevAmount)
 			runningAmt += fee
@@ -687,12 +687,15 @@ func generateHops(payAmt lnwire.MilliSatoshi, startingHeight uint32,
 			amount = runningAmt - fee
 		}
 
-		hops[i] = hop.ForwardingInfo{
+		var nextHopBytes [8]byte
-			Network:         hop.BitcoinNetwork,
+		binary.BigEndian.PutUint64(nextHopBytes[:], nextHop.ToUint64())
-			NextHop:         nextHop,
+
-			AmountToForward: amount,
+		hops[i] = hop.NewLegacyPayload(&sphinx.HopData{
-			OutgoingCTLV:    timeLock,
+			Realm:         [1]byte{}, // hop.BitcoinNetwork
-		}
+			NextAddress:   nextHopBytes,
+			ForwardAmount: uint64(amount),
+			OutgoingCltv:  timeLock,
+		})
 	}
 
 	return runningAmt, totalTimelock, hops
@@ -739,7 +742,7 @@ func waitForPayFuncResult(payFunc func() error, d time.Duration) error {
 // * from Alice to Carol through the Bob
 // * from Alice to some another peer through the Bob
 func makePayment(sendingPeer, receivingPeer lnpeer.Peer,
-	firstHop lnwire.ShortChannelID, hops []hop.ForwardingInfo,
+	firstHop lnwire.ShortChannelID, hops []*hop.Payload,
 	invoiceAmt, htlcAmt lnwire.MilliSatoshi,
 	timelock uint32) *paymentResponse {
 
@@ -773,7 +776,7 @@ func makePayment(sendingPeer, receivingPeer lnpeer.Peer,
 // preparePayment creates an invoice at the receivingPeer and returns a function
 // that, when called, launches the payment from the sendingPeer.
 func preparePayment(sendingPeer, receivingPeer lnpeer.Peer,
-	firstHop lnwire.ShortChannelID, hops []hop.ForwardingInfo,
+	firstHop lnwire.ShortChannelID, hops []*hop.Payload,
 	invoiceAmt, htlcAmt lnwire.MilliSatoshi,
 	timelock uint32) (*channeldb.Invoice, func() error, error) {
 
@@ -1265,7 +1268,7 @@ func (n *twoHopNetwork) stop() {
 }
 
 func (n *twoHopNetwork) makeHoldPayment(sendingPeer, receivingPeer lnpeer.Peer,
-	firstHop lnwire.ShortChannelID, hops []hop.ForwardingInfo,
+	firstHop lnwire.ShortChannelID, hops []*hop.Payload,
 	invoiceAmt, htlcAmt lnwire.MilliSatoshi,
 	timelock uint32, preimage lntypes.Preimage) chan error {
 

invoices/interface.go

@@ -0,0 +1,11 @@
+package invoices
+
+import "github.com/lightningnetwork/lnd/record"
+
+// Payload abstracts access to any additional fields provided in the final hop's
+// TLV onion payload.
+type Payload interface {
+	// MultiPath returns the record corresponding the option_mpp parsed from
+	// the onion payload.
+	MultiPath() *record.MPP
+}

invoices/invoiceregistry.go

@@ -429,7 +429,7 @@ func (i *InvoiceRegistry) LookupInvoice(rHash lntypes.Hash) (channeldb.Invoice,
 func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
 	amtPaid lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
 	circuitKey channeldb.CircuitKey, hodlChan chan<- interface{},
-	eob []byte) (*HodlEvent, error) {
+	payload Payload) (*HodlEvent, error) {
 
 	i.Lock()
 	defer i.Unlock()

lnrpc/routerrpc/router_backend.go

@@ -13,7 +13,9 @@ import (
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/lnrpc"
+	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/tlv"
@@ -352,6 +354,17 @@ func (r *RouterBackend) MarshallRoute(route *route.Route) (*lnrpc.Route, error)
 			chanCapacity = incomingAmt.ToSatoshis()
 		}
 
+		// Extract the MPP fields if present on this hop.
+		var mpp *lnrpc.MPPRecord
+		if hop.MPP != nil {
+			addr := hop.MPP.PaymentAddr()
+
+			mpp = &lnrpc.MPPRecord{
+				PaymentAddr:  addr[:],
+				TotalAmtMsat: int64(hop.MPP.TotalMsat()),
+			}
+		}
+
 		resp.Hops[i] = &lnrpc.Hop{
 			ChanId:           hop.ChannelID,
 			ChanCapacity:     int64(chanCapacity),
@@ -364,6 +377,7 @@ func (r *RouterBackend) MarshallRoute(route *route.Route) (*lnrpc.Route, error)
 				hop.PubKeyBytes[:],
 			),
 			TlvPayload: !hop.LegacyPayload,
+			MppRecord:  mpp,
 		}
 		incomingAmt = hop.AmtToForward
 	}
@@ -396,6 +410,11 @@ func (r *RouterBackend) UnmarshallHopByChannelLookup(hop *lnrpc.Hop,
 
 	var tlvRecords []tlv.Record
 
+	mpp, err := UnmarshalMPP(hop.MppRecord)
+	if err != nil {
+		return nil, err
+	}
+
 	return &route.Hop{
 		OutgoingTimeLock: hop.Expiry,
 		AmtToForward:     lnwire.MilliSatoshi(hop.AmtToForwardMsat),
@@ -403,6 +422,7 @@ func (r *RouterBackend) UnmarshallHopByChannelLookup(hop *lnrpc.Hop,
 		ChannelID:        hop.ChanId,
 		TLVRecords:       tlvRecords,
 		LegacyPayload:    !hop.TlvPayload,
+		MPP:              mpp,
 	}, nil
 }
 
@@ -420,6 +440,11 @@ func UnmarshallKnownPubkeyHop(hop *lnrpc.Hop) (*route.Hop, error) {
 
 	var tlvRecords []tlv.Record
 
+	mpp, err := UnmarshalMPP(hop.MppRecord)
+	if err != nil {
+		return nil, err
+	}
+
 	return &route.Hop{
 		OutgoingTimeLock: hop.Expiry,
 		AmtToForward:     lnwire.MilliSatoshi(hop.AmtToForwardMsat),
@@ -427,6 +452,7 @@ func UnmarshallKnownPubkeyHop(hop *lnrpc.Hop) (*route.Hop, error) {
 		ChannelID:        hop.ChanId,
 		TLVRecords:       tlvRecords,
 		LegacyPayload:    !hop.TlvPayload,
+		MPP:              mpp,
 	}, nil
 }
 
@@ -712,3 +738,45 @@ func ValidateCLTVLimit(val, max uint32) (uint32, error) {
 		return val, nil
 	}
 }
+
+// UnmarshalMPP accepts the mpp_total_amt_msat and mpp_payment_addr fields from
+// an RPC request and converts into an record.MPP object. An error is returned
+// if the payment address is not 0 or 32 bytes. If the total amount and payment
+// address are zero-value, the return value will be nil signaling there is no
+// MPP record to attach to this hop. Otherwise, a non-nil reocrd will be
+// contained combining the provided values.
+func UnmarshalMPP(reqMPP *lnrpc.MPPRecord) (*record.MPP, error) {
+	// If no MPP record was submitted, assume the user wants to send a
+	// regular payment.
+	if reqMPP == nil {
+		return nil, nil
+	}
+
+	reqTotal := reqMPP.TotalAmtMsat
+	reqAddr := reqMPP.PaymentAddr
+
+	switch {
+
+	// No MPP fields were provided.
+	case reqTotal == 0 && len(reqAddr) == 0:
+		return nil, fmt.Errorf("missing total_msat and payment_addr")
+
+	// Total is present, but payment address is missing.
+	case reqTotal > 0 && len(reqAddr) == 0:
+		return nil, fmt.Errorf("missing payment_addr")
+
+	// Payment address is present, but total is missing.
+	case reqTotal == 0 && len(reqAddr) > 0:
+		return nil, fmt.Errorf("missing total_msat")
+	}
+
+	addr, err := lntypes.MakeHash(reqAddr)
+	if err != nil {
+		return nil, fmt.Errorf("unable to parse "+
+			"payment_addr: %v", err)
+	}
+
+	total := lnwire.MilliSatoshi(reqTotal)
+
+	return record.NewMPP(total, addr), nil
+}

lnrpc/routerrpc/router_backend_test.go

@@ -180,3 +180,123 @@ func (m *mockMissionControl) GetPairHistorySnapshot(fromNode,
 
 	return routing.TimedPairResult{}
 }
+
+type mppOutcome byte
+
+const (
+	valid mppOutcome = iota
+	invalid
+	nompp
+)
+
+type unmarshalMPPTest struct {
+	name    string
+	mpp     *lnrpc.MPPRecord
+	outcome mppOutcome
+}
+
+// TestUnmarshalMPP checks both positive and negative cases of UnmarshalMPP to
+// assert that an MPP record is only returned when both fields are properly
+// specified. It also asserts that zero-values for both inputs is also valid,
+// but returns a nil record.
+func TestUnmarshalMPP(t *testing.T) {
+	tests := []unmarshalMPPTest{
+		{
+			name:    "nil record",
+			mpp:     nil,
+			outcome: nompp,
+		},
+		{
+			name: "invalid total or addr",
+			mpp: &lnrpc.MPPRecord{
+				PaymentAddr:  nil,
+				TotalAmtMsat: 0,
+			},
+			outcome: invalid,
+		},
+		{
+			name: "valid total only",
+			mpp: &lnrpc.MPPRecord{
+				PaymentAddr:  nil,
+				TotalAmtMsat: 8,
+			},
+			outcome: invalid,
+		},
+		{
+			name: "valid addr only",
+			mpp: &lnrpc.MPPRecord{
+				PaymentAddr:  bytes.Repeat([]byte{0x02}, 32),
+				TotalAmtMsat: 0,
+			},
+			outcome: invalid,
+		},
+		{
+			name: "valid total and invalid addr",
+			mpp: &lnrpc.MPPRecord{
+				PaymentAddr:  []byte{0x02},
+				TotalAmtMsat: 8,
+			},
+			outcome: invalid,
+		},
+		{
+			name: "valid total and valid addr",
+			mpp: &lnrpc.MPPRecord{
+				PaymentAddr:  bytes.Repeat([]byte{0x02}, 32),
+				TotalAmtMsat: 8,
+			},
+			outcome: valid,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			testUnmarshalMPP(t, test)
+		})
+	}
+}
+
+func testUnmarshalMPP(t *testing.T, test unmarshalMPPTest) {
+	mpp, err := UnmarshalMPP(test.mpp)
+	switch test.outcome {
+
+	// Valid arguments should result in no error, a non-nil MPP record, and
+	// the fields should be set correctly.
+	case valid:
+		if err != nil {
+			t.Fatalf("unable to parse mpp record: %v", err)
+		}
+		if mpp == nil {
+			t.Fatalf("mpp payload should be non-nil")
+		}
+		if int64(mpp.TotalMsat()) != test.mpp.TotalAmtMsat {
+			t.Fatalf("incorrect total msat")
+		}
+		addr := mpp.PaymentAddr()
+		if !bytes.Equal(addr[:], test.mpp.PaymentAddr) {
+			t.Fatalf("incorrect payment addr")
+		}
+
+	// Invalid arguments should produce a failure and nil MPP record.
+	case invalid:
+		if err == nil {
+			t.Fatalf("expected failure for invalid mpp")
+		}
+		if mpp != nil {
+			t.Fatalf("mpp payload should be nil for failure")
+		}
+
+	// Arguments that produce no MPP field should return no error and no MPP
+	// record.
+	case nompp:
+		if err != nil {
+			t.Fatalf("failure for args resulting for no-mpp")
+		}
+		if mpp != nil {
+			t.Fatalf("mpp payload should be nil for no-mpp")
+		}
+
+	default:
+		t.Fatalf("test case has non-standard outcome")
+	}
+}

lnrpc/rpc.proto

@@ -1836,6 +1836,32 @@ message Hop {
     TLV format.
     */
     bool tlv_payload = 9 [json_name = "tlv_payload"];
+
+    /**
+    An optional TLV record tha singals the use of an MPP payment. If present,
+    the receiver will enforce that that the same mpp_record is included in the
+    final hop payload of all non-zero payments in the HTLC set. If empty, a
+    regular single-shot payment is or was attempted.
+    */
+    MPPRecord mpp_record = 10 [json_name = "mpp_record"];
+}
+
+message MPPRecord {
+    /**
+    A unique, random identifier used to authenticate the sender as the intended
+    payer of a multi-path payment. The payment_addr must be the same for all
+    subpayments, and match the payment_addr provided in the receiver's invoice.
+    The same payment_addr must be used on all subpayments.
+    */
+    bytes payment_addr = 11 [json_name = "payment_addr"];
+
+    /**
+    The total amount in milli-satoshis being sent as part of a larger multi-path
+    payment. The caller is responsible for ensuring subpayments to the same node
+    and payment_hash sum exactly to total_amt_msat. The same
+    total_amt_msat must be used on all subpayments.
+    */
+    int64 total_amt_msat = 10 [json_name = "total_amt_msat"];
 }
 
 /**

lnrpc/rpc.swagger.json

@@ -2530,6 +2530,10 @@
           "type": "boolean",
           "format": "boolean",
           "description": "* \nIf set to true, then this hop will be encoded using the new variable length\nTLV format."
+        },
+        "mpp_record": {
+          "$ref": "#/definitions/lnrpcMPPRecord",
+          "description": "*\nAn optional TLV record tha singals the use of an MPP payment. If present,\nthe receiver will enforce that that the same mpp_record is included in the\nfinal hop payload of all non-zero payments in the HTLC set. If empty, a\nregular single-shot payment is or was attempted."
         }
       }
     },
@@ -2873,6 +2877,21 @@
         }
       }
     },
+    "lnrpcMPPRecord": {
+      "type": "object",
+      "properties": {
+        "payment_addr": {
+          "type": "string",
+          "format": "byte",
+          "description": "*\nA unique, random identifier used to authenticate the sender as the intended\npayer of a multi-path payment. The payment_addr must be the same for all\nsubpayments, and match the payment_addr provided in the receiver's invoice.\nThe same payment_addr must be used on all subpayments."
+        },
+        "total_amt_msat": {
+          "type": "string",
+          "format": "int64",
+          "description": "*\nThe total amount in milli-satoshis being sent as part of a larger multi-path\npayment. The caller is responsible for ensuring subpayments to the same node\nand payment_hash sum exactly to total_amt_msat. The same\ntotal_amt_msat must be used on all subpayments."
+        }
+      }
+    },
     "lnrpcMacaroonPermission": {
       "type": "object",
       "properties": {

lntest/itest/lnd_test.go

@@ -106,7 +106,6 @@ func (h *harnessTest) Fatalf(format string, a ...interface{}) {
 // RunTestCase executes a harness test case. Any errors or panics will be
 // represented as fatal.
 func (h *harnessTest) RunTestCase(testCase *testCase) {
-
 	h.testCase = testCase
 	defer func() {
 		h.testCase = nil
@@ -4406,43 +4405,135 @@ func testMultiHopPayments(net *lntest.NetworkHarness, t *harnessTest) {
 	closeChannelAndAssert(ctxt, t, net, carol, chanPointCarol, false)
 }
 
-// testSingleHopSendToRoute tests that payments are properly processed
+type singleHopSendToRouteCase struct {
-// through a provided route with a single hop. We'll create the
+	name string
-// following network topology:
+
-//      Alice --100k--> Bob
+	// streaming tests streaming SendToRoute if true, otherwise tests
-// We'll query the daemon for routes from Alice to Bob and then
+	// synchronous SenToRoute.
-// send payments through the route.
+	streaming bool
+
+	// routerrpc submits the request to the routerrpc subserver if true,
+	// otherwise submits to the main rpc server.
+	routerrpc bool
+
+	// mpp sets the MPP fields on the request if true, otherwise submits a
+	// regular payment.
+	mpp bool
+}
+
+var singleHopSendToRouteCases = []singleHopSendToRouteCase{
+	{
+		name: "regular main sync",
+	},
+	{
+		name:      "regular main stream",
+		streaming: true,
+	},
+	{
+		name:      "regular routerrpc sync",
+		routerrpc: true,
+	},
+	{
+		name: "mpp main sync",
+		mpp:  true,
+	},
+	{
+		name:      "mpp main stream",
+		streaming: true,
+		mpp:       true,
+	},
+	{
+		name:      "mpp routerrpc sync",
+		routerrpc: true,
+		mpp:       true,
+	},
+}
+
+// testSingleHopSendToRoute tests that payments are properly processed through a
+// provided route with a single hop. We'll create the following network
+// topology:
+//      Carol --100k--> Dave
+// We'll query the daemon for routes from Carol to Dave and then send payments
+// by feeding the route back into the various SendToRoute RPC methods. Here we
+// test all three SendToRoute endpoints, forcing each to perform both a regular
+// payment and an MPP payment.
 func testSingleHopSendToRoute(net *lntest.NetworkHarness, t *harnessTest) {
-	ctxb := context.Background()
+	for _, test := range singleHopSendToRouteCases {
+		test := test
+
+		t.t.Run(test.name, func(t1 *testing.T) {
+			ht := newHarnessTest(t1, t.lndHarness)
+			ht.RunTestCase(&testCase{
+				name: test.name,
+				test: func(_ *lntest.NetworkHarness, tt *harnessTest) {
+					testSingleHopSendToRouteCase(net, tt, test)
+				},
+			})
+		})
+	}
+}
+
+func testSingleHopSendToRouteCase(net *lntest.NetworkHarness, t *harnessTest,
+	test singleHopSendToRouteCase) {
 
 	const chanAmt = btcutil.Amount(100000)
+	const paymentAmtSat = 1000
+	const numPayments = 5
+	const amountPaid = int64(numPayments * paymentAmtSat)
+
+	ctxb := context.Background()
 	var networkChans []*lnrpc.ChannelPoint
 
-	// Open a channel with 100k satoshis between Alice and Bob with Alice
+	// Create Carol and Dave, then establish a channel between them. Carol
+	// is the sole funder of the channel with 100k satoshis. The network
+	// topology should look like:
+	// Carol -> 100k -> Dave
+	carol, err := net.NewNode("Carol", nil)
+	if err != nil {
+		t.Fatalf("unable to create new nodes: %v", err)
+	}
+	defer shutdownAndAssert(net, t, carol)
+
+	dave, err := net.NewNode("Dave", nil)
+	if err != nil {
+		t.Fatalf("unable to create new nodes: %v", err)
+	}
+	defer shutdownAndAssert(net, t, dave)
+
+	ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
+	if err := net.ConnectNodes(ctxt, carol, dave); err != nil {
+		t.Fatalf("unable to connect carol to dave: %v", err)
+	}
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	err = net.SendCoins(ctxt, btcutil.SatoshiPerBitcoin, carol)
+	if err != nil {
+		t.Fatalf("unable to send coins to carol: %v", err)
+	}
+
+	// Open a channel with 100k satoshis between Carol and Dave with Carol
 	// being the sole funder of the channel.
-	ctxt, _ := context.WithTimeout(ctxb, channelOpenTimeout)
+	ctxt, _ = context.WithTimeout(ctxb, channelOpenTimeout)
-	chanPointAlice := openChannelAndAssert(
+	chanPointCarol := openChannelAndAssert(
-		ctxt, t, net, net.Alice, net.Bob,
+		ctxt, t, net, carol, dave,
 		lntest.OpenChannelParams{
 			Amt: chanAmt,
 		},
 	)
-	networkChans = append(networkChans, chanPointAlice)
+	networkChans = append(networkChans, chanPointCarol)
 
-	aliceChanTXID, err := lnd.GetChanPointFundingTxid(chanPointAlice)
+	carolChanTXID, err := lnd.GetChanPointFundingTxid(chanPointCarol)
 	if err != nil {
 		t.Fatalf("unable to get txid: %v", err)
 	}
-	aliceFundPoint := wire.OutPoint{
+	carolFundPoint := wire.OutPoint{
-		Hash:  *aliceChanTXID,
+		Hash:  *carolChanTXID,
-		Index: chanPointAlice.OutputIndex,
+		Index: chanPointCarol.OutputIndex,
 	}
 
 	// Wait for all nodes to have seen all channels.
-	nodes := []*lntest.HarnessNode{net.Alice, net.Bob}
+	nodes := []*lntest.HarnessNode{carol, dave}
-	nodeNames := []string{"Alice", "Bob"}
 	for _, chanPoint := range networkChans {
-		for i, node := range nodes {
+		for _, node := range nodes {
 			txid, err := lnd.GetChanPointFundingTxid(chanPoint)
 			if err != nil {
 				t.Fatalf("unable to get txid: %v", err)
@@ -4456,57 +4547,97 @@ func testSingleHopSendToRoute(net *lntest.NetworkHarness, t *harnessTest) {
 			err = node.WaitForNetworkChannelOpen(ctxt, chanPoint)
 			if err != nil {
 				t.Fatalf("%s(%d): timeout waiting for "+
-					"channel(%s) open: %v", nodeNames[i],
+					"channel(%s) open: %v", node.Name(),
 					node.NodeID, point, err)
 			}
 		}
 	}
 
-	// Query for routes to pay from Alice to Bob.
+	// Create invoices for Dave, which expect a payment from Carol.
-	// We set FinalCltvDelta to 40 since by default QueryRoutes returns
-	// the last hop with a final cltv delta of 9 where as the default in
-	// htlcswitch is 40.
-	const paymentAmt = 1000
-	routesReq := &lnrpc.QueryRoutesRequest{
-		PubKey:         net.Bob.PubKeyStr,
-		Amt:            paymentAmt,
-		FinalCltvDelta: lnd.DefaultBitcoinTimeLockDelta,
-	}
-	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
-	routes, err := net.Alice.QueryRoutes(ctxt, routesReq)
-	if err != nil {
-		t.Fatalf("unable to get route: %v", err)
-	}
-
-	// Create 5 invoices for Bob, which expect a payment from Alice for 1k
-	// satoshis with a different preimage each time.
-	const numPayments = 5
 	_, rHashes, _, err := createPayReqs(
-		net.Bob, paymentAmt, numPayments,
+		dave, paymentAmtSat, numPayments,
 	)
 	if err != nil {
 		t.Fatalf("unable to create pay reqs: %v", err)
 	}
 
-	// We'll wait for all parties to recognize the new channels within the
+	// Query for routes to pay from Carol to Dave.
-	// network.
+	// We set FinalCltvDelta to 40 since by default QueryRoutes returns
+	// the last hop with a final cltv delta of 9 where as the default in
+	// htlcswitch is 40.
+	routesReq := &lnrpc.QueryRoutesRequest{
+		PubKey:         dave.PubKeyStr,
+		Amt:            paymentAmtSat,
+		FinalCltvDelta: lnd.DefaultBitcoinTimeLockDelta,
+	}
 	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
-	err = net.Bob.WaitForNetworkChannelOpen(ctxt, chanPointAlice)
+	routes, err := carol.QueryRoutes(ctxt, routesReq)
 	if err != nil {
-		t.Fatalf("alice didn't advertise her channel in time: %v", err)
+		t.Fatalf("unable to get route from %s: %v",
+			carol.Name(), err)
 	}
 
-	time.Sleep(time.Millisecond * 50)
+	// There should only be one route to try, so take the first item.
+	r := routes.Routes[0]
 
-	// Using Alice as the source, pay to the 5 invoices from Carol created
+	// Construct a closure that will set MPP fields on the route, which
-	// above.
+	// allows us to test MPP payments.
-	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	setMPPFields := func(i int) {
-	alicePayStream, err := net.Alice.SendToRoute(ctxt)
+		addr := [32]byte{byte(i)}
-	if err != nil {
+
-		t.Fatalf("unable to create payment stream for alice: %v", err)
+		hop := r.Hops[len(r.Hops)-1]
+		hop.TlvPayload = true
+		hop.MppRecord = &lnrpc.MPPRecord{
+			PaymentAddr:  addr[:],
+			TotalAmtMsat: paymentAmtSat * 1000,
+		}
+	}
+
+	// Construct closures for each of the payment types covered:
+	//  - main rpc server sync
+	//  - main rpc server streaming
+	//  - routerrpc server sync
+	sendToRouteSync := func() {
+		for i, rHash := range rHashes {
+			// Populate the MPP fields for the final hop if we are
+			// testing MPP payments.
+			if test.mpp {
+				setMPPFields(i)
+			}
+
+			sendReq := &lnrpc.SendToRouteRequest{
+				PaymentHash: rHash,
+				Route:       r,
+			}
+			ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+			resp, err := carol.SendToRouteSync(
+				ctxt, sendReq,
+			)
+			if err != nil {
+				t.Fatalf("unable to send to route for "+
+					"%s: %v", carol.Name(), err)
+			}
+			if resp.PaymentError != "" {
+				t.Fatalf("received payment error from %s: %v",
+					carol.Name(), resp.PaymentError)
+			}
+		}
+	}
+	sendToRouteStream := func() {
+		ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+		alicePayStream, err := carol.SendToRoute(ctxt)
+		if err != nil {
+			t.Fatalf("unable to create payment stream for "+
+				"carol: %v", err)
+		}
+
+		for i, rHash := range rHashes {
+			// Populate the MPP fields for the final hop if we are
+			// testing MPP payments.
+			if test.mpp {
+				setMPPFields(i)
 			}
 
-	for _, rHash := range rHashes {
 			sendReq := &lnrpc.SendToRouteRequest{
 				PaymentHash: rHash,
 				Route:       routes.Routes[0],
@@ -4516,51 +4647,141 @@ func testSingleHopSendToRoute(net *lntest.NetworkHarness, t *harnessTest) {
 			if err != nil {
 				t.Fatalf("unable to send payment: %v", err)
 			}
-	}
 
-	for range rHashes {
 			resp, err := alicePayStream.Recv()
 			if err != nil {
 				t.Fatalf("unable to send payment: %v", err)
 			}
 			if resp.PaymentError != "" {
-			t.Fatalf("received payment error: %v", resp.PaymentError)
+				t.Fatalf("received payment error: %v",
+					resp.PaymentError)
 			}
 		}
+	}
+	sendToRouteRouterRPC := func() {
+		for i, rHash := range rHashes {
+			// Populate the MPP fields for the final hop if we are
+			// testing MPP payments.
+			if test.mpp {
+				setMPPFields(i)
+			}
 
-	req := &lnrpc.ListPaymentsRequest{}
+			sendReq := &routerrpc.SendToRouteRequest{
-	ctxt, _ = context.WithTimeout(ctxt, defaultTimeout)
+				PaymentHash: rHash,
-	paymentsResp, err := net.Alice.ListPayments(ctxt, req)
+				Route:       r,
+			}
+			ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+			resp, err := carol.RouterClient.SendToRoute(
+				ctxt, sendReq,
+			)
 			if err != nil {
-		t.Fatalf("error when obtaining Alice payments: %v", err)
+				t.Fatalf("unable to send to route for "+
+					"%s: %v", carol.Name(), err)
+			}
+			if resp.Failure != nil {
+				t.Fatalf("received payment error from %s: %v",
+					carol.Name(), resp.Failure)
+			}
 		}
-	if len(paymentsResp.Payments) != 5 {
-		t.Fatalf("incorrect number of payments, got %v, want %v",
-			len(paymentsResp.Payments), 5)
 	}
 
-	// Verify that the ListPayments displays the payment without an invoice
+	// Using Carol as the node as the source, send the payments
-	// since the payment was completed with SendToRoute.
+	// synchronously via the the routerrpc's SendToRoute, or via the main RPC
-	for _, p := range paymentsResp.Payments {
+	// server's SendToRoute streaming or sync calls.
+	switch {
+	case !test.routerrpc && test.streaming:
+		sendToRouteStream()
+	case !test.routerrpc && !test.streaming:
+		sendToRouteSync()
+	case test.routerrpc && !test.streaming:
+		sendToRouteRouterRPC()
+	default:
+		t.Fatalf("routerrpc does not support streaming send_to_route")
+	}
+
+	// Verify that the payment's from Carol's PoV have the correct payment
+	// hash and amount.
+	ctxt, _ = context.WithTimeout(ctxt, defaultTimeout)
+	paymentsResp, err := carol.ListPayments(
+		ctxt, &lnrpc.ListPaymentsRequest{},
+	)
+	if err != nil {
+		t.Fatalf("error when obtaining %s payments: %v",
+			carol.Name(), err)
+	}
+	if len(paymentsResp.Payments) != numPayments {
+		t.Fatalf("incorrect number of payments, got %v, want %v",
+			len(paymentsResp.Payments), numPayments)
+	}
+
+	for i, p := range paymentsResp.Payments {
+		// Assert that the payment hashes for each payment match up.
+		rHashHex := hex.EncodeToString(rHashes[i])
+		if p.PaymentHash != rHashHex {
+			t.Fatalf("incorrect payment hash for payment %d, "+
+				"want: %s got: %s",
+				i, rHashHex, p.PaymentHash)
+		}
+
+		// Assert that each payment has no invoice since the payment was
+		// completed using SendToRoute.
 		if p.PaymentRequest != "" {
-			t.Fatalf("incorrect payreq, want: \"\", got: %v",
+			t.Fatalf("incorrect payment request for payment: %d, "+
-				p.PaymentRequest)
+				"want: \"\", got: %s",
+				i, p.PaymentRequest)
+		}
+
+		// Assert the payment ammount is correct.
+		if p.ValueSat != paymentAmtSat {
+			t.Fatalf("incorrect payment amt for payment %d, "+
+				"want: %d, got: %d",
+				i, paymentAmtSat, p.ValueSat)
+		}
+	}
+
+	// Verify that the invoices's from Dave's PoV have the correct payment
+	// hash and amount.
+	ctxt, _ = context.WithTimeout(ctxt, defaultTimeout)
+	invoicesResp, err := dave.ListInvoices(
+		ctxt, &lnrpc.ListInvoiceRequest{},
+	)
+	if err != nil {
+		t.Fatalf("error when obtaining %s payments: %v",
+			dave.Name(), err)
+	}
+	if len(invoicesResp.Invoices) != numPayments {
+		t.Fatalf("incorrect number of invoices, got %v, want %v",
+			len(invoicesResp.Invoices), numPayments)
+	}
+
+	for i, inv := range invoicesResp.Invoices {
+		// Assert that the payment hashes match up.
+		if !bytes.Equal(inv.RHash, rHashes[i]) {
+			t.Fatalf("incorrect payment hash for invoice %d, "+
+				"want: %x got: %x",
+				i, rHashes[i], inv.RHash)
+		}
+
+		// Assert that the amount paid to the invoice is correct.
+		if inv.AmtPaidSat != paymentAmtSat {
+			t.Fatalf("incorrect payment amt for invoice %d, "+
+				"want: %d, got %d",
+				i, paymentAmtSat, inv.AmtPaidSat)
 		}
 	}
 
 	// At this point all the channels within our proto network should be
-	// shifted by 5k satoshis in the direction of Bob, the sink within the
+	// shifted by 5k satoshis in the direction of Dave, the sink within the
 	// payment flow generated above. The order of asserts corresponds to
 	// increasing of time is needed to embed the HTLC in commitment
-	// transaction, in channel Alice->Bob, order is Bob and then Alice.
+	// transaction, in channel Carol->Dave, order is Dave and then Carol.
-	const amountPaid = int64(5000)
+	assertAmountPaid(t, "Carol(local) => Dave(remote)", dave,
-	assertAmountPaid(t, "Alice(local) => Bob(remote)", net.Bob,
+		carolFundPoint, int64(0), amountPaid)
-		aliceFundPoint, int64(0), amountPaid)
+	assertAmountPaid(t, "Carol(local) => Dave(remote)", carol,
-	assertAmountPaid(t, "Alice(local) => Bob(remote)", net.Alice,
+		carolFundPoint, amountPaid, int64(0))
-		aliceFundPoint, amountPaid, int64(0))
 
 	ctxt, _ = context.WithTimeout(ctxb, channelCloseTimeout)
-	closeChannelAndAssert(ctxt, t, net, net.Alice, chanPointAlice, false)
+	closeChannelAndAssert(ctxt, t, net, carol, chanPointCarol, false)
 }
 
 // testMultiHopSendToRoute tests that payments are properly processed

record/mpp.go

@@ -0,0 +1,98 @@
+package record
+
+import (
+	"io"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+// MPPOnionType is the type used in the onion to reference the MPP fields:
+// total_amt and payment_addr.
+const MPPOnionType tlv.Type = 8
+
+// MPP is a record that encodes the fields necessary for multi-path payments.
+type MPP struct {
+	// paymentAddr is a random, receiver-generated value used to avoid
+	// collisions with concurrent payers.
+	paymentAddr [32]byte
+
+	// totalMsat is the total value of the payment, potentially spread
+	// across more than one HTLC.
+	totalMsat lnwire.MilliSatoshi
+}
+
+// NewMPP generates a new MPP record with the given total and payment address.
+func NewMPP(total lnwire.MilliSatoshi, addr [32]byte) *MPP {
+	return &MPP{
+		paymentAddr: addr,
+		totalMsat:   total,
+	}
+}
+
+// PaymentAddr returns the payment address contained in the MPP record.
+func (r *MPP) PaymentAddr() [32]byte {
+	return r.paymentAddr
+}
+
+// TotalMsat returns the total value of an MPP payment in msats.
+func (r *MPP) TotalMsat() lnwire.MilliSatoshi {
+	return r.totalMsat
+}
+
+// MPPEncoder writes the MPP record to the provided io.Writer.
+func MPPEncoder(w io.Writer, val interface{}, buf *[8]byte) error {
+	if v, ok := val.(*MPP); ok {
+		err := tlv.EBytes32(w, &v.paymentAddr, buf)
+		if err != nil {
+			return err
+		}
+
+		return tlv.ETUint64T(w, uint64(v.totalMsat), buf)
+	}
+	return tlv.NewTypeForEncodingErr(val, "MPP")
+}
+
+const (
+	// minMPPLength is the minimum length of a serialized MPP TLV record,
+	// which occurs when the truncated encoding of total_amt_msat takes 0
+	// bytes, leaving only the payment_addr.
+	minMPPLength = 32
+
+	// maxMPPLength is the maximum length of a serialized MPP TLV record,
+	// which occurs when the truncated encoding of total_amt_msat takes 8
+	// bytes.
+	maxMPPLength = 40
+)
+
+// MPPDecoder reads the MPP record to the provided io.Reader.
+func MPPDecoder(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
+	if v, ok := val.(*MPP); ok && minMPPLength <= l && l <= maxMPPLength {
+		if err := tlv.DBytes32(r, &v.paymentAddr, buf, 32); err != nil {
+			return err
+		}
+
+		var total uint64
+		if err := tlv.DTUint64(r, &total, buf, l-32); err != nil {
+			return err
+		}
+		v.totalMsat = lnwire.MilliSatoshi(total)
+
+		return nil
+
+	}
+	return tlv.NewTypeForDecodingErr(val, "MPP", l, maxMPPLength)
+}
+
+// Record returns a tlv.Record that can be used to encode or decode this record.
+func (r *MPP) Record() tlv.Record {
+	// Fixed-size, 32 byte payment address followed by truncated 64-bit
+	// total msat.
+	size := func() uint64 {
+		return 32 + tlv.SizeTUint64(uint64(r.totalMsat))
+	}
+
+	return tlv.MakeDynamicRecord(
+		MPPOnionType, r, size, MPPEncoder, MPPDecoder,
+	)
+}

record/record_test.go

@@ -0,0 +1,73 @@
+package record_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+type recordEncDecTest struct {
+	name      string
+	encRecord func() tlv.RecordProducer
+	decRecord func() tlv.RecordProducer
+	assert    func(*testing.T, interface{})
+}
+
+var (
+	testTotal = lnwire.MilliSatoshi(45)
+	testAddr  = [32]byte{0x01, 0x02}
+)
+
+var recordEncDecTests = []recordEncDecTest{
+	{
+		name: "mpp",
+		encRecord: func() tlv.RecordProducer {
+			return record.NewMPP(testTotal, testAddr)
+		},
+		decRecord: func() tlv.RecordProducer {
+			return new(record.MPP)
+		},
+		assert: func(t *testing.T, r interface{}) {
+			mpp := r.(*record.MPP)
+			if mpp.TotalMsat() != testTotal {
+				t.Fatal("incorrect total msat")
+			}
+			if mpp.PaymentAddr() != testAddr {
+				t.Fatal("incorrect payment addr")
+			}
+		},
+	},
+}
+
+// TestRecordEncodeDecode is a generic test framework for custom TLV records. It
+// asserts that records can encode and decode themselves, and that the value of
+// the original record matches the decoded record.
+func TestRecordEncodeDecode(t *testing.T) {
+	for _, test := range recordEncDecTests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			r := test.encRecord()
+			r2 := test.decRecord()
+			encStream := tlv.MustNewStream(r.Record())
+			decStream := tlv.MustNewStream(r2.Record())
+
+			test.assert(t, r)
+
+			var b bytes.Buffer
+			err := encStream.Encode(&b)
+			if err != nil {
+				t.Fatalf("unable to encode record: %v", err)
+			}
+
+			err = decStream.Decode(bytes.NewReader(b.Bytes()))
+			if err != nil {
+				t.Fatalf("unable to decode record: %v", err)
+			}
+
+			test.assert(t, r2)
+		})
+	}
+}

routing/route/route.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
 	"strconv"
@@ -19,9 +20,17 @@ import (
 // VertexSize is the size of the array to store a vertex.
 const VertexSize = 33
 
-// ErrNoRouteHopsProvided is returned when a caller attempts to construct a new
+var (
-// sphinx packet, but provides an empty set of hops for each route.
+	// ErrNoRouteHopsProvided is returned when a caller attempts to
-var ErrNoRouteHopsProvided = fmt.Errorf("empty route hops provided")
+	// construct a new sphinx packet, but provides an empty set of hops for
+	// each route.
+	ErrNoRouteHopsProvided = fmt.Errorf("empty route hops provided")
+
+	// ErrIntermediateMPPHop is returned when a hop tries to deliver an MPP
+	// record to an intermediate hop, only final hops can receive MPP
+	// records.
+	ErrIntermediateMPPHop = errors.New("cannot send MPP to intermediate")
+)
 
 // Vertex is a simple alias for the serialization of a compressed Bitcoin
 // public key.
@@ -94,6 +103,10 @@ type Hop struct {
 	// carries as a fee will be subtracted by the hop.
 	AmtToForward lnwire.MilliSatoshi
 
+	// MPP encapsulates the data required for option_mpp. This field should
+	// only be set for the final hop.
+	MPP *record.MPP
+
 	// TLVRecords if non-nil are a set of additional TLV records that
 	// should be included in the forwarding instructions for this node.
 	TLVRecords []tlv.Record
@@ -140,6 +153,17 @@ func (h *Hop) PackHopPayload(w io.Writer, nextChanID uint64) error {
 		)
 	}
 
+	// If an MPP record is destined for this hop, ensure that we only ever
+	// attach it to the final hop. Otherwise the route was constructed
+	// incorrectly.
+	if h.MPP != nil {
+		if nextChanID == 0 {
+			records = append(records, h.MPP.Record())
+		} else {
+			return ErrIntermediateMPPHop
+		}
+	}
+
 	// Append any custom types destined for this hop.
 	records = append(records, h.TLVRecords...)
 

routing/route/route_test.go

@@ -1,9 +1,11 @@
 package route
 
 import (
+	"bytes"
 	"testing"
 
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
 )
 
 // TestRouteTotalFees checks that a route reports the expected total fee.
@@ -56,3 +58,38 @@ func TestRouteTotalFees(t *testing.T) {
 	}
 
 }
+
+var (
+	testAmt  = lnwire.MilliSatoshi(1000)
+	testAddr = [32]byte{0x01, 0x02}
+)
+
+// TestMPPHop asserts that a Hop will encode a non-nil to final nodes, and fail
+// when trying to send to intermediaries.
+func TestMPPHop(t *testing.T) {
+	t.Parallel()
+
+	hop := Hop{
+		ChannelID:        1,
+		OutgoingTimeLock: 44,
+		AmtToForward:     testAmt,
+		LegacyPayload:    false,
+		MPP:              record.NewMPP(testAmt, testAddr),
+	}
+
+	// Encoding an MPP record to an intermediate hop should result in a
+	// failure.
+	var b bytes.Buffer
+	err := hop.PackHopPayload(&b, 2)
+	if err != ErrIntermediateMPPHop {
+		t.Fatalf("expected err: %v, got: %v",
+			ErrIntermediateMPPHop, err)
+	}
+
+	// Encoding an MPP record to a final hop should be successful.
+	b.Reset()
+	err = hop.PackHopPayload(&b, 0)
+	if err != nil {
+		t.Fatalf("expected err: %v, got: %v", nil, err)
+	}
+}

tlv/record.go

@@ -43,6 +43,14 @@ func SizeVarBytes(e *[]byte) SizeFunc {
 	}
 }
 
+// RecorderProducer is an interface for objects that can produce a Record object
+// capable of encoding and/or decoding the RecordProducer as a Record.
+type RecordProducer interface {
+	// Record returns a Record that can be used to encode or decode the
+	// backing object.
+	Record() Record
+}
+
 // Record holds the required information to encode or decode a TLV record.
 type Record struct {
 	value      interface{}
@@ -77,6 +85,14 @@ func (f *Record) Encode(w io.Writer) error {
 	return f.encoder(w, f.value, &b)
 }
 
+// Decode read in the TLV record from the passed reader. This is useful when a
+// caller wants decode a *single* TLV record, outside the context of the Stream
+// struct.
+func (f *Record) Decode(r io.Reader, l uint64) error {
+	var b [8]byte
+	return f.decoder(r, f.value, &b, l)
+}
+
 // MakePrimitiveRecord creates a record for common types.
 func MakePrimitiveRecord(typ Type, val interface{}) Record {
 	var (

tlv/truncated.go

@@ -40,6 +40,15 @@ func ETUint16(w io.Writer, val interface{}, buf *[8]byte) error {
 	return NewTypeForEncodingErr(val, "uint16")
 }
 
+// ETUint16T is an Encoder for truncated uint16 values, where leading zeros will
+// be omitted. An error is returned if val is not a *uint16.
+func ETUint16T(w io.Writer, val uint16, buf *[8]byte) error {
+	binary.BigEndian.PutUint16(buf[:2], val)
+	numZeros := numLeadingZeroBytes16(val)
+	_, err := w.Write(buf[numZeros:2])
+	return err
+}
+
 // DTUint16 is an Decoder for truncated uint16 values, where leading zeros will
 // be resurrected. An error is returned if val is not a *uint16.
 func DTUint16(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
@@ -92,6 +101,15 @@ func ETUint32(w io.Writer, val interface{}, buf *[8]byte) error {
 	return NewTypeForEncodingErr(val, "uint32")
 }
 
+// ETUint32T is an Encoder for truncated uint32 values, where leading zeros will
+// be omitted. An error is returned if val is not a *uint32.
+func ETUint32T(w io.Writer, val uint32, buf *[8]byte) error {
+	binary.BigEndian.PutUint32(buf[:4], val)
+	numZeros := numLeadingZeroBytes32(val)
+	_, err := w.Write(buf[numZeros:4])
+	return err
+}
+
 // DTUint32 is an Decoder for truncated uint32 values, where leading zeros will
 // be resurrected. An error is returned if val is not a *uint32.
 func DTUint32(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
@@ -154,6 +172,15 @@ func ETUint64(w io.Writer, val interface{}, buf *[8]byte) error {
 	return NewTypeForEncodingErr(val, "uint64")
 }
 
+// ETUint64T is an Encoder for truncated uint64 values, where leading zeros will
+// be omitted. An error is returned if val is not a *uint64.
+func ETUint64T(w io.Writer, val uint64, buf *[8]byte) error {
+	binary.BigEndian.PutUint64(buf[:], val)
+	numZeros := numLeadingZeroBytes64(val)
+	_, err := w.Write(buf[numZeros:])
+	return err
+}
+
 // DTUint64 is an Decoder for truncated uint64 values, where leading zeros will
 // be resurrected. An error is returned if val is not a *uint64.
 func DTUint64(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {

tlv/truncated_test.go

@@ -60,6 +60,8 @@ func TestSizeTUint16(t *testing.T) {
 func TestTUint16(t *testing.T) {
 	var buf [8]byte
 	for _, test := range tuint16Tests {
+		test := test
+
 		if len(test.bytes) != int(test.size) {
 			t.Fatalf("invalid test case, "+
 				"len(bytes)[%d] != size[%d]",
@@ -68,6 +70,7 @@ func TestTUint16(t *testing.T) {
 
 		name := fmt.Sprintf("0x%x", test.value)
 		t.Run(name, func(t *testing.T) {
+			// Test generic encoder.
 			var b bytes.Buffer
 			err := tlv.ETUint16(&b, &test.value, &buf)
 			if err != nil {
@@ -80,6 +83,19 @@ func TestTUint16(t *testing.T) {
 					test.bytes, b.Bytes())
 			}
 
+			// Test non-generic encoder.
+			var b2 bytes.Buffer
+			err = tlv.ETUint16T(&b2, test.value, &buf)
+			if err != nil {
+				t.Fatalf("unable to encode tuint16: %v", err)
+			}
+
+			if !bytes.Equal(b2.Bytes(), test.bytes) {
+				t.Fatalf("encoding mismatch, "+
+					"expected: %x, got: %x",
+					test.bytes, b2.Bytes())
+			}
+
 			var value uint16
 			r := bytes.NewReader(b.Bytes())
 			err = tlv.DTUint16(r, &value, &buf, test.size)
@@ -168,6 +184,8 @@ func TestSizeTUint32(t *testing.T) {
 func TestTUint32(t *testing.T) {
 	var buf [8]byte
 	for _, test := range tuint32Tests {
+		test := test
+
 		if len(test.bytes) != int(test.size) {
 			t.Fatalf("invalid test case, "+
 				"len(bytes)[%d] != size[%d]",
@@ -176,6 +194,7 @@ func TestTUint32(t *testing.T) {
 
 		name := fmt.Sprintf("0x%x", test.value)
 		t.Run(name, func(t *testing.T) {
+			// Test generic encoder.
 			var b bytes.Buffer
 			err := tlv.ETUint32(&b, &test.value, &buf)
 			if err != nil {
@@ -188,6 +207,19 @@ func TestTUint32(t *testing.T) {
 					test.bytes, b.Bytes())
 			}
 
+			// Test non-generic encoder.
+			var b2 bytes.Buffer
+			err = tlv.ETUint32T(&b2, test.value, &buf)
+			if err != nil {
+				t.Fatalf("unable to encode tuint32: %v", err)
+			}
+
+			if !bytes.Equal(b2.Bytes(), test.bytes) {
+				t.Fatalf("encoding mismatch, "+
+					"expected: %x, got: %x",
+					test.bytes, b2.Bytes())
+			}
+
 			var value uint32
 			r := bytes.NewReader(b.Bytes())
 			err = tlv.DTUint32(r, &value, &buf, test.size)
@@ -322,6 +354,8 @@ func TestSizeTUint64(t *testing.T) {
 func TestTUint64(t *testing.T) {
 	var buf [8]byte
 	for _, test := range tuint64Tests {
+		test := test
+
 		if len(test.bytes) != int(test.size) {
 			t.Fatalf("invalid test case, "+
 				"len(bytes)[%d] != size[%d]",
@@ -330,6 +364,7 @@ func TestTUint64(t *testing.T) {
 
 		name := fmt.Sprintf("0x%x", test.value)
 		t.Run(name, func(t *testing.T) {
+			// Test generic encoder.
 			var b bytes.Buffer
 			err := tlv.ETUint64(&b, &test.value, &buf)
 			if err != nil {
@@ -342,6 +377,19 @@ func TestTUint64(t *testing.T) {
 					test.bytes, b.Bytes())
 			}
 
+			// Test non-generic encoder.
+			var b2 bytes.Buffer
+			err = tlv.ETUint64T(&b2, test.value, &buf)
+			if err != nil {
+				t.Fatalf("unable to encode tuint64: %v", err)
+			}
+
+			if !bytes.Equal(b2.Bytes(), test.bytes) {
+				t.Fatalf("encoding mismatch, "+
+					"expected: %x, got: %x",
+					test.bytes, b2.Bytes())
+			}
+
 			var value uint64
 			r := bytes.NewReader(b.Bytes())
 			err = tlv.DTUint64(r, &value, &buf, test.size)