Merge pull request #3441 from cfromknecht/truncated-sid

htlcswitch+routing: omit next_hop_id in final hop payload

htlcswitch/iterator.go

@@ -9,6 +9,7 @@ import (
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
@@ -175,15 +176,9 @@ func (r *sphinxHopIterator) ForwardingInstructions() (ForwardingInfo, error) {
 		var cid uint64
 
 		tlvStream, err := tlv.NewStream(
-			tlv.MakeDynamicRecord(
+			record.NewAmtToFwdRecord(&amt),
-				tlv.AmtOnionType, &amt, nil,
+			record.NewLockTimeRecord(&cltv),
-				tlv.ETUint64, tlv.DTUint64,
+			record.NewNextHopIDRecord(&cid),
-			),
-			tlv.MakeDynamicRecord(
-				tlv.LockTimeOnionType, &cltv, nil,
-				tlv.ETUint32, tlv.DTUint32,
-			),
-			tlv.MakePrimitiveRecord(tlv.NextHopOnionType, &cid),
 		)
 		if err != nil {
 			return ForwardingInfo{}, err

htlcswitch/iterator_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/davecgh/go-spew/spew"
 	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
@@ -38,19 +39,9 @@ func TestSphinxHopIteratorForwardingInstructions(t *testing.T) {
 	// as we would normally in the routing network.
 	var b bytes.Buffer
 	tlvRecords := []tlv.Record{
-		tlv.MakeDynamicRecord(
+		record.NewAmtToFwdRecord(&hopData.ForwardAmount),
-			tlv.AmtOnionType, &hopData.ForwardAmount, func() uint64 {
+		record.NewLockTimeRecord(&hopData.OutgoingCltv),
-				return tlv.SizeTUint64(hopData.ForwardAmount)
+		record.NewNextHopIDRecord(&nextAddrInt),
-			},
-			tlv.ETUint64, tlv.DTUint64,
-		),
-		tlv.MakeDynamicRecord(
-			tlv.LockTimeOnionType, &hopData.OutgoingCltv, func() uint64 {
-				return tlv.SizeTUint32(hopData.OutgoingCltv)
-			},
-			tlv.ETUint32, tlv.DTUint32,
-		),
-		tlv.MakePrimitiveRecord(tlv.NextHopOnionType, &nextAddrInt),
 	}
 	tlvStream, err := tlv.NewStream(tlvRecords...)
 	if err != nil {

record/hop.go

@@ -0,0 +1,47 @@
+package record
+
+import (
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+const (
+	// AmtOnionType is the type used in the onion to refrence the amount to
+	// send to the next hop.
+	AmtOnionType tlv.Type = 2
+
+	// LockTimeTLV is the type used in the onion to refenernce the CLTV
+	// value that should be used for the next hop's HTLC.
+	LockTimeOnionType tlv.Type = 4
+
+	// NextHopOnionType is the type used in the onion to reference the ID
+	// of the next hop.
+	NextHopOnionType tlv.Type = 6
+)
+
+// NewAmtToFwdRecord creates a tlv.Record that encodes the amount_to_forward
+// (type 2) for an onion payload.
+func NewAmtToFwdRecord(amt *uint64) tlv.Record {
+	return tlv.MakeDynamicRecord(
+		AmtOnionType, amt, func() uint64 {
+			return tlv.SizeTUint64(*amt)
+		},
+		tlv.ETUint64, tlv.DTUint64,
+	)
+}
+
+// NewLockTimeRecord creates a tlv.Record that encodes the outgoing_cltv_value
+// (type 4) for an onion payload.
+func NewLockTimeRecord(lockTime *uint32) tlv.Record {
+	return tlv.MakeDynamicRecord(
+		LockTimeOnionType, lockTime, func() uint64 {
+			return tlv.SizeTUint32(*lockTime)
+		},
+		tlv.ETUint32, tlv.DTUint32,
+	)
+}
+
+// NewNextHopIDRecord creates a tlv.Record that encodes the short_channel_id
+// (type 6) for an onion payload.
+func NewNextHopIDRecord(cid *uint64) tlv.Record {
+	return tlv.MakePrimitiveRecord(NextHopOnionType, cid)
+}

routing/route/route.go

@@ -11,6 +11,7 @@ import (
 	"github.com/btcsuite/btcd/btcec"
 	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
@@ -103,28 +104,33 @@ func (h *Hop) PackHopPayload(w io.Writer, nextChanID uint64) error {
 
 	// Otherwise, we'll need to make a new stream that includes our
 	// required routing fields, as well as these optional values.
+	var records []tlv.Record
+
+	// Every hop must have an amount to forward and CLTV expiry.
 	amt := uint64(h.AmtToForward)
-	combinedRecords := append(h.TLVRecords,
+	records = append(records,
-		tlv.MakeDynamicRecord(
+		record.NewAmtToFwdRecord(&amt),
-			tlv.AmtOnionType, &amt, func() uint64 {
+		record.NewLockTimeRecord(&h.OutgoingTimeLock),
-				return tlv.SizeTUint64(amt)
-			},
-			tlv.ETUint64, tlv.DTUint64,
-		),
-		tlv.MakeDynamicRecord(
-			tlv.LockTimeOnionType, &h.OutgoingTimeLock, func() uint64 {
-				return tlv.SizeTUint32(h.OutgoingTimeLock)
-			},
-			tlv.ETUint32, tlv.DTUint32,
-		),
-		tlv.MakePrimitiveRecord(tlv.NextHopOnionType, &nextChanID),
 	)
 
+	// BOLT 04 says the next_hop_id should be omitted for the final hop,
+	// but present for all others.
+	//
+	// TODO(conner): test using hop.Exit once available
+	if nextChanID != 0 {
+		records = append(records,
+			record.NewNextHopIDRecord(&nextChanID),
+		)
+	}
+
+	// Append any custom types destined for this hop.
+	records = append(records, h.TLVRecords...)
+
 	// To ensure we produce a canonical stream, we'll sort the records
 	// before encoding them as a stream in the hop payload.
-	tlv.SortRecords(combinedRecords)
+	tlv.SortRecords(records)
 
-	tlvStream, err := tlv.NewStream(combinedRecords...)
+	tlvStream, err := tlv.NewStream(records...)
 	if err != nil {
 		return err
 	}

tlv/onion_types.go

@@ -1,15 +0,0 @@
-package tlv
-
-const (
-	// AmtOnionType is the type used in the onion to refrence the amount to
-	// send to the next hop.
-	AmtOnionType Type = 2
-
-	// LockTimeTLV is the type used in the onion to refenernce the CLTV
-	// value that should be used for the next hop's HTLC.
-	LockTimeOnionType Type = 4
-
-	// NextHopOnionType is the type used in the onion to reference the ID
-	// of the next hop.
-	NextHopOnionType Type = 6
-)