lnwire: add blinding point to update_add_htlc TLVs

Add blinding points to update_add_htlc. This TLV will be set for
nodes that are relaying payments in blinded routes that are _not_
the introduction node.

lnwire/update_add_htlc.go

@@ -3,6 +3,9 @@ package lnwire
 import (
 	"bytes"
 	"io"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 // OnionPacketSize is the size of the serialized Sphinx onion packet included
@@ -11,6 +14,17 @@ import (
 // of per-hop data, and a 32-byte HMAC over the entire packet.
 const OnionPacketSize = 1366
 
+type (
+	// BlindingPointTlvType is the type for ephemeral pubkeys used in
+	// route blinding.
+	BlindingPointTlvType = tlv.TlvType0
+
+	// BlindingPointRecord holds an optional blinding point on update add
+	// htlc.
+	//nolint:lll
+	BlindingPointRecord = tlv.OptionalRecordT[BlindingPointTlvType, *btcec.PublicKey]
+)
+
 // UpdateAddHTLC is the message sent by Alice to Bob when she wishes to add an
 // HTLC to his remote commitment transaction. In addition to information
 // detailing the value, the ID, expiry, and the onion blob is also included
@@ -54,6 +68,10 @@ type UpdateAddHTLC struct {
 	// used in the subsequent UpdateAddHTLC message.
 	OnionBlob [OnionPacketSize]byte
 
+	// BlindingPoint is the ephemeral pubkey used to optionally blind the
+	// next hop for this htlc.
+	BlindingPoint BlindingPointRecord
+
 	// ExtraData is the set of data that was appended to this message to
 	// fill out the full maximum transport message size. These fields can
 	// be used to specify optional data such as custom TLV fields.
@@ -74,7 +92,7 @@ var _ Message = (*UpdateAddHTLC)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (c *UpdateAddHTLC) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r,
+	if err := ReadElements(r,
 		&c.ChanID,
 		&c.ID,
 		&c.Amount,
@@ -82,7 +100,27 @@ func (c *UpdateAddHTLC) Decode(r io.Reader, pver uint32) error {
 		&c.Expiry,
 		c.OnionBlob[:],
 		&c.ExtraData,
-	)
+	); err != nil {
+		return err
+	}
+
+	blindingRecord := c.BlindingPoint.Zero()
+	tlvMap, err := c.ExtraData.ExtractRecords(&blindingRecord)
+	if err != nil {
+		return err
+	}
+
+	if val, ok := tlvMap[c.BlindingPoint.TlvType()]; ok && val == nil {
+		c.BlindingPoint = tlv.SomeRecordT(blindingRecord)
+	}
+
+	// Set extra data to nil if we didn't parse anything out of it so that
+	// we can use assert.Equal in tests.
+	if len(tlvMap) == 0 {
+		c.ExtraData = nil
+	}
+
+	return nil
 }
 
 // Encode serializes the target UpdateAddHTLC into the passed io.Writer
@@ -114,6 +152,20 @@ func (c *UpdateAddHTLC) Encode(w *bytes.Buffer, pver uint32) error {
 		return err
 	}
 
+	// Only include blinding point in extra data if present.
+	var records []tlv.RecordProducer
+
+	c.BlindingPoint.WhenSome(func(b tlv.RecordT[BlindingPointTlvType,
+		*btcec.PublicKey]) {
+
+		records = append(records, &b)
+	})
+
+	err := EncodeMessageExtraData(&c.ExtraData, records...)
+	if err != nil {
+		return err
+	}
+
 	return WriteBytes(w, c.ExtraData)
 }