lnwire: add custom records field to type UpdateAddHtlc

- Introduce the field `CustomRecords` to the type `UpdateAddHtlc`.
- Encode and decode the new field into the `ExtraData` field of
  the `update_add_htlc` wire message.

lnwire/extra_bytes_test.go

@@ -86,14 +86,6 @@ func TestExtraOpaqueDataEncodeDecode(t *testing.T) {
 	}
 }
 
-type recordProducer struct {
-	record tlv.Record
-}
-
-func (r *recordProducer) Record() tlv.Record {
-	return r.record
-}
-
 // TestExtraOpaqueDataPackUnpackRecords tests that we're able to pack a set of
 // tlv.Records into a stream, and unpack them on the other side to obtain the
 // same set of records.

lnwire/update_add_htlc.go

@@ -72,6 +72,11 @@ type UpdateAddHTLC struct {
 	// next hop for this htlc.
 	BlindingPoint BlindingPointRecord
 
+	// CustomRecords maps TLV types to byte slices, storing arbitrary data
+	// intended for inclusion in the ExtraData field of the UpdateAddHTLC
+	// message.
+	CustomRecords CustomRecords
+
 	// 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.
@@ -104,7 +109,9 @@ func (c *UpdateAddHTLC) Decode(r io.Reader, pver uint32) error {
 		return err
 	}
 
+	// Extract TLV records from the extra data field.
 	blindingRecord := c.BlindingPoint.Zero()
+
 	tlvMap, err := c.ExtraData.ExtractRecords(&blindingRecord)
 	if err != nil {
 		return err
@@ -112,8 +119,19 @@ func (c *UpdateAddHTLC) Decode(r io.Reader, pver uint32) error {
 
 	if val, ok := tlvMap[c.BlindingPoint.TlvType()]; ok && val == nil {
 		c.BlindingPoint = tlv.SomeRecordT(blindingRecord)
+
+		// Remove the entry from the TLV map. Anything left in the map
+		// will be included in the custom records field.
+		delete(tlvMap, c.BlindingPoint.TlvType())
 	}
 
+	// Set the custom records field to the remaining TLV records.
+	customRecords, err := NewCustomRecordsFromTlvTypeMap(tlvMap)
+	if err != nil {
+		return err
+	}
+	c.CustomRecords = *customRecords
+
 	// 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 {
@@ -152,16 +170,26 @@ func (c *UpdateAddHTLC) Encode(w *bytes.Buffer, pver uint32) error {
 		return err
 	}
 
-	// Only include blinding point in extra data if present.
+	// Construct a slice of all the records that we should include in the
+	// extra data field.
 	var records []tlv.RecordProducer
 
+	// Only include blinding point in extra data if present.
 	c.BlindingPoint.WhenSome(func(b tlv.RecordT[BlindingPointTlvType,
 		*btcec.PublicKey]) {
 
 		records = append(records, &b)
 	})
 
-	err := EncodeMessageExtraData(&c.ExtraData, records...)
+	// Extend the 'records' slice with TLV records from the custom records
+	// field.
+	records, err := c.CustomRecords.ExtendRecordProducers(records)
+	if err != nil {
+		return err
+	}
+
+	// Encode the records into the extra data field.
+	err = EncodeMessageExtraData(&c.ExtraData, records...)
 	if err != nil {
 		return err
 	}

peer/brontide.go

@@ -2074,9 +2074,9 @@ func messageSummary(msg lnwire.Message) string {
 		)
 
 		return fmt.Sprintf("chan_id=%v, id=%v, amt=%v, expiry=%v, "+
-			"hash=%x, blinding_point=%x", msg.ChanID, msg.ID,
-			msg.Amount, msg.Expiry, msg.PaymentHash[:],
-			blindingPoint)
+			"hash=%x, blinding_point=%x, custom_records=%v",
+			msg.ChanID, msg.ID, msg.Amount, msg.Expiry,
+			msg.PaymentHash[:], blindingPoint, msg.CustomRecords)
 
 	case *lnwire.UpdateFailHTLC:
 		return fmt.Sprintf("chan_id=%v, id=%v, reason=%x", msg.ChanID,