multi: add blinded path TLVs to onion payload / hops

This commit adds the encrypted_data, blinding_point and total_amt_msat
tlvs to the known set of even tlvs for the onion payload. These TLVs
are added in two places (the onion payload and hop struct) because
lnd uses the same set of TLV types for both structs (and they
inherently represent the same thing).

Note: in some places, unit tests intentionally mimic the style
of older tests, so as to be more consistently readable.

channeldb/payments.go

@@ -9,6 +9,7 @@ import (
 	"sort"
 	"time"
 
+	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -1143,10 +1144,30 @@ func serializeHop(w io.Writer, h *route.Hop) error {
 		records = append(records, h.MPP.Record())
 	}
 
+	// Add blinding point and encrypted data if present.
+	if h.EncryptedData != nil {
+		records = append(records, record.NewEncryptedDataRecord(
+			&h.EncryptedData,
+		))
+	}
+
+	if h.BlindingPoint != nil {
+		records = append(records, record.NewBlindingPointRecord(
+			&h.BlindingPoint,
+		))
+	}
+
 	if h.Metadata != nil {
 		records = append(records, record.NewMetadataRecord(&h.Metadata))
 	}
 
+	if h.TotalAmtMsat != 0 {
+		totalMsatInt := uint64(h.TotalAmtMsat)
+		records = append(
+			records, record.NewTotalAmtMsatBlinded(&totalMsatInt),
+		)
+	}
+
 	// 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 {
@@ -1261,6 +1282,27 @@ func deserializeHop(r io.Reader) (*route.Hop, error) {
 		h.MPP = mpp
 	}
 
+	// If encrypted data or blinding key are present, remove them from
+	// the TLV map and parse into proper types.
+	encryptedDataType := uint64(record.EncryptedDataOnionType)
+	if data, ok := tlvMap[encryptedDataType]; ok {
+		delete(tlvMap, encryptedDataType)
+		h.EncryptedData = data
+	}
+
+	blindingType := uint64(record.BlindingPointOnionType)
+	if blindingPoint, ok := tlvMap[blindingType]; ok {
+		delete(tlvMap, blindingType)
+
+		h.BlindingPoint, err = btcec.ParsePubKey(blindingPoint)
+		if err != nil {
+			return nil, fmt.Errorf("invalid blinding point: %w",
+				err)
+		}
+	}
+
+	// If the metatdata type is present, remove it from the tlv map and
+	// populate directly on the hop.
 	metadataType := uint64(record.MetadataOnionType)
 	if metadata, ok := tlvMap[metadataType]; ok {
 		delete(tlvMap, metadataType)
@@ -1268,6 +1310,26 @@ func deserializeHop(r io.Reader) (*route.Hop, error) {
 		h.Metadata = metadata
 	}
 
+	totalAmtMsatType := uint64(record.TotalAmtMsatBlindedType)
+	if totalAmtMsat, ok := tlvMap[totalAmtMsatType]; ok {
+		delete(tlvMap, totalAmtMsatType)
+
+		var (
+			totalAmtMsatInt uint64
+			buf             [8]byte
+		)
+		if err := tlv.DTUint64(
+			bytes.NewReader(totalAmtMsat),
+			&totalAmtMsatInt,
+			&buf,
+			uint64(len(totalAmtMsat)),
+		); err != nil {
+			return nil, err
+		}
+
+		h.TotalAmtMsat = lnwire.MilliSatoshi(totalAmtMsatInt)
+	}
+
 	h.CustomRecords = tlvMap
 
 	return h, nil