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.

htlcswitch/hop/payload.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 
+	"github.com/btcsuite/btcd/btcec/v2"
 	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
@@ -94,9 +95,20 @@ type Payload struct {
 	// were included in the payload.
 	customRecords record.CustomSet
 
+	// encryptedData is a blob of data encrypted by the receiver for use
+	// in blinded routes.
+	encryptedData []byte
+
+	// blindingPoint is an ephemeral pubkey for use in blinded routes.
+	blindingPoint *btcec.PublicKey
+
 	// metadata is additional data that is sent along with the payment to
 	// the payee.
 	metadata []byte
+
+	// totalAmtMsat holds the info provided in total_amount_msat when
+	// parsed from a TLV onion payload.
+	totalAmtMsat lnwire.MilliSatoshi
 }
 
 // NewLegacyPayload builds a Payload from the amount, cltv, and next hop
@@ -118,12 +130,15 @@ func NewLegacyPayload(f *sphinx.HopData) *Payload {
 // should correspond to the bytes encapsulated in a TLV onion payload.
 func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 	var (
-		cid      uint64
-		amt      uint64
-		cltv     uint32
-		mpp      = &record.MPP{}
-		amp      = &record.AMP{}
-		metadata []byte
+		cid           uint64
+		amt           uint64
+		totalAmtMsat  uint64
+		cltv          uint32
+		mpp           = &record.MPP{}
+		amp           = &record.AMP{}
+		encryptedData []byte
+		blindingPoint *btcec.PublicKey
+		metadata      []byte
 	)
 
 	tlvStream, err := tlv.NewStream(
@@ -131,8 +146,11 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		record.NewLockTimeRecord(&cltv),
 		record.NewNextHopIDRecord(&cid),
 		mpp.Record(),
+		record.NewEncryptedDataRecord(&encryptedData),
+		record.NewBlindingPointRecord(&blindingPoint),
 		amp.Record(),
 		record.NewMetadataRecord(&metadata),
+		record.NewTotalAmtMsatBlinded(&totalAmtMsat),
 	)
 	if err != nil {
 		return nil, err
@@ -175,6 +193,12 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		amp = nil
 	}
 
+	// If no encrypted data was parsed, set the field on our resulting
+	// payload to nil.
+	if _, ok := parsedTypes[record.EncryptedDataOnionType]; !ok {
+		encryptedData = nil
+	}
+
 	// If no metadata field was parsed, set the metadata field on the
 	// resulting payload to nil.
 	if _, ok := parsedTypes[record.MetadataOnionType]; !ok {
@@ -193,7 +217,10 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		MPP:           mpp,
 		AMP:           amp,
 		metadata:      metadata,
+		encryptedData: encryptedData,
+		blindingPoint: blindingPoint,
 		customRecords: customRecords,
+		totalAmtMsat:  lnwire.MilliSatoshi(totalAmtMsat),
 	}, nil
 }
 
@@ -297,12 +324,29 @@ func (h *Payload) CustomRecords() record.CustomSet {
 	return h.customRecords
 }
 
+// EncryptedData returns the route blinding encrypted data parsed from the
+// onion payload.
+func (h *Payload) EncryptedData() []byte {
+	return h.encryptedData
+}
+
+// BlindingPoint returns the route blinding point parsed from the onion payload.
+func (h *Payload) BlindingPoint() *btcec.PublicKey {
+	return h.blindingPoint
+}
+
 // Metadata returns the additional data that is sent along with the
 // payment to the payee.
 func (h *Payload) Metadata() []byte {
 	return h.metadata
 }
 
+// TotalAmtMsat returns the total amount sent to the final hop, as set by the
+// payee.
+func (h *Payload) TotalAmtMsat() lnwire.MilliSatoshi {
+	return h.totalAmtMsat
+}
+
 // getMinRequiredViolation checks for unrecognized required (even) fields in the
 // standard range and returns the lowest required type. Always returning the
 // lowest required type allows a failure message to be deterministic.