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_test.go

@@ -2,15 +2,23 @@ package hop_test
 
 import (
 	"bytes"
+	"encoding/hex"
 	"reflect"
 	"testing"
 
+	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/lightningnetwork/lnd/htlcswitch/hop"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
 	"github.com/stretchr/testify/require"
 )
 
+var (
+	//nolint:lll
+	testPrivKeyBytes, _ = hex.DecodeString("e126f68f7eafcc8b74f54d269fe206be715000f94dac067d1c04a8ca3b2db734")
+	_, testPubKey       = btcec.PrivKeyFromBytes(testPrivKeyBytes)
+)
+
 const testUnknownRequiredType = 0x80
 
 type decodePayloadTest struct {
@@ -20,7 +28,10 @@ type decodePayloadTest struct {
 	expCustomRecords   map[uint64][]byte
 	shouldHaveMPP      bool
 	shouldHaveAMP      bool
+	shouldHaveEncData  bool
+	shouldHaveBlinding bool
 	shouldHaveMetadata bool
+	shouldHaveTotalAmt bool
 }
 
 var decodePayloadTests = []decodePayloadTest{
@@ -217,6 +228,33 @@ var decodePayloadTests = []decodePayloadTest{
 			FinalHop:  false,
 		},
 	},
+	{
+		name: "intermediate hop with encrypted data",
+		payload: []byte{
+			// amount
+			0x02, 0x00,
+			// cltv
+			0x04, 0x00,
+			// encrypted data
+			0x0a, 0x03, 0x03, 0x02, 0x01,
+		},
+		shouldHaveEncData: true,
+	},
+	{
+		name: "intermediate hop with blinding point",
+		payload: append([]byte{
+			// amount
+			0x02, 0x00,
+			// cltv
+			0x04, 0x00,
+			// blinding point (type / length)
+			0x0c, 0x21,
+		},
+			// blinding point (value)
+			testPubKey.SerializeCompressed()...,
+		),
+		shouldHaveBlinding: true,
+	},
 	{
 		name: "final hop with mpp",
 		payload: []byte{
@@ -271,6 +309,18 @@ var decodePayloadTests = []decodePayloadTest{
 		},
 		shouldHaveMetadata: true,
 	},
+	{
+		name: "final hop with total amount",
+		payload: []byte{
+			// amount
+			0x02, 0x00,
+			// cltv
+			0x04, 0x00,
+			// total amount
+			0x12, 0x01, 0x01,
+		},
+		shouldHaveTotalAmt: true,
+	},
 }
 
 // TestDecodeHopPayloadRecordValidation asserts that parsing the payloads in the
@@ -306,6 +356,7 @@ func testDecodeHopPayloadValidation(t *testing.T, test decodePayloadTest) {
 			0x13, 0x13, 0x13, 0x13, 0x13, 0x13, 0x13, 0x13,
 			0x13, 0x13, 0x13, 0x13, 0x13, 0x13, 0x13, 0x13,
 		}
+		testEncData    = []byte{3, 2, 1}
 		testMetadata   = []byte{1, 2, 3}
 		testChildIndex = uint32(9)
 	)
@@ -354,6 +405,29 @@ func testDecodeHopPayloadValidation(t *testing.T, test decodePayloadTest) {
 		t.Fatalf("unexpected metadata")
 	}
 
+	if test.shouldHaveEncData {
+		require.NotNil(t, p.EncryptedData(),
+			"payment should have encrypted data")
+
+		require.Equal(t, testEncData, p.EncryptedData())
+	} else {
+		require.Nil(t, p.EncryptedData())
+	}
+
+	if test.shouldHaveBlinding {
+		require.NotNil(t, p.BlindingPoint())
+
+		require.Equal(t, testPubKey, p.BlindingPoint())
+	} else {
+		require.Nil(t, p.BlindingPoint())
+	}
+
+	if test.shouldHaveTotalAmt {
+		require.NotZero(t, p.TotalAmtMsat())
+	} else {
+		require.Zero(t, p.TotalAmtMsat())
+	}
+
 	// Convert expected nil map to empty map, because we always expect an
 	// initiated map from the payload.
 	expCustomRecords := make(record.CustomSet)