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/update_add_htlc_test.go

@@ -0,0 +1,188 @@
+package lnwire
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/require"
+)
+
+// testCase is a test case for the UpdateAddHTLC message.
+type testCase struct {
+	// Msg is the message to be encoded and decoded.
+	Msg UpdateAddHTLC
+
+	// ExpectEncodeError is a flag that indicates whether we expect the
+	// encoding of the message to fail.
+	ExpectEncodeError bool
+}
+
+// generateTestCases generates a set of UpdateAddHTLC message test cases.
+func generateTestCases(t *testing.T) []testCase {
+	// Firstly, we'll set basic values for the message fields.
+	//
+	// Generate random channel ID.
+	chanIDBytes, err := generateRandomBytes(32)
+	require.NoError(t, err)
+
+	var chanID ChannelID
+	copy(chanID[:], chanIDBytes)
+
+	// Generate random payment hash.
+	paymentHashBytes, err := generateRandomBytes(32)
+	require.NoError(t, err)
+
+	var paymentHash [32]byte
+	copy(paymentHash[:], paymentHashBytes)
+
+	// Generate random onion blob.
+	onionBlobBytes, err := generateRandomBytes(OnionPacketSize)
+	require.NoError(t, err)
+
+	var onionBlob [OnionPacketSize]byte
+	copy(onionBlob[:], onionBlobBytes)
+
+	// Define the blinding point.
+	blinding, err := pubkeyFromHex(
+		"0228f2af0abe322403480fb3ee172f7f1601e67d1da6cad40b54c4468d4" +
+			"8236c39",
+	)
+	require.NoError(t, err)
+
+	blindingPoint := tlv.SomeRecordT(
+		tlv.NewPrimitiveRecord[BlindingPointTlvType](blinding),
+	)
+
+	// Define custom records.
+	recordKey1 := uint64(MinCustomRecordsTlvType + 1)
+	recordValue1, err := generateRandomBytes(10)
+	require.NoError(t, err)
+
+	recordKey2 := uint64(MinCustomRecordsTlvType + 2)
+	recordValue2, err := generateRandomBytes(10)
+	require.NoError(t, err)
+
+	customRecords := CustomRecords{
+		recordKey1: recordValue1,
+		recordKey2: recordValue2,
+	}
+
+	// Construct an instance of extra data that contains records with TLV
+	// types below the minimum custom records threshold and that lack
+	// corresponding fields in the message struct. Content should persist in
+	// the extra data field after encoding and decoding.
+	var (
+		recordBytes45 = []byte("recordBytes45")
+		tlvRecord45   = tlv.NewPrimitiveRecord[tlv.TlvType45](
+			recordBytes45,
+		)
+
+		recordBytes55 = []byte("recordBytes55")
+		tlvRecord55   = tlv.NewPrimitiveRecord[tlv.TlvType55](
+			recordBytes55,
+		)
+	)
+
+	var extraData ExtraOpaqueData
+	err = extraData.PackRecords(
+		[]tlv.RecordProducer{&tlvRecord45, &tlvRecord55}...,
+	)
+	require.NoError(t, err)
+
+	invalidCustomRecords := CustomRecords{
+		MinCustomRecordsTlvType - 1: recordValue1,
+	}
+
+	return []testCase{
+		{
+			Msg: UpdateAddHTLC{
+				ChanID:        chanID,
+				ID:            42,
+				Amount:        MilliSatoshi(1000),
+				PaymentHash:   paymentHash,
+				Expiry:        43,
+				OnionBlob:     onionBlob,
+				BlindingPoint: blindingPoint,
+				CustomRecords: customRecords,
+				ExtraData:     extraData,
+			},
+		},
+		// Add a test case where the blinding point field is not
+		// populated.
+		{
+			Msg: UpdateAddHTLC{
+				ChanID:        chanID,
+				ID:            42,
+				Amount:        MilliSatoshi(1000),
+				PaymentHash:   paymentHash,
+				Expiry:        43,
+				OnionBlob:     onionBlob,
+				CustomRecords: customRecords,
+			},
+		},
+		// Add a test case where the custom records field is not
+		// populated.
+		{
+			Msg: UpdateAddHTLC{
+				ChanID:        chanID,
+				ID:            42,
+				Amount:        MilliSatoshi(1000),
+				PaymentHash:   paymentHash,
+				Expiry:        43,
+				OnionBlob:     onionBlob,
+				BlindingPoint: blindingPoint,
+			},
+		},
+		// Add a case where the custom records are invalid.
+		{
+			Msg: UpdateAddHTLC{
+				ChanID:        chanID,
+				ID:            42,
+				Amount:        MilliSatoshi(1000),
+				PaymentHash:   paymentHash,
+				Expiry:        43,
+				OnionBlob:     onionBlob,
+				BlindingPoint: blindingPoint,
+				CustomRecords: invalidCustomRecords,
+			},
+			ExpectEncodeError: true,
+		},
+	}
+}
+
+// TestUpdateAddHtlcEncodeDecode tests UpdateAddHTLC message encoding and
+// decoding for all supported field values.
+func TestUpdateAddHtlcEncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	// Generate test cases.
+	testCases := generateTestCases(t)
+
+	// Execute test cases.
+	for tcIdx, tc := range testCases {
+		t.Run(fmt.Sprintf("testcase-%d", tcIdx), func(t *testing.T) {
+			// Encode test case message.
+			var buf bytes.Buffer
+			err := tc.Msg.Encode(&buf, 0)
+
+			// Check if we expect an encoding error.
+			if tc.ExpectEncodeError {
+				require.Error(t, err)
+				return
+			}
+
+			require.NoError(t, err)
+
+			// Decode the encoded message bytes message.
+			var actualMsg UpdateAddHTLC
+			decodeReader := bytes.NewReader(buf.Bytes())
+			err = actualMsg.Decode(decodeReader, 0)
+			require.NoError(t, err)
+
+			// Compare the two messages to ensure equality.
+			require.Equal(t, tc.Msg, actualMsg)
+		})
+	}
+}