lnwire+netann: update ChannelUpdate2

diff --git a/lnwire/channel_update_2.go b/lnwire/channel_update_2.go
index 343af6b..b832bc5 100644
--- a/lnwire/channel_update_2.go
+++ b/lnwire/channel_update_2.go
@@ -22,10 +22,6 @@ const (
 // HTLCs and other parameters. This message is also used to redeclare initially
 // set channel parameters.
 type ChannelUpdate2 struct {
-	// Signature is used to validate the announced data and prove the
-	// ownership of node id.
-	Signature Sig
-
 	// ChainHash denotes the target chain that this channel was opened
 	// within. This value should be the genesis hash of the target chain.
 	// Along with the short channel ID, this uniquely identifies the
@@ -74,10 +70,22 @@ type ChannelUpdate2 struct {
 	// millionth of a satoshi.
 	FeeProportionalMillionths tlv.RecordT[tlv.TlvType18, uint32]
 
-	// ExtraOpaqueData 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.
-	ExtraOpaqueData ExtraOpaqueData
+	// Signature is used to validate the announced data and prove the
+	// ownership of node id.
+	Signature tlv.RecordT[tlv.TlvType160, Sig]
+
+	// Any extra fields in the signed range that we do not yet know about,
+	// but we need to keep them for signature validation and to produce a
+	// valid message.
+	ExtraSignedFields
+}
+
+// Encode serializes the target ChannelUpdate2 into the passed io.Writer
+// observing the protocol version specified.
+//
+// This is part of the lnwire.Message interface.
+func (c *ChannelUpdate2) Encode(w *bytes.Buffer, _ uint32) error {
+	return EncodePureTLVMessage(c, w)
 }
 
 // Decode deserializes a serialized ChannelUpdate2 stored in the passed
@@ -85,17 +93,6 @@ type ChannelUpdate2 struct {
 //
 // This is part of the lnwire.Message interface.
 func (c *ChannelUpdate2) Decode(r io.Reader, _ uint32) error {
-	err := ReadElement(r, &c.Signature)
-	if err != nil {
-		return err
-	}
-	c.Signature.ForceSchnorr()
-
-	return c.DecodeTLVRecords(r)
-}
-
-// DecodeTLVRecords decodes only the TLV section of the message.
-func (c *ChannelUpdate2) DecodeTLVRecords(r io.Reader) error {
 	// First extract into extra opaque data.
 	var tlvRecords ExtraOpaqueData
 	if err := ReadElements(r, &tlvRecords); err != nil {
@@ -111,10 +108,12 @@ func (c *ChannelUpdate2) DecodeTLVRecords(r io.Reader) error {
 		&secondPeer, &c.CLTVExpiryDelta, &c.HTLCMinimumMsat,
 		&c.HTLCMaximumMsat, &c.FeeBaseMsat,
 		&c.FeeProportionalMillionths,
+		&c.Signature,
 	)
 	if err != nil {
 		return err
 	}
+	c.Signature.Val.ForceSchnorr()
 
 	// By default, the chain-hash is the bitcoin mainnet genesis block hash.
 	c.ChainHash.Val = *chaincfg.MainNetParams.GenesisHash
@@ -150,38 +149,21 @@ func (c *ChannelUpdate2) DecodeTLVRecords(r io.Reader) error {
 		c.FeeProportionalMillionths.Val = defaultFeeProportionalMillionths //nolint:ll
 	}
 
-	if len(tlvRecords) != 0 {
-		c.ExtraOpaqueData = tlvRecords
-	}
+	c.ExtraSignedFields = ExtraSignedFieldsFromTypeMap(typeMap)
 
-	return c.ExtraOpaqueData.ValidateTLV()
+	return nil
 }
 
-// Encode serializes the target ChannelUpdate2 into the passed io.Writer
-// observing the protocol version specified.
+// AllRecords returns all the TLV records for the message. This will include all
+// the records we know about along with any that we don't know about but that
+// fall in the signed TLV range.
 //
-// This is part of the lnwire.Message interface.
-func (c *ChannelUpdate2) Encode(w *bytes.Buffer, _ uint32) error {
-	_, err := w.Write(c.Signature.RawBytes())
-	if err != nil {
-		return err
-	}
-
-	_, err = c.DataToSign()
-	if err != nil {
-		return err
-	}
-
-	return WriteBytes(w, c.ExtraOpaqueData)
-}
+// NOTE: this is part of the PureTLVMessage interface.
+func (c *ChannelUpdate2) AllRecords() []tlv.Record {
+	var recordProducers []tlv.RecordProducer
 
-// DataToSign is used to retrieve part of the announcement message which should
-// be signed. For the ChannelUpdate2 message, this includes the serialised TLV
-// records.
-func (c *ChannelUpdate2) DataToSign() ([]byte, error) {
 	// The chain-hash record is only included if it is _not_ equal to the
 	// bitcoin mainnet genisis block hash.
-	var recordProducers []tlv.RecordProducer
 	if !c.ChainHash.Val.IsEqual(chaincfg.MainNetParams.GenesisHash) {
 		hash := tlv.ZeroRecordT[tlv.TlvType0, [32]byte]()
 		hash.Val = c.ChainHash.Val
@@ -190,7 +172,7 @@ func (c *ChannelUpdate2) DataToSign() ([]byte, error) {
 	}
 
 	recordProducers = append(recordProducers,
-		&c.ShortChannelID, &c.BlockHeight,
+		&c.ShortChannelID, &c.BlockHeight, &c.Signature,
 	)
 
 	// Only include the disable flags if any bit is set.
@@ -225,12 +207,11 @@ func (c *ChannelUpdate2) DataToSign() ([]byte, error) {
 		)
 	}
 
-	err := EncodeMessageExtraData(&c.ExtraOpaqueData, recordProducers...)
-	if err != nil {
-		return nil, err
-	}
+	recordProducers = append(recordProducers, RecordsAsProducers(
+		tlv.MapToRecords(c.ExtraSignedFields),
+	)...)
 
-	return c.ExtraOpaqueData, nil
+	return ProduceRecordsSorted(recordProducers...)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -248,14 +229,14 @@ func (c *ChannelUpdate2) SerializedSize() (uint32, error) {
 	return MessageSerializedSize(c)
 }
 
-func (c *ChannelUpdate2) ExtraData() ExtraOpaqueData {
-	return c.ExtraOpaqueData
-}
-
 // A compile time check to ensure ChannelUpdate2 implements the
 // lnwire.Message interface.
 var _ Message = (*ChannelUpdate2)(nil)
 
+// A compile time check to ensure ChannelUpdate2 implements the
+// lnwire.PureTLVMessage interface.
+var _ PureTLVMessage = (*ChannelUpdate2)(nil)
+
 // SCID returns the ShortChannelID of the channel that the update applies to.
 //
 // NOTE: this is part of the ChannelUpdate interface.
diff --git a/lnwire/channel_update_2_test.go b/lnwire/channel_update_2_test.go
new file mode 100644
index 0000000..4e771d8
--- /dev/null
+++ b/lnwire/channel_update_2_test.go
@@ -0,0 +1,119 @@
+package lnwire
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/require"
+)
+
+// TestChanUpdate2EncodeDecode tests the encoding and decoding of the
+// ChannelUpdate2 message using hardcoded byte slices.
+func TestChanUpdate2EncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	// We'll create a raw byte stream that represents a valid ChannelUpdate2
+	// message. This includes the signature and a TLV stream with both known
+	// and unknown records.
+	rawBytes := []byte{
+		// ChainHash record (optional, not mainnet).
+		0x0,  // type.
+		0x20, // length.
+		0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1,
+		0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1,
+		0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1, 0x1,
+
+		// ShortChannelID record.
+		0x2,                                    // type.
+		0x8,                                    // length.
+		0x0, 0x0, 0x1, 0x0, 0x0, 0x2, 0x0, 0x3, // value.
+
+		// BlockHeight record.
+		0x4,                // type.
+		0x4,                // length.
+		0x0, 0x0, 0x1, 0x0, // value.
+
+		// DisabledFlags record.
+		0x6, // type.
+		0x1, // length.
+		0x1, // value.
+
+		// SecondPeer record.
+		0x8, // type.
+		0x0, // length.
+
+		// Unknown odd-type TLV record.
+		0x9,        // type.
+		0x2,        // length.
+		0xab, 0xcd, // value.
+
+		// CLTVExpiryDelta record.
+		0xa,       // type.
+		0x2,       // length.
+		0x0, 0x10, // value.
+
+		// HTLCMinimumMsat record.
+		0xc,                        // type.
+		0x5,                        // length.
+		0xfe, 0x0, 0xf, 0x42, 0x40, // value (BigSize: 1_000_000).
+
+		// HTLCMaximumMsat record.
+		0xe,                        // type.
+		0x5,                        // length.
+		0xfe, 0x0, 0xf, 0x42, 0x40, // value (BigSize: 1_000_000).
+
+		// FeeBaseMsat record.
+		0x10,               // type.
+		0x4,                // length.
+		0x0, 0x0, 0x1, 0x0, // value.
+
+		// FeeProportionalMillionths record.
+		0x12,               // type.
+		0x4,                // length.
+		0x0, 0x0, 0x1, 0x0, // value.
+
+		// Extra Opaque Data - Unknown Record.
+		0x14,       // type.
+		0x2,        // length.
+		0x79, 0x79, // value.
+
+		// Signature.
+		0xa0, // type.
+		0x40, // length.
+		0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb,
+		0xc, 0xd, 0xe, 0xf, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
+		0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,
+		0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a,
+		0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
+		0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e,
+		0x3f, // value
+	}
+
+	secondSignedRangeType := new(bytes.Buffer)
+	var buf [8]byte
+	err := tlv.WriteVarInt(
+		secondSignedRangeType, pureTLVSignedSecondRangeStart+1, &buf,
+	)
+	require.NoError(t, err)
+	rawBytes = append(rawBytes, secondSignedRangeType.Bytes()...) // type.
+	rawBytes = append(rawBytes, []byte{
+		0x02,       // length.
+		0x79, 0x79, // value.
+	}...)
+
+	// Now, create a new empty message and decode the raw bytes into it.
+	msg := &ChannelUpdate2{}
+	r := bytes.NewReader(rawBytes)
+	err = msg.Decode(r, 0)
+	require.NoError(t, err)
+
+	// Next, encode the message back into a new byte buffer.
+	var b bytes.Buffer
+	err = msg.Encode(&b, 0)
+	require.NoError(t, err)
+
+	// The re-encoded bytes should be exactly the same as the original raw
+	// bytes.
+	require.Equal(t, rawBytes, b.Bytes())
+}
diff --git a/lnwire/test_message.go b/lnwire/test_message.go
index 8e2e46b..77432fd 100644
--- a/lnwire/test_message.go
+++ b/lnwire/test_message.go
@@ -518,7 +518,6 @@ func (c *ChannelUpdate2) RandTestMessage(t *rapid.T) Message {
 
 	//nolint:ll
 	msg := &ChannelUpdate2{
-		Signature: RandSignature(t),
 		ChainHash: tlv.NewPrimitiveRecord[tlv.TlvType0, chainhash.Hash](
 			chainHashObj,
 		),
@@ -546,10 +545,11 @@ func (c *ChannelUpdate2) RandTestMessage(t *rapid.T) Message {
 		FeeProportionalMillionths: tlv.NewPrimitiveRecord[tlv.TlvType18, uint32](
 			feeProportionalMillionths,
 		),
-		ExtraOpaqueData: RandExtraOpaqueData(t, nil),
+		ExtraSignedFields: make(map[uint64][]byte),
 	}
 
-	msg.Signature.ForceSchnorr()
+	msg.Signature.Val = RandSignature(t)
+	msg.Signature.Val.ForceSchnorr()
 
 	if rapid.Bool().Draw(t, "isSecondPeer") {
 		msg.SecondPeer = tlv.SomeRecordT(
diff --git a/netann/channel_update.go b/netann/channel_update.go
index d453b53..f262103 100644
--- a/netann/channel_update.go
+++ b/netann/channel_update.go
@@ -242,7 +242,7 @@ func verifyChannelUpdate2Signature(c *lnwire.ChannelUpdate2,
 		return fmt.Errorf("unable to reconstruct message data: %w", err)
 	}
 
-	nodeSig, err := c.Signature.ToSignature()
+	nodeSig, err := c.Signature.Val.ToSignature()
 	if err != nil {
 		return err
 	}
@@ -330,7 +330,7 @@ func ChanUpdate2DigestTag() []byte {
 // chanUpdate2DigestToSign computes the digest of the ChannelUpdate2 message to
 // be signed.
 func chanUpdate2DigestToSign(c *lnwire.ChannelUpdate2) ([]byte, error) {
-	data, err := c.DataToSign()
+	data, err := lnwire.SerialiseFieldsToSign(c)
 	if err != nil {
 		return nil, err
 	}