lnwire: update AnnounceSigs2 to use pure TLV

diff --git a/lnwire/announcement_signatures_2.go b/lnwire/announcement_signatures_2.go
index 6e893da..04e4c0a 100644
--- a/lnwire/announcement_signatures_2.go
+++ b/lnwire/announcement_signatures_2.go
@@ -3,6 +3,8 @@ package lnwire
 import (
 	"bytes"
 	"io"
+
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 // AnnounceSignatures2 is a direct message between two endpoints of a
@@ -14,27 +16,40 @@ type AnnounceSignatures2 struct {
 	// Channel id is better for users and debugging and short channel id is
 	// used for quick test on existence of the particular utxo inside the
 	// blockchain, because it contains information about block.
-	ChannelID ChannelID
+	ChannelID tlv.RecordT[tlv.TlvType0, ChannelID]
 
 	// ShortChannelID is the unique description of the funding transaction.
 	// It is constructed with the most significant 3 bytes as the block
 	// height, the next 3 bytes indicating the transaction index within the
 	// block, and the least significant two bytes indicating the output
 	// index which pays to the channel.
-	ShortChannelID ShortChannelID
+	ShortChannelID tlv.RecordT[tlv.TlvType2, ShortChannelID]
 
 	// PartialSignature is the combination of the partial Schnorr signature
 	// created for the node's bitcoin key with the partial signature created
 	// for the node's node ID key.
-	PartialSignature PartialSig
-
-	// ExtraOpaqueData is the set of data that was appended to this
-	// message, some of which we may not actually know how to iterate or
-	// parse. By holding onto this data, we ensure that we're able to
-	// properly validate the set of signatures that cover these new fields,
-	// and ensure we're able to make upgrades to the network in a forwards
-	// compatible manner.
-	ExtraOpaqueData ExtraOpaqueData
+	PartialSignature tlv.RecordT[tlv.TlvType4, PartialSig]
+
+	// 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
+}
+
+// NewAnnSigs2 is a constructor for AnnounceSignatures2.
+func NewAnnSigs2(chanID ChannelID, scid ShortChannelID,
+	partialSig PartialSig) *AnnounceSignatures2 {
+
+	return &AnnounceSignatures2{
+		ChannelID: tlv.NewRecordT[tlv.TlvType0, ChannelID](chanID),
+		ShortChannelID: tlv.NewRecordT[tlv.TlvType2, ShortChannelID](
+			scid,
+		),
+		PartialSignature: tlv.NewRecordT[tlv.TlvType4, PartialSig](
+			partialSig,
+		),
+		ExtraSignedFields: make(ExtraSignedFields),
+	}
 }
 
 // A compile time check to ensure AnnounceSignatures2 implements the
@@ -45,37 +60,38 @@ var _ Message = (*AnnounceSignatures2)(nil)
 // lnwire.SizeableMessage interface.
 var _ SizeableMessage = (*AnnounceSignatures2)(nil)
 
+// A compile time check to ensure ChannelAnnouncement2 implements the
+// lnwire.PureTLVMessage interface.
+var _ PureTLVMessage = (*AnnounceSignatures2)(nil)
+
 // Decode deserializes a serialized AnnounceSignatures2 stored in the passed
 // io.Reader observing the specified protocol version.
 //
 // This is part of the lnwire.Message interface.
 func (a *AnnounceSignatures2) Decode(r io.Reader, _ uint32) error {
-	return ReadElements(r,
-		&a.ChannelID,
-		&a.ShortChannelID,
-		&a.PartialSignature,
-		&a.ExtraOpaqueData,
-	)
-}
-
-// Encode serializes the target AnnounceSignatures2 into the passed io.Writer
-// observing the protocol version specified.
-//
-// This is part of the lnwire.Message interface.
-func (a *AnnounceSignatures2) Encode(w *bytes.Buffer, _ uint32) error {
-	if err := WriteChannelID(w, a.ChannelID); err != nil {
+	stream, err := tlv.NewStream(ProduceRecordsSorted(
+		&a.ChannelID, &a.ShortChannelID, &a.PartialSignature,
+	)...)
+	if err != nil {
 		return err
 	}
 
-	if err := WriteShortChannelID(w, a.ShortChannelID); err != nil {
+	typeMap, err := stream.DecodeWithParsedTypesP2P(r)
+	if err != nil {
 		return err
 	}
 
-	if err := WriteElement(w, a.PartialSignature); err != nil {
-		return err
-	}
+	a.ExtraSignedFields = ExtraSignedFieldsFromTypeMap(typeMap)
+
+	return nil
+}
 
-	return WriteBytes(w, a.ExtraOpaqueData)
+// Encode serializes the target AnnounceSignatures2 into the passed io.Writer
+// observing the protocol version specified.
+//
+// This is part of the lnwire.Message interface.
+func (a *AnnounceSignatures2) Encode(w *bytes.Buffer, _ uint32) error {
+	return EncodePureTLVMessage(a, w)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -93,16 +109,34 @@ func (a *AnnounceSignatures2) SerializedSize() (uint32, error) {
 	return MessageSerializedSize(a)
 }
 
+// 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.
+//
+// NOTE: this is part of the PureTLVMessage interface.
+func (a *AnnounceSignatures2) AllRecords() []tlv.Record {
+	recordProducers := []tlv.RecordProducer{
+		&a.ChannelID, &a.ShortChannelID,
+		&a.PartialSignature,
+	}
+
+	recordProducers = append(recordProducers, RecordsAsProducers(
+		tlv.MapToRecords(a.ExtraSignedFields),
+	)...)
+
+	return ProduceRecordsSorted(recordProducers...)
+}
+
 // SCID returns the ShortChannelID of the channel.
 //
 // NOTE: this is part of the AnnounceSignatures interface.
 func (a *AnnounceSignatures2) SCID() ShortChannelID {
-	return a.ShortChannelID
+	return a.ShortChannelID.Val
 }
 
 // ChanID returns the ChannelID identifying the channel.
 //
 // NOTE: this is part of the AnnounceSignatures interface.
 func (a *AnnounceSignatures2) ChanID() ChannelID {
-	return a.ChannelID
+	return a.ChannelID.Val
 }
diff --git a/lnwire/announcement_signatures_2_test.go b/lnwire/announcement_signatures_2_test.go
new file mode 100644
index 0000000..6b945ed
--- /dev/null
+++ b/lnwire/announcement_signatures_2_test.go
@@ -0,0 +1,78 @@
+package lnwire
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/tlv"
+	"github.com/stretchr/testify/require"
+)
+
+// TestAnnSigs2EncodeDecode tests the encoding and decoding of the
+// AnnounceSignatures2 message using hardcoded byte slices.
+func TestAnnSigs2EncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	// We'll create a raw byte stream that represents a valid
+	// AnnounceSignatures2 message with various known and unknown fields in
+	// the signed TLV ranges.
+	var rawBytes []byte
+
+	// ChannelID.
+	rawBytes = append(rawBytes, []byte{
+		0x00, // type
+		0x20, // length
+	}...)
+	rawBytes = append(rawBytes, make([]byte, 32)...) // value
+
+	// ShortChannelID.
+	rawBytes = append(rawBytes, []byte{
+		0x02,                   // type
+		0x08,                   // length
+		0, 0, 1, 0, 0, 2, 0, 3, // value
+	}...)
+
+	// PartialSignature.
+	rawBytes = append(rawBytes, []byte{
+		0x04, // type
+		0x20, // length
+	}...)
+	rawBytes = append(rawBytes, make([]byte, 32)...) // value
+
+	// Extra field in the first signed range.
+	rawBytes = append(rawBytes, []byte{
+		0x30,       // type
+		0x02,       // length
+		0xab, 0xcd, // value
+	}...)
+
+	w := new(bytes.Buffer)
+	var buf [8]byte
+	err := tlv.WriteVarInt(w, pureTLVSignedSecondRangeStart+1, &buf)
+	require.NoError(t, err)
+
+	// Extra field in the second signed range.
+	rawBytes = append(rawBytes, w.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 := &AnnounceSignatures2{}
+	r := bytes.NewReader(rawBytes)
+	err = msg.Decode(r, 0)
+	require.NoError(t, err)
+
+	// At this point, we expect 2 extra signed fields.
+	require.Len(t, msg.ExtraSignedFields, 2)
+
+	// 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 77432fd..8f946f1 100644
--- a/lnwire/test_message.go
+++ b/lnwire/test_message.go
@@ -129,12 +129,29 @@ var _ TestMessage = (*AnnounceSignatures2)(nil)
 //
 // This is part of the TestMessage interface.
 func (a *AnnounceSignatures2) RandTestMessage(t *rapid.T) Message {
-	return &AnnounceSignatures2{
-		ChannelID:        RandChannelID(t),
-		ShortChannelID:   RandShortChannelID(t),
-		PartialSignature: *RandPartialSig(t),
-		ExtraOpaqueData:  RandExtraOpaqueData(t, nil),
+	var (
+		chanID = RandChannelID(t)
+		scid   = RandShortChannelID(t)
+		pSig   = RandPartialSig(t)
+	)
+
+	msg := &AnnounceSignatures2{
+		ChannelID: tlv.NewRecordT[tlv.TlvType0, ChannelID](
+			chanID,
+		),
+		ShortChannelID: tlv.NewRecordT[tlv.TlvType2](scid),
+		PartialSignature: tlv.NewRecordT[tlv.TlvType4, PartialSig](
+			*pSig,
+		),
+		ExtraSignedFields: make(map[uint64][]byte),
+	}
+
+	randRecs, _ := RandSignedRangeRecords(t)
+	if len(randRecs) > 0 {
+		msg.ExtraSignedFields = ExtraSignedFields(randRecs)
 	}
+
+	return msg
 }
 
 // A compile time check to ensure ChannelAnnouncement1 implements the