multi: upgrade new taproot TLVs to use tlv.OptionalRecordT

In this commit, we update new Taproot related TLVs (nonces, partial sig,
sig with nonce, etc). Along the way we were able to get rid of some
boiler plate, but most importantly, we're able to better protect against
API misuse (using a nonce that isn't initialized, etc) with the new
options API. In some areas this introduces a bit of extra boiler plate,
and where applicable I used some new helper functions to help cut down
on the noise.

Note to reviewers: this is done as a single commit, as changing the API
breaks all callers, so if we want things to compile it needs to be in a
wumbo commit.

lnwire/shutdown.go

@@ -4,52 +4,21 @@ import (
 	"bytes"
 	"io"
 
-	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
-const (
-	// ShutdownNonceRecordType is the type of the shutdown nonce TLV record.
-	ShutdownNonceRecordType = 8
+type (
+	// ShutdownNonceType is the type of the shutdown nonce TLV record.
+	ShutdownNonceType = tlv.TlvType8
+
+	// ShutdownNonceTLV is the TLV record that contains the shutdown nonce.
+	ShutdownNonceTLV = tlv.OptionalRecordT[ShutdownNonceType, Musig2Nonce]
 )
 
-// ShutdownNonce is the type of the nonce we send during the shutdown flow.
-// Unlike the other nonces, this nonce is symmetric w.r.t the message being
-// signed (there's only one message for shutdown: the co-op close txn).
-type ShutdownNonce Musig2Nonce
-
-// Record returns a TLV record that can be used to encode/decode the musig2
-// nonce from a given TLV stream.
-func (s *ShutdownNonce) Record() tlv.Record {
-	return tlv.MakeStaticRecord(
-		ShutdownNonceRecordType, s, musig2.PubNonceSize,
-		shutdownNonceTypeEncoder, shutdownNonceTypeDecoder,
-	)
-}
-
-// shutdownNonceTypeEncoder is a custom TLV encoder for the Musig2Nonce type.
-func shutdownNonceTypeEncoder(w io.Writer, val interface{},
-	_ *[8]byte) error {
-
-	if v, ok := val.(*ShutdownNonce); ok {
-		_, err := w.Write(v[:])
-		return err
-	}
-
-	return tlv.NewTypeForEncodingErr(val, "lnwire.Musig2Nonce")
-}
-
-// shutdownNonceTypeDecoder is a custom TLV decoder for the Musig2Nonce record.
-func shutdownNonceTypeDecoder(r io.Reader, val interface{}, _ *[8]byte,
-	l uint64) error {
-
-	if v, ok := val.(*ShutdownNonce); ok {
-		_, err := io.ReadFull(r, v[:])
-		return err
-	}
-
-	return tlv.NewTypeForDecodingErr(
-		val, "lnwire.ShutdownNonce", l, musig2.PubNonceSize,
+// SomeShutdownNonce returns a ShutdownNonceTLV with the given nonce.
+func SomeShutdownNonce(nonce Musig2Nonce) ShutdownNonceTLV {
+	return tlv.SomeRecordT(
+		tlv.NewRecordT[ShutdownNonceType, Musig2Nonce](nonce),
 	)
 }
 
@@ -67,7 +36,7 @@ type Shutdown struct {
 
 	// ShutdownNonce is the nonce the sender will use to sign the first
 	// co-op sign offer.
-	ShutdownNonce *ShutdownNonce
+	ShutdownNonce ShutdownNonceTLV
 
 	// ExtraData is the set of data that was appended to this message to
 	// fill out the full maximum transport message size. These fields can
@@ -102,15 +71,15 @@ func (s *Shutdown) Decode(r io.Reader, pver uint32) error {
 		return err
 	}
 
-	var musigNonce ShutdownNonce
+	musigNonce := s.ShutdownNonce.Zero()
 	typeMap, err := tlvRecords.ExtractRecords(&musigNonce)
 	if err != nil {
 		return err
 	}
 
 	// Set the corresponding TLV types if they were included in the stream.
-	if val, ok := typeMap[ShutdownNonceRecordType]; ok && val == nil {
-		s.ShutdownNonce = &musigNonce
+	if val, ok := typeMap[s.ShutdownNonce.TlvType()]; ok && val == nil {
+		s.ShutdownNonce = tlv.SomeRecordT(musigNonce)
 	}
 
 	if len(tlvRecords) != 0 {
@@ -126,9 +95,11 @@ func (s *Shutdown) Decode(r io.Reader, pver uint32) error {
 // This is part of the lnwire.Message interface.
 func (s *Shutdown) Encode(w *bytes.Buffer, pver uint32) error {
 	recordProducers := make([]tlv.RecordProducer, 0, 1)
-	if s.ShutdownNonce != nil {
-		recordProducers = append(recordProducers, s.ShutdownNonce)
-	}
+	s.ShutdownNonce.WhenSome(
+		func(nonce tlv.RecordT[ShutdownNonceType, Musig2Nonce]) {
+			recordProducers = append(recordProducers, &nonce)
+		},
+	)
 	err := EncodeMessageExtraData(&s.ExtraData, recordProducers...)
 	if err != nil {
 		return err