lnwire: add ShutdownNonce to Shutdown

lnwire/closing_signed.go

@@ -5,6 +5,7 @@ import (
 	"io"
 
 	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
 // ClosingSigned is sent by both parties to a channel once the channel is clear
@@ -29,6 +30,14 @@ type ClosingSigned struct {
 	// Signature is for the proposed channel close transaction.
 	Signature Sig
 
+	// PartialSig is used to transmit a musig2 extended partial signature
+	// that signs the latest fee offer. The nonce isn't sent along side, as
+	// that has already been sent in the initial shutdown message.
+	//
+	// NOTE: This field is only populated if a musig2 taproot channel is
+	// being signed for. In this case, the above Sig type MUST be blank.
+	PartialSig *PartialSig
+
 	// ExtraData 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.
@@ -55,9 +64,36 @@ var _ Message = (*ClosingSigned)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(
-		r, &c.ChannelID, &c.FeeSatoshis, &c.Signature, &c.ExtraData,
+	err := ReadElements(
+		r, &c.ChannelID, &c.FeeSatoshis, &c.Signature,
 	)
+	if err != nil {
+		return err
+	}
+
+	var tlvRecords ExtraOpaqueData
+	if err := ReadElements(r, &tlvRecords); err != nil {
+		return err
+	}
+
+	var (
+		partialSig PartialSig
+	)
+	typeMap, err := tlvRecords.ExtractRecords(&partialSig)
+	if err != nil {
+		return err
+	}
+
+	// Set the corresponding TLV types if they were included in the stream.
+	if val, ok := typeMap[PartialSigRecordType]; ok && val == nil {
+		c.PartialSig = &partialSig
+	}
+
+	if len(tlvRecords) != 0 {
+		c.ExtraData = tlvRecords
+	}
+
+	return nil
 }
 
 // Encode serializes the target ClosingSigned into the passed io.Writer
@@ -65,6 +101,15 @@ func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
 //
 // This is part of the lnwire.Message interface.
 func (c *ClosingSigned) Encode(w *bytes.Buffer, pver uint32) error {
+	recordProducers := make([]tlv.RecordProducer, 0, 1)
+	if c.PartialSig != nil {
+		recordProducers = append(recordProducers, c.PartialSig)
+	}
+	err := EncodeMessageExtraData(&c.ExtraData, recordProducers...)
+	if err != nil {
+		return err
+	}
+
 	if err := WriteChannelID(w, c.ChannelID); err != nil {
 		return err
 	}

lnwire/shutdown.go

@@ -3,8 +3,56 @@ package lnwire
 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
+)
+
+// 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{},
+	buf *[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{}, buf *[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,
+	)
+}
+
 // Shutdown is sent by either side in order to initiate the cooperative closure
 // of a channel. This message is sparse as both sides implicitly have the
 // information necessary to construct a transaction that will send the settled
@@ -17,6 +65,10 @@ type Shutdown struct {
 	// Address is the script to which the channel funds will be paid.
 	Address DeliveryAddress
 
+	// ShutdownNonce is the nonce the sender will use to sign the first
+	// co-op sign offer.
+	ShutdownNonce *ShutdownNonce
+
 	// ExtraData 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.
@@ -40,7 +92,32 @@ var _ Message = (*Shutdown)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (s *Shutdown) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r, &s.ChannelID, &s.Address, &s.ExtraData)
+	err := ReadElements(r, &s.ChannelID, &s.Address)
+	if err != nil {
+		return err
+	}
+
+	var tlvRecords ExtraOpaqueData
+	if err := ReadElements(r, &tlvRecords); err != nil {
+		return err
+	}
+
+	var musigNonce ShutdownNonce
+	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 len(tlvRecords) != 0 {
+		s.ExtraData = tlvRecords
+	}
+
+	return nil
 }
 
 // Encode serializes the target Shutdown into the passed io.Writer observing
@@ -48,6 +125,15 @@ 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)
+	}
+	err := EncodeMessageExtraData(&s.ExtraData, recordProducers...)
+	if err != nil {
+		return err
+	}
+
 	if err := WriteChannelID(w, s.ChannelID); err != nil {
 		return err
 	}