lnwire: add musig2 taproot execution messages for dynamic commitments

lnwire/dyn_ack.go

@@ -3,6 +3,17 @@ package lnwire
 import (
 	"bytes"
 	"io"
+
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
+	"github.com/lightningnetwork/lnd/fn"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+const (
+	// DALocalMusig2Pubnonce is the TLV type number that identifies the
+	// musig2 public nonce that we need to verify the commitment transaction
+	// signature.
+	DALocalMusig2Pubnonce tlv.Type = 0
 )
 
 // DynAck is the message used to accept the parameters of a dynamic commitment
@@ -13,6 +24,13 @@ type DynAck struct {
 	// a dynamic commitment negotiation
 	ChanID ChannelID
 
+	// LocalNonce is an optional field that is transmitted when accepting
+	// a dynamic commitment upgrade to Taproot Channels. This nonce will be
+	// used to verify the first commitment transaction signature. This will
+	// only be populated if the DynPropose we are responding to specifies
+	// taproot channels in the ChannelType field.
+	LocalNonce fn.Option[Musig2Nonce]
+
 	// 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.
@@ -32,6 +50,30 @@ func (da *DynAck) Encode(w *bytes.Buffer, _ uint32) error {
 		return err
 	}
 
+	var tlvRecords []tlv.Record
+	da.LocalNonce.WhenSome(func(nonce Musig2Nonce) {
+		tlvRecords = append(
+			tlvRecords, tlv.MakeStaticRecord(
+				DALocalMusig2Pubnonce, &nonce,
+				musig2.PubNonceSize, nonceTypeEncoder,
+				nonceTypeDecoder,
+			),
+		)
+	})
+	tlv.SortRecords(tlvRecords)
+
+	tlvStream, err := tlv.NewStream(tlvRecords...)
+	if err != nil {
+		return err
+	}
+
+	var extraBytesWriter bytes.Buffer
+	if err := tlvStream.Encode(&extraBytesWriter); err != nil {
+		return err
+	}
+
+	da.ExtraData = ExtraOpaqueData(extraBytesWriter.Bytes())
+
 	return WriteBytes(w, da.ExtraData)
 }
 
@@ -41,7 +83,50 @@ func (da *DynAck) Encode(w *bytes.Buffer, _ uint32) error {
 //
 // This is a part of the lnwire.Message interface.
 func (da *DynAck) Decode(r io.Reader, _ uint32) error {
-	return ReadElements(r, &da.ChanID, &da.ExtraData)
+	// Parse out main message.
+	if err := ReadElements(r, &da.ChanID); err != nil {
+		return err
+	}
+
+	// Parse out TLV records.
+	var tlvRecords ExtraOpaqueData
+	if err := ReadElement(r, &tlvRecords); err != nil {
+		return err
+	}
+
+	// Prepare receiving buffers to be filled by TLV extraction.
+	var localNonceScratch Musig2Nonce
+	localNonce := tlv.MakeStaticRecord(
+		DALocalMusig2Pubnonce, &localNonceScratch, musig2.PubNonceSize,
+		nonceTypeEncoder, nonceTypeDecoder,
+	)
+
+	// Create set of Records to read TLV bytestream into.
+	records := []tlv.Record{localNonce}
+	tlv.SortRecords(records)
+
+	// Read TLV stream into record set.
+	extraBytesReader := bytes.NewReader(tlvRecords)
+	tlvStream, err := tlv.NewStream(records...)
+	if err != nil {
+		return err
+	}
+	typeMap, err := tlvStream.DecodeWithParsedTypesP2P(extraBytesReader)
+	if err != nil {
+		return err
+	}
+
+	// Check the results of the TLV Stream decoding and appropriately set
+	// message fields.
+	if val, ok := typeMap[DALocalMusig2Pubnonce]; ok && val == nil {
+		da.LocalNonce = fn.Some(localNonceScratch)
+	}
+
+	if len(tlvRecords) != 0 {
+		da.ExtraData = tlvRecords
+	}
+
+	return nil
 }
 
 // MsgType returns the MessageType code which uniquely identifies this message