lnd/lnwire/closing_signed.go

package lnwire

import (
	"bytes"
	"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
// of HTLCs, and is primarily concerned with negotiating fees for the close
// transaction. Each party provides a signature for a transaction with a fee
// that they believe is fair. The process terminates when both sides agree on
// the same fee, or when one side force closes the channel.
//
// NOTE: The responder is able to send a signature without any additional
// messages as all transactions are assembled observing BIP 69 which defines a
// canonical ordering for input/outputs. Therefore, both sides are able to
// arrive at an identical closure transaction as they know the order of the
// inputs/outputs.
type ClosingSigned struct {
	// ChannelID serves to identify which channel is to be closed.
	ChannelID ChannelID

	// FeeSatoshis is the total fee in satoshis that the party to the
	// channel would like to propose for the close transaction.
	FeeSatoshis btcutil.Amount

	// 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 OptPartialSigTLV

	// 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.
	ExtraData ExtraOpaqueData
}

// NewClosingSigned creates a new empty ClosingSigned message.
func NewClosingSigned(cid ChannelID, fs btcutil.Amount,
	sig Sig) *ClosingSigned {

	return &ClosingSigned{
		ChannelID:   cid,
		FeeSatoshis: fs,
		Signature:   sig,
	}
}

// A compile time check to ensure ClosingSigned implements the lnwire.Message
// interface.
var _ Message = (*ClosingSigned)(nil)

// Decode deserializes a serialized ClosingSigned message stored in the passed
// io.Reader observing the specified protocol version.
//
// This is part of the lnwire.Message interface.
func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
	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
	}

	partialSig := c.PartialSig.Zero()
	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[c.PartialSig.TlvType()]; ok && val == nil {
		c.PartialSig = tlv.SomeRecordT(partialSig)
	}

	if len(tlvRecords) != 0 {
		c.ExtraData = tlvRecords
	}

	return nil
}

// Encode serializes the target ClosingSigned into the passed io.Writer
// observing the protocol version specified.
//
// This is part of the lnwire.Message interface.
func (c *ClosingSigned) Encode(w *bytes.Buffer, pver uint32) error {
	recordProducers := make([]tlv.RecordProducer, 0, 1)
	c.PartialSig.WhenSome(func(sig PartialSigTLV) {
		recordProducers = append(recordProducers, &sig)
	})
	err := EncodeMessageExtraData(&c.ExtraData, recordProducers...)
	if err != nil {
		return err
	}

	if err := WriteChannelID(w, c.ChannelID); err != nil {
		return err
	}

	if err := WriteSatoshi(w, c.FeeSatoshis); err != nil {
		return err
	}

	if err := WriteSig(w, c.Signature); err != nil {
		return err
	}

	return WriteBytes(w, c.ExtraData)
}

// MsgType returns the integer uniquely identifying this message type on the
// wire.
//
// This is part of the lnwire.Message interface.
func (c *ClosingSigned) MsgType() MessageType {
	return MsgClosingSigned
}