9915780197

Committed 13 Jul 2024 12:30AM UTC coverage: 49.268% (-9.1%) from 58.413%

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Merge pull request #8653 from ProofOfKeags/fn-prim

DynComms [0/n]: `fn` package additions

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/lnwallet/chancloser/chancloser.go

package chancloser

import (
        "bytes"
        "fmt"

        "github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
        "github.com/davecgh/go-spew/spew"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/fn"
        "github.com/lightningnetwork/lnd/htlcswitch"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/labels"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/lnwallet/chainfee"
        "github.com/lightningnetwork/lnd/lnwire"
)

var (
        // ErrChanAlreadyClosing is returned when a channel shutdown is
        // attempted more than once.
        ErrChanAlreadyClosing = fmt.Errorf("channel shutdown already initiated")

        // ErrChanCloseNotFinished is returned when a caller attempts to access
        // a field or function that is contingent on the channel closure
        // negotiation already being completed.
        ErrChanCloseNotFinished = fmt.Errorf("close negotiation not finished")

        // ErrInvalidState is returned when the closing state machine receives a
        // message while it is in an unknown state.
        ErrInvalidState = fmt.Errorf("invalid state")

        // ErrUpfrontShutdownScriptMismatch is returned when a peer or end user
        // provides a cooperative close script which does not match the upfront
        // shutdown script previously set for that party.
        ErrUpfrontShutdownScriptMismatch = fmt.Errorf("shutdown script does not " +
                "match upfront shutdown script")

        // ErrProposalExceedsMaxFee is returned when as the initiator, the
        // latest fee proposal sent by the responder exceed our max fee.
        // responder.
        ErrProposalExceedsMaxFee = fmt.Errorf("latest fee proposal exceeds " +
                "max fee")

        // ErrInvalidShutdownScript is returned when we receive an address from
        // a peer that isn't either a p2wsh or p2tr address.
        ErrInvalidShutdownScript = fmt.Errorf("invalid shutdown script")

        // errNoShutdownNonce is returned when a shutdown message is received
        // w/o a nonce for a taproot channel.
        errNoShutdownNonce = fmt.Errorf("shutdown nonce not populated")
)

// closeState represents all the possible states the channel closer state
// machine can be in. Each message will either advance to the next state, or
// remain at the current state. Once the state machine reaches a state of
// closeFinished, then negotiation is over.
type closeState uint8

const (
        // closeIdle is the initial starting state. In this state, the state
        // machine has been instantiated, but no state transitions have been
        // attempted. If a state machine receives a message while in this state,
        // then it is the responder to an initiated cooperative channel closure.
        closeIdle closeState = iota

        // closeShutdownInitiated is the state that's transitioned to once the
        // initiator of a closing workflow sends the shutdown message. At this
        // point, they're waiting for the remote party to respond with their own
        // shutdown message. After which, they'll both enter the fee negotiation
        // phase.
        closeShutdownInitiated

        // closeAwaitingFlush is the state that's transitioned to once both
        // Shutdown messages have been exchanged but we are waiting for the
        // HTLCs to clear out of the channel.
        closeAwaitingFlush

        // closeFeeNegotiation is the third, and most persistent state. Both
        // parties enter this state after they've sent and received a shutdown
        // message. During this phase, both sides will send monotonically
        // increasing fee requests until one side accepts the last fee rate
        // offered by the other party. In this case, the party will broadcast
        // the closing transaction, and send the accepted fee to the remote
        // party. This then causes a shift into the closeFinished state.
        closeFeeNegotiation

        // closeFinished is the final state of the state machine. In this state,
        // a side has accepted a fee offer and has broadcast the valid closing
        // transaction to the network. During this phase, the closing
        // transaction becomes available for examination.
        closeFinished
)

const (
        // defaultMaxFeeMultiplier is a multiplier we'll apply to the ideal fee
        // of the initiator, to decide when the negotiated fee is too high. By
        // default, we want to bail out if we attempt to negotiate a fee that's
        // 3x higher than our max fee.
        defaultMaxFeeMultiplier = 3
)

// ChanCloseCfg holds all the items that a ChanCloser requires to carry out its
// duties.
type ChanCloseCfg struct {
        // Channel is the channel that should be closed.
        Channel Channel

        // MusigSession is used to handle generating musig2 nonces, and also
        // creating the proper set of closing options for taproot channels.
        MusigSession MusigSession

        // BroadcastTx broadcasts the passed transaction to the network.
        BroadcastTx func(*wire.MsgTx, string) error

        // DisableChannel disables a channel, resulting in it not being able to
        // forward payments.
        DisableChannel func(wire.OutPoint) error

        // Disconnect will disconnect from the remote peer in this close.
        Disconnect func() error

        // MaxFee, is non-zero represents the highest fee that the initiator is
        // willing to pay to close the channel.
        MaxFee chainfee.SatPerKWeight

        // ChainParams holds the parameters of the chain that we're active on.
        ChainParams *chaincfg.Params

        // Quit is a channel that should be sent upon in the occasion the state
        // machine should cease all progress and shutdown.
        Quit chan struct{}

        // FeeEstimator is used to estimate the absolute starting co-op close
        // fee.
        FeeEstimator CoopFeeEstimator
}

// ChanCloser is a state machine that handles the cooperative channel closure
// procedure. This includes shutting down a channel, marking it ineligible for
// routing HTLC's, negotiating fees with the remote party, and finally
// broadcasting the fully signed closure transaction to the network.
type ChanCloser struct {
        // state is the current state of the state machine.
        state closeState

        // cfg holds the configuration for this ChanCloser instance.
        cfg ChanCloseCfg

        // chanPoint is the full channel point of the target channel.
        chanPoint wire.OutPoint

        // cid is the full channel ID of the target channel.
        cid lnwire.ChannelID

        // negotiationHeight is the height that the fee negotiation begun at.
        negotiationHeight uint32

        // closingTx is the final, fully signed closing transaction. This will
        // only be populated once the state machine shifts to the closeFinished
        // state.
        closingTx *wire.MsgTx

        // idealFeeSat is the ideal fee that the state machine should initially
        // offer when starting negotiation. This will be used as a baseline.
        idealFeeSat btcutil.Amount

        // maxFee is the highest fee the initiator is willing to pay to close
        // out the channel. This is either a use specified value, or a default
        // multiplier based of the initial starting ideal fee.
        maxFee btcutil.Amount

        // idealFeeRate is our ideal fee rate.
        idealFeeRate chainfee.SatPerKWeight

        // lastFeeProposal is the last fee that we proposed to the remote party.
        // We'll use this as a pivot point to ratchet our next offer up, down,
        // or simply accept the remote party's prior offer.
        lastFeeProposal btcutil.Amount

        // priorFeeOffers is a map that keeps track of all the proposed fees
        // that we've offered during the fee negotiation. We use this map to cut
        // the negotiation early if the remote party ever sends an offer that
        // we've sent in the past. Once negotiation terminates, we can extract
        // the prior signature of our accepted offer from this map.
        //
        // TODO(roasbeef): need to ensure if they broadcast w/ any of our prior
        // sigs, we are aware of
        priorFeeOffers map[btcutil.Amount]*lnwire.ClosingSigned

        // closeReq is the initial closing request. This will only be populated
        // if we're the initiator of this closing negotiation.
        //
        // TODO(roasbeef): abstract away
        closeReq *htlcswitch.ChanClose

        // localDeliveryScript is the script that we'll send our settled channel
        // funds to.
        localDeliveryScript []byte

        // remoteDeliveryScript is the script that we'll send the remote party's
        // settled channel funds to.
        remoteDeliveryScript []byte

        // locallyInitiated is true if we initiated the channel close.
        locallyInitiated bool

        // cachedClosingSigned is a cached copy of a received ClosingSigned that
        // we use to handle a specific race condition caused by the independent
        // message processing queues.
        cachedClosingSigned fn.Option[lnwire.ClosingSigned]
}

// calcCoopCloseFee computes an "ideal" absolute co-op close fee given the
// delivery scripts of both parties and our ideal fee rate.
func calcCoopCloseFee(chanType channeldb.ChannelType,
        localOutput, remoteOutput *wire.TxOut,
        idealFeeRate chainfee.SatPerKWeight) btcutil.Amount {

        var weightEstimator input.TxWeightEstimator

        if chanType.IsTaproot() {
                weightEstimator.AddWitnessInput(
                        input.TaprootSignatureWitnessSize,
                )
        } else {
                weightEstimator.AddWitnessInput(input.MultiSigWitnessSize)
        }

        // One of these outputs might be dust, so we'll skip adding it to our
        // mock transaction, so the fees are more accurate.
        if localOutput != nil {
                weightEstimator.AddTxOutput(localOutput)
        }
        if remoteOutput != nil {
                weightEstimator.AddTxOutput(remoteOutput)
        }

        totalWeight := weightEstimator.Weight()

        return idealFeeRate.FeeForWeight(totalWeight)
}

// SimpleCoopFeeEstimator is the default co-op close fee estimator. It assumes
// a normal segwit v0 channel, and that no outputs on the closing transaction
// are dust.
type SimpleCoopFeeEstimator struct {
}

// EstimateFee estimates an _absolute_ fee for a co-op close transaction given
// the local+remote tx outs (for the co-op close transaction), channel type,
// and ideal fee rate.
func (d *SimpleCoopFeeEstimator) EstimateFee(chanType channeldb.ChannelType,
        localTxOut, remoteTxOut *wire.TxOut,
        idealFeeRate chainfee.SatPerKWeight) btcutil.Amount {

        return calcCoopCloseFee(chanType, localTxOut, remoteTxOut, idealFeeRate)
}

// NewChanCloser creates a new instance of the channel closure given the passed
// configuration, and delivery+fee preference. The final argument should only
// be populated iff, we're the initiator of this closing request.
func NewChanCloser(cfg ChanCloseCfg, deliveryScript []byte,
        idealFeePerKw chainfee.SatPerKWeight, negotiationHeight uint32,
        closeReq *htlcswitch.ChanClose, locallyInitiated bool) *ChanCloser {

        chanPoint := cfg.Channel.ChannelPoint()
        cid := lnwire.NewChanIDFromOutPoint(chanPoint)
        return &ChanCloser{
                closeReq:            closeReq,
                state:               closeIdle,
                chanPoint:           chanPoint,
                cid:                 cid,
                cfg:                 cfg,
                negotiationHeight:   negotiationHeight,
                idealFeeRate:        idealFeePerKw,
                localDeliveryScript: deliveryScript,
                priorFeeOffers: make(
                        map[btcutil.Amount]*lnwire.ClosingSigned,
                ),
                locallyInitiated: locallyInitiated,
        }
}

// initFeeBaseline computes our ideal fee rate, and also the largest fee we'll
// accept given information about the delivery script of the remote party.
func (c *ChanCloser) initFeeBaseline() {
        // Depending on if a balance ends up being dust or not, we'll pass a
        // nil TxOut into the EstimateFee call which can handle it.
        var localTxOut, remoteTxOut *wire.TxOut
        if !c.cfg.Channel.LocalBalanceDust() {
                localTxOut = &wire.TxOut{
                        PkScript: c.localDeliveryScript,
                        Value:    0,
                }
        }
        if !c.cfg.Channel.RemoteBalanceDust() {
                remoteTxOut = &wire.TxOut{
                        PkScript: c.remoteDeliveryScript,
                        Value:    0,
                }
        }

        // Given the target fee-per-kw, we'll compute what our ideal _total_
        // fee will be starting at for this fee negotiation.
        c.idealFeeSat = c.cfg.FeeEstimator.EstimateFee(
                0, localTxOut, remoteTxOut, c.idealFeeRate,
        )

        // When we're the initiator, we'll want to also factor in the highest
        // fee we want to pay. This'll either be 3x the ideal fee, or the
        // specified explicit max fee.
        c.maxFee = c.idealFeeSat * defaultMaxFeeMultiplier
        if c.cfg.MaxFee > 0 {
                c.maxFee = c.cfg.FeeEstimator.EstimateFee(
                        0, localTxOut, remoteTxOut, c.cfg.MaxFee,
                )
        }

        chancloserLog.Infof("Ideal fee for closure of ChannelPoint(%v) "+
                "is: %v sat (max_fee=%v sat)", c.cfg.Channel.ChannelPoint(),
                int64(c.idealFeeSat), int64(c.maxFee))
}

// initChanShutdown begins the shutdown process by un-registering the channel,
// and creating a valid shutdown message to our target delivery address.
func (c *ChanCloser) initChanShutdown() (*lnwire.Shutdown, error) {
        // With both items constructed we'll now send the shutdown message for
        // this particular channel, advertising a shutdown request to our
        // desired closing script.
        shutdown := lnwire.NewShutdown(c.cid, c.localDeliveryScript)

        // If this is a taproot channel, then we'll need to also generate a
        // nonce that'll be used sign the co-op close transaction offer.
        if c.cfg.Channel.ChanType().IsTaproot() {
                firstClosingNonce, err := c.cfg.MusigSession.ClosingNonce()
                if err != nil {
                        return nil, err
                }

                shutdown.ShutdownNonce = lnwire.SomeShutdownNonce(
                        firstClosingNonce.PubNonce,
                )

                chancloserLog.Infof("Initiating shutdown w/ nonce: %v",
                        spew.Sdump(firstClosingNonce.PubNonce))
        }

        // Before closing, we'll attempt to send a disable update for the
        // channel.  We do so before closing the channel as otherwise the
        // current edge policy won't be retrievable from the graph.
        if err := c.cfg.DisableChannel(c.chanPoint); err != nil {
                chancloserLog.Warnf("Unable to disable channel %v on close: %v",
                        c.chanPoint, err)
        }

        chancloserLog.Infof("ChannelPoint(%v): sending shutdown message",
                c.chanPoint)

        // At this point, we persist any relevant info regarding the Shutdown
        // message we are about to send in order to ensure that if a
        // re-establish occurs then we will re-send the same Shutdown message.
        shutdownInfo := channeldb.NewShutdownInfo(
                c.localDeliveryScript, c.locallyInitiated,
        )
        err := c.cfg.Channel.MarkShutdownSent(shutdownInfo)
        if err != nil {
                return nil, err
        }

        return shutdown, nil
}

// ShutdownChan is the first method that's to be called by the initiator of the
// cooperative channel closure. This message returns the shutdown message to
// send to the remote party. Upon completion, we enter the
// closeShutdownInitiated phase as we await a response.
func (c *ChanCloser) ShutdownChan() (*lnwire.Shutdown, error) {
        // If we attempt to shutdown the channel for the first time, and we're not
        // in the closeIdle state, then the caller made an error.
        if c.state != closeIdle {
                return nil, ErrChanAlreadyClosing
        }

        chancloserLog.Infof("ChannelPoint(%v): initiating shutdown", c.chanPoint)

        shutdownMsg, err := c.initChanShutdown()
        if err != nil {
                return nil, err
        }

        // With the opening steps complete, we'll transition into the
        // closeShutdownInitiated state. In this state, we'll wait until the
        // other party sends their version of the shutdown message.
        c.state = closeShutdownInitiated

        // Finally, we'll return the shutdown message to the caller so it can
        // send it to the remote peer.
        return shutdownMsg, nil
}

// ClosingTx returns the fully signed, final closing transaction.
//
// NOTE: This transaction is only available if the state machine is in the
// closeFinished state.
func (c *ChanCloser) ClosingTx() (*wire.MsgTx, error) {
        // If the state machine hasn't finished closing the channel, then we'll
        // return an error as we haven't yet computed the closing tx.
        if c.state != closeFinished {
                return nil, ErrChanCloseNotFinished
        }

        return c.closingTx, nil
}

// CloseRequest returns the original close request that prompted the creation
// of the state machine.
//
// NOTE: This will only return a non-nil pointer if we were the initiator of
// the cooperative closure workflow.
func (c *ChanCloser) CloseRequest() *htlcswitch.ChanClose {
        return c.closeReq
}

// Channel returns the channel stored in the config as a
// *lnwallet.LightningChannel.
//
// NOTE: This method will PANIC if the underlying channel implementation isn't
// the desired type.
func (c *ChanCloser) Channel() *lnwallet.LightningChannel {
        // TODO(roasbeef): remove this
        return c.cfg.Channel.(*lnwallet.LightningChannel)
}

// NegotiationHeight returns the negotiation height.
func (c *ChanCloser) NegotiationHeight() uint32 {
        return c.negotiationHeight
}

// validateShutdownScript attempts to match and validate the script provided in
// our peer's shutdown message with the upfront shutdown script we have on
// record. For any script specified, we also make sure it matches our
// requirements. If no upfront shutdown script was set, we do not need to
// enforce option upfront shutdown, so the function returns early. If an
// upfront script is set, we check whether it matches the script provided by
// our peer. If they do not match, we use the disconnect function provided to
// disconnect from the peer.
func validateShutdownScript(disconnect func() error, upfrontScript,
        peerScript lnwire.DeliveryAddress, netParams *chaincfg.Params) error {

        // Either way, we'll make sure that the script passed meets our
        // standards. The upfrontScript should have already been checked at an
        // earlier stage, but we'll repeat the check here for defense in depth.
        if len(upfrontScript) != 0 {
                if !lnwallet.ValidateUpfrontShutdown(upfrontScript, netParams) {
                        return ErrInvalidShutdownScript
                }
        }
        if len(peerScript) != 0 {
                if !lnwallet.ValidateUpfrontShutdown(peerScript, netParams) {
                        return ErrInvalidShutdownScript
                }
        }

        // If no upfront shutdown script was set, return early because we do
        // not need to enforce closure to a specific script.
        if len(upfrontScript) == 0 {
                return nil
        }

        // If an upfront shutdown script was provided, disconnect from the peer, as
        // per BOLT 2, and return an error.
        if !bytes.Equal(upfrontScript, peerScript) {
                chancloserLog.Warnf("peer's script: %x does not match upfront "+
                        "shutdown script: %x", peerScript, upfrontScript)

                // Disconnect from the peer because they have violated option upfront
                // shutdown.
                if err := disconnect(); err != nil {
                        return err
                }

                return ErrUpfrontShutdownScriptMismatch
        }

        return nil
}

// ReceiveShutdown takes a raw Shutdown message and uses it to try and advance
// the ChanCloser state machine, failing if it is coming in at an invalid time.
// If appropriate, it will also generate a Shutdown message of its own to send
// out to the peer. It is possible for this method to return None when no error
// occurred.
func (c *ChanCloser) ReceiveShutdown(msg lnwire.Shutdown) (
        fn.Option[lnwire.Shutdown], error) {

        noShutdown := fn.None[lnwire.Shutdown]()

        switch c.state {
        // If we're in the close idle state, and we're receiving a channel
        // closure related message, then this indicates that we're on the
        // receiving side of an initiated channel closure.
        case closeIdle:
                // As we're the responder to this shutdown (the other party
                // wants to close), we'll check if this is a frozen channel or
                // not. If the channel is frozen and we were not also the
                // initiator of the channel opening, then we'll deny their close
                // attempt.
                chanInitiator := c.cfg.Channel.IsInitiator()
                if !chanInitiator {
                        absoluteThawHeight, err :=
                                c.cfg.Channel.AbsoluteThawHeight()
                        if err != nil {
                                return noShutdown, err
                        }
                        if c.negotiationHeight < absoluteThawHeight {
                                return noShutdown, fmt.Errorf("initiator "+
                                        "attempting to co-op close frozen "+
                                        "ChannelPoint(%v) (current_height=%v, "+
                                        "thaw_height=%v)", c.chanPoint,
                                        c.negotiationHeight, absoluteThawHeight)
                        }
                }

                // If the remote node opened the channel with option upfront
                // shutdown script, check that the script they provided matches.
                if err := validateShutdownScript(
                        c.cfg.Disconnect,
                        c.cfg.Channel.RemoteUpfrontShutdownScript(),
                        msg.Address, c.cfg.ChainParams,
                ); err != nil {
                        return noShutdown, err
                }

                // Once we have checked that the other party has not violated
                // option upfront shutdown we set their preference for delivery
                // address. We'll use this when we craft the closure
                // transaction.
                c.remoteDeliveryScript = msg.Address

                // We'll generate a shutdown message of our own to send across
                // the wire.
                localShutdown, err := c.initChanShutdown()
                if err != nil {
                        return noShutdown, err
                }

                // If this is a taproot channel, then we'll want to stash the
                // remote nonces so we can properly create a new musig
                // session for signing.
                if c.cfg.Channel.ChanType().IsTaproot() {
                        shutdownNonce, err := msg.ShutdownNonce.UnwrapOrErrV(
                                errNoShutdownNonce,
                        )
                        if err != nil {
                                return noShutdown, err
                        }

                        c.cfg.MusigSession.InitRemoteNonce(&musig2.Nonces{
                                PubNonce: shutdownNonce,
                        })
                }

                chancloserLog.Infof("ChannelPoint(%v): responding to shutdown",
                        c.chanPoint)

                // After the other party receives this message, we'll actually
                // start the final stage of the closure process: fee
                // negotiation. So we'll update our internal state to reflect
                // this, so we can handle the next message sent.
                c.state = closeAwaitingFlush

                return fn.Some(*localShutdown), err

        case closeShutdownInitiated:
                // If the remote node opened the channel with option upfront
                // shutdown script, check that the script they provided matches.
                if err := validateShutdownScript(
                        c.cfg.Disconnect,
                        c.cfg.Channel.RemoteUpfrontShutdownScript(),
                        msg.Address, c.cfg.ChainParams,
                ); err != nil {
                        return noShutdown, err
                }

                // Now that we know this is a valid shutdown message and
                // address, we'll record their preferred delivery closing
                // script.
                c.remoteDeliveryScript = msg.Address

                // At this point, we can now start the fee negotiation state, by
                // constructing and sending our initial signature for what we
                // think the closing transaction should look like.
                c.state = closeAwaitingFlush

                // If this is a taproot channel, then we'll want to stash the
                // local+remote nonces so we can properly create a new musig
                // session for signing.
                if c.cfg.Channel.ChanType().IsTaproot() {
                        shutdownNonce, err := msg.ShutdownNonce.UnwrapOrErrV(
                                errNoShutdownNonce,
                        )
                        if err != nil {
                                return noShutdown, err
                        }

                        c.cfg.MusigSession.InitRemoteNonce(&musig2.Nonces{
                                PubNonce: shutdownNonce,
                        })
                }

                chancloserLog.Infof("ChannelPoint(%v): shutdown response "+
                        "received, entering fee negotiation", c.chanPoint)

                return noShutdown, nil

        default:
                // Otherwise we are not in a state where we can accept this
                // message.
                return noShutdown, ErrInvalidState
        }
}

// BeginNegotiation should be called when we have definitively reached a clean
// channel state and are ready to cooperatively arrive at a closing transaction.
// If it is our responsibility to kick off the negotiation, this method will
// generate a ClosingSigned message. If it is the remote's responsibility, then
// it will not. In either case it will transition the ChanCloser state machine
// to the negotiation phase wherein ClosingSigned messages are exchanged until
// a mutually agreeable result is achieved.
func (c *ChanCloser) BeginNegotiation() (fn.Option[lnwire.ClosingSigned],
        error) {

        noClosingSigned := fn.None[lnwire.ClosingSigned]()

        switch c.state {
        case closeAwaitingFlush:
                // Now that we know their desired delivery script, we can
                // compute what our max/ideal fee will be.
                c.initFeeBaseline()

                // Before continuing, mark the channel as cooperatively closed
                // with a nil txn. Even though we haven't negotiated the final
                // txn, this guarantees that our listchannels rpc will be
                // externally consistent, and reflect that the channel is being
                // shutdown by the time the closing request returns.
                err := c.cfg.Channel.MarkCoopBroadcasted(
                        nil, c.locallyInitiated,
                )
                if err != nil {
                        return noClosingSigned, err
                }

                // At this point, we can now start the fee negotiation state, by
                // constructing and sending our initial signature for what we
                // think the closing transaction should look like.
                c.state = closeFeeNegotiation

                if !c.cfg.Channel.IsInitiator() {
                        // By default this means we do nothing, but we do want
                        // to check if we have a cached remote offer to process.
                        // If we do, we'll process it here.
                        res := noClosingSigned
                        err = nil
                        c.cachedClosingSigned.WhenSome(
                                func(cs lnwire.ClosingSigned) {
                                        res, err = c.ReceiveClosingSigned(cs)
                                },
                        )

                        return res, err
                }

                // We'll craft our initial close proposal in order to keep the
                // negotiation moving, but only if we're the initiator.
                closingSigned, err := c.proposeCloseSigned(c.idealFeeSat)
                if err != nil {
                        return noClosingSigned,
                                fmt.Errorf("unable to sign new co op "+
                                        "close offer: %w", err)
                }

                return fn.Some(*closingSigned), nil

        default:
                return noClosingSigned, ErrInvalidState
        }
}

// ReceiveClosingSigned is a method that should be called whenever we receive a
// ClosingSigned message from the wire. It may or may not return a
// ClosingSigned of our own to send back to the remote.
func (c *ChanCloser) ReceiveClosingSigned( //nolint:funlen
        msg lnwire.ClosingSigned) (fn.Option[lnwire.ClosingSigned], error) {

        noClosing := fn.None[lnwire.ClosingSigned]()

        switch c.state {
        case closeAwaitingFlush:
                // If we hit this case it either means there's a protocol
                // violation or that our chanCloser received the remote offer
                // before the link finished processing the channel flush.
                c.cachedClosingSigned = fn.Some(msg)
                return fn.None[lnwire.ClosingSigned](), nil

        case closeFeeNegotiation:
                // If this is a taproot channel, then it MUST have a partial
                // signature set at this point.
                isTaproot := c.cfg.Channel.ChanType().IsTaproot()
                if isTaproot && msg.PartialSig.IsNone() {
                        return noClosing,
                                fmt.Errorf("partial sig not set " +
                                        "for taproot chan")
                }

                isInitiator := c.cfg.Channel.IsInitiator()

                // We'll compare the proposed total fee, to what we've proposed
                // during the negotiations. If it doesn't match any of our
                // prior offers, then we'll attempt to ratchet the fee closer
                // to our ideal fee.
                remoteProposedFee := msg.FeeSatoshis

                _, feeMatchesOffer := c.priorFeeOffers[remoteProposedFee]
                switch {
                // For taproot channels, since nonces are involved, we can't do
                // the existing co-op close negotiation process without going
                // to a fully round based model. Rather than do this, we'll
                // just accept the very first offer by the initiator.
                case isTaproot && !isInitiator:
                        chancloserLog.Infof("ChannelPoint(%v) accepting "+
                                "initiator fee of %v", c.chanPoint,
                                remoteProposedFee)

                        // To auto-accept the initiators proposal, we'll just
                        // send back a signature w/ the same offer. We don't
                        // send the message here, as we can drop down and
                        // finalize the closure and broadcast, then echo back
                        // to Alice the final signature.
                        _, err := c.proposeCloseSigned(remoteProposedFee)
                        if err != nil {
                                return noClosing, fmt.Errorf("unable to sign "+
                                        "new co op close offer: %w", err)
                        }

                // Otherwise, if we are the initiator, and we just sent a
                // signature for a taproot channel, then we'll ensure that the
                // fee rate matches up exactly.
                case isTaproot && isInitiator && !feeMatchesOffer:
                        return noClosing,
                                fmt.Errorf("fee rate for "+
                                        "taproot channels was not accepted: "+
                                        "sent %v, got %v",
                                        c.idealFeeSat, remoteProposedFee)

                // If we're the initiator of the taproot channel, and we had
                // our fee echo'd back, then it's all good, and we can proceed
                // with final broadcast.
                case isTaproot && isInitiator && feeMatchesOffer:
                        break

                // Otherwise, if this is a normal segwit v0 channel, and the
                // fee doesn't match our offer, then we'll try to "negotiate" a
                // new fee.
                case !feeMatchesOffer:
                        // We'll now attempt to ratchet towards a fee deemed
                        // acceptable by both parties, factoring in our ideal
                        // fee rate, and the last proposed fee by both sides.
                        proposal := calcCompromiseFee(
                                c.chanPoint, c.idealFeeSat, c.lastFeeProposal,
                                remoteProposedFee,
                        )
                        if c.cfg.Channel.IsInitiator() && proposal > c.maxFee {
                                return noClosing, fmt.Errorf(
                                        "%w: %v > %v",
                                        ErrProposalExceedsMaxFee,
                                        proposal, c.maxFee)
                        }

                        // With our new fee proposal calculated, we'll craft a
                        // new close signed signature to send to the other
                        // party so we can continue the fee negotiation
                        // process.
                        closeSigned, err := c.proposeCloseSigned(proposal)
                        if err != nil {
                                return noClosing, fmt.Errorf("unable to sign "+
                                        "new co op close offer: %w", err)
                        }

                        // If the compromise fee doesn't match what the peer
                        // proposed, then we'll return this latest close signed
                        // message so we can continue negotiation.
                        if proposal != remoteProposedFee {
                                chancloserLog.Debugf("ChannelPoint(%v): close "+
                                        "tx fee disagreement, continuing "+
                                        "negotiation", c.chanPoint)

                                return fn.Some(*closeSigned), nil
                        }
                }

                chancloserLog.Infof("ChannelPoint(%v) fee of %v accepted, "+
                        "ending negotiation", c.chanPoint, remoteProposedFee)

                // Otherwise, we've agreed on a fee for the closing
                // transaction! We'll craft the final closing transaction so we
                // can broadcast it to the network.
                var (
                        localSig, remoteSig input.Signature
                        closeOpts           []lnwallet.ChanCloseOpt
                        err                 error
                )
                matchingSig := c.priorFeeOffers[remoteProposedFee]
                if c.cfg.Channel.ChanType().IsTaproot() {
                        localWireSig, err := matchingSig.PartialSig.UnwrapOrErrV( //nolint:lll
                                fmt.Errorf("none local sig"),
                        )
                        if err != nil {
                                return noClosing, err
                        }
                        remoteWireSig, err := msg.PartialSig.UnwrapOrErrV(
                                fmt.Errorf("none remote sig"),
                        )
                        if err != nil {
                                return noClosing, err
                        }

                        muSession := c.cfg.MusigSession
                        localSig, remoteSig, closeOpts, err = muSession.CombineClosingOpts( //nolint:lll
                                localWireSig, remoteWireSig,
                        )
                        if err != nil {
                                return noClosing, err
                        }
                } else {
                        localSig, err = matchingSig.Signature.ToSignature()
                        if err != nil {
                                return noClosing, err
                        }
                        remoteSig, err = msg.Signature.ToSignature()
                        if err != nil {
                                return noClosing, err
                        }
                }

                closeTx, _, err := c.cfg.Channel.CompleteCooperativeClose(
                        localSig, remoteSig, c.localDeliveryScript,
                        c.remoteDeliveryScript, remoteProposedFee, closeOpts...,
                )
                if err != nil {
                        return noClosing, err
                }
                c.closingTx = closeTx

                // Before publishing the closing tx, we persist it to the
                // database, such that it can be republished if something goes
                // wrong.
                err = c.cfg.Channel.MarkCoopBroadcasted(
                        closeTx, c.locallyInitiated,
                )
                if err != nil {
                        return noClosing, err
                }

                // With the closing transaction crafted, we'll now broadcast it
                // to the network.
                chancloserLog.Infof("Broadcasting cooperative close tx: %v",
                        newLogClosure(func() string {
                                return spew.Sdump(closeTx)
                        }),
                )

                // Create a close channel label.
                chanID := c.cfg.Channel.ShortChanID()
                closeLabel := labels.MakeLabel(
                        labels.LabelTypeChannelClose, &chanID,
                )

                if err := c.cfg.BroadcastTx(closeTx, closeLabel); err != nil {
                        return noClosing, err
                }

                // Finally, we'll transition to the closeFinished state, and
                // also return the final close signed message we sent.
                // Additionally, we return true for the second argument to
                // indicate we're finished with the channel closing
                // negotiation.
                c.state = closeFinished
                matchingOffer := c.priorFeeOffers[remoteProposedFee]

                return fn.Some(*matchingOffer), nil

        // If we received a message while in the closeFinished state, then this
        // should only be the remote party echoing the last ClosingSigned
        // message that we agreed on.
        case closeFinished:

                // There's no more to do as both sides should have already
                // broadcast the closing transaction at this state.
                return noClosing, nil

        default:
                return noClosing, ErrInvalidState
        }
}

// proposeCloseSigned attempts to propose a new signature for the closing
// transaction for a channel based on the prior fee negotiations and our current
// compromise fee.
func (c *ChanCloser) proposeCloseSigned(fee btcutil.Amount) (
        *lnwire.ClosingSigned, error) {

        var (
                closeOpts []lnwallet.ChanCloseOpt
                err       error
        )

        // If this is a taproot channel, then we'll include the musig session
        // generated for the next co-op close negotiation round.
        if c.cfg.Channel.ChanType().IsTaproot() {
                closeOpts, err = c.cfg.MusigSession.ProposalClosingOpts()
                if err != nil {
                        return nil, err
                }
        }

        rawSig, _, _, err := c.cfg.Channel.CreateCloseProposal(
                fee, c.localDeliveryScript, c.remoteDeliveryScript,
                closeOpts...,
        )
        if err != nil {
                return nil, err
        }

        // We'll note our last signature and proposed fee so when the remote
        // party responds we'll be able to decide if we've agreed on fees or
        // not.
        var (
                parsedSig  lnwire.Sig
                partialSig *lnwire.PartialSigWithNonce
        )
        if c.cfg.Channel.ChanType().IsTaproot() {
                musig, ok := rawSig.(*lnwallet.MusigPartialSig)
                if !ok {
                        return nil, fmt.Errorf("expected MusigPartialSig, "+
                                "got %T", rawSig)
                }

                partialSig = musig.ToWireSig()
        } else {
                parsedSig, err = lnwire.NewSigFromSignature(rawSig)
                if err != nil {
                        return nil, err
                }
        }

        c.lastFeeProposal = fee

        chancloserLog.Infof("ChannelPoint(%v): proposing fee of %v sat to "+
                "close chan", c.chanPoint, int64(fee))

        // We'll assemble a ClosingSigned message using this information and
        // return it to the caller so we can kick off the final stage of the
        // channel closure process.
        closeSignedMsg := lnwire.NewClosingSigned(c.cid, fee, parsedSig)

        // For musig2 channels, the main sig is blank, and instead we'll send
        // over a partial signature which'll be combined once our offer is
        // accepted.
        if partialSig != nil {
                closeSignedMsg.PartialSig = lnwire.SomePartialSig(
                        partialSig.PartialSig,
                )
        }

        // We'll also save this close signed, in the case that the remote party
        // accepts our offer. This way, we don't have to re-sign.
        c.priorFeeOffers[fee] = closeSignedMsg

        return closeSignedMsg, nil
}

// feeInAcceptableRange returns true if the passed remote fee is deemed to be
// in an "acceptable" range to our local fee. This is an attempt at a
// compromise and to ensure that the fee negotiation has a stopping point. We
// consider their fee acceptable if it's within 30% of our fee.
func feeInAcceptableRange(localFee, remoteFee btcutil.Amount) bool {
        // If our offer is lower than theirs, then we'll accept their offer if
        // it's no more than 30% *greater* than our current offer.
        if localFee < remoteFee {
                acceptableRange := localFee + ((localFee * 3) / 10)
                return remoteFee <= acceptableRange
        }

        // If our offer is greater than theirs, then we'll accept their offer if
        // it's no more than 30% *less* than our current offer.
        acceptableRange := localFee - ((localFee * 3) / 10)
        return remoteFee >= acceptableRange
}

// ratchetFee is our step function used to inch our fee closer to something
// that both sides can agree on. If up is true, then we'll attempt to increase
// our offered fee. Otherwise, if up is false, then we'll attempt to decrease
// our offered fee.
func ratchetFee(fee btcutil.Amount, up bool) btcutil.Amount {
        // If we need to ratchet up, then we'll increase our fee by 10%.
        if up {
                return fee + ((fee * 1) / 10)
        }

        // Otherwise, we'll *decrease* our fee by 10%.
        return fee - ((fee * 1) / 10)
}

// calcCompromiseFee performs the current fee negotiation algorithm, taking
// into consideration our ideal fee based on current fee environment, the fee
// we last proposed (if any), and the fee proposed by the peer.
func calcCompromiseFee(chanPoint wire.OutPoint, ourIdealFee, lastSentFee,
        remoteFee btcutil.Amount) btcutil.Amount {

        // TODO(roasbeef): take in number of rounds as well?

        chancloserLog.Infof("ChannelPoint(%v): computing fee compromise, "+
                "ideal=%v, last_sent=%v, remote_offer=%v", chanPoint,
                int64(ourIdealFee), int64(lastSentFee), int64(remoteFee))

        // Otherwise, we'll need to attempt to make a fee compromise if this is
        // the second round, and neither side has agreed on fees.
        switch {
        // If their proposed fee is identical to our ideal fee, then we'll go
        // with that as we can short circuit the fee negotiation. Similarly, if
        // we haven't sent an offer yet, we'll default to our ideal fee.
        case ourIdealFee == remoteFee || lastSentFee == 0:
                return ourIdealFee

        // If the last fee we sent, is equal to the fee the remote party is
        // offering, then we can simply return this fee as the negotiation is
        // over.
        case remoteFee == lastSentFee:
                return lastSentFee

        // If the fee the remote party is offering is less than the last one we
        // sent, then we'll need to ratchet down in order to move our offer
        // closer to theirs.
        case remoteFee < lastSentFee:
                // If the fee is lower, but still acceptable, then we'll just
                // return this fee and end the negotiation.
                if feeInAcceptableRange(lastSentFee, remoteFee) {
                        chancloserLog.Infof("ChannelPoint(%v): proposed "+
                                "remote fee is close enough, capitulating",
                                chanPoint)

                        return remoteFee
                }

                // Otherwise, we'll ratchet the fee *down* using our current
                // algorithm.
                return ratchetFee(lastSentFee, false)

        // If the fee the remote party is offering is greater than the last one
        // we sent, then we'll ratchet up in order to ensure we terminate
        // eventually.
        case remoteFee > lastSentFee:
                // If the fee is greater, but still acceptable, then we'll just
                // return this fee in order to put an end to the negotiation.
                if feeInAcceptableRange(lastSentFee, remoteFee) {
                        chancloserLog.Infof("ChannelPoint(%v): proposed "+
                                "remote fee is close enough, capitulating",
                                chanPoint)

                        return remoteFee
                }

                // Otherwise, we'll ratchet the fee up using our current
                // algorithm.
                return ratchetFee(lastSentFee, true)

        default:
                // TODO(roasbeef): fail if their fee isn't in expected range
                return remoteFee
        }
}

// ParseUpfrontShutdownAddress attempts to parse an upfront shutdown address.
// If the address is empty, it returns nil. If it successfully decoded the
// address, it returns a script that pays out to the address.
func ParseUpfrontShutdownAddress(address string,
        params *chaincfg.Params) (lnwire.DeliveryAddress, error) {

        if len(address) == 0 {
                return nil, nil
        }

        addr, err := btcutil.DecodeAddress(
                address, params,
        )
        if err != nil {
                return nil, fmt.Errorf("invalid address: %w", err)
        }

        if !addr.IsForNet(params) {
                return nil, fmt.Errorf("invalid address: %v is not a %s "+
                        "address", addr, params.Name)
        }

        return txscript.PayToAddrScript(addr)
}

lightningnetwork / lnd / 9915780197

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