13157844420

Committed 05 Feb 2025 12:55PM UTC coverage: 58.821% (+1.1%) from 57.712%

Build # 13157844420

Build Type

Pull #9448

github

Committed by

yyforyongyu

Commit Message

docs: add release notes

Pull Request Pull Request #9448: sweep: properly handle failed sweeping txns

Run Details

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35 existing lines in 7 files now uncovered.

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Source File
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91.04

/sweep/sweeper.go

package sweep

import (
        "errors"
        "fmt"
        "sync"
        "sync/atomic"

        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/wire"
        "github.com/davecgh/go-spew/spew"
        "github.com/lightningnetwork/lnd/chainio"
        "github.com/lightningnetwork/lnd/chainntnfs"
        "github.com/lightningnetwork/lnd/fn/v2"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/lnwallet/chainfee"
)

var (
        // ErrRemoteSpend is returned in case an output that we try to sweep is
        // confirmed in a tx of the remote party.
        ErrRemoteSpend = errors.New("remote party swept utxo")

        // ErrFeePreferenceTooLow is returned when the fee preference gives a
        // fee rate that's below the relay fee rate.
        ErrFeePreferenceTooLow = errors.New("fee preference too low")

        // ErrExclusiveGroupSpend is returned in case a different input of the
        // same exclusive group was spent.
        ErrExclusiveGroupSpend = errors.New("other member of exclusive group " +
                "was spent")

        // ErrSweeperShuttingDown is an error returned when a client attempts to
        // make a request to the UtxoSweeper, but it is unable to handle it as
        // it is/has already been stopped.
        ErrSweeperShuttingDown = errors.New("utxo sweeper shutting down")

        // DefaultDeadlineDelta defines a default deadline delta (1 week) to be
        // used when sweeping inputs with no deadline pressure.
        DefaultDeadlineDelta = int32(1008)
)

// Params contains the parameters that control the sweeping process.
type Params struct {
        // ExclusiveGroup is an identifier that, if set, prevents other inputs
        // with the same identifier from being batched together.
        ExclusiveGroup *uint64

        // DeadlineHeight specifies an absolute block height that this input
        // should be confirmed by. This value is used by the fee bumper to
        // decide its urgency and adjust its feerate used.
        DeadlineHeight fn.Option[int32]

        // Budget specifies the maximum amount of satoshis that can be spent on
        // fees for this sweep.
        Budget btcutil.Amount

        // Immediate indicates that the input should be swept immediately
        // without waiting for blocks to come to trigger the sweeping of
        // inputs.
        Immediate bool

        // StartingFeeRate is an optional parameter that can be used to specify
        // the initial fee rate to use for the fee function.
        StartingFeeRate fn.Option[chainfee.SatPerKWeight]
}

// String returns a human readable interpretation of the sweep parameters.
func (p Params) String() string {
        deadline := "none"
        p.DeadlineHeight.WhenSome(func(d int32) {
                deadline = fmt.Sprintf("%d", d)
        })

        exclusiveGroup := "none"
        if p.ExclusiveGroup != nil {
                exclusiveGroup = fmt.Sprintf("%d", *p.ExclusiveGroup)
        }

        return fmt.Sprintf("startingFeeRate=%v, immediate=%v, "+
                "exclusive_group=%v, budget=%v, deadline=%v", p.StartingFeeRate,
                p.Immediate, exclusiveGroup, p.Budget, deadline)
}

// SweepState represents the current state of a pending input.
//
//nolint:revive
type SweepState uint8

const (
        // Init is the initial state of a pending input. This is set when a new
        // sweeping request for a given input is made.
        Init SweepState = iota

        // PendingPublish specifies an input's state where it's already been
        // included in a sweeping tx but the tx is not published yet.  Inputs
        // in this state should not be used for grouping again.
        PendingPublish

        // Published is the state where the input's sweeping tx has
        // successfully been published. Inputs in this state can only be
        // updated via RBF.
        Published

        // PublishFailed is the state when an error is returned from publishing
        // the sweeping tx. Inputs in this state can be re-grouped in to a new
        // sweeping tx.
        PublishFailed

        // Swept is the final state of a pending input. This is set when the
        // input has been successfully swept.
        Swept

        // Excluded is the state of a pending input that has been excluded and
        // can no longer be swept. For instance, when one of the three anchor
        // sweeping transactions confirmed, the remaining two will be excluded.
        Excluded

        // Fatal is the final state of a pending input. Inputs ending in this
        // state won't be retried. This could happen,
        // - when a pending input has too many failed publish attempts;
        // - the input has been spent by another party;
        // - unknown broadcast error is returned.
        Fatal
)

// String gives a human readable text for the sweep states.
func (s SweepState) String() string {
        switch s {
        case Init:
                return "Init"

        case PendingPublish:
                return "PendingPublish"

        case Published:
                return "Published"

        case PublishFailed:
                return "PublishFailed"

        case Swept:
                return "Swept"

        case Excluded:
                return "Excluded"

        case Fatal:
                return "Fatal"

        default:
                return "Unknown"
        }
}

// RBFInfo stores the information required to perform a RBF bump on a pending
// sweeping tx.
type RBFInfo struct {
        // Txid is the txid of the sweeping tx.
        Txid chainhash.Hash

        // FeeRate is the fee rate of the sweeping tx.
        FeeRate chainfee.SatPerKWeight

        // Fee is the total fee of the sweeping tx.
        Fee btcutil.Amount
}

// SweeperInput is created when an input reaches the main loop for the first
// time. It wraps the input and tracks all relevant state that is needed for
// sweeping.
type SweeperInput struct {
        input.Input

        // state tracks the current state of the input.
        state SweepState

        // listeners is a list of channels over which the final outcome of the
        // sweep needs to be broadcasted.
        listeners []chan Result

        // publishAttempts records the number of attempts that have already been
        // made to sweep this tx.
        publishAttempts int

        // params contains the parameters that control the sweeping process.
        params Params

        // lastFeeRate is the most recent fee rate used for this input within a
        // transaction broadcast to the network.
        lastFeeRate chainfee.SatPerKWeight

        // rbf records the RBF constraints.
        rbf fn.Option[RBFInfo]

        // DeadlineHeight is the deadline height for this input. This is
        // different from the DeadlineHeight in its params as it's an actual
        // value than an option.
        DeadlineHeight int32
}

// String returns a human readable interpretation of the pending input.
func (p *SweeperInput) String() string {
        return fmt.Sprintf("%v (%v)", p.Input.OutPoint(), p.Input.WitnessType())
}

// terminated returns a boolean indicating whether the input has reached a
// final state.
func (p *SweeperInput) terminated() bool {
        switch p.state {
        // If the input has reached a final state, that it's either
        // been swept, or failed, or excluded, we will remove it from
        // our sweeper.
        case Fatal, Swept, Excluded:
                return true

        default:
                return false
        }
}

// isMature returns a boolean indicating whether the input has a timelock that
// has been reached or not. The locktime found is also returned.
func (p *SweeperInput) isMature(currentHeight uint32) (bool, uint32) {
        locktime, _ := p.RequiredLockTime()
        if currentHeight < locktime {
                log.Debugf("Input %v has locktime=%v, current height is %v",
                        p, locktime, currentHeight)

                return false, locktime
        }

        // If the input has a CSV that's not yet reached, we will skip
        // this input and wait for the expiry.
        //
        // NOTE: We need to consider whether this input can be included in the
        // next block or not, which means the CSV will be checked against the
        // currentHeight plus one.
        locktime = p.BlocksToMaturity() + p.HeightHint()
        if currentHeight+1 < locktime {
                log.Debugf("Input %v has CSV expiry=%v, current height is %v, "+
                        "skipped sweeping", p, locktime, currentHeight)

                return false, locktime
        }

        return true, locktime
}

// InputsMap is a type alias for a set of pending inputs.
type InputsMap = map[wire.OutPoint]*SweeperInput

// inputsMapToString returns a human readable interpretation of the pending
// inputs.
func inputsMapToString(inputs InputsMap) string {
        if len(inputs) == 0 {
                return ""
        }

        inps := make([]input.Input, 0, len(inputs))
        for _, in := range inputs {
                inps = append(inps, in)
        }

        return "\n" + inputTypeSummary(inps)
}

// pendingSweepsReq is an internal message we'll use to represent an external
// caller's intent to retrieve all of the pending inputs the UtxoSweeper is
// attempting to sweep.
type pendingSweepsReq struct {
        respChan chan map[wire.OutPoint]*PendingInputResponse
        errChan  chan error
}

// PendingInputResponse contains information about an input that is currently
// being swept by the UtxoSweeper.
type PendingInputResponse struct {
        // OutPoint is the identify outpoint of the input being swept.
        OutPoint wire.OutPoint

        // WitnessType is the witness type of the input being swept.
        WitnessType input.WitnessType

        // Amount is the amount of the input being swept.
        Amount btcutil.Amount

        // LastFeeRate is the most recent fee rate used for the input being
        // swept within a transaction broadcast to the network.
        LastFeeRate chainfee.SatPerKWeight

        // BroadcastAttempts is the number of attempts we've made to sweept the
        // input.
        BroadcastAttempts int

        // Params contains the sweep parameters for this pending request.
        Params Params

        // DeadlineHeight records the deadline height of this input.
        DeadlineHeight uint32
}

// updateReq is an internal message we'll use to represent an external caller's
// intent to update the sweep parameters of a given input.
type updateReq struct {
        input        wire.OutPoint
        params       Params
        responseChan chan *updateResp
}

// updateResp is an internal message we'll use to hand off the response of a
// updateReq from the UtxoSweeper's main event loop back to the caller.
type updateResp struct {
        resultChan chan Result
        err        error
}

// UtxoSweeper is responsible for sweeping outputs back into the wallet
type UtxoSweeper struct {
        started uint32 // To be used atomically.
        stopped uint32 // To be used atomically.

        // Embed the blockbeat consumer struct to get access to the method
        // `NotifyBlockProcessed` and the `BlockbeatChan`.
        chainio.BeatConsumer

        cfg *UtxoSweeperConfig

        newInputs chan *sweepInputMessage

        // pendingSweepsReq is a channel that will be sent requests by external
        // callers in order to retrieve the set of pending inputs the
        // UtxoSweeper is attempting to sweep.
        pendingSweepsReqs chan *pendingSweepsReq

        // updateReqs is a channel that will be sent requests by external
        // callers who wish to bump the fee rate of a given input.
        updateReqs chan *updateReq

        // inputs is the total set of inputs the UtxoSweeper has been requested
        // to sweep.
        inputs InputsMap

        currentOutputScript fn.Option[lnwallet.AddrWithKey]

        relayFeeRate chainfee.SatPerKWeight

        quit chan struct{}
        wg   sync.WaitGroup

        // currentHeight is the best known height of the main chain. This is
        // updated whenever a new block epoch is received.
        currentHeight int32

        // bumpRespChan is a channel that receives broadcast results from the
        // TxPublisher.
        bumpRespChan chan *bumpResp
}

// Compile-time check for the chainio.Consumer interface.
var _ chainio.Consumer = (*UtxoSweeper)(nil)

// UtxoSweeperConfig contains dependencies of UtxoSweeper.
type UtxoSweeperConfig struct {
        // GenSweepScript generates a P2WKH script belonging to the wallet where
        // funds can be swept.
        GenSweepScript func() fn.Result[lnwallet.AddrWithKey]

        // FeeEstimator is used when crafting sweep transactions to estimate
        // the necessary fee relative to the expected size of the sweep
        // transaction.
        FeeEstimator chainfee.Estimator

        // Wallet contains the wallet functions that sweeper requires.
        Wallet Wallet

        // Notifier is an instance of a chain notifier we'll use to watch for
        // certain on-chain events.
        Notifier chainntnfs.ChainNotifier

        // Mempool is the mempool watcher that will be used to query whether a
        // given input is already being spent by a transaction in the mempool.
        Mempool chainntnfs.MempoolWatcher

        // Store stores the published sweeper txes.
        //
        // TODO(yy): remove this store - we can use walletdb to do the job.
        Store SweeperStore

        // Signer is used by the sweeper to generate valid witnesses at the
        // time the incubated outputs need to be spent.
        Signer input.Signer

        // MaxInputsPerTx specifies the default maximum number of inputs allowed
        // in a single sweep tx. If more need to be swept, multiple txes are
        // created and published.
        MaxInputsPerTx uint32

        // MaxFeeRate is the maximum fee rate allowed within the UtxoSweeper.
        MaxFeeRate chainfee.SatPerVByte

        // Aggregator is used to group inputs into clusters based on its
        // implemention-specific strategy.
        Aggregator UtxoAggregator

        // Publisher is used to publish the sweep tx crafted here and monitors
        // it for potential fee bumps.
        Publisher Bumper

        // NoDeadlineConfTarget is the conf target to use when sweeping
        // non-time-sensitive outputs.
        NoDeadlineConfTarget uint32
}

// Result is the struct that is pushed through the result channel. Callers can
// use this to be informed of the final sweep result. In case of a remote
// spend, Err will be ErrRemoteSpend.
type Result struct {
        // Err is the final result of the sweep. It is nil when the input is
        // swept successfully by us. ErrRemoteSpend is returned when another
        // party took the input.
        Err error

        // Tx is the transaction that spent the input.
        Tx *wire.MsgTx
}

// sweepInputMessage structs are used in the internal channel between the
// SweepInput call and the sweeper main loop.
type sweepInputMessage struct {
        input      input.Input
        params     Params
        resultChan chan Result
}

// New returns a new Sweeper instance.
func New(cfg *UtxoSweeperConfig) *UtxoSweeper {
        s := &UtxoSweeper{
                cfg:               cfg,
                newInputs:         make(chan *sweepInputMessage),
                updateReqs:        make(chan *updateReq),
                pendingSweepsReqs: make(chan *pendingSweepsReq),
                quit:              make(chan struct{}),
                inputs:            make(InputsMap),
                bumpRespChan:      make(chan *bumpResp, 100),
        }

        // Mount the block consumer.
        s.BeatConsumer = chainio.NewBeatConsumer(s.quit, s.Name())

        return s
}

// Start starts the process of constructing and publish sweep txes.
func (s *UtxoSweeper) Start(beat chainio.Blockbeat) error {
        if !atomic.CompareAndSwapUint32(&s.started, 0, 1) {
                return nil
        }

        log.Info("Sweeper starting")

        // Retrieve relay fee for dust limit calculation. Assume that this will
        // not change from here on.
        s.relayFeeRate = s.cfg.FeeEstimator.RelayFeePerKW()

        // Set the current height.
        s.currentHeight = beat.Height()

        // Start sweeper main loop.
        s.wg.Add(1)
        go s.collector()

        return nil
}

// RelayFeePerKW returns the minimum fee rate required for transactions to be
// relayed.
func (s *UtxoSweeper) RelayFeePerKW() chainfee.SatPerKWeight {
        return s.relayFeeRate
}

// Stop stops sweeper from listening to block epochs and constructing sweep
// txes.
func (s *UtxoSweeper) Stop() error {
        if !atomic.CompareAndSwapUint32(&s.stopped, 0, 1) {
                return nil
        }

        log.Info("Sweeper shutting down...")
        defer log.Debug("Sweeper shutdown complete")

        close(s.quit)
        s.wg.Wait()

        return nil
}

// NOTE: part of the `chainio.Consumer` interface.
func (s *UtxoSweeper) Name() string {
        return "UtxoSweeper"
}

// SweepInput sweeps inputs back into the wallet. The inputs will be batched and
// swept after the batch time window ends. A custom fee preference can be
// provided to determine what fee rate should be used for the input. Note that
// the input may not always be swept with this exact value, as its possible for
// it to be batched under the same transaction with other similar fee rate
// inputs.
//
// NOTE: Extreme care needs to be taken that input isn't changed externally.
// Because it is an interface and we don't know what is exactly behind it, we
// cannot make a local copy in sweeper.
//
// TODO(yy): make sure the caller is using the Result chan.
func (s *UtxoSweeper) SweepInput(inp input.Input,
        params Params) (chan Result, error) {

        if inp == nil || inp.OutPoint() == input.EmptyOutPoint ||
                inp.SignDesc() == nil {

                return nil, errors.New("nil input received")
        }

        absoluteTimeLock, _ := inp.RequiredLockTime()
        log.Debugf("Sweep request received: out_point=%v, witness_type=%v, "+
                "relative_time_lock=%v, absolute_time_lock=%v, amount=%v, "+
                "parent=(%v), params=(%v)", inp.OutPoint(), inp.WitnessType(),
                inp.BlocksToMaturity(), absoluteTimeLock,
                btcutil.Amount(inp.SignDesc().Output.Value),
                inp.UnconfParent(), params)

        sweeperInput := &sweepInputMessage{
                input:      inp,
                params:     params,
                resultChan: make(chan Result, 1),
        }

        // Deliver input to the main event loop.
        select {
        case s.newInputs <- sweeperInput:
        case <-s.quit:
                return nil, ErrSweeperShuttingDown
        }

        return sweeperInput.resultChan, nil
}

// removeConflictSweepDescendants removes any transactions from the wallet that
// spend outputs included in the passed outpoint set. This needs to be done in
// cases where we're not the only ones that can sweep an output, but there may
// exist unconfirmed spends that spend outputs created by a sweep transaction.
// The most common case for this is when someone sweeps our anchor outputs
// after 16 blocks. Moreover this is also needed for wallets which use neutrino
// as a backend when a channel is force closed and anchor cpfp txns are
// created to bump the initial commitment transaction. In this case an anchor
// cpfp is broadcasted for up to 3 commitment transactions (local,
// remote-dangling, remote). Using neutrino all of those transactions will be
// accepted (the commitment tx will be different in all of those cases) and have
// to be removed as soon as one of them confirmes (they do have the same
// ExclusiveGroup). For neutrino backends the corresponding BIP 157 serving full
// nodes do not signal invalid transactions anymore.
func (s *UtxoSweeper) removeConflictSweepDescendants(
        outpoints map[wire.OutPoint]struct{}) error {

        // Obtain all the past sweeps that we've done so far. We'll need these
        // to ensure that if the spendingTx spends any of the same inputs, then
        // we remove any transaction that may be spending those inputs from the
        // wallet.
        //
        // TODO(roasbeef): can be last sweep here if we remove anything confirmed
        // from the store?
        pastSweepHashes, err := s.cfg.Store.ListSweeps()
        if err != nil {
                return err
        }

        // We'll now go through each past transaction we published during this
        // epoch and cross reference the spent inputs. If there're any inputs
        // in common with the inputs the spendingTx spent, then we'll remove
        // those.
        //
        // TODO(roasbeef): need to start to remove all transaction hashes after
        // every N blocks (assumed point of no return)
        for _, sweepHash := range pastSweepHashes {
                sweepTx, err := s.cfg.Wallet.FetchTx(sweepHash)
                if err != nil {
                        return err
                }

                // Transaction wasn't found in the wallet, may have already
                // been replaced/removed.
                if sweepTx == nil {
                        // If it was removed, then we'll play it safe and mark
                        // it as no longer need to be rebroadcasted.
                        s.cfg.Wallet.CancelRebroadcast(sweepHash)
                        continue
                }

                // Check to see if this past sweep transaction spent any of the
                // same inputs as spendingTx.
                var isConflicting bool
                for _, txIn := range sweepTx.TxIn {
                        if _, ok := outpoints[txIn.PreviousOutPoint]; ok {
                                isConflicting = true
                                break
                        }
                }

                if !isConflicting {
                        continue
                }

                // If it is conflicting, then we'll signal the wallet to remove
                // all the transactions that are descendants of outputs created
                // by the sweepTx and the sweepTx itself.
                log.Debugf("Removing sweep txid=%v from wallet: %v",
                        sweepTx.TxHash(), spew.Sdump(sweepTx))

                err = s.cfg.Wallet.RemoveDescendants(sweepTx)
                if err != nil {
                        log.Warnf("Unable to remove descendants: %v", err)
                }

                // If this transaction was conflicting, then we'll stop
                // rebroadcasting it in the background.
                s.cfg.Wallet.CancelRebroadcast(sweepHash)
        }

        return nil
}

// collector is the sweeper main loop. It processes new inputs, spend
// notifications and counts down to publication of the sweep tx.
func (s *UtxoSweeper) collector() {
        defer s.wg.Done()

        for {
                // Clean inputs, which will remove inputs that are swept,
                // failed, or excluded from the sweeper and return inputs that
                // are either new or has been published but failed back, which
                // will be retried again here.
                s.updateSweeperInputs()

                select {
                // A new inputs is offered to the sweeper. We check to see if
                // we are already trying to sweep this input and if not, set up
                // a listener to spend and schedule a sweep.
                case input := <-s.newInputs:
                        err := s.handleNewInput(input)
                        if err != nil {
                                log.Criticalf("Unable to handle new input: %v",
                                        err)

                                return
                        }

                        // If this input is forced, we perform an sweep
                        // immediately.
                        //
                        // TODO(ziggie): Make sure when `immediate` is selected
                        // as a parameter that we only trigger the sweeping of
                        // this specific input rather than triggering the sweeps
                        // of all current pending inputs registered with the
                        // sweeper.
                        if input.params.Immediate {
                                inputs := s.updateSweeperInputs()
                                s.sweepPendingInputs(inputs)
                        }

                // A new external request has been received to retrieve all of
                // the inputs we're currently attempting to sweep.
                case req := <-s.pendingSweepsReqs:
                        s.handlePendingSweepsReq(req)

                // A new external request has been received to bump the fee rate
                // of a given input.
                case req := <-s.updateReqs:
                        resultChan, err := s.handleUpdateReq(req)
                        req.responseChan <- &updateResp{
                                resultChan: resultChan,
                                err:        err,
                        }

                        // Perform an sweep immediately if asked.
                        if req.params.Immediate {
                                inputs := s.updateSweeperInputs()
                                s.sweepPendingInputs(inputs)
                        }

                case resp := <-s.bumpRespChan:
                        // Handle the bump event.
                        err := s.handleBumpEvent(resp)
                        if err != nil {
                                log.Errorf("Failed to handle bump event: %v",
                                        err)
                        }

                // A new block comes in, update the bestHeight, perform a check
                // over all pending inputs and publish sweeping txns if needed.
                case beat := <-s.BlockbeatChan:
                        // Update the sweeper to the best height.
                        s.currentHeight = beat.Height()

                        // Update the inputs with the latest height.
                        inputs := s.updateSweeperInputs()

                        log.Debugf("Received new block: height=%v, attempt "+
                                "sweeping %d inputs:%s", s.currentHeight,
                                len(inputs),
                                lnutils.NewLogClosure(func() string {
                                        return inputsMapToString(inputs)
                                }))

                        // Attempt to sweep any pending inputs.
                        s.sweepPendingInputs(inputs)

                        // Notify we've processed the block.
                        s.NotifyBlockProcessed(beat, nil)

                case <-s.quit:
                        return
                }
        }
}

// removeExclusiveGroup removes all inputs in the given exclusive group. This
// function is called when one of the exclusive group inputs has been spent. The
// other inputs won't ever be spendable and can be removed. This also prevents
// them from being part of future sweep transactions that would fail. In
// addition sweep transactions of those inputs will be removed from the wallet.
func (s *UtxoSweeper) removeExclusiveGroup(group uint64) {
        for outpoint, input := range s.inputs {
                outpoint := outpoint

                // Skip inputs that aren't exclusive.
                if input.params.ExclusiveGroup == nil {
                        continue
                }

                // Skip inputs from other exclusive groups.
                if *input.params.ExclusiveGroup != group {
                        continue
                }

                // Skip inputs that are already terminated.
                if input.terminated() {
                        log.Tracef("Skipped sending error result for "+
                                "input %v, state=%v", outpoint, input.state)

                        continue
                }

                // Signal result channels.
                s.signalResult(input, Result{
                        Err: ErrExclusiveGroupSpend,
                })

                // Update the input's state as it can no longer be swept.
                input.state = Excluded

                // Remove all unconfirmed transactions from the wallet which
                // spend the passed outpoint of the same exclusive group.
                outpoints := map[wire.OutPoint]struct{}{
                        outpoint: {},
                }
                err := s.removeConflictSweepDescendants(outpoints)
                if err != nil {
                        log.Warnf("Unable to remove conflicting sweep tx from "+
                                "wallet for outpoint %v : %v", outpoint, err)
                }
        }
}

// signalResult notifies the listeners of the final result of the input sweep.
// It also cancels any pending spend notification.
func (s *UtxoSweeper) signalResult(pi *SweeperInput, result Result) {
        op := pi.OutPoint()
        listeners := pi.listeners

        if result.Err == nil {
                log.Tracef("Dispatching sweep success for %v to %v listeners",
                        op, len(listeners),
                )
        } else {
                log.Tracef("Dispatching sweep error for %v to %v listeners: %v",
                        op, len(listeners), result.Err,
                )
        }

        // Signal all listeners. Channel is buffered. Because we only send once
        // on every channel, it should never block.
        for _, resultChan := range listeners {
                resultChan <- result
        }
}

// sweep takes a set of preselected inputs, creates a sweep tx and publishes
// the tx. The output address is only marked as used if the publish succeeds.
func (s *UtxoSweeper) sweep(set InputSet) error {
        // Generate an output script if there isn't an unused script available.
        if s.currentOutputScript.IsNone() {
                addr, err := s.cfg.GenSweepScript().Unpack()
                if err != nil {
                        return fmt.Errorf("gen sweep script: %w", err)
                }
                s.currentOutputScript = fn.Some(addr)
        }

        sweepAddr, err := s.currentOutputScript.UnwrapOrErr(
                fmt.Errorf("none sweep script"),
        )
        if err != nil {
                return err
        }

        // Create a fee bump request and ask the publisher to broadcast it. The
        // publisher will then take over and start monitoring the tx for
        // potential fee bump.
        req := &BumpRequest{
                Inputs:          set.Inputs(),
                Budget:          set.Budget(),
                DeadlineHeight:  set.DeadlineHeight(),
                DeliveryAddress: sweepAddr,
                MaxFeeRate:      s.cfg.MaxFeeRate.FeePerKWeight(),
                StartingFeeRate: set.StartingFeeRate(),
                Immediate:       set.Immediate(),
                // TODO(yy): pass the strategy here.
        }

        // Reschedule the inputs that we just tried to sweep. This is done in
        // case the following publish fails, we'd like to update the inputs'
        // publish attempts and rescue them in the next sweep.
        s.markInputsPendingPublish(set)

        // Broadcast will return a read-only chan that we will listen to for
        // this publish result and future RBF attempt.
        resp := s.cfg.Publisher.Broadcast(req)

        // Successfully sent the broadcast attempt, we now handle the result by
        // subscribing to the result chan and listen for future updates about
        // this tx.
        s.wg.Add(1)
        go s.monitorFeeBumpResult(set, resp)

        return nil
}

// markInputsPendingPublish updates the pending inputs with the given tx
// inputs. It also increments the `publishAttempts`.
func (s *UtxoSweeper) markInputsPendingPublish(set InputSet) {
        // Reschedule sweep.
        for _, input := range set.Inputs() {
                op := input.OutPoint()
                pi, ok := s.inputs[op]
                if !ok {
                        // It could be that this input is an additional wallet
                        // input that was attached. In that case there also
                        // isn't a pending input to update.
                        log.Tracef("Skipped marking input as pending "+
                                "published: %v not found in pending inputs", op)

                        continue
                }

                // If this input has already terminated, there's clearly
                // something wrong as it would have been removed. In this case
                // we log an error and skip marking this input as pending
                // publish.
                if pi.terminated() {
                        log.Errorf("Expect input %v to not have terminated "+
                                "state, instead it has %v", op, pi.state)

                        continue
                }

                // Update the input's state.
                pi.state = PendingPublish

                // Record another publish attempt.
                pi.publishAttempts++
        }
}

// markInputsPublished updates the sweeping tx in db and marks the list of
// inputs as published.
func (s *UtxoSweeper) markInputsPublished(tr *TxRecord, set InputSet) error {
        // Mark this tx in db once successfully published.
        //
        // NOTE: this will behave as an overwrite, which is fine as the record
        // is small.
        tr.Published = true
        err := s.cfg.Store.StoreTx(tr)
        if err != nil {
                return fmt.Errorf("store tx: %w", err)
        }

        // Reschedule sweep.
        for _, input := range set.Inputs() {
                op := input.OutPoint()
                pi, ok := s.inputs[op]
                if !ok {
                        // It could be that this input is an additional wallet
                        // input that was attached. In that case there also
                        // isn't a pending input to update.
                        log.Tracef("Skipped marking input as published: %v "+
                                "not found in pending inputs", op)

                        continue
                }

                // Valdiate that the input is in an expected state.
                if pi.state != PendingPublish {
                        // We may get a Published if this is a replacement tx.
                        log.Debugf("Expect input %v to have %v, instead it "+
                                "has %v", op, PendingPublish, pi.state)

                        continue
                }

                // Update the input's state.
                pi.state = Published

                // Update the input's latest fee rate.
                pi.lastFeeRate = chainfee.SatPerKWeight(tr.FeeRate)
        }

        return nil
}

// markInputsPublishFailed marks the list of inputs as failed to be published.
func (s *UtxoSweeper) markInputsPublishFailed(set InputSet) {
        // Reschedule sweep.
        for _, inp := range set.Inputs() {
                op := inp.OutPoint()
                pi, ok := s.inputs[op]
                if !ok {
                        // It could be that this input is an additional wallet
                        // input that was attached. In that case there also
                        // isn't a pending input to update.
                        log.Tracef("Skipped marking input as publish failed: "+
                                "%v not found in pending inputs", op)

                        continue
                }

                // Valdiate that the input is in an expected state.
                if pi.state != PendingPublish && pi.state != Published {
                        log.Debugf("Expect input %v to have %v, instead it "+
                                "has %v", op, PendingPublish, pi.state)

                        continue
                }

                log.Warnf("Failed to publish input %v", op)

                // Update the input's state.
                pi.state = PublishFailed
        }
}

// PendingInputs returns the set of inputs that the UtxoSweeper is currently
// attempting to sweep.
func (s *UtxoSweeper) PendingInputs() (
        map[wire.OutPoint]*PendingInputResponse, error) {

        respChan := make(chan map[wire.OutPoint]*PendingInputResponse, 1)
        errChan := make(chan error, 1)
        select {
        case s.pendingSweepsReqs <- &pendingSweepsReq{
                respChan: respChan,
                errChan:  errChan,
        }:
        case <-s.quit:
                return nil, ErrSweeperShuttingDown
        }

        select {
        case pendingSweeps := <-respChan:
                return pendingSweeps, nil
        case err := <-errChan:
                return nil, err
        case <-s.quit:
                return nil, ErrSweeperShuttingDown
        }
}

// handlePendingSweepsReq handles a request to retrieve all pending inputs the
// UtxoSweeper is attempting to sweep.
func (s *UtxoSweeper) handlePendingSweepsReq(
        req *pendingSweepsReq) map[wire.OutPoint]*PendingInputResponse {

        resps := make(map[wire.OutPoint]*PendingInputResponse, len(s.inputs))
        for _, inp := range s.inputs {
                // Skip immature inputs for compatibility.
                mature, _ := inp.isMature(uint32(s.currentHeight))
                if !mature {
                        continue
                }

                // Only the exported fields are set, as we expect the response
                // to only be consumed externally.
                op := inp.OutPoint()
                resps[op] = &PendingInputResponse{
                        OutPoint:    op,
                        WitnessType: inp.WitnessType(),
                        Amount: btcutil.Amount(
                                inp.SignDesc().Output.Value,
                        ),
                        LastFeeRate:       inp.lastFeeRate,
                        BroadcastAttempts: inp.publishAttempts,
                        Params:            inp.params,
                        DeadlineHeight:    uint32(inp.DeadlineHeight),
                }
        }

        select {
        case req.respChan <- resps:
        case <-s.quit:
                log.Debug("Skipped sending pending sweep response due to " +
                        "UtxoSweeper shutting down")
        }

        return resps
}

// UpdateParams allows updating the sweep parameters of a pending input in the
// UtxoSweeper. This function can be used to provide an updated fee preference
// and force flag that will be used for a new sweep transaction of the input
// that will act as a replacement transaction (RBF) of the original sweeping
// transaction, if any. The exclusive group is left unchanged.
//
// NOTE: This currently doesn't do any fee rate validation to ensure that a bump
// is actually successful. The responsibility of doing so should be handled by
// the caller.
func (s *UtxoSweeper) UpdateParams(input wire.OutPoint,
        params Params) (chan Result, error) {

        responseChan := make(chan *updateResp, 1)
        select {
        case s.updateReqs <- &updateReq{
                input:        input,
                params:       params,
                responseChan: responseChan,
        }:
        case <-s.quit:
                return nil, ErrSweeperShuttingDown
        }

        select {
        case response := <-responseChan:
                return response.resultChan, response.err
        case <-s.quit:
                return nil, ErrSweeperShuttingDown
        }
}

// handleUpdateReq handles an update request by simply updating the sweep
// parameters of the pending input. Currently, no validation is done on the new
// fee preference to ensure it will properly create a replacement transaction.
//
// TODO(wilmer):
//   - Validate fee preference to ensure we'll create a valid replacement
//     transaction to allow the new fee rate to propagate throughout the
//     network.
//   - Ensure we don't combine this input with any other unconfirmed inputs that
//     did not exist in the original sweep transaction, resulting in an invalid
//     replacement transaction.
func (s *UtxoSweeper) handleUpdateReq(req *updateReq) (
        chan Result, error) {

        // If the UtxoSweeper is already trying to sweep this input, then we can
        // simply just increase its fee rate. This will allow the input to be
        // batched with others which also have a similar fee rate, creating a
        // higher fee rate transaction that replaces the original input's
        // sweeping transaction.
        sweeperInput, ok := s.inputs[req.input]
        if !ok {
                return nil, lnwallet.ErrNotMine
        }

        // Create the updated parameters struct. Leave the exclusive group
        // unchanged.
        newParams := Params{
                StartingFeeRate: req.params.StartingFeeRate,
                Immediate:       req.params.Immediate,
                Budget:          req.params.Budget,
                DeadlineHeight:  req.params.DeadlineHeight,
                ExclusiveGroup:  sweeperInput.params.ExclusiveGroup,
        }

        log.Debugf("Updating parameters for %v(state=%v) from (%v) to (%v)",
                req.input, sweeperInput.state, sweeperInput.params, newParams)

        sweeperInput.params = newParams

        // We need to reset the state so this input will be attempted again by
        // our sweeper.
        //
        // TODO(yy): a dedicated state?
        sweeperInput.state = Init

        // If the new input specifies a deadline, update the deadline height.
        sweeperInput.DeadlineHeight = req.params.DeadlineHeight.UnwrapOr(
                sweeperInput.DeadlineHeight,
        )

        resultChan := make(chan Result, 1)
        sweeperInput.listeners = append(sweeperInput.listeners, resultChan)

        return resultChan, nil
}

// ListSweeps returns a list of the sweeps recorded by the sweep store.
func (s *UtxoSweeper) ListSweeps() ([]chainhash.Hash, error) {
        return s.cfg.Store.ListSweeps()
}

// mempoolLookup takes an input's outpoint and queries the mempool to see
// whether it's already been spent in a transaction found in the mempool.
// Returns the transaction if found.
func (s *UtxoSweeper) mempoolLookup(op wire.OutPoint) fn.Option[wire.MsgTx] {
        // For neutrino backend, there's no mempool available, so we exit
        // early.
        if s.cfg.Mempool == nil {
                log.Debugf("Skipping mempool lookup for %v, no mempool ", op)

                return fn.None[wire.MsgTx]()
        }

        // Query this input in the mempool. If this outpoint is already spent
        // in mempool, we should get a spending event back immediately.
        return s.cfg.Mempool.LookupInputMempoolSpend(op)
}

// calculateDefaultDeadline calculates the default deadline height for a sweep
// request that has no deadline height specified.
func (s *UtxoSweeper) calculateDefaultDeadline(pi *SweeperInput) int32 {
        // Create a default deadline height, which will be used when there's no
        // DeadlineHeight specified for a given input.
        defaultDeadline := s.currentHeight + int32(s.cfg.NoDeadlineConfTarget)

        // If the input is immature and has a locktime, we'll use the locktime
        // height as the starting height.
        matured, locktime := pi.isMature(uint32(s.currentHeight))
        if !matured {
                defaultDeadline = int32(locktime + s.cfg.NoDeadlineConfTarget)
                log.Debugf("Input %v is immature, using locktime=%v instead "+
                        "of current height=%d as starting height",
                        pi.OutPoint(), locktime, s.currentHeight)
        }

        return defaultDeadline
}

// handleNewInput processes a new input by registering spend notification and
// scheduling sweeping for it.
func (s *UtxoSweeper) handleNewInput(input *sweepInputMessage) error {
        outpoint := input.input.OutPoint()
        pi, pending := s.inputs[outpoint]
        if pending {
                log.Infof("Already has pending input %v received, old params: "+
                        "%v, new params %v", outpoint, pi.params, input.params)

                s.handleExistingInput(input, pi)

                return nil
        }

        // This is a new input, and we want to query the mempool to see if this
        // input has already been spent. If so, we'll start the input with the
        // RBFInfo.
        rbfInfo := s.decideRBFInfo(input.input.OutPoint())

        // Create a new pendingInput and initialize the listeners slice with
        // the passed in result channel. If this input is offered for sweep
        // again, the result channel will be appended to this slice.
        pi = &SweeperInput{
                state:     Init,
                listeners: []chan Result{input.resultChan},
                Input:     input.input,
                params:    input.params,
                rbf:       rbfInfo,
        }

        // Set the starting fee rate if a previous sweeping tx is found.
        rbfInfo.WhenSome(func(info RBFInfo) {
                pi.params.StartingFeeRate = fn.Some(info.FeeRate)
        })

        // Set the acutal deadline height.
        pi.DeadlineHeight = input.params.DeadlineHeight.UnwrapOr(
                s.calculateDefaultDeadline(pi),
        )

        s.inputs[outpoint] = pi
        log.Tracef("input %v, state=%v, added to inputs", outpoint, pi.state)

        log.Infof("Registered sweep request at block %d: out_point=%v, "+
                "witness_type=%v, amount=%v, deadline=%d, state=%v, "+
                "params=(%v)", s.currentHeight, pi.OutPoint(), pi.WitnessType(),
                btcutil.Amount(pi.SignDesc().Output.Value), pi.DeadlineHeight,
                pi.state, pi.params)

        // Once the input is registered, quickly check whether it has already
        // been spent.
        err := s.checkInputSpent(pi)
        if err != nil {
                log.Errorf("Failed to check input spend: %v", err)
                return err
        }

        return nil
}

// checkInputSpent checks whether the registered input has already been spent.
// If so, we will hanlde it immediately via handleThirdPartySpent.
func (s *UtxoSweeper) checkInputSpent(inp *SweeperInput) error {
        op := inp.OutPoint()

        // If the input has already been spent after the height hint, a spend
        // event is sent back immediately.
        spendEvent, err := s.cfg.Notifier.RegisterSpendNtfn(
                &op, inp.SignDesc().Output.PkScript, inp.HeightHint(),
        )
        if err != nil {
                return err
        }

        // Remove the subscription when exit.
        defer spendEvent.Cancel()

        // Do a non-blocking read to see if the output has been spent.
        select {
        case spend, ok := <-spendEvent.Spend:
                if !ok {
                        log.Debugf("Spend ntfn for %v canceled", op)
                        return nil
                }

                spendingTx := spend.SpendingTx

                log.Debugf("Detected spent of input=%v in tx=%v", op,
                        spendingTx.TxHash())

                s.handleThirdPartySpent(inp, spendingTx)

                return nil

        default:
                log.Tracef("Input %v not spent yet", op)
        }

        return nil
}

// decideRBFInfo queries the mempool to see whether the given input has already
// been spent. When spent, it will query the sweeper store to fetch the fee info
// of the spending transction, and construct an RBFInfo based on it. Suppose an
// error occurs, fn.None is returned.
func (s *UtxoSweeper) decideRBFInfo(
        op wire.OutPoint) fn.Option[RBFInfo] {

        // Check if we can find the spending tx of this input in mempool.
        txOption := s.mempoolLookup(op)

        // Extract the spending tx from the option.
        var tx *wire.MsgTx
        txOption.WhenSome(func(t wire.MsgTx) {
                tx = &t
        })

        // Exit early if it's not found.
        //
        // NOTE: this is not accurate for backends that don't support mempool
        // lookup:
        // - for neutrino we don't have a mempool.
        // - for btcd below v0.24.1 we don't have `gettxspendingprevout`.
        if tx == nil {
                return fn.None[RBFInfo]()
        }

        // Otherwise the input is already spent in the mempool, so eventually
        // we will return Published.
        //
        // We also need to update the RBF info for this input. If the sweeping
        // transaction is broadcast by us, we can find the fee info in the
        // sweeper store.
        txid := tx.TxHash()
        tr, err := s.cfg.Store.GetTx(txid)

        log.Debugf("Found spending tx %v in mempool for input %v", tx.TxHash(),
                op)

        // If the tx is not found in the store, it means it's not broadcast by
        // us, hence we can't find the fee info. This is fine as, later on when
        // this tx is confirmed, we will remove the input from our inputs.
        if errors.Is(err, ErrTxNotFound) {
                log.Warnf("Spending tx %v not found in sweeper store", txid)
                return fn.None[RBFInfo]()
        }

        // Exit if we get an db error.
        if err != nil {
                log.Errorf("Unable to get tx %v from sweeper store: %v",
                        txid, err)

                return fn.None[RBFInfo]()
        }

        // Prepare the fee info and return it.
        rbf := fn.Some(RBFInfo{
                Txid:    txid,
                Fee:     btcutil.Amount(tr.Fee),
                FeeRate: chainfee.SatPerKWeight(tr.FeeRate),
        })

        return rbf
}

// handleExistingInput processes an input that is already known to the sweeper.
// It will overwrite the params of the old input with the new ones.
func (s *UtxoSweeper) handleExistingInput(input *sweepInputMessage,
        oldInput *SweeperInput) {

        // Before updating the input details, check if an exclusive group was
        // set. In case the same input is registered again without an exclusive
        // group set, the previous input and its sweep parameters are outdated
        // hence need to be replaced. This scenario currently only happens for
        // anchor outputs. When a channel is force closed, in the worst case 3
        // different sweeps with the same exclusive group are registered with
        // the sweeper to bump the closing transaction (cpfp) when its time
        // critical. Receiving an input which was already registered with the
        // sweeper but now without an exclusive group means non of the previous
        // inputs were used as CPFP, so we need to make sure we update the
        // sweep parameters but also remove all inputs with the same exclusive
        // group because the are outdated too.
        var prevExclGroup *uint64
        if oldInput.params.ExclusiveGroup != nil &&
                input.params.ExclusiveGroup == nil {

                prevExclGroup = new(uint64)
                *prevExclGroup = *oldInput.params.ExclusiveGroup
        }

        // Update input details and sweep parameters. The re-offered input
        // details may contain a change to the unconfirmed parent tx info.
        oldInput.params = input.params
        oldInput.Input = input.input

        // If the new input specifies a deadline, update the deadline height.
        oldInput.DeadlineHeight = input.params.DeadlineHeight.UnwrapOr(
                oldInput.DeadlineHeight,
        )

        // Add additional result channel to signal spend of this input.
        oldInput.listeners = append(oldInput.listeners, input.resultChan)

        if prevExclGroup != nil {
                s.removeExclusiveGroup(*prevExclGroup)
        }
}

// handleBumpEventTxConfirmed marks all inputs swept by the spending transaction
// as swept. It will also notify all the subscribers of this input.
func (s *UtxoSweeper) handleBumpEventTxConfirmed(r *bumpResp) {
        tx := r.result.Tx

        for _, txIn := range tx.TxIn {
                outpoint := txIn.PreviousOutPoint

                // Check if this input is known to us. It could probably be
                // unknown if we canceled the registration, deleted from inputs
                // map but the ntfn was in-flight already. Or this could be not
                // one of our inputs.
                input, ok := s.inputs[outpoint]
                if !ok {
                        // It's very likely that a spending tx contains inputs
                        // that we don't know.
                        log.Tracef("Skipped marking input as swept: %v not "+
                                "found in pending inputs", outpoint)

                        continue
                }

                // This input may already been marked as swept by a previous
                // spend notification, which is likely to happen as one sweep
                // transaction usually sweeps multiple inputs.
                if input.terminated() {
                        log.Debugf("Skipped marking input as swept: %v "+
                                "state=%v", outpoint, input.state)

                        continue
                }

                input.state = Swept

                // Signal result channels.
                s.signalResult(input, Result{
                        Tx: tx,
                })

                // Remove all other inputs in this exclusive group.
                if input.params.ExclusiveGroup != nil {
                        s.removeExclusiveGroup(*input.params.ExclusiveGroup)
                }
        }
}

// markInputFatal marks the given input as fatal and won't be retried. It
// will also notify all the subscribers of this input.
func (s *UtxoSweeper) markInputFatal(pi *SweeperInput, tx *wire.MsgTx,
        err error) {

        log.Errorf("Failed to sweep input: %v, error: %v", pi, err)

        pi.state = Fatal

        s.signalResult(pi, Result{
                Tx:  tx,
                Err: err,
        })
}

// updateSweeperInputs updates the sweeper's internal state and returns a map
// of inputs to be swept. It will remove the inputs that are in final states,
// and returns a map of inputs that have either state Init or PublishFailed.
func (s *UtxoSweeper) updateSweeperInputs() InputsMap {
        // Create a map of inputs to be swept.
        inputs := make(InputsMap)

        // Iterate the pending inputs and update the sweeper's state.
        //
        // TODO(yy): sweeper is made to communicate via go channels, so no
        // locks are needed to access the map. However, it'd be safer if we
        // turn this inputs map into a SyncMap in case we wanna add concurrent
        // access to the map in the future.
        for op, input := range s.inputs {
                log.Tracef("Checking input: %s, state=%v", input, input.state)

                // If the input has reached a final state, that it's either
                // been swept, or failed, or excluded, we will remove it from
                // our sweeper.
                if input.terminated() {
                        log.Debugf("Removing input(State=%v) %v from sweeper",
                                input.state, op)

                        delete(s.inputs, op)

                        continue
                }

                // If this input has been included in a sweep tx that's not
                // published yet, we'd skip this input and wait for the sweep
                // tx to be published.
                if input.state == PendingPublish {
                        continue
                }

                // If this input has already been published, we will need to
                // check the RBF condition before attempting another sweeping.
                if input.state == Published {
                        continue
                }

                // If the input has a locktime that's not yet reached, we will
                // skip this input and wait for the locktime to be reached.
                mature, _ := input.isMature(uint32(s.currentHeight))
                if !mature {
                        continue
                }

                // If this input is new or has been failed to be published,
                // we'd retry it. The assumption here is that when an error is
                // returned from `PublishTransaction`, it means the tx has
                // failed to meet the policy, hence it's not in the mempool.
                inputs[op] = input
        }

        return inputs
}

// sweepPendingInputs is called when the ticker fires. It will create clusters
// and attempt to create and publish the sweeping transactions.
func (s *UtxoSweeper) sweepPendingInputs(inputs InputsMap) {
        log.Debugf("Sweeping %v inputs", len(inputs))

        // Cluster all of our inputs based on the specific Aggregator.
        sets := s.cfg.Aggregator.ClusterInputs(inputs)

        // sweepWithLock is a helper closure that executes the sweep within a
        // coin select lock to prevent the coins being selected for other
        // transactions like funding of a channel.
        sweepWithLock := func(set InputSet) error {
                return s.cfg.Wallet.WithCoinSelectLock(func() error {
                        // Try to add inputs from our wallet.
                        err := set.AddWalletInputs(s.cfg.Wallet)
                        if err != nil {
                                return err
                        }

                        // Create sweeping transaction for each set.
                        err = s.sweep(set)
                        if err != nil {
                                return err
                        }

                        return nil
                })
        }

        for _, set := range sets {
                var err error
                if set.NeedWalletInput() {
                        // Sweep the set of inputs that need the wallet inputs.
                        err = sweepWithLock(set)
                } else {
                        // Sweep the set of inputs that don't need the wallet
                        // inputs.
                        err = s.sweep(set)
                }

                if err != nil {
                        log.Errorf("Failed to sweep %v: %v", set, err)
                }
        }
}

// bumpResp wraps the result of a bump attempt returned from the fee bumper and
// the inputs being used.
type bumpResp struct {
        // result is the result of the bump attempt returned from the fee
        // bumper.
        result *BumpResult

        // set is the input set that was used in the bump attempt.
        set InputSet
}

// monitorFeeBumpResult subscribes to the passed result chan to listen for
// future updates about the sweeping tx.
//
// NOTE: must run as a goroutine.
func (s *UtxoSweeper) monitorFeeBumpResult(set InputSet,
        resultChan <-chan *BumpResult) {

        defer s.wg.Done()

        for {
                select {
                case r := <-resultChan:
                        // Validate the result is valid.
                        if err := r.Validate(); err != nil {
                                log.Errorf("Received invalid result: %v", err)
                                continue
                        }

                        resp := &bumpResp{
                                result: r,
                                set:    set,
                        }

                        // Send the result back to the main event loop.
                        select {
                        case s.bumpRespChan <- resp:
                        case <-s.quit:
                                log.Debug("Sweeper shutting down, skip " +
                                        "sending bump result")

                                return
                        }

                        // The sweeping tx has been confirmed, we can exit the
                        // monitor now.
                        //
                        // TODO(yy): can instead remove the spend subscription
                        // in sweeper and rely solely on this event to mark
                        // inputs as Swept?
                        if r.Event == TxConfirmed || r.Event == TxFailed {
                                // Exit if the tx is failed to be created.
                                if r.Tx == nil {
                                        log.Debugf("Received %v for nil tx, "+
                                                "exit monitor", r.Event)

                                        return
                                }

                                log.Debugf("Received %v for sweep tx %v, exit "+
                                        "fee bump monitor", r.Event,
                                        r.Tx.TxHash())

                                // Cancel the rebroadcasting of the failed tx.
                                s.cfg.Wallet.CancelRebroadcast(r.Tx.TxHash())

                                return
                        }

                case <-s.quit:
                        log.Debugf("Sweeper shutting down, exit fee " +
                                "bump handler")

                        return
                }
        }
}

// handleBumpEventTxFailed handles the case where the tx has been failed to
// publish.
func (s *UtxoSweeper) handleBumpEventTxFailed(resp *bumpResp) {
        r := resp.result
        tx, err := r.Tx, r.Err

        if tx != nil {
                log.Warnf("Fee bump attempt failed for tx=%v: %v", tx.TxHash(),
                        err)
        }

        // NOTE: When marking the inputs as failed, we are using the input set
        // instead of the inputs found in the tx. This is fine for current
        // version of the sweeper because we always create a tx using ALL of
        // the inputs specified by the set.
        //
        // TODO(yy): should we also remove the failed tx from db?
        s.markInputsPublishFailed(resp.set)
}

// handleBumpEventTxReplaced handles the case where the sweeping tx has been
// replaced by a new one.
func (s *UtxoSweeper) handleBumpEventTxReplaced(resp *bumpResp) error {
        r := resp.result
        oldTx := r.ReplacedTx
        newTx := r.Tx

        // Prepare a new record to replace the old one.
        tr := &TxRecord{
                Txid:    newTx.TxHash(),
                FeeRate: uint64(r.FeeRate),
                Fee:     uint64(r.Fee),
        }

        // Get the old record for logging purpose.
        oldTxid := oldTx.TxHash()
        record, err := s.cfg.Store.GetTx(oldTxid)
        if err != nil {
                log.Errorf("Fetch tx record for %v: %v", oldTxid, err)
                return err
        }

        // Cancel the rebroadcasting of the replaced tx.
        s.cfg.Wallet.CancelRebroadcast(oldTxid)

        log.Infof("RBFed tx=%v(fee=%v sats, feerate=%v sats/kw) with new "+
                "tx=%v(fee=%v, "+"feerate=%v)", record.Txid, record.Fee,
                record.FeeRate, tr.Txid, tr.Fee, tr.FeeRate)

        // The old sweeping tx has been replaced by a new one, we will update
        // the tx record in the sweeper db.
        //
        // TODO(yy): we may also need to update the inputs in this tx to a new
        // state. Suppose a replacing tx only spends a subset of the inputs
        // here, we'd end up with the rest being marked as `Published` and
        // won't be aggregated in the next sweep. Atm it's fine as we always
        // RBF the same input set.
        if err := s.cfg.Store.DeleteTx(oldTxid); err != nil {
                log.Errorf("Delete tx record for %v: %v", oldTxid, err)
                return err
        }

        // Mark the inputs as published using the replacing tx.
        return s.markInputsPublished(tr, resp.set)
}

// handleBumpEventTxPublished handles the case where the sweeping tx has been
// successfully published.
func (s *UtxoSweeper) handleBumpEventTxPublished(resp *bumpResp) error {
        r := resp.result
        tx := r.Tx
        tr := &TxRecord{
                Txid:    tx.TxHash(),
                FeeRate: uint64(r.FeeRate),
                Fee:     uint64(r.Fee),
        }

        // Inputs have been successfully published so we update their
        // states.
        err := s.markInputsPublished(tr, resp.set)
        if err != nil {
                return err
        }

        log.Debugf("Published sweep tx %v, num_inputs=%v, height=%v",
                tx.TxHash(), len(tx.TxIn), s.currentHeight)

        // If there's no error, remove the output script. Otherwise keep it so
        // that it can be reused for the next transaction and causes no address
        // inflation.
        s.currentOutputScript = fn.None[lnwallet.AddrWithKey]()

        return nil
}

// handleBumpEventTxFatal handles the case where there's an unexpected error
// when creating or publishing the sweeping tx. In this case, the tx will be
// removed from the sweeper store and the inputs will be marked as `Failed`,
// which means they will not be retried.
func (s *UtxoSweeper) handleBumpEventTxFatal(resp *bumpResp) error {
        r := resp.result

        // Remove the tx from the sweeper store if there is one. Since this is
        // a broadcast error, it's likely there isn't a tx here.
        if r.Tx != nil {
                txid := r.Tx.TxHash()
                log.Infof("Tx=%v failed with unexpected error: %v", txid, r.Err)

                // Remove the tx from the sweeper db if it exists.
                if err := s.cfg.Store.DeleteTx(txid); err != nil {
                        return fmt.Errorf("delete tx record for %v: %w", txid,
                                err)
                }
        }

        // Mark the inputs as fatal.
        s.markInputsFatal(resp.set, r.Tx, r.Err)

        return nil
}

// markInputsFatal  marks all inputs in the input set as failed. It will also
// notify all the subscribers of these inputs.
func (s *UtxoSweeper) markInputsFatal(set InputSet, tx *wire.MsgTx, err error) {
        for _, inp := range set.Inputs() {
                outpoint := inp.OutPoint()

                input, ok := s.inputs[outpoint]
                if !ok {
                        // It's very likely that a spending tx contains inputs
                        // that we don't know.
                        log.Tracef("Skipped marking input as failed: %v not "+
                                "found in pending inputs", outpoint)

                        continue
                }

                // If the input is already in a terminal state, we don't want
                // to rewrite it, which also indicates an error as we only get
                // an error event during the initial broadcast.
                if input.terminated() {
                        log.Errorf("Skipped marking input=%v as failed due to "+
                                "unexpected state=%v", outpoint, input.state)

                        continue
                }

                s.markInputFatal(input, tx, err)
        }
}

// handleBumpEvent handles the result sent from the bumper based on its event
// type.
//
// NOTE: TxConfirmed event is not handled, since we already subscribe to the
// input's spending event, we don't need to do anything here.
func (s *UtxoSweeper) handleBumpEvent(r *bumpResp) error {
        log.Debugf("Received bump result %v", r.result)

        switch r.result.Event {
        // The tx has been published, we update the inputs' state and create a
        // record to be stored in the sweeper db.
        case TxPublished:
                return s.handleBumpEventTxPublished(r)

        // The tx has failed, we update the inputs' state.
        case TxFailed:
                s.handleBumpEventTxFailed(r)
                return nil

        // The tx has been replaced, we will remove the old tx and replace it
        // with the new one.
        case TxReplaced:
                return s.handleBumpEventTxReplaced(r)

        // There are inputs being spent in a tx which the fee bumper doesn't
        // understand. We will remove the tx from the sweeper db and mark the
        // inputs as swept.
        case TxUnknownSpend:
                s.handleBumpEventTxUnknownSpent(r)

        // There's a fatal error in creating the tx, we will remove the tx from
        // the sweeper db and mark the inputs as failed.
        case TxFatal:
                return s.handleBumpEventTxFatal(r)

        // The sweeping tx is confirmed, we now mark the inputs as swept.
        case TxConfirmed:
                // We now use the spending tx to update the state of the inputs.
                s.handleBumpEventTxConfirmed(r)
        }

        return nil
}

// IsSweeperOutpoint determines whether the outpoint was created by the sweeper.
//
// NOTE: It is enough to check the txid because the sweeper will create
// outpoints which solely belong to the internal LND wallet.
func (s *UtxoSweeper) IsSweeperOutpoint(op wire.OutPoint) bool {
        found, err := s.cfg.Store.IsOurTx(op.Hash)
        // In case there is an error fetching the transaction details from the
        // sweeper store we assume the outpoint is still used by the sweeper
        // (worst case scenario).
        //
        // TODO(ziggie): Ensure that confirmed outpoints are deleted from the
        // bucket.
        if err != nil && !errors.Is(err, errNoTxHashesBucket) {
                log.Errorf("failed to fetch info for outpoint(%v:%d) "+
                        "with: %v, we assume it is still in use by the sweeper",
                        op.Hash, op.Index, err)

                return true
        }

        return found
}

// markInputSwept marks the given input as swept by the tx. It will also notify
// all the subscribers of this input.
func (s *UtxoSweeper) markInputSwept(inp *SweeperInput, tx *wire.MsgTx) {
        log.Debugf("Marking input as swept: %v from state=%v", inp.OutPoint(),
                inp.state)

        inp.state = Swept

        // Signal result channels.
        s.signalResult(inp, Result{
                Tx: tx,
        })

        // Remove all other inputs in this exclusive group.
        if inp.params.ExclusiveGroup != nil {
                s.removeExclusiveGroup(*inp.params.ExclusiveGroup)
        }
}

// handleThirdPartySpent takes an input and its spending tx. If the spending tx
// cannot be found in the sweeper store, the input will be marked as fatal,
// otherwise it will be marked as swept.
func (s *UtxoSweeper) handleThirdPartySpent(inp *SweeperInput, tx *wire.MsgTx) {
        op := inp.OutPoint()
        txid := tx.TxHash()

        isOurTx, err := s.cfg.Store.IsOurTx(txid)
        if err != nil {
                log.Errorf("Cannot determine if tx %v is ours: %v", txid, err)
                return
        }

        // If this is our tx, it means it's a previous sweeping tx that got
        // confirmed, which could happen when a restart happens during the
        // sweeping process.
        if isOurTx {
                log.Debugf("Found our sweeping tx %v, marking input %v as "+
                        "swept", txid, op)

                // We now use the spending tx to update the state of the inputs.
                s.markInputSwept(inp, tx)

                return
        }

        // Since the input is spent by others, we now mark it as fatal and won't
        // be retried.
        s.markInputFatal(inp, tx, ErrRemoteSpend)

        log.Debugf("Removing descendant txns invalidated by (txid=%v): %v",
                tx.TxHash(), lnutils.SpewLogClosure(tx))

        // Construct a map of the inputs this transaction spends.
        spentInputs := make(map[wire.OutPoint]struct{}, len(tx.TxIn))
        for _, txIn := range tx.TxIn {
                spentInputs[txIn.PreviousOutPoint] = struct{}{}
        }

        err = s.removeConflictSweepDescendants(spentInputs)
        if err != nil {
                log.Warnf("unable to remove descendant transactions "+
                        "due to tx %v: ", txid)
        }
}

// handleBumpEventTxUnknownSpent handles the case where the confirmed tx is
// unknown to the fee bumper. In the case when the sweeping tx has been replaced
// by another party with their tx being confirmed. It will retry sweeping the
// "good" inputs once the "bad" ones are kicked out.
func (s *UtxoSweeper) handleBumpEventTxUnknownSpent(r *bumpResp) {
        // Mark the inputs as publish failed, which means they will be retried
        // later.
        s.markInputsPublishFailed(r.set)

        // Get all the inputs that are not spent in the current sweeping tx.
        spentInputs := r.result.SpentInputs

        // Create a slice to track inputs to be retried.
        inputsToRetry := make([]input.Input, 0, len(r.set.Inputs()))

        // Iterate all the inputs found in this bump and mark the ones spent by
        // the third party as failed. The rest of inputs will then be updated
        // with a new fee rate and be retried immediately.
        for _, inp := range r.set.Inputs() {
                op := inp.OutPoint()
                input, ok := s.inputs[op]

                // Wallet inputs are not tracked so we will not find them from
                // the inputs map.
                if !ok {
                        log.Debugf("Skipped marking input: %v not found in "+
                                "pending inputs", op)

                        continue
                }

                // Check whether this input has been spent, if so we mark it as
                // fatal or swept based on whether this is one of our previous
                // sweeping txns, then move to the next.
                tx, spent := spentInputs[op]
                if spent {
                        s.handleThirdPartySpent(input, tx)

                        continue
                }

                log.Debugf("Input(%v): updating params: starting fee rate "+
                        "[%v -> %v], immediate [%v -> true]", op,
                        input.params.StartingFeeRate, r.result.FeeRate,
                        input.params.Immediate)

                // Update the input using the fee rate specified from the
                // BumpResult, which should be the starting fee rate to use for
                // the next sweeping attempt.
                input.params.StartingFeeRate = fn.Some(r.result.FeeRate)
                input.params.Immediate = true
                inputsToRetry = append(inputsToRetry, input)
        }

        // Exit early if there are no inputs to be retried.
        if len(inputsToRetry) == 0 {
                return
        }

        log.Debugf("Retry sweeping inputs with updated params: %v",
                inputTypeSummary(inputsToRetry))

        // Get the latest inputs, which should put the PublishFailed inputs back
        // to the sweeping queue.
        inputs := s.updateSweeperInputs()

        // Immediately sweep the remaining inputs - the previous inputs should
        // now be swept with the updated StartingFeeRate immediately. We may
        // also include more inputs in the new sweeping tx if new ones with the
        // same deadline are offered.
        s.sweepPendingInputs(inputs)
}

lightningnetwork / lnd / 13157844420

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