13157733617

Committed 05 Feb 2025 12:49PM UTC coverage: 57.712% (-1.1%) from 58.82%

Build # 13157733617

Build Type

Pull #9447

github

Committed by

yyforyongyu

Commit Message

sweep: rename methods for clarity

We now rename "third party" to "unknown" as the inputs can be spent via
an older sweeping tx, a third party (anchor), or a remote party (pin).
In fee bumper we don't have the info to distinguish the above cases, and
leave them to be further handled by the sweeper as it has more context.

Pull Request Pull Request #9447: sweep: start tracking input spending status in the fee bumper

Run Details

83 of 87 new or added lines in 2 files covered. (95.4%)

19472 existing lines in 252 files now uncovered.

103634 of 179570 relevant lines covered (57.71%)

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Source File
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79.68

/contractcourt/htlc_success_resolver.go

package contractcourt

import (
        "encoding/binary"
        "fmt"
        "io"
        "sync"

        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/fn/v2"
        "github.com/lightningnetwork/lnd/graph/db/models"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/labels"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/sweep"
)

// htlcSuccessResolver is a resolver that's capable of sweeping an incoming
// HTLC output on-chain. If this is the remote party's commitment, we'll sweep
// it directly from the commitment output *immediately*. If this is our
// commitment, we'll first broadcast the success transaction, then send it to
// the incubator for sweeping. That's it, no need to send any clean up
// messages.
//
// TODO(roasbeef): don't need to broadcast?
type htlcSuccessResolver struct {
        // htlcResolution is the incoming HTLC resolution for this HTLC. It
        // contains everything we need to properly resolve this HTLC.
        htlcResolution lnwallet.IncomingHtlcResolution

        // outputIncubating returns true if we've sent the output to the output
        // incubator (utxo nursery). In case the htlcResolution has non-nil
        // SignDetails, it means we will let the Sweeper handle broadcasting
        // the secondd-level transaction, and sweeping its output. In this case
        // we let this field indicate whether we need to broadcast the
        // second-level tx (false) or if it has confirmed and we must sweep the
        // second-level output (true).
        outputIncubating bool

        // broadcastHeight is the height that the original contract was
        // broadcast to the main-chain at. We'll use this value to bound any
        // historical queries to the chain for spends/confirmations.
        broadcastHeight uint32

        // htlc contains information on the htlc that we are resolving on-chain.
        htlc channeldb.HTLC

        // currentReport stores the current state of the resolver for reporting
        // over the rpc interface. This should only be reported in case we have
        // a non-nil SignDetails on the htlcResolution, otherwise the nursery
        // will produce reports.
        currentReport ContractReport

        // reportLock prevents concurrent access to the resolver report.
        reportLock sync.Mutex

        contractResolverKit

        htlcLeaseResolver
}

// newSuccessResolver instanties a new htlc success resolver.
func newSuccessResolver(res lnwallet.IncomingHtlcResolution,
        broadcastHeight uint32, htlc channeldb.HTLC,
        resCfg ResolverConfig) *htlcSuccessResolver {

        h := &htlcSuccessResolver{
                contractResolverKit: *newContractResolverKit(resCfg),
                htlcResolution:      res,
                broadcastHeight:     broadcastHeight,
                htlc:                htlc,
        }

        h.initReport()
        h.initLogger(fmt.Sprintf("%T(%v)", h, h.outpoint()))

        return h
}

// outpoint returns the outpoint of the HTLC output we're attempting to sweep.
func (h *htlcSuccessResolver) outpoint() wire.OutPoint {
        // The primary key for this resolver will be the outpoint of the HTLC
        // on the commitment transaction itself. If this is our commitment,
        // then the output can be found within the signed success tx,
        // otherwise, it's just the ClaimOutpoint.
        if h.htlcResolution.SignedSuccessTx != nil {
                return h.htlcResolution.SignedSuccessTx.TxIn[0].PreviousOutPoint
        }

        return h.htlcResolution.ClaimOutpoint
}

// ResolverKey returns an identifier which should be globally unique for this
// particular resolver within the chain the original contract resides within.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) ResolverKey() []byte {
        key := newResolverID(h.outpoint())
        return key[:]
}

// Resolve attempts to resolve an unresolved incoming HTLC that we know the
// preimage to. If the HTLC is on the commitment of the remote party, then we'll
// simply sweep it directly. Otherwise, we'll hand this off to the utxo nursery
// to do its duty. There is no need to make a call to the invoice registry
// anymore. Every HTLC has already passed through the incoming contest resolver
// and in there the invoice was already marked as settled.
//
// NOTE: Part of the ContractResolver interface.
//
// TODO(yy): refactor the interface method to return an error only.
func (h *htlcSuccessResolver) Resolve() (ContractResolver, error) {
        var err error

        switch {
        // If we're already resolved, then we can exit early.
        case h.IsResolved():
                h.log.Errorf("already resolved")

        // If this is an output on the remote party's commitment transaction,
        // use the direct-spend path to sweep the htlc.
        case h.isRemoteCommitOutput():
                err = h.resolveRemoteCommitOutput()

        // If this is an output on our commitment transaction using post-anchor
        // channel type, it will be handled by the sweeper.
        case h.isZeroFeeOutput():
                err = h.resolveSuccessTx()

        // If this is an output on our own commitment using pre-anchor channel
        // type, we will publish the success tx and offer the output to the
        // nursery.
        default:
                err = h.resolveLegacySuccessTx()
        }

        return nil, err
}

// resolveRemoteCommitOutput handles sweeping an HTLC output on the remote
// commitment with the preimage. In this case we can sweep the output directly,
// and don't have to broadcast a second-level transaction.
func (h *htlcSuccessResolver) resolveRemoteCommitOutput() error {
        h.log.Info("waiting for direct-preimage spend of the htlc to confirm")

        // Wait for the direct-preimage HTLC sweep tx to confirm.
        //
        // TODO(yy): use the result chan returned from `SweepInput`.
        sweepTxDetails, err := waitForSpend(
                &h.htlcResolution.ClaimOutpoint,
                h.htlcResolution.SweepSignDesc.Output.PkScript,
                h.broadcastHeight, h.Notifier, h.quit,
        )
        if err != nil {
                return err
        }

        // TODO(yy): should also update the `RecoveredBalance` and
        // `LimboBalance` like other paths?

        // Checkpoint the resolver, and write the outcome to disk.
        return h.checkpointClaim(sweepTxDetails.SpenderTxHash)
}

// checkpointClaim checkpoints the success resolver with the reports it needs.
// If this htlc was claimed two stages, it will write reports for both stages,
// otherwise it will just write for the single htlc claim.
func (h *htlcSuccessResolver) checkpointClaim(spendTx *chainhash.Hash) error {
        // Mark the htlc as final settled.
        err := h.ChainArbitratorConfig.PutFinalHtlcOutcome(
                h.ChannelArbitratorConfig.ShortChanID, h.htlc.HtlcIndex, true,
        )
        if err != nil {
                return err
        }

        // Send notification.
        h.ChainArbitratorConfig.HtlcNotifier.NotifyFinalHtlcEvent(
                models.CircuitKey{
                        ChanID: h.ShortChanID,
                        HtlcID: h.htlc.HtlcIndex,
                },
                channeldb.FinalHtlcInfo{
                        Settled:  true,
                        Offchain: false,
                },
        )

        // Create a resolver report for claiming of the htlc itself.
        amt := btcutil.Amount(h.htlcResolution.SweepSignDesc.Output.Value)
        reports := []*channeldb.ResolverReport{
                {
                        OutPoint:        h.htlcResolution.ClaimOutpoint,
                        Amount:          amt,
                        ResolverType:    channeldb.ResolverTypeIncomingHtlc,
                        ResolverOutcome: channeldb.ResolverOutcomeClaimed,
                        SpendTxID:       spendTx,
                },
        }

        // If we have a success tx, we append a report to represent our first
        // stage claim.
        if h.htlcResolution.SignedSuccessTx != nil {
                // If the SignedSuccessTx is not nil, we are claiming the htlc
                // in two stages, so we need to create a report for the first
                // stage transaction as well.
                spendTx := h.htlcResolution.SignedSuccessTx
                spendTxID := spendTx.TxHash()

                report := &channeldb.ResolverReport{
                        OutPoint:        spendTx.TxIn[0].PreviousOutPoint,
                        Amount:          h.htlc.Amt.ToSatoshis(),
                        ResolverType:    channeldb.ResolverTypeIncomingHtlc,
                        ResolverOutcome: channeldb.ResolverOutcomeFirstStage,
                        SpendTxID:       &spendTxID,
                }
                reports = append(reports, report)
        }

        // Finally, we checkpoint the resolver with our report(s).
        h.markResolved()
        return h.Checkpoint(h, reports...)
}

// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) Stop() {
        h.log.Debugf("stopping...")
        defer h.log.Debugf("stopped")

        close(h.quit)
}

// report returns a report on the resolution state of the contract.
func (h *htlcSuccessResolver) report() *ContractReport {
        // If the sign details are nil, the report will be created by handled
        // by the nursery.
        if h.htlcResolution.SignDetails == nil {
                return nil
        }

        h.reportLock.Lock()
        defer h.reportLock.Unlock()
        cpy := h.currentReport
        return &cpy
}

func (h *htlcSuccessResolver) initReport() {
        // We create the initial report. This will only be reported for
        // resolvers not handled by the nursery.
        finalAmt := h.htlc.Amt.ToSatoshis()
        if h.htlcResolution.SignedSuccessTx != nil {
                finalAmt = btcutil.Amount(
                        h.htlcResolution.SignedSuccessTx.TxOut[0].Value,
                )
        }

        h.currentReport = ContractReport{
                Outpoint:       h.htlcResolution.ClaimOutpoint,
                Type:           ReportOutputIncomingHtlc,
                Amount:         finalAmt,
                MaturityHeight: h.htlcResolution.CsvDelay,
                LimboBalance:   finalAmt,
                Stage:          1,
        }
}

// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcSuccessResolver) Encode(w io.Writer) error {
        // First we'll encode our inner HTLC resolution.
        if err := encodeIncomingResolution(w, &h.htlcResolution); err != nil {
                return err
        }

        // Next, we'll write out the fields that are specified to the contract
        // resolver.
        if err := binary.Write(w, endian, h.outputIncubating); err != nil {
                return err
        }
        if err := binary.Write(w, endian, h.IsResolved()); err != nil {
                return err
        }
        if err := binary.Write(w, endian, h.broadcastHeight); err != nil {
                return err
        }
        if _, err := w.Write(h.htlc.RHash[:]); err != nil {
                return err
        }

        // We encode the sign details last for backwards compatibility.
        err := encodeSignDetails(w, h.htlcResolution.SignDetails)
        if err != nil {
                return err
        }

        return nil
}

// newSuccessResolverFromReader attempts to decode an encoded ContractResolver
// from the passed Reader instance, returning an active ContractResolver
// instance.
func newSuccessResolverFromReader(r io.Reader, resCfg ResolverConfig) (
        *htlcSuccessResolver, error) {

        h := &htlcSuccessResolver{
                contractResolverKit: *newContractResolverKit(resCfg),
        }

        // First we'll decode our inner HTLC resolution.
        if err := decodeIncomingResolution(r, &h.htlcResolution); err != nil {
                return nil, err
        }

        // Next, we'll read all the fields that are specified to the contract
        // resolver.
        if err := binary.Read(r, endian, &h.outputIncubating); err != nil {
                return nil, err
        }

        var resolved bool
        if err := binary.Read(r, endian, &resolved); err != nil {
                return nil, err
        }
        if resolved {
                h.markResolved()
        }

        if err := binary.Read(r, endian, &h.broadcastHeight); err != nil {
                return nil, err
        }
        if _, err := io.ReadFull(r, h.htlc.RHash[:]); err != nil {
                return nil, err
        }

        // Sign details is a new field that was added to the htlc resolution,
        // so it is serialized last for backwards compatibility. We try to read
        // it, but don't error out if there are not bytes left.
        signDetails, err := decodeSignDetails(r)
        if err == nil {
                h.htlcResolution.SignDetails = signDetails
        } else if err != io.EOF && err != io.ErrUnexpectedEOF {
                return nil, err
        }

        h.initReport()
        h.initLogger(fmt.Sprintf("%T(%v)", h, h.outpoint()))

        return h, nil
}

// Supplement adds additional information to the resolver that is required
// before Resolve() is called.
//
// NOTE: Part of the htlcContractResolver interface.
func (h *htlcSuccessResolver) Supplement(htlc channeldb.HTLC) {
        h.htlc = htlc
}

// HtlcPoint returns the htlc's outpoint on the commitment tx.
//
// NOTE: Part of the htlcContractResolver interface.
func (h *htlcSuccessResolver) HtlcPoint() wire.OutPoint {
        return h.htlcResolution.HtlcPoint()
}

// SupplementDeadline does nothing for an incoming htlc resolver.
//
// NOTE: Part of the htlcContractResolver interface.
func (h *htlcSuccessResolver) SupplementDeadline(_ fn.Option[int32]) {
}

// A compile time assertion to ensure htlcSuccessResolver meets the
// ContractResolver interface.
var _ htlcContractResolver = (*htlcSuccessResolver)(nil)

// isRemoteCommitOutput returns a bool to indicate whether the htlc output is
// on the remote commitment.
func (h *htlcSuccessResolver) isRemoteCommitOutput() bool {
        // If we don't have a success transaction, then this means that this is
        // an output on the remote party's commitment transaction.
        return h.htlcResolution.SignedSuccessTx == nil
}

// isZeroFeeOutput returns a boolean indicating whether the htlc output is from
// a anchor-enabled channel, which uses the sighash SINGLE|ANYONECANPAY.
func (h *htlcSuccessResolver) isZeroFeeOutput() bool {
        // If we have non-nil SignDetails, this means it has a 2nd level HTLC
        // transaction that is signed using sighash SINGLE|ANYONECANPAY (the
        // case for anchor type channels). In this case we can re-sign it and
        // attach fees at will.
        return h.htlcResolution.SignedSuccessTx != nil &&
                h.htlcResolution.SignDetails != nil
}

// isTaproot returns true if the resolver is for a taproot output.
func (h *htlcSuccessResolver) isTaproot() bool {
        return txscript.IsPayToTaproot(
                h.htlcResolution.SweepSignDesc.Output.PkScript,
        )
}

// sweepRemoteCommitOutput creates a sweep request to sweep the HTLC output on
// the remote commitment via the direct preimage-spend.
func (h *htlcSuccessResolver) sweepRemoteCommitOutput() error {
        // Before we can craft out sweeping transaction, we need to create an
        // input which contains all the items required to add this input to a
        // sweeping transaction, and generate a witness.
        var inp input.Input

        if h.isTaproot() {
                inp = lnutils.Ptr(input.MakeTaprootHtlcSucceedInput(
                        &h.htlcResolution.ClaimOutpoint,
                        &h.htlcResolution.SweepSignDesc,
                        h.htlcResolution.Preimage[:],
                        h.broadcastHeight,
                        h.htlcResolution.CsvDelay,
                        input.WithResolutionBlob(
                                h.htlcResolution.ResolutionBlob,
                        ),
                ))
        } else {
                inp = lnutils.Ptr(input.MakeHtlcSucceedInput(
                        &h.htlcResolution.ClaimOutpoint,
                        &h.htlcResolution.SweepSignDesc,
                        h.htlcResolution.Preimage[:],
                        h.broadcastHeight,
                        h.htlcResolution.CsvDelay,
                ))
        }

        // Calculate the budget for this sweep.
        budget := calculateBudget(
                btcutil.Amount(inp.SignDesc().Output.Value),
                h.Budget.DeadlineHTLCRatio,
                h.Budget.DeadlineHTLC,
        )

        deadline := fn.Some(int32(h.htlc.RefundTimeout))

        log.Infof("%T(%x): offering direct-preimage HTLC output to sweeper "+
                "with deadline=%v, budget=%v", h, h.htlc.RHash[:],
                h.htlc.RefundTimeout, budget)

        // We'll now offer the direct preimage HTLC to the sweeper.
        _, err := h.Sweeper.SweepInput(
                inp,
                sweep.Params{
                        Budget:         budget,
                        DeadlineHeight: deadline,
                },
        )

        return err
}

// sweepSuccessTx attempts to sweep the second level success tx.
func (h *htlcSuccessResolver) sweepSuccessTx() error {
        var secondLevelInput input.HtlcSecondLevelAnchorInput
        if h.isTaproot() {
                secondLevelInput = input.MakeHtlcSecondLevelSuccessTaprootInput(
                        h.htlcResolution.SignedSuccessTx,
                        h.htlcResolution.SignDetails, h.htlcResolution.Preimage,
                        h.broadcastHeight, input.WithResolutionBlob(
                                h.htlcResolution.ResolutionBlob,
                        ),
                )
        } else {
                secondLevelInput = input.MakeHtlcSecondLevelSuccessAnchorInput(
                        h.htlcResolution.SignedSuccessTx,
                        h.htlcResolution.SignDetails, h.htlcResolution.Preimage,
                        h.broadcastHeight,
                )
        }

        // Calculate the budget for this sweep.
        value := btcutil.Amount(secondLevelInput.SignDesc().Output.Value)
        budget := calculateBudget(
                value, h.Budget.DeadlineHTLCRatio, h.Budget.DeadlineHTLC,
        )

        // The deadline would be the CLTV in this HTLC output. If we are the
        // initiator of this force close, with the default
        // `IncomingBroadcastDelta`, it means we have 10 blocks left when going
        // onchain.
        deadline := fn.Some(int32(h.htlc.RefundTimeout))

        h.log.Infof("offering second-level HTLC success tx to sweeper with "+
                "deadline=%v, budget=%v", h.htlc.RefundTimeout, budget)

        // We'll now offer the second-level transaction to the sweeper.
        _, err := h.Sweeper.SweepInput(
                &secondLevelInput,
                sweep.Params{
                        Budget:         budget,
                        DeadlineHeight: deadline,
                },
        )

        return err
}

// sweepSuccessTxOutput attempts to sweep the output of the second level
// success tx.
func (h *htlcSuccessResolver) sweepSuccessTxOutput() error {
        h.log.Debugf("sweeping output %v from 2nd-level HTLC success tx",
                h.htlcResolution.ClaimOutpoint)

        // This should be non-blocking as we will only attempt to sweep the
        // output when the second level tx has already been confirmed. In other
        // words, waitForSpend will return immediately.
        commitSpend, err := waitForSpend(
                &h.htlcResolution.SignedSuccessTx.TxIn[0].PreviousOutPoint,
                h.htlcResolution.SignDetails.SignDesc.Output.PkScript,
                h.broadcastHeight, h.Notifier, h.quit,
        )
        if err != nil {
                return err
        }

        // The HTLC success tx has a CSV lock that we must wait for, and if
        // this is a lease enforced channel and we're the imitator, we may need
        // to wait for longer.
        waitHeight := h.deriveWaitHeight(h.htlcResolution.CsvDelay, commitSpend)

        // Now that the sweeper has broadcasted the second-level transaction,
        // it has confirmed, and we have checkpointed our state, we'll sweep
        // the second level output. We report the resolver has moved the next
        // stage.
        h.reportLock.Lock()
        h.currentReport.Stage = 2
        h.currentReport.MaturityHeight = waitHeight
        h.reportLock.Unlock()

        if h.hasCLTV() {
                log.Infof("%T(%x): waiting for CSV and CLTV lock to expire at "+
                        "height %v", h, h.htlc.RHash[:], waitHeight)
        } else {
                log.Infof("%T(%x): waiting for CSV lock to expire at height %v",
                        h, h.htlc.RHash[:], waitHeight)
        }

        // We'll use this input index to determine the second-level output
        // index on the transaction, as the signatures requires the indexes to
        // be the same. We don't look for the second-level output script
        // directly, as there might be more than one HTLC output to the same
        // pkScript.
        op := &wire.OutPoint{
                Hash:  *commitSpend.SpenderTxHash,
                Index: commitSpend.SpenderInputIndex,
        }

        // Let the sweeper sweep the second-level output now that the
        // CSV/CLTV locks have expired.
        var witType input.StandardWitnessType
        if h.isTaproot() {
                witType = input.TaprootHtlcAcceptedSuccessSecondLevel
        } else {
                witType = input.HtlcAcceptedSuccessSecondLevel
        }
        inp := h.makeSweepInput(
                op, witType,
                input.LeaseHtlcAcceptedSuccessSecondLevel,
                &h.htlcResolution.SweepSignDesc,
                h.htlcResolution.CsvDelay, uint32(commitSpend.SpendingHeight),
                h.htlc.RHash, h.htlcResolution.ResolutionBlob,
        )

        // Calculate the budget for this sweep.
        budget := calculateBudget(
                btcutil.Amount(inp.SignDesc().Output.Value),
                h.Budget.NoDeadlineHTLCRatio,
                h.Budget.NoDeadlineHTLC,
        )

        log.Infof("%T(%x): offering second-level success tx output to sweeper "+
                "with no deadline and budget=%v at height=%v", h,
                h.htlc.RHash[:], budget, waitHeight)

        // TODO(yy): use the result chan returned from SweepInput.
        _, err = h.Sweeper.SweepInput(
                inp,
                sweep.Params{
                        Budget: budget,

                        // For second level success tx, there's no rush to get
                        // it confirmed, so we use a nil deadline.
                        DeadlineHeight: fn.None[int32](),
                },
        )

        return err
}

// resolveLegacySuccessTx handles an HTLC output from a pre-anchor type channel
// by broadcasting the second-level success transaction.
func (h *htlcSuccessResolver) resolveLegacySuccessTx() error {
        // Otherwise we'll publish the second-level transaction directly and
        // offer the resolution to the nursery to handle.
        h.log.Infof("broadcasting legacy second-level success tx: %v",
                h.htlcResolution.SignedSuccessTx.TxHash())

        // We'll now broadcast the second layer transaction so we can kick off
        // the claiming process.
        //
        // TODO(yy): offer it to the sweeper instead.
        label := labels.MakeLabel(
                labels.LabelTypeChannelClose, &h.ShortChanID,
        )
        err := h.PublishTx(h.htlcResolution.SignedSuccessTx, label)
        if err != nil {
                return err
        }

        // Fast-forward to resolve the output from the success tx if the it has
        // already been sent to the UtxoNursery.
        if h.outputIncubating {
                return h.resolveSuccessTxOutput(h.htlcResolution.ClaimOutpoint)
        }

        h.log.Infof("incubating incoming htlc output")

        // Send the output to the incubator.
        err = h.IncubateOutputs(
                h.ChanPoint, fn.None[lnwallet.OutgoingHtlcResolution](),
                fn.Some(h.htlcResolution),
                h.broadcastHeight, fn.Some(int32(h.htlc.RefundTimeout)),
        )
        if err != nil {
                return err
        }

        // Mark the output as incubating and checkpoint it.
        h.outputIncubating = true
        if err := h.Checkpoint(h); err != nil {
                return err
        }

        // Move to resolve the output.
        return h.resolveSuccessTxOutput(h.htlcResolution.ClaimOutpoint)
}

// resolveSuccessTx waits for the sweeping tx of the second-level success tx to
// confirm and offers the output from the success tx to the sweeper.
func (h *htlcSuccessResolver) resolveSuccessTx() error {
        h.log.Infof("waiting for 2nd-level HTLC success transaction to confirm")

        // Create aliases to make the code more readable.
        outpoint := h.htlcResolution.SignedSuccessTx.TxIn[0].PreviousOutPoint
        pkScript := h.htlcResolution.SignDetails.SignDesc.Output.PkScript

        // Wait for the second level transaction to confirm.
        commitSpend, err := waitForSpend(
                &outpoint, pkScript, h.broadcastHeight, h.Notifier, h.quit,
        )
        if err != nil {
                return err
        }

        // We'll use this input index to determine the second-level output
        // index on the transaction, as the signatures requires the indexes to
        // be the same. We don't look for the second-level output script
        // directly, as there might be more than one HTLC output to the same
        // pkScript.
        op := wire.OutPoint{
                Hash:  *commitSpend.SpenderTxHash,
                Index: commitSpend.SpenderInputIndex,
        }

        // If the 2nd-stage sweeping has already been started, we can
        // fast-forward to start the resolving process for the stage two
        // output.
        if h.outputIncubating {
                return h.resolveSuccessTxOutput(op)
        }

        // Now that the second-level transaction has confirmed, we checkpoint
        // the state so we'll go to the next stage in case of restarts.
        h.outputIncubating = true
        if err := h.Checkpoint(h); err != nil {
                log.Errorf("unable to Checkpoint: %v", err)
                return err
        }

        h.log.Infof("2nd-level HTLC success tx=%v confirmed",
                commitSpend.SpenderTxHash)

        // Send the sweep request for the output from the success tx.
        if err := h.sweepSuccessTxOutput(); err != nil {
                return err
        }

        return h.resolveSuccessTxOutput(op)
}

// resolveSuccessTxOutput waits for the spend of the output from the 2nd-level
// success tx.
func (h *htlcSuccessResolver) resolveSuccessTxOutput(op wire.OutPoint) error {
        // To wrap this up, we'll wait until the second-level transaction has
        // been spent, then fully resolve the contract.
        log.Infof("%T(%x): waiting for second-level HTLC output to be spent "+
                "after csv_delay=%v", h, h.htlc.RHash[:],
                h.htlcResolution.CsvDelay)

        spend, err := waitForSpend(
                &op, h.htlcResolution.SweepSignDesc.Output.PkScript,
                h.broadcastHeight, h.Notifier, h.quit,
        )
        if err != nil {
                return err
        }

        h.reportLock.Lock()
        h.currentReport.RecoveredBalance = h.currentReport.LimboBalance
        h.currentReport.LimboBalance = 0
        h.reportLock.Unlock()

        return h.checkpointClaim(spend.SpenderTxHash)
}

// Launch creates an input based on the details of the incoming htlc resolution
// and offers it to the sweeper.
func (h *htlcSuccessResolver) Launch() error {
        if h.isLaunched() {
                h.log.Tracef("already launched")
                return nil
        }

        h.log.Debugf("launching resolver...")
        h.markLaunched()

        switch {
        // If we're already resolved, then we can exit early.
        case h.IsResolved():
                h.log.Errorf("already resolved")
                return nil

        // If this is an output on the remote party's commitment transaction,
        // use the direct-spend path.
        case h.isRemoteCommitOutput():
                return h.sweepRemoteCommitOutput()

        // If this is an anchor type channel, we now sweep either the
        // second-level success tx or the output from the second-level success
        // tx.
        case h.isZeroFeeOutput():
                // If the second-level success tx has already been swept, we
                // can go ahead and sweep its output.
                if h.outputIncubating {
                        return h.sweepSuccessTxOutput()
                }

                // Otherwise, sweep the second level tx.
                return h.sweepSuccessTx()

        // If this is a legacy channel type, the output is handled by the
        // nursery via the Resolve so we do nothing here.
        //
        // TODO(yy): handle the legacy output by offering it to the sweeper.
        default:
                return nil
        }
}

lightningnetwork / lnd / 13157733617

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