12426855566

Committed 20 Dec 2024 06:42AM UTC coverage: 58.73% (+0.09%) from 58.64%

Build # 12426855566

Build Type

Pull #9315

github

Committed by

yyforyongyu

Commit Message

contractcourt: include custom records on replayed htlc

Add another case in addition to #9357.

Pull Request Pull Request #9315: Implement `blockbeat`

Run Details

2262 of 2729 new or added lines in 35 files covered. (82.89%)

132 existing lines in 25 files now uncovered.

135298 of 230373 relevant lines covered (58.73%)

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Source File
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91.52

/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 / 12426855566

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