9840691252

Committed 08 Jul 2024 01:34PM UTC coverage: 58.404% (+0.08%) from 58.325%

Build # 9840691252

Build Type

Pull #8900

github

Committed by

guggero

Commit Message

Makefile: add GOCC variable

Pull Request Pull Request #8900: Makefile: add GOCC variable

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81.84

/contractcourt/breach_arbitrator.go

package contractcourt

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

        "github.com/btcsuite/btcd/blockchain"
        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
        "github.com/davecgh/go-spew/spew"
        "github.com/lightningnetwork/lnd/chainntnfs"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/kvdb"
        "github.com/lightningnetwork/lnd/labels"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/lnwallet/chainfee"
)

const (
        // justiceTxConfTarget is the number of blocks we'll use as a
        // confirmation target when creating the justice transaction. We'll
        // choose an aggressive target, since we want to be sure it confirms
        // quickly.
        justiceTxConfTarget = 2

        // blocksPassedSplitPublish is the number of blocks without
        // confirmation of the justice tx we'll wait before starting to publish
        // smaller variants of the justice tx. We do this to mitigate an attack
        // the channel peer can do by pinning the HTLC outputs of the
        // commitment with low-fee HTLC transactions.
        blocksPassedSplitPublish = 4
)

var (
        // retributionBucket stores retribution state on disk between detecting
        // a contract breach, broadcasting a justice transaction that sweeps the
        // channel, and finally witnessing the justice transaction confirm on
        // the blockchain. It is critical that such state is persisted on disk,
        // so that if our node restarts at any point during the retribution
        // procedure, we can recover and continue from the persisted state.
        retributionBucket = []byte("retribution")

        // taprootRetributionBucket stores the tarpoot specific retribution
        // information. This includes things like the control blocks for both
        // commitment outputs, and the taptweak needed to sweep each HTLC (one
        // for the first and one for the second level).
        taprootRetributionBucket = []byte("tap-retribution")

        // errBrarShuttingDown is an error returned if the BreachArbitrator has
        // been signalled to exit.
        errBrarShuttingDown = errors.New("BreachArbitrator shutting down")
)

// ContractBreachEvent is an event the BreachArbitrator will receive in case a
// contract breach is observed on-chain. It contains the necessary information
// to handle the breach, and a ProcessACK closure we will use to ACK the event
// when we have safely stored all the necessary information.
type ContractBreachEvent struct {
        // ChanPoint is the channel point of the breached channel.
        ChanPoint wire.OutPoint

        // ProcessACK is an closure that should be called with a nil error iff
        // the breach retribution info is safely stored in the retribution
        // store. In case storing the information to the store fails, a non-nil
        // error should be used. When this closure returns, it means that the
        // contract court has marked the channel pending close in the DB, and
        // it is safe for the BreachArbitrator to carry on its duty.
        ProcessACK func(error)

        // BreachRetribution is the information needed to act on this contract
        // breach.
        BreachRetribution *lnwallet.BreachRetribution
}

// ChannelCloseType is an enum which signals the type of channel closure the
// peer should execute.
type ChannelCloseType uint8

const (
        // CloseRegular indicates a regular cooperative channel closure
        // should be attempted.
        CloseRegular ChannelCloseType = iota

        // CloseBreach indicates that a channel breach has been detected, and
        // the link should immediately be marked as unavailable.
        CloseBreach
)

// RetributionStorer provides an interface for managing a persistent map from
// wire.OutPoint -> retributionInfo. Upon learning of a breach, a
// BreachArbitrator should record the retributionInfo for the breached channel,
// which serves a checkpoint in the event that retribution needs to be resumed
// after failure. A RetributionStore provides an interface for managing the
// persisted set, as well as mapping user defined functions over the entire
// on-disk contents.
//
// Calls to RetributionStore may occur concurrently. A concrete instance of
// RetributionStore should use appropriate synchronization primitives, or
// be otherwise safe for concurrent access.
type RetributionStorer interface {
        // Add persists the retributionInfo to disk, using the information's
        // chanPoint as the key. This method should overwrite any existing
        // entries found under the same key, and an error should be raised if
        // the addition fails.
        Add(retInfo *retributionInfo) error

        // IsBreached queries the retribution store to see if the breach arbiter
        // is aware of any breaches for the provided channel point.
        IsBreached(chanPoint *wire.OutPoint) (bool, error)

        // Remove deletes the retributionInfo from disk, if any exists, under
        // the given key. An error should be re raised if the removal fails.
        Remove(key *wire.OutPoint) error

        // ForAll iterates over the existing on-disk contents and applies a
        // chosen, read-only callback to each. This method should ensure that it
        // immediately propagate any errors generated by the callback.
        ForAll(cb func(*retributionInfo) error, reset func()) error
}

// BreachConfig bundles the required subsystems used by the breach arbiter. An
// instance of BreachConfig is passed to NewBreachArbitrator during
// instantiation.
type BreachConfig struct {
        // CloseLink allows the breach arbiter to shutdown any channel links for
        // which it detects a breach, ensuring now further activity will
        // continue across the link. The method accepts link's channel point and
        // a close type to be included in the channel close summary.
        CloseLink func(*wire.OutPoint, ChannelCloseType)

        // DB provides access to the user's channels, allowing the breach
        // arbiter to determine the current state of a user's channels, and how
        // it should respond to channel closure.
        DB *channeldb.ChannelStateDB

        // Estimator is used by the breach arbiter to determine an appropriate
        // fee level when generating, signing, and broadcasting sweep
        // transactions.
        Estimator chainfee.Estimator

        // GenSweepScript generates the receiving scripts for swept outputs.
        GenSweepScript func() ([]byte, error)

        // Notifier provides a publish/subscribe interface for event driven
        // notifications regarding the confirmation of txids.
        Notifier chainntnfs.ChainNotifier

        // PublishTransaction facilitates the process of broadcasting a
        // transaction to the network.
        PublishTransaction func(*wire.MsgTx, string) error

        // ContractBreaches is a channel where the BreachArbitrator will receive
        // notifications in the event of a contract breach being observed. A
        // ContractBreachEvent must be ACKed by the BreachArbitrator, such that
        // the sending subsystem knows that the event is properly handed off.
        ContractBreaches <-chan *ContractBreachEvent

        // Signer is used by the breach arbiter to generate sweep transactions,
        // which move coins from previously open channels back to the user's
        // wallet.
        Signer input.Signer

        // Store is a persistent resource that maintains information regarding
        // breached channels. This is used in conjunction with DB to recover
        // from crashes, restarts, or other failures.
        Store RetributionStorer
}

// BreachArbitrator is a special subsystem which is responsible for watching and
// acting on the detection of any attempted uncooperative channel breaches by
// channel counterparties. This file essentially acts as deterrence code for
// those attempting to launch attacks against the daemon. In practice it's
// expected that the logic in this file never gets executed, but it is
// important to have it in place just in case we encounter cheating channel
// counterparties.
// TODO(roasbeef): closures in config for subsystem pointers to decouple?
type BreachArbitrator struct {
        started sync.Once
        stopped sync.Once

        cfg *BreachConfig

        subscriptions map[wire.OutPoint]chan struct{}

        quit chan struct{}
        wg   sync.WaitGroup
        sync.Mutex
}

// NewBreachArbitrator creates a new instance of a BreachArbitrator initialized
// with its dependent objects.
func NewBreachArbitrator(cfg *BreachConfig) *BreachArbitrator {
        return &BreachArbitrator{
                cfg:           cfg,
                subscriptions: make(map[wire.OutPoint]chan struct{}),
                quit:          make(chan struct{}),
        }
}

// Start is an idempotent method that officially starts the BreachArbitrator
// along with all other goroutines it needs to perform its functions.
func (b *BreachArbitrator) Start() error {
        var err error
        b.started.Do(func() {
                brarLog.Info("Breach arbiter starting")
                err = b.start()
        })
        return err
}

func (b *BreachArbitrator) start() error {
        // Load all retributions currently persisted in the retribution store.
        var breachRetInfos map[wire.OutPoint]retributionInfo
        if err := b.cfg.Store.ForAll(func(ret *retributionInfo) error {
                breachRetInfos[ret.chanPoint] = *ret
                return nil
        }, func() {
                breachRetInfos = make(map[wire.OutPoint]retributionInfo)
        }); err != nil {
                brarLog.Errorf("Unable to create retribution info: %v", err)
                return err
        }

        // Load all currently closed channels from disk, we will use the
        // channels that have been marked fully closed to filter the retribution
        // information loaded from disk. This is necessary in the event that the
        // channel was marked fully closed, but was not removed from the
        // retribution store.
        closedChans, err := b.cfg.DB.FetchClosedChannels(false)
        if err != nil {
                brarLog.Errorf("Unable to fetch closing channels: %v", err)
                return err
        }

        brarLog.Debugf("Found %v closing channels, %v retribution records",
                len(closedChans), len(breachRetInfos))

        // Using the set of non-pending, closed channels, reconcile any
        // discrepancies between the channeldb and the retribution store by
        // removing any retribution information for which we have already
        // finished our responsibilities. If the removal is successful, we also
        // remove the entry from our in-memory map, to avoid any further action
        // for this channel.
        // TODO(halseth): no need continue on IsPending once closed channels
        // actually means close transaction is confirmed.
        for _, chanSummary := range closedChans {
                brarLog.Debugf("Working on close channel: %v, is_pending: %v",
                        chanSummary.ChanPoint, chanSummary.IsPending)

                if chanSummary.IsPending {
                        continue
                }

                chanPoint := &chanSummary.ChanPoint
                if _, ok := breachRetInfos[*chanPoint]; ok {
                        if err := b.cfg.Store.Remove(chanPoint); err != nil {
                                brarLog.Errorf("Unable to remove closed "+
                                        "chanid=%v from breach arbiter: %v",
                                        chanPoint, err)
                                return err
                        }
                        delete(breachRetInfos, *chanPoint)

                        brarLog.Debugf("Skipped closed channel: %v",
                                chanSummary.ChanPoint)
                }
        }

        // Spawn the exactRetribution tasks to monitor and resolve any breaches
        // that were loaded from the retribution store.
        for chanPoint := range breachRetInfos {
                retInfo := breachRetInfos[chanPoint]

                brarLog.Debugf("Handling breach handoff on startup "+
                        "for ChannelPoint(%v)", chanPoint)

                // Register for a notification when the breach transaction is
                // confirmed on chain.
                breachTXID := retInfo.commitHash
                breachScript := retInfo.breachedOutputs[0].signDesc.Output.PkScript
                confChan, err := b.cfg.Notifier.RegisterConfirmationsNtfn(
                        &breachTXID, breachScript, 1, retInfo.breachHeight,
                )
                if err != nil {
                        brarLog.Errorf("Unable to register for conf updates "+
                                "for txid: %v, err: %v", breachTXID, err)
                        return err
                }

                // Launch a new goroutine which to finalize the channel
                // retribution after the breach transaction confirms.
                b.wg.Add(1)
                go b.exactRetribution(confChan, &retInfo)
        }

        // Start watching the remaining active channels!
        b.wg.Add(1)
        go b.contractObserver()

        return nil
}

// Stop is an idempotent method that signals the BreachArbitrator to execute a
// graceful shutdown. This function will block until all goroutines spawned by
// the BreachArbitrator have gracefully exited.
func (b *BreachArbitrator) Stop() error {
        b.stopped.Do(func() {
                brarLog.Infof("Breach arbiter shutting down...")
                defer brarLog.Debug("Breach arbiter shutdown complete")

                close(b.quit)
                b.wg.Wait()
        })
        return nil
}

// IsBreached queries the breach arbiter's retribution store to see if it is
// aware of any channel breaches for a particular channel point.
func (b *BreachArbitrator) IsBreached(chanPoint *wire.OutPoint) (bool, error) {
        return b.cfg.Store.IsBreached(chanPoint)
}

// SubscribeBreachComplete is used by outside subsystems to be notified of a
// successful breach resolution.
func (b *BreachArbitrator) SubscribeBreachComplete(chanPoint *wire.OutPoint,
        c chan struct{}) (bool, error) {

        breached, err := b.cfg.Store.IsBreached(chanPoint)
        if err != nil {
                // If an error occurs, no subscription will be registered.
                return false, err
        }

        if !breached {
                // If chanPoint no longer exists in the Store, then the breach
                // was cleaned up successfully. Any subscription that occurs
                // happens after the breach information was persisted to the
                // underlying store.
                return true, nil
        }

        // Otherwise since the channel point is not resolved, add a
        // subscription. There can only be one subscription per channel point.
        b.Lock()
        defer b.Unlock()
        b.subscriptions[*chanPoint] = c

        return false, nil
}

// notifyBreachComplete is used by the BreachArbitrator to notify outside
// subsystems that the breach resolution process is complete.
func (b *BreachArbitrator) notifyBreachComplete(chanPoint *wire.OutPoint) {
        b.Lock()
        defer b.Unlock()
        if c, ok := b.subscriptions[*chanPoint]; ok {
                close(c)
        }

        // Remove the subscription.
        delete(b.subscriptions, *chanPoint)
}

// contractObserver is the primary goroutine for the BreachArbitrator. This
// goroutine is responsible for handling breach events coming from the
// contractcourt on the ContractBreaches channel. If a channel breach is
// detected, then the contractObserver will execute the retribution logic
// required to sweep ALL outputs from a contested channel into the daemon's
// wallet.
//
// NOTE: This MUST be run as a goroutine.
func (b *BreachArbitrator) contractObserver() {
        defer b.wg.Done()

        brarLog.Infof("Starting contract observer, watching for breaches.")

        for {
                select {
                case breachEvent := <-b.cfg.ContractBreaches:
                        // We have been notified about a contract breach!
                        // Handle the handoff, making sure we ACK the event
                        // after we have safely added it to the retribution
                        // store.
                        b.wg.Add(1)
                        go b.handleBreachHandoff(breachEvent)

                case <-b.quit:
                        return
                }
        }
}

// spend is used to wrap the index of the retributionInfo output that gets
// spent together with the spend details.
type spend struct {
        index  int
        detail *chainntnfs.SpendDetail
}

// waitForSpendEvent waits for any of the breached outputs to get spent, and
// returns the spend details for those outputs. The spendNtfns map is a cache
// used to store registered spend subscriptions, in case we must call this
// method multiple times.
func (b *BreachArbitrator) waitForSpendEvent(breachInfo *retributionInfo,
        spendNtfns map[wire.OutPoint]*chainntnfs.SpendEvent) ([]spend, error) {

        inputs := breachInfo.breachedOutputs

        // We create a channel the first goroutine that gets a spend event can
        // signal. We make it buffered in case multiple spend events come in at
        // the same time.
        anySpend := make(chan struct{}, len(inputs))

        // The allSpends channel will be used to pass spend events from all the
        // goroutines that detects a spend before they are signalled to exit.
        allSpends := make(chan spend, len(inputs))

        // exit will be used to signal the goroutines that they can exit.
        exit := make(chan struct{})
        var wg sync.WaitGroup

        // We'll now launch a goroutine for each of the HTLC outputs, that will
        // signal the moment they detect a spend event.
        for i := range inputs {
                breachedOutput := &inputs[i]

                brarLog.Infof("Checking spend from %v(%v) for ChannelPoint(%v)",
                        breachedOutput.witnessType, breachedOutput.outpoint,
                        breachInfo.chanPoint)

                // If we have already registered for a notification for this
                // output, we'll reuse it.
                spendNtfn, ok := spendNtfns[breachedOutput.outpoint]
                if !ok {
                        var err error
                        spendNtfn, err = b.cfg.Notifier.RegisterSpendNtfn(
                                &breachedOutput.outpoint,
                                breachedOutput.signDesc.Output.PkScript,
                                breachInfo.breachHeight,
                        )
                        if err != nil {
                                brarLog.Errorf("Unable to check for spentness "+
                                        "of outpoint=%v: %v",
                                        breachedOutput.outpoint, err)

                                // Registration may have failed if we've been
                                // instructed to shutdown. If so, return here
                                // to avoid entering an infinite loop.
                                select {
                                case <-b.quit:
                                        return nil, errBrarShuttingDown
                                default:
                                        continue
                                }
                        }
                        spendNtfns[breachedOutput.outpoint] = spendNtfn
                }

                // Launch a goroutine waiting for a spend event.
                b.wg.Add(1)
                wg.Add(1)
                go func(index int, spendEv *chainntnfs.SpendEvent) {
                        defer b.wg.Done()
                        defer wg.Done()

                        select {
                        // The output has been taken to the second level!
                        case sp, ok := <-spendEv.Spend:
                                if !ok {
                                        return
                                }

                                brarLog.Infof("Detected spend on %s(%v) by "+
                                        "txid(%v) for ChannelPoint(%v)",
                                        inputs[index].witnessType,
                                        inputs[index].outpoint,
                                        sp.SpenderTxHash,
                                        breachInfo.chanPoint)

                                // First we send the spend event on the
                                // allSpends channel, such that it can be
                                // handled after all go routines have exited.
                                allSpends <- spend{index, sp}

                                // Finally we'll signal the anySpend channel
                                // that a spend was detected, such that the
                                // other goroutines can be shut down.
                                anySpend <- struct{}{}
                        case <-exit:
                                return
                        case <-b.quit:
                                return
                        }
                }(i, spendNtfn)
        }

        // We'll wait for any of the outputs to be spent, or that we are
        // signalled to exit.
        select {
        // A goroutine have signalled that a spend occurred.
        case <-anySpend:
                // Signal for the remaining goroutines to exit.
                close(exit)
                wg.Wait()

                // At this point all goroutines that can send on the allSpends
                // channel have exited. We can therefore safely close the
                // channel before ranging over its content.
                close(allSpends)

                // Gather all detected spends and return them.
                var spends []spend
                for s := range allSpends {
                        breachedOutput := &inputs[s.index]
                        delete(spendNtfns, breachedOutput.outpoint)

                        spends = append(spends, s)
                }

                return spends, nil

        case <-b.quit:
                return nil, errBrarShuttingDown
        }
}

// convertToSecondLevelRevoke takes a breached output, and a transaction that
// spends it to the second level, and mutates the breach output into one that
// is able to properly sweep that second level output. We'll use this function
// when we go to sweep a breached commitment transaction, but the cheating
// party has already attempted to take it to the second level.
func convertToSecondLevelRevoke(bo *breachedOutput, breachInfo *retributionInfo,
        spendDetails *chainntnfs.SpendDetail) {

        // In this case, we'll modify the witness type of this output to
        // actually prepare for a second level revoke.
        isTaproot := txscript.IsPayToTaproot(bo.signDesc.Output.PkScript)
        if isTaproot {
                bo.witnessType = input.TaprootHtlcSecondLevelRevoke
        } else {
                bo.witnessType = input.HtlcSecondLevelRevoke
        }

        // We'll also redirect the outpoint to this second level output, so the
        // spending transaction updates it inputs accordingly.
        spendingTx := spendDetails.SpendingTx
        spendInputIndex := spendDetails.SpenderInputIndex
        oldOp := bo.outpoint
        bo.outpoint = wire.OutPoint{
                Hash:  spendingTx.TxHash(),
                Index: spendInputIndex,
        }

        // Next, we need to update the amount so we can do fee estimation
        // properly, and also so we can generate a valid signature as we need
        // to know the new input value (the second level transactions shaves
        // off some funds to fees).
        newAmt := spendingTx.TxOut[spendInputIndex].Value
        bo.amt = btcutil.Amount(newAmt)
        bo.signDesc.Output.Value = newAmt
        bo.signDesc.Output.PkScript = spendingTx.TxOut[spendInputIndex].PkScript

        // For taproot outputs, the taptweak also needs to be swapped out. We
        // do this unconditionally as this field isn't used at all for segwit
        // v0 outputs.
        bo.signDesc.TapTweak = bo.secondLevelTapTweak[:]

        // Finally, we'll need to adjust the witness program in the
        // SignDescriptor.
        bo.signDesc.WitnessScript = bo.secondLevelWitnessScript

        brarLog.Warnf("HTLC(%v) for ChannelPoint(%v) has been spent to the "+
                "second-level, adjusting -> %v", oldOp, breachInfo.chanPoint,
                bo.outpoint)
}

// updateBreachInfo mutates the passed breachInfo by removing or converting any
// outputs among the spends. It also counts the total and revoked funds swept
// by our justice spends.
func updateBreachInfo(breachInfo *retributionInfo, spends []spend) (
        btcutil.Amount, btcutil.Amount) {

        inputs := breachInfo.breachedOutputs
        doneOutputs := make(map[int]struct{})

        var totalFunds, revokedFunds btcutil.Amount
        for _, s := range spends {
                breachedOutput := &inputs[s.index]
                txIn := s.detail.SpendingTx.TxIn[s.detail.SpenderInputIndex]

                switch breachedOutput.witnessType {
                case input.TaprootHtlcAcceptedRevoke:
                        fallthrough
                case input.TaprootHtlcOfferedRevoke:
                        fallthrough
                case input.HtlcAcceptedRevoke:
                        fallthrough
                case input.HtlcOfferedRevoke:
                        // If the HTLC output was spent using the revocation
                        // key, it is our own spend, and we can forget the
                        // output. Otherwise it has been taken to the second
                        // level.
                        signDesc := &breachedOutput.signDesc
                        ok, err := input.IsHtlcSpendRevoke(txIn, signDesc)
                        if err != nil {
                                brarLog.Errorf("Unable to determine if "+
                                        "revoke spend: %v", err)
                                break
                        }

                        if ok {
                                brarLog.Debugf("HTLC spend was our own " +
                                        "revocation spend")
                                break
                        }

                        brarLog.Infof("Spend on second-level "+
                                "%s(%v) for ChannelPoint(%v) "+
                                "transitions to second-level output",
                                breachedOutput.witnessType,
                                breachedOutput.outpoint, breachInfo.chanPoint)

                        // In this case we'll morph our initial revoke
                        // spend to instead point to the second level
                        // output, and update the sign descriptor in the
                        // process.
                        convertToSecondLevelRevoke(
                                breachedOutput, breachInfo, s.detail,
                        )

                        continue
                }

                // Now that we have determined the spend is done by us, we
                // count the total and revoked funds swept depending on the
                // input type.
                switch breachedOutput.witnessType {
                // If the output being revoked is the remote commitment output
                // or an offered HTLC output, its amount contributes to the
                // value of funds being revoked from the counter party.
                case input.CommitmentRevoke, input.TaprootCommitmentRevoke,
                        input.HtlcSecondLevelRevoke,
                        input.TaprootHtlcSecondLevelRevoke,
                        input.TaprootHtlcOfferedRevoke, input.HtlcOfferedRevoke:

                        revokedFunds += breachedOutput.Amount()
                }

                totalFunds += breachedOutput.Amount()
                brarLog.Infof("Spend on %s(%v) for ChannelPoint(%v) "+
                        "transitions output to terminal state, "+
                        "removing input from justice transaction",
                        breachedOutput.witnessType,
                        breachedOutput.outpoint, breachInfo.chanPoint)

                doneOutputs[s.index] = struct{}{}
        }

        // Filter the inputs for which we can no longer proceed.
        var nextIndex int
        for i := range inputs {
                if _, ok := doneOutputs[i]; ok {
                        continue
                }

                inputs[nextIndex] = inputs[i]
                nextIndex++
        }

        // Update our remaining set of outputs before continuing with
        // another attempt at publication.
        breachInfo.breachedOutputs = inputs[:nextIndex]
        return totalFunds, revokedFunds
}

// exactRetribution is a goroutine which is executed once a contract breach has
// been detected by a breachObserver. This function is responsible for
// punishing a counterparty for violating the channel contract by sweeping ALL
// the lingering funds within the channel into the daemon's wallet.
//
// NOTE: This MUST be run as a goroutine.
//
//nolint:funlen
func (b *BreachArbitrator) exactRetribution(
        confChan *chainntnfs.ConfirmationEvent, breachInfo *retributionInfo) {

        defer b.wg.Done()

        // TODO(roasbeef): state needs to be checkpointed here
        select {
        case _, ok := <-confChan.Confirmed:
                // If the second value is !ok, then the channel has been closed
                // signifying a daemon shutdown, so we exit.
                if !ok {
                        return
                }

                // Otherwise, if this is a real confirmation notification, then
                // we fall through to complete our duty.
        case <-b.quit:
                return
        }

        brarLog.Debugf("Breach transaction %v has been confirmed, sweeping "+
                "revoked funds", breachInfo.commitHash)

        // We may have to wait for some of the HTLC outputs to be spent to the
        // second level before broadcasting the justice tx. We'll store the
        // SpendEvents between each attempt to not re-register unnecessarily.
        spendNtfns := make(map[wire.OutPoint]*chainntnfs.SpendEvent)

        // Compute both the total value of funds being swept and the
        // amount of funds that were revoked from the counter party.
        var totalFunds, revokedFunds btcutil.Amount

justiceTxBroadcast:
        // With the breach transaction confirmed, we now create the
        // justice tx which will claim ALL the funds within the
        // channel.
        justiceTxs, err := b.createJusticeTx(breachInfo.breachedOutputs)
        if err != nil {
                brarLog.Errorf("Unable to create justice tx: %v", err)
                return
        }
        finalTx := justiceTxs.spendAll

        brarLog.Debugf("Broadcasting justice tx: %v", newLogClosure(func() string {
                return spew.Sdump(finalTx)
        }))

        // We'll now attempt to broadcast the transaction which finalized the
        // channel's retribution against the cheating counter party.
        label := labels.MakeLabel(labels.LabelTypeJusticeTransaction, nil)
        err = b.cfg.PublishTransaction(finalTx, label)
        if err != nil {
                brarLog.Errorf("Unable to broadcast justice tx: %v", err)
        }

        // Regardless of publication succeeded or not, we now wait for any of
        // the inputs to be spent. If any input got spent by the remote, we
        // must recreate our justice transaction.
        var (
                spendChan = make(chan []spend, 1)
                errChan   = make(chan error, 1)
                wg        sync.WaitGroup
        )

        wg.Add(1)
        go func() {
                defer wg.Done()

                spends, err := b.waitForSpendEvent(breachInfo, spendNtfns)
                if err != nil {
                        errChan <- err
                        return
                }
                spendChan <- spends
        }()

        // We'll also register for block notifications, such that in case our
        // justice tx doesn't confirm within a reasonable timeframe, we can
        // start to more aggressively sweep the time sensitive outputs.
        newBlockChan, err := b.cfg.Notifier.RegisterBlockEpochNtfn(nil)
        if err != nil {
                brarLog.Errorf("Unable to register for block notifications: %v",
                        err)
                return
        }
        defer newBlockChan.Cancel()

Loop:
        for {
                select {
                case spends := <-spendChan:
                        // Update the breach info with the new spends.
                        t, r := updateBreachInfo(breachInfo, spends)
                        totalFunds += t
                        revokedFunds += r

                        brarLog.Infof("%v spends from breach tx for "+
                                "ChannelPoint(%v) has been detected, %v "+
                                "revoked funds (%v total) have been claimed",
                                len(spends), breachInfo.chanPoint,
                                revokedFunds, totalFunds)

                        if len(breachInfo.breachedOutputs) == 0 {
                                brarLog.Infof("Justice for ChannelPoint(%v) "+
                                        "has been served, %v revoked funds "+
                                        "(%v total) have been claimed. No "+
                                        "more outputs to sweep, marking fully "+
                                        "resolved", breachInfo.chanPoint,
                                        revokedFunds, totalFunds)

                                err = b.cleanupBreach(&breachInfo.chanPoint)
                                if err != nil {
                                        brarLog.Errorf("Failed to cleanup "+
                                                "breached ChannelPoint(%v): %v",
                                                breachInfo.chanPoint, err)
                                }

                                // TODO(roasbeef): add peer to blacklist?

                                // TODO(roasbeef): close other active channels
                                // with offending peer
                                break Loop
                        }

                        brarLog.Infof("Attempting another justice tx "+
                                "with %d inputs",
                                len(breachInfo.breachedOutputs))

                        wg.Wait()
                        goto justiceTxBroadcast

                // On every new block, we check whether we should republish the
                // transactions.
                case epoch, ok := <-newBlockChan.Epochs:
                        if !ok {
                                return
                        }

                        // If less than four blocks have passed since the
                        // breach confirmed, we'll continue waiting. It was
                        // published with a 2-block fee estimate, so it's not
                        // unexpected that four blocks without confirmation can
                        // pass.
                        splitHeight := breachInfo.breachHeight +
                                blocksPassedSplitPublish
                        if uint32(epoch.Height) < splitHeight {
                                continue Loop
                        }

                        brarLog.Warnf("Block height %v arrived without "+
                                "justice tx confirming (breached at "+
                                "height %v), splitting justice tx.",
                                epoch.Height, breachInfo.breachHeight)

                        // Otherwise we'll attempt to publish the two separate
                        // justice transactions that sweeps the commitment
                        // outputs and the HTLC outputs separately. This is to
                        // mitigate the case where our "spend all" justice TX
                        // doesn't propagate because the HTLC outputs have been
                        // pinned by low fee HTLC txs.
                        label := labels.MakeLabel(
                                labels.LabelTypeJusticeTransaction, nil,
                        )
                        if justiceTxs.spendCommitOuts != nil {
                                tx := justiceTxs.spendCommitOuts

                                brarLog.Debugf("Broadcasting justice tx "+
                                        "spending commitment outs: %v",
                                        newLogClosure(func() string {
                                                return spew.Sdump(tx)
                                        }))

                                err = b.cfg.PublishTransaction(tx, label)
                                if err != nil {
                                        brarLog.Warnf("Unable to broadcast "+
                                                "commit out spending justice "+
                                                "tx: %v", err)
                                }
                        }

                        if justiceTxs.spendHTLCs != nil {
                                tx := justiceTxs.spendHTLCs

                                brarLog.Debugf("Broadcasting justice tx "+
                                        "spending HTLC outs: %v",
                                        newLogClosure(func() string {
                                                return spew.Sdump(tx)
                                        }))

                                err = b.cfg.PublishTransaction(tx, label)
                                if err != nil {
                                        brarLog.Warnf("Unable to broadcast "+
                                                "HTLC out spending justice "+
                                                "tx: %v", err)
                                }
                        }

                        for _, tx := range justiceTxs.spendSecondLevelHTLCs {
                                tx := tx

                                brarLog.Debugf("Broadcasting justice tx "+
                                        "spending second-level HTLC output: %v",
                                        newLogClosure(func() string {
                                                return spew.Sdump(tx)
                                        }))

                                err = b.cfg.PublishTransaction(tx, label)
                                if err != nil {
                                        brarLog.Warnf("Unable to broadcast "+
                                                "second-level HTLC out "+
                                                "spending justice tx: %v", err)
                                }
                        }

                case err := <-errChan:
                        if err != errBrarShuttingDown {
                                brarLog.Errorf("error waiting for "+
                                        "spend event: %v", err)
                        }
                        break Loop

                case <-b.quit:
                        break Loop
                }
        }

        // Wait for our go routine to exit.
        wg.Wait()
}

// cleanupBreach marks the given channel point as fully resolved and removes the
// retribution for that the channel from the retribution store.
func (b *BreachArbitrator) cleanupBreach(chanPoint *wire.OutPoint) error {
        // With the channel closed, mark it in the database as such.
        err := b.cfg.DB.MarkChanFullyClosed(chanPoint)
        if err != nil {
                return fmt.Errorf("unable to mark chan as closed: %w", err)
        }

        // Justice has been carried out; we can safely delete the retribution
        // info from the database.
        err = b.cfg.Store.Remove(chanPoint)
        if err != nil {
                return fmt.Errorf("unable to remove retribution from db: %w",
                        err)
        }

        // This is after the Remove call so that the chan passed in via
        // SubscribeBreachComplete is always notified, no matter when it is
        // called. Otherwise, if notifyBreachComplete was before Remove, a
        // very rare edge case could occur in which SubscribeBreachComplete
        // is called after notifyBreachComplete and before Remove, meaning the
        // caller would never be notified.
        b.notifyBreachComplete(chanPoint)

        return nil
}

// handleBreachHandoff handles a new breach event, by writing it to disk, then
// notifies the BreachArbitrator contract observer goroutine that a channel's
// contract has been breached by the prior counterparty. Once notified the
// BreachArbitrator will attempt to sweep ALL funds within the channel using the
// information provided within the BreachRetribution generated due to the
// breach of channel contract. The funds will be swept only after the breaching
// transaction receives a necessary number of confirmations.
//
// NOTE: This MUST be run as a goroutine.
func (b *BreachArbitrator) handleBreachHandoff(
        breachEvent *ContractBreachEvent) {

        defer b.wg.Done()

        chanPoint := breachEvent.ChanPoint
        brarLog.Debugf("Handling breach handoff for ChannelPoint(%v)",
                chanPoint)

        // A read from this channel indicates that a channel breach has been
        // detected! So we notify the main coordination goroutine with the
        // information needed to bring the counterparty to justice.
        breachInfo := breachEvent.BreachRetribution
        brarLog.Warnf("REVOKED STATE #%v FOR ChannelPoint(%v) "+
                "broadcast, REMOTE PEER IS DOING SOMETHING "+
                "SKETCHY!!!", breachInfo.RevokedStateNum,
                chanPoint)

        // Immediately notify the HTLC switch that this link has been
        // breached in order to ensure any incoming or outgoing
        // multi-hop HTLCs aren't sent over this link, nor any other
        // links associated with this peer.
        b.cfg.CloseLink(&chanPoint, CloseBreach)

        // TODO(roasbeef): need to handle case of remote broadcast
        // mid-local initiated state-transition, possible
        // false-positive?

        // Acquire the mutex to ensure consistency between the call to
        // IsBreached and Add below.
        b.Lock()

        // We first check if this breach info is already added to the
        // retribution store.
        breached, err := b.cfg.Store.IsBreached(&chanPoint)
        if err != nil {
                b.Unlock()
                brarLog.Errorf("Unable to check breach info in DB: %v", err)

                // Notify about the failed lookup and return.
                breachEvent.ProcessACK(err)
                return
        }

        // If this channel is already marked as breached in the retribution
        // store, we already have handled the handoff for this breach. In this
        // case we can safely ACK the handoff, and return.
        if breached {
                b.Unlock()
                breachEvent.ProcessACK(nil)
                return
        }

        // Using the breach information provided by the wallet and the
        // channel snapshot, construct the retribution information that
        // will be persisted to disk.
        retInfo := newRetributionInfo(&chanPoint, breachInfo)

        // Persist the pending retribution state to disk.
        err = b.cfg.Store.Add(retInfo)
        b.Unlock()
        if err != nil {
                brarLog.Errorf("Unable to persist retribution "+
                        "info to db: %v", err)
        }

        // Now that the breach has been persisted, try to send an
        // acknowledgment back to the close observer with the error. If
        // the ack is successful, the close observer will mark the
        // channel as pending-closed in the channeldb.
        breachEvent.ProcessACK(err)

        // Bail if we failed to persist retribution info.
        if err != nil {
                return
        }

        // Now that a new channel contract has been added to the retribution
        // store, we first register for a notification to be dispatched once
        // the breach transaction (the revoked commitment transaction) has been
        // confirmed in the chain to ensure we're not dealing with a moving
        // target.
        breachTXID := &retInfo.commitHash
        breachScript := retInfo.breachedOutputs[0].signDesc.Output.PkScript
        cfChan, err := b.cfg.Notifier.RegisterConfirmationsNtfn(
                breachTXID, breachScript, 1, retInfo.breachHeight,
        )
        if err != nil {
                brarLog.Errorf("Unable to register for conf updates for "+
                        "txid: %v, err: %v", breachTXID, err)
                return
        }

        brarLog.Warnf("A channel has been breached with txid: %v. Waiting "+
                "for confirmation, then justice will be served!", breachTXID)

        // With the retribution state persisted, channel close persisted, and
        // notification registered, we launch a new goroutine which will
        // finalize the channel retribution after the breach transaction has
        // been confirmed.
        b.wg.Add(1)
        go b.exactRetribution(cfChan, retInfo)
}

// breachedOutput contains all the information needed to sweep a breached
// output. A breached output is an output that we are now entitled to due to a
// revoked commitment transaction being broadcast.
type breachedOutput struct {
        amt         btcutil.Amount
        outpoint    wire.OutPoint
        witnessType input.StandardWitnessType
        signDesc    input.SignDescriptor
        confHeight  uint32

        secondLevelWitnessScript []byte
        secondLevelTapTweak      [32]byte

        witnessFunc input.WitnessGenerator
}

// makeBreachedOutput assembles a new breachedOutput that can be used by the
// breach arbiter to construct a justice or sweep transaction.
func makeBreachedOutput(outpoint *wire.OutPoint,
        witnessType input.StandardWitnessType,
        secondLevelScript []byte,
        signDescriptor *input.SignDescriptor,
        confHeight uint32) breachedOutput {

        amount := signDescriptor.Output.Value

        return breachedOutput{
                amt:                      btcutil.Amount(amount),
                outpoint:                 *outpoint,
                secondLevelWitnessScript: secondLevelScript,
                witnessType:              witnessType,
                signDesc:                 *signDescriptor,
                confHeight:               confHeight,
        }
}

// Amount returns the number of satoshis contained in the breached output.
func (bo *breachedOutput) Amount() btcutil.Amount {
        return bo.amt
}

// OutPoint returns the breached output's identifier that is to be included as a
// transaction input.
func (bo *breachedOutput) OutPoint() wire.OutPoint {
        return bo.outpoint
}

// RequiredTxOut returns a non-nil TxOut if input commits to a certain
// transaction output. This is used in the SINGLE|ANYONECANPAY case to make
// sure any presigned input is still valid by including the output.
func (bo *breachedOutput) RequiredTxOut() *wire.TxOut {
        return nil
}

// RequiredLockTime returns whether this input commits to a tx locktime that
// must be used in the transaction including it.
func (bo *breachedOutput) RequiredLockTime() (uint32, bool) {
        return 0, false
}

// WitnessType returns the type of witness that must be generated to spend the
// breached output.
func (bo *breachedOutput) WitnessType() input.WitnessType {
        return bo.witnessType
}

// SignDesc returns the breached output's SignDescriptor, which is used during
// signing to compute the witness.
func (bo *breachedOutput) SignDesc() *input.SignDescriptor {
        return &bo.signDesc
}

// CraftInputScript computes a valid witness that allows us to spend from the
// breached output. It does so by first generating and memoizing the witness
// generation function, which parameterized primarily by the witness type and
// sign descriptor. The method then returns the witness computed by invoking
// this function on the first and subsequent calls.
func (bo *breachedOutput) CraftInputScript(signer input.Signer, txn *wire.MsgTx,
        hashCache *txscript.TxSigHashes,
        prevOutputFetcher txscript.PrevOutputFetcher,
        txinIdx int) (*input.Script, error) {

        // First, we ensure that the witness generation function has been
        // initialized for this breached output.
        signDesc := bo.SignDesc()
        signDesc.PrevOutputFetcher = prevOutputFetcher
        bo.witnessFunc = bo.witnessType.WitnessGenerator(signer, signDesc)

        // Now that we have ensured that the witness generation function has
        // been initialized, we can proceed to execute it and generate the
        // witness for this particular breached output.
        return bo.witnessFunc(txn, hashCache, txinIdx)
}

// BlocksToMaturity returns the relative timelock, as a number of blocks, that
// must be built on top of the confirmation height before the output can be
// spent.
func (bo *breachedOutput) BlocksToMaturity() uint32 {
        // If the output is a to_remote output we can claim, and it's of the
        // confirmed type (or is a taproot channel that always has the CSV 1),
        // we must wait one block before claiming it.
        switch bo.witnessType {
        case input.CommitmentToRemoteConfirmed, input.TaprootRemoteCommitSpend:
                return 1
        }

        // All other breached outputs have no CSV delay.
        return 0
}

// HeightHint returns the minimum height at which a confirmed spending tx can
// occur.
func (bo *breachedOutput) HeightHint() uint32 {
        return bo.confHeight
}

// UnconfParent returns information about a possibly unconfirmed parent tx.
func (bo *breachedOutput) UnconfParent() *input.TxInfo {
        return nil
}

// Add compile-time constraint ensuring breachedOutput implements the Input
// interface.
var _ input.Input = (*breachedOutput)(nil)

// retributionInfo encapsulates all the data needed to sweep all the contested
// funds within a channel whose contract has been breached by the prior
// counterparty. This struct is used to create the justice transaction which
// spends all outputs of the commitment transaction into an output controlled
// by the wallet.
type retributionInfo struct {
        commitHash   chainhash.Hash
        chanPoint    wire.OutPoint
        chainHash    chainhash.Hash
        breachHeight uint32

        breachedOutputs []breachedOutput
}

// newRetributionInfo constructs a retributionInfo containing all the
// information required by the breach arbiter to recover funds from breached
// channels.  The information is primarily populated using the BreachRetribution
// delivered by the wallet when it detects a channel breach.
func newRetributionInfo(chanPoint *wire.OutPoint,
        breachInfo *lnwallet.BreachRetribution) *retributionInfo {

        // Determine the number of second layer HTLCs we will attempt to sweep.
        nHtlcs := len(breachInfo.HtlcRetributions)

        // Initialize a slice to hold the outputs we will attempt to sweep. The
        // maximum capacity of the slice is set to 2+nHtlcs to handle the case
        // where the local, remote, and all HTLCs are not dust outputs.  All
        // HTLC outputs provided by the wallet are guaranteed to be non-dust,
        // though the commitment outputs are conditionally added depending on
        // the nil-ness of their sign descriptors.
        breachedOutputs := make([]breachedOutput, 0, nHtlcs+2)

        isTaproot := func() bool {
                if breachInfo.LocalOutputSignDesc != nil {
                        return txscript.IsPayToTaproot(
                                breachInfo.LocalOutputSignDesc.Output.PkScript,
                        )
                }

                return txscript.IsPayToTaproot(
                        breachInfo.RemoteOutputSignDesc.Output.PkScript,
                )
        }()

        // First, record the breach information for the local channel point if
        // it is not considered dust, which is signaled by a non-nil sign
        // descriptor. Here we use CommitmentNoDelay (or
        // CommitmentNoDelayTweakless for newer commitments) since this output
        // belongs to us and has no time-based constraints on spending. For
        // taproot channels, this is a normal spend from our output on the
        // commitment of the remote party.
        if breachInfo.LocalOutputSignDesc != nil {
                var witnessType input.StandardWitnessType
                switch {
                case isTaproot:
                        witnessType = input.TaprootRemoteCommitSpend

                case !isTaproot &&
                        breachInfo.LocalOutputSignDesc.SingleTweak == nil:

                        witnessType = input.CommitSpendNoDelayTweakless

                case !isTaproot:
                        witnessType = input.CommitmentNoDelay
                }

                // If the local delay is non-zero, it means this output is of
                // the confirmed to_remote type.
                if !isTaproot && breachInfo.LocalDelay != 0 {
                        witnessType = input.CommitmentToRemoteConfirmed
                }

                localOutput := makeBreachedOutput(
                        &breachInfo.LocalOutpoint,
                        witnessType,
                        // No second level script as this is a commitment
                        // output.
                        nil,
                        breachInfo.LocalOutputSignDesc,
                        breachInfo.BreachHeight,
                )

                breachedOutputs = append(breachedOutputs, localOutput)
        }

        // Second, record the same information regarding the remote outpoint,
        // again if it is not dust, which belongs to the party who tried to
        // steal our money! Here we set witnessType of the breachedOutput to
        // CommitmentRevoke, since we will be using a revoke key, withdrawing
        // the funds from the commitment transaction immediately.
        if breachInfo.RemoteOutputSignDesc != nil {
                var witType input.StandardWitnessType
                if isTaproot {
                        witType = input.TaprootCommitmentRevoke
                } else {
                        witType = input.CommitmentRevoke
                }

                remoteOutput := makeBreachedOutput(
                        &breachInfo.RemoteOutpoint,
                        witType,
                        // No second level script as this is a commitment
                        // output.
                        nil,
                        breachInfo.RemoteOutputSignDesc,
                        breachInfo.BreachHeight,
                )

                breachedOutputs = append(breachedOutputs, remoteOutput)
        }

        // Lastly, for each of the breached HTLC outputs, record each as a
        // breached output with the appropriate witness type based on its
        // directionality. All HTLC outputs provided by the wallet are assumed
        // to be non-dust.
        for i, breachedHtlc := range breachInfo.HtlcRetributions {
                // Using the breachedHtlc's incoming flag, determine the
                // appropriate witness type that needs to be generated in order
                // to sweep the HTLC output.
                var htlcWitnessType input.StandardWitnessType
                switch {
                case isTaproot && breachedHtlc.IsIncoming:
                        htlcWitnessType = input.TaprootHtlcAcceptedRevoke

                case isTaproot && !breachedHtlc.IsIncoming:
                        htlcWitnessType = input.TaprootHtlcOfferedRevoke

                case !isTaproot && breachedHtlc.IsIncoming:
                        htlcWitnessType = input.HtlcAcceptedRevoke

                case !isTaproot && !breachedHtlc.IsIncoming:
                        htlcWitnessType = input.HtlcOfferedRevoke
                }

                htlcOutput := makeBreachedOutput(
                        &breachInfo.HtlcRetributions[i].OutPoint,
                        htlcWitnessType,
                        breachInfo.HtlcRetributions[i].SecondLevelWitnessScript,
                        &breachInfo.HtlcRetributions[i].SignDesc,
                        breachInfo.BreachHeight,
                )

                // For taproot outputs, we also need to hold onto the second
                // level tap tweak as well.
                //nolint:lll
                htlcOutput.secondLevelTapTweak = breachedHtlc.SecondLevelTapTweak

                breachedOutputs = append(breachedOutputs, htlcOutput)
        }

        return &retributionInfo{
                commitHash:      breachInfo.BreachTxHash,
                chainHash:       breachInfo.ChainHash,
                chanPoint:       *chanPoint,
                breachedOutputs: breachedOutputs,
                breachHeight:    breachInfo.BreachHeight,
        }
}

// justiceTxVariants is a struct that holds transactions which exacts "justice"
// by sweeping ALL the funds within the channel which we are now entitled to
// due to a breach of the channel's contract by the counterparty. There are
// four variants of justice transactions:
//
// 1. The "normal" justice tx that spends all breached outputs.
// 2. A tx that spends only the breached to_local output and to_remote output
// (can be nil if none of these exist).
// 3. A tx that spends all the breached commitment level HTLC outputs (can be
// nil if none of these exist or if all have been taken to the second level).
// 4. A set of txs that spend all the second-level HTLC outputs (can be empty if
// no HTLC second-level txs have been confirmed).
//
// The reason we create these three variants, is that in certain cases (like
// with the anchor output HTLC malleability), the channel counter party can pin
// the HTLC outputs with low fee children, hindering our normal justice tx that
// attempts to spend these outputs from propagating. In this case we want to
// spend the to_local output and commitment level HTLC outputs separately,
// before the CSV locks expire.
type justiceTxVariants struct {
        spendAll              *wire.MsgTx
        spendCommitOuts       *wire.MsgTx
        spendHTLCs            *wire.MsgTx
        spendSecondLevelHTLCs []*wire.MsgTx
}

// createJusticeTx creates transactions which exacts "justice" by sweeping ALL
// the funds within the channel which we are now entitled to due to a breach of
// the channel's contract by the counterparty. This function returns a *fully*
// signed transaction with the witness for each input fully in place.
func (b *BreachArbitrator) createJusticeTx(
        breachedOutputs []breachedOutput) (*justiceTxVariants, error) {

        var (
                allInputs         []input.Input
                commitInputs      []input.Input
                htlcInputs        []input.Input
                secondLevelInputs []input.Input
        )

        for i := range breachedOutputs {
                // Grab locally scoped reference to breached output.
                inp := &breachedOutputs[i]
                allInputs = append(allInputs, inp)

                // Check if the input is from a commitment output, a commitment
                // level HTLC output or a second level HTLC output.
                switch inp.WitnessType() {
                case input.HtlcAcceptedRevoke, input.HtlcOfferedRevoke,
                        input.TaprootHtlcAcceptedRevoke,
                        input.TaprootHtlcOfferedRevoke:

                        htlcInputs = append(htlcInputs, inp)

                case input.HtlcSecondLevelRevoke,
                        input.TaprootHtlcSecondLevelRevoke:

                        secondLevelInputs = append(secondLevelInputs, inp)

                default:
                        commitInputs = append(commitInputs, inp)
                }
        }

        var (
                txs = &justiceTxVariants{}
                err error
        )

        // For each group of inputs, create a tx that spends them.
        txs.spendAll, err = b.createSweepTx(allInputs...)
        if err != nil {
                return nil, err
        }

        txs.spendCommitOuts, err = b.createSweepTx(commitInputs...)
        if err != nil {
                brarLog.Errorf("could not create sweep tx for commitment "+
                        "outputs: %v", err)
        }

        txs.spendHTLCs, err = b.createSweepTx(htlcInputs...)
        if err != nil {
                brarLog.Errorf("could not create sweep tx for HTLC outputs: %v",
                        err)
        }

        secondLevelSweeps := make([]*wire.MsgTx, 0, len(secondLevelInputs))
        for _, input := range secondLevelInputs {
                sweepTx, err := b.createSweepTx(input)
                if err != nil {
                        brarLog.Errorf("could not create sweep tx for "+
                                "second-level HTLC output: %v", err)

                        continue
                }

                secondLevelSweeps = append(secondLevelSweeps, sweepTx)
        }
        txs.spendSecondLevelHTLCs = secondLevelSweeps

        return txs, nil
}

// createSweepTx creates a tx that sweeps the passed inputs back to our wallet.
func (b *BreachArbitrator) createSweepTx(inputs ...input.Input) (*wire.MsgTx,
        error) {

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

        // We will assemble the breached outputs into a slice of spendable
        // outputs, while simultaneously computing the estimated weight of the
        // transaction.
        var (
                spendableOutputs []input.Input
                weightEstimate   input.TxWeightEstimator
        )

        // Allocate enough space to potentially hold each of the breached
        // outputs in the retribution info.
        spendableOutputs = make([]input.Input, 0, len(inputs))

        // The justice transaction we construct will be a segwit transaction
        // that pays to a p2tr output. Components such as the version,
        // nLockTime, and output are already included in the TxWeightEstimator.
        weightEstimate.AddP2TROutput()

        // Next, we iterate over the breached outputs contained in the
        // retribution info.  For each, we switch over the witness type such
        // that we contribute the appropriate weight for each input and
        // witness, finally adding to our list of spendable outputs.
        for i := range inputs {
                // Grab locally scoped reference to breached output.
                inp := inputs[i]

                // First, determine the appropriate estimated witness weight
                // for the give witness type of this breached output. If the
                // witness weight cannot be estimated, we will omit it from the
                // transaction.
                witnessWeight, _, err := inp.WitnessType().SizeUpperBound()
                if err != nil {
                        brarLog.Warnf("could not determine witness weight "+
                                "for breached output in retribution info: %v",
                                err)
                        continue
                }
                weightEstimate.AddWitnessInput(witnessWeight)

                // Finally, append this input to our list of spendable outputs.
                spendableOutputs = append(spendableOutputs, inp)
        }

        txWeight := weightEstimate.Weight()

        return b.sweepSpendableOutputsTxn(txWeight, spendableOutputs...)
}

// sweepSpendableOutputsTxn creates a signed transaction from a sequence of
// spendable outputs by sweeping the funds into a single p2wkh output.
func (b *BreachArbitrator) sweepSpendableOutputsTxn(txWeight lntypes.WeightUnit,
        inputs ...input.Input) (*wire.MsgTx, error) {

        // First, we obtain a new public key script from the wallet which we'll
        // sweep the funds to.
        // TODO(roasbeef): possibly create many outputs to minimize change in
        // the future?
        pkScript, err := b.cfg.GenSweepScript()
        if err != nil {
                return nil, err
        }

        // Compute the total amount contained in the inputs.
        var totalAmt btcutil.Amount
        for _, inp := range inputs {
                totalAmt += btcutil.Amount(inp.SignDesc().Output.Value)
        }

        // We'll actually attempt to target inclusion within the next two
        // blocks as we'd like to sweep these funds back into our wallet ASAP.
        feePerKw, err := b.cfg.Estimator.EstimateFeePerKW(justiceTxConfTarget)
        if err != nil {
                return nil, err
        }
        txFee := feePerKw.FeeForWeight(txWeight)

        // TODO(roasbeef): already start to siphon their funds into fees
        sweepAmt := int64(totalAmt - txFee)

        // With the fee calculated, we can now create the transaction using the
        // information gathered above and the provided retribution information.
        txn := wire.NewMsgTx(2)

        // We begin by adding the output to which our funds will be deposited.
        txn.AddTxOut(&wire.TxOut{
                PkScript: pkScript,
                Value:    sweepAmt,
        })

        // Next, we add all of the spendable outputs as inputs to the
        // transaction.
        for _, inp := range inputs {
                txn.AddTxIn(&wire.TxIn{
                        PreviousOutPoint: inp.OutPoint(),
                        Sequence:         inp.BlocksToMaturity(),
                })
        }

        // Before signing the transaction, check to ensure that it meets some
        // basic validity requirements.
        btx := btcutil.NewTx(txn)
        if err := blockchain.CheckTransactionSanity(btx); err != nil {
                return nil, err
        }

        // Create a sighash cache to improve the performance of hashing and
        // signing SigHashAll inputs.
        prevOutputFetcher, err := input.MultiPrevOutFetcher(inputs)
        if err != nil {
                return nil, err
        }
        hashCache := txscript.NewTxSigHashes(txn, prevOutputFetcher)

        // Create a closure that encapsulates the process of initializing a
        // particular output's witness generation function, computing the
        // witness, and attaching it to the transaction. This function accepts
        // an integer index representing the intended txin index, and the
        // breached output from which it will spend.
        addWitness := func(idx int, so input.Input) error {
                // First, we construct a valid witness for this outpoint and
                // transaction using the SpendableOutput's witness generation
                // function.
                inputScript, err := so.CraftInputScript(
                        b.cfg.Signer, txn, hashCache, prevOutputFetcher, idx,
                )
                if err != nil {
                        return err
                }

                // Then, we add the witness to the transaction at the
                // appropriate txin index.
                txn.TxIn[idx].Witness = inputScript.Witness

                return nil
        }

        // Finally, generate a witness for each output and attach it to the
        // transaction.
        for i, inp := range inputs {
                if err := addWitness(i, inp); err != nil {
                        return nil, err
                }
        }

        return txn, nil
}

// RetributionStore handles persistence of retribution states to disk and is
// backed by a boltdb bucket. The primary responsibility of the retribution
// store is to ensure that we can recover from a restart in the middle of a
// breached contract retribution.
type RetributionStore struct {
        db kvdb.Backend
}

// NewRetributionStore creates a new instance of a RetributionStore.
func NewRetributionStore(db kvdb.Backend) *RetributionStore {
        return &RetributionStore{
                db: db,
        }
}

// taprootBriefcaseFromRetInfo creates a taprootBriefcase from a retribution
// info struct. This stores all the tap tweak informatoin we need to inrder to
// be able to hadnel breaches after a restart.
func taprootBriefcaseFromRetInfo(retInfo *retributionInfo) *taprootBriefcase {
        tapCase := newTaprootBriefcase()

        for _, bo := range retInfo.breachedOutputs {
                switch bo.WitnessType() {
                // For spending from our commitment output on the remote
                // commitment, we'll need to stash the control block.
                case input.TaprootRemoteCommitSpend:
                        //nolint:lll
                        tapCase.CtrlBlocks.CommitSweepCtrlBlock = bo.signDesc.ControlBlock

                // To spend the revoked output again, we'll store the same
                // control block value as above, but in a different place.
                case input.TaprootCommitmentRevoke:
                        //nolint:lll
                        tapCase.CtrlBlocks.RevokeSweepCtrlBlock = bo.signDesc.ControlBlock

                // For spending the HTLC outputs, we'll store the first and
                // second level tweak values.
                case input.TaprootHtlcAcceptedRevoke:
                        fallthrough
                case input.TaprootHtlcOfferedRevoke:
                        resID := newResolverID(bo.OutPoint())

                        var firstLevelTweak [32]byte
                        copy(firstLevelTweak[:], bo.signDesc.TapTweak)
                        secondLevelTweak := bo.secondLevelTapTweak

                        //nolint:lll
                        tapCase.TapTweaks.BreachedHtlcTweaks[resID] = firstLevelTweak

                        //nolint:lll
                        tapCase.TapTweaks.BreachedSecondLevelHltcTweaks[resID] = secondLevelTweak
                }
        }

        return tapCase
}

// applyTaprootRetInfo attaches the taproot specific inforamtion in the tapCase
// to the passed retInfo struct.
func applyTaprootRetInfo(tapCase *taprootBriefcase,
        retInfo *retributionInfo) error {

        for i := range retInfo.breachedOutputs {
                bo := retInfo.breachedOutputs[i]

                switch bo.WitnessType() {
                // For spending from our commitment output on the remote
                // commitment, we'll apply the control block.
                case input.TaprootRemoteCommitSpend:
                        //nolint:lll
                        bo.signDesc.ControlBlock = tapCase.CtrlBlocks.CommitSweepCtrlBlock

                // To spend the revoked output again, we'll apply the same
                // control block value as above, but to a different place.
                case input.TaprootCommitmentRevoke:
                        //nolint:lll
                        bo.signDesc.ControlBlock = tapCase.CtrlBlocks.RevokeSweepCtrlBlock

                // For spending the HTLC outputs, we'll apply the first and
                // second level tweak values.
                case input.TaprootHtlcAcceptedRevoke:
                        fallthrough
                case input.TaprootHtlcOfferedRevoke:
                        resID := newResolverID(bo.OutPoint())

                        tap1, ok := tapCase.TapTweaks.BreachedHtlcTweaks[resID]
                        if !ok {
                                return fmt.Errorf("unable to find taproot "+
                                        "tweak for: %v", bo.OutPoint())
                        }
                        bo.signDesc.TapTweak = tap1[:]

                        //nolint:lll
                        tap2, ok := tapCase.TapTweaks.BreachedSecondLevelHltcTweaks[resID]
                        if !ok {
                                return fmt.Errorf("unable to find taproot "+
                                        "tweak for: %v", bo.OutPoint())
                        }
                        bo.secondLevelTapTweak = tap2
                }

                retInfo.breachedOutputs[i] = bo
        }

        return nil
}

// Add adds a retribution state to the RetributionStore, which is then persisted
// to disk.
func (rs *RetributionStore) Add(ret *retributionInfo) error {
        return kvdb.Update(rs.db, func(tx kvdb.RwTx) error {
                // If this is our first contract breach, the retributionBucket
                // won't exist, in which case, we just create a new bucket.
                retBucket, err := tx.CreateTopLevelBucket(retributionBucket)
                if err != nil {
                        return err
                }
                tapRetBucket, err := tx.CreateTopLevelBucket(
                        taprootRetributionBucket,
                )
                if err != nil {
                        return err
                }

                var outBuf bytes.Buffer
                if err := writeOutpoint(&outBuf, &ret.chanPoint); err != nil {
                        return err
                }

                var retBuf bytes.Buffer
                if err := ret.Encode(&retBuf); err != nil {
                        return err
                }

                err = retBucket.Put(outBuf.Bytes(), retBuf.Bytes())
                if err != nil {
                        return err
                }

                // If this isn't a taproot channel, then we can exit early here
                // as there's no extra data to write.
                switch {
                case len(ret.breachedOutputs) == 0:
                        return nil

                case !txscript.IsPayToTaproot(
                        ret.breachedOutputs[0].signDesc.Output.PkScript,
                ):
                        return nil
                }

                // We'll also map the ret info into the taproot storage
                // structure we need for taproot channels.
                var b bytes.Buffer
                tapRetcase := taprootBriefcaseFromRetInfo(ret)
                if err := tapRetcase.Encode(&b); err != nil {
                        return err
                }

                return tapRetBucket.Put(outBuf.Bytes(), b.Bytes())
        }, func() {})
}

// IsBreached queries the retribution store to discern if this channel was
// previously breached. This is used when connecting to a peer to determine if
// it is safe to add a link to the htlcswitch, as we should never add a channel
// that has already been breached.
func (rs *RetributionStore) IsBreached(chanPoint *wire.OutPoint) (bool, error) {
        var found bool
        err := kvdb.View(rs.db, func(tx kvdb.RTx) error {
                retBucket := tx.ReadBucket(retributionBucket)
                if retBucket == nil {
                        return nil
                }

                var chanBuf bytes.Buffer
                if err := writeOutpoint(&chanBuf, chanPoint); err != nil {
                        return err
                }

                retInfo := retBucket.Get(chanBuf.Bytes())
                if retInfo != nil {
                        found = true
                }

                return nil
        }, func() {
                found = false
        })

        return found, err
}

// Remove removes a retribution state and finalized justice transaction by
// channel point  from the retribution store.
func (rs *RetributionStore) Remove(chanPoint *wire.OutPoint) error {
        return kvdb.Update(rs.db, func(tx kvdb.RwTx) error {
                retBucket := tx.ReadWriteBucket(retributionBucket)
                tapRetBucket, err := tx.CreateTopLevelBucket(
                        taprootRetributionBucket,
                )
                if err != nil {
                        return err
                }

                // We return an error if the bucket is not already created,
                // since normal operation of the breach arbiter should never
                // try to remove a finalized retribution state that is not
                // already stored in the db.
                if retBucket == nil {
                        return errors.New("unable to remove retribution " +
                                "because the retribution bucket doesn't exist")
                }

                // Serialize the channel point we are intending to remove.
                var chanBuf bytes.Buffer
                if err := writeOutpoint(&chanBuf, chanPoint); err != nil {
                        return err
                }
                chanBytes := chanBuf.Bytes()

                // Remove the persisted retribution info and finalized justice
                // transaction.
                if err := retBucket.Delete(chanBytes); err != nil {
                        return err
                }

                return tapRetBucket.Delete(chanBytes)
        }, func() {})
}

// ForAll iterates through all stored retributions and executes the passed
// callback function on each retribution.
func (rs *RetributionStore) ForAll(cb func(*retributionInfo) error,
        reset func()) error {

        return kvdb.View(rs.db, func(tx kvdb.RTx) error {
                // If the bucket does not exist, then there are no pending
                // retributions.
                retBucket := tx.ReadBucket(retributionBucket)
                if retBucket == nil {
                        return nil
                }
                tapRetBucket := tx.ReadBucket(
                        taprootRetributionBucket,
                )

                // Otherwise, we fetch each serialized retribution info,
                // deserialize it, and execute the passed in callback function
                // on it.
                return retBucket.ForEach(func(k, retBytes []byte) error {
                        ret := &retributionInfo{}
                        err := ret.Decode(bytes.NewBuffer(retBytes))
                        if err != nil {
                                return err
                        }

                        tapInfoBytes := tapRetBucket.Get(k)
                        if tapInfoBytes != nil {
                                var tapCase taprootBriefcase
                                err := tapCase.Decode(
                                        bytes.NewReader(tapInfoBytes),
                                )
                                if err != nil {
                                        return err
                                }

                                err = applyTaprootRetInfo(&tapCase, ret)
                                if err != nil {
                                        return err
                                }
                        }

                        return cb(ret)
                })
        }, reset)
}

// Encode serializes the retribution into the passed byte stream.
func (ret *retributionInfo) Encode(w io.Writer) error {
        var scratch [4]byte

        if _, err := w.Write(ret.commitHash[:]); err != nil {
                return err
        }

        if err := writeOutpoint(w, &ret.chanPoint); err != nil {
                return err
        }

        if _, err := w.Write(ret.chainHash[:]); err != nil {
                return err
        }

        binary.BigEndian.PutUint32(scratch[:], ret.breachHeight)
        if _, err := w.Write(scratch[:]); err != nil {
                return err
        }

        nOutputs := len(ret.breachedOutputs)
        if err := wire.WriteVarInt(w, 0, uint64(nOutputs)); err != nil {
                return err
        }

        for _, output := range ret.breachedOutputs {
                if err := output.Encode(w); err != nil {
                        return err
                }
        }

        return nil
}

// Decode deserializes a retribution from the passed byte stream.
func (ret *retributionInfo) Decode(r io.Reader) error {
        var scratch [32]byte

        if _, err := io.ReadFull(r, scratch[:]); err != nil {
                return err
        }
        hash, err := chainhash.NewHash(scratch[:])
        if err != nil {
                return err
        }
        ret.commitHash = *hash

        if err := readOutpoint(r, &ret.chanPoint); err != nil {
                return err
        }

        if _, err := io.ReadFull(r, scratch[:]); err != nil {
                return err
        }
        chainHash, err := chainhash.NewHash(scratch[:])
        if err != nil {
                return err
        }
        ret.chainHash = *chainHash

        if _, err := io.ReadFull(r, scratch[:4]); err != nil {
                return err
        }
        ret.breachHeight = binary.BigEndian.Uint32(scratch[:4])

        nOutputsU64, err := wire.ReadVarInt(r, 0)
        if err != nil {
                return err
        }
        nOutputs := int(nOutputsU64)

        ret.breachedOutputs = make([]breachedOutput, nOutputs)
        for i := range ret.breachedOutputs {
                if err := ret.breachedOutputs[i].Decode(r); err != nil {
                        return err
                }
        }

        return nil
}

// Encode serializes a breachedOutput into the passed byte stream.
func (bo *breachedOutput) Encode(w io.Writer) error {
        var scratch [8]byte

        binary.BigEndian.PutUint64(scratch[:8], uint64(bo.amt))
        if _, err := w.Write(scratch[:8]); err != nil {
                return err
        }

        if err := writeOutpoint(w, &bo.outpoint); err != nil {
                return err
        }

        err := input.WriteSignDescriptor(w, &bo.signDesc)
        if err != nil {
                return err
        }

        err = wire.WriteVarBytes(w, 0, bo.secondLevelWitnessScript)
        if err != nil {
                return err
        }

        binary.BigEndian.PutUint16(scratch[:2], uint16(bo.witnessType))
        if _, err := w.Write(scratch[:2]); err != nil {
                return err
        }

        return nil
}

// Decode deserializes a breachedOutput from the passed byte stream.
func (bo *breachedOutput) Decode(r io.Reader) error {
        var scratch [8]byte

        if _, err := io.ReadFull(r, scratch[:8]); err != nil {
                return err
        }
        bo.amt = btcutil.Amount(binary.BigEndian.Uint64(scratch[:8]))

        if err := readOutpoint(r, &bo.outpoint); err != nil {
                return err
        }

        if err := input.ReadSignDescriptor(r, &bo.signDesc); err != nil {
                return err
        }

        wScript, err := wire.ReadVarBytes(r, 0, 1000, "witness script")
        if err != nil {
                return err
        }
        bo.secondLevelWitnessScript = wScript

        if _, err := io.ReadFull(r, scratch[:2]); err != nil {
                return err
        }
        bo.witnessType = input.StandardWitnessType(
                binary.BigEndian.Uint16(scratch[:2]),
        )

        return nil
}

lightningnetwork / lnd / 9840691252

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