lnd.xprv/contractcourt/commit_sweep_resolver.go

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package contractcourt
import (
"encoding/binary"
"fmt"
"io"
"sync"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/lightningnetwork/lnd/sweep"
)
const (
// commitOutputConfTarget is the default confirmation target we'll use
// for sweeps of commit outputs that belong to us.
commitOutputConfTarget = 6
)
// commitSweepResolver is a resolver that will attempt to sweep the commitment
// output paying to us, in the case that the remote party broadcasts their
// version of the commitment transaction. We can sweep this output immediately,
// as it doesn't have a time-lock delay.
type commitSweepResolver struct {
// commitResolution contains all data required to successfully sweep
// this HTLC on-chain.
commitResolution lnwallet.CommitOutputResolution
// resolved reflects if the contract has been fully resolved or not.
resolved 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
// chanPoint is the channel point of the original contract.
chanPoint wire.OutPoint
// currentReport stores the current state of the resolver for reporting
// over the rpc interface.
currentReport ContractReport
// reportLock prevents concurrent access to the resolver report.
reportLock sync.Mutex
contractResolverKit
}
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// newCommitSweepResolver instantiates a new direct commit output resolver.
func newCommitSweepResolver(res lnwallet.CommitOutputResolution,
broadcastHeight uint32,
chanPoint wire.OutPoint, resCfg ResolverConfig) *commitSweepResolver {
r := &commitSweepResolver{
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contractResolverKit: *newContractResolverKit(resCfg),
commitResolution: res,
broadcastHeight: broadcastHeight,
chanPoint: chanPoint,
}
r.initLogger(r)
r.initReport()
return r
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}
// ResolverKey returns an identifier which should be globally unique for this
// particular resolver within the chain the original contract resides within.
func (c *commitSweepResolver) ResolverKey() []byte {
key := newResolverID(c.commitResolution.SelfOutPoint)
return key[:]
}
// waitForHeight registers for block notifications and waits for the provided
// block height to be reached.
func (c *commitSweepResolver) waitForHeight(waitHeight uint32) error {
// Register for block epochs. After registration, the current height
// will be sent on the channel immediately.
blockEpochs, err := c.Notifier.RegisterBlockEpochNtfn(nil)
if err != nil {
return err
}
defer blockEpochs.Cancel()
for {
select {
case newBlock, ok := <-blockEpochs.Epochs:
if !ok {
return errResolverShuttingDown
}
height := newBlock.Height
if height >= int32(waitHeight) {
return nil
}
case <-c.quit:
return errResolverShuttingDown
}
}
}
// getCommitTxConfHeight waits for confirmation of the commitment tx and returns
// the confirmation height.
func (c *commitSweepResolver) getCommitTxConfHeight() (uint32, error) {
txID := c.commitResolution.SelfOutPoint.Hash
signDesc := c.commitResolution.SelfOutputSignDesc
pkScript := signDesc.Output.PkScript
const confDepth = 1
confChan, err := c.Notifier.RegisterConfirmationsNtfn(
&txID, pkScript, confDepth, c.broadcastHeight,
)
if err != nil {
return 0, err
}
defer confChan.Cancel()
select {
case txConfirmation, ok := <-confChan.Confirmed:
if !ok {
return 0, fmt.Errorf("cannot get confirmation "+
"for commit tx %v", txID)
}
return txConfirmation.BlockHeight, nil
case <-c.quit:
return 0, errResolverShuttingDown
}
}
// Resolve instructs the contract resolver to resolve the output on-chain. Once
// the output has been *fully* resolved, the function should return immediately
// with a nil ContractResolver value for the first return value. In the case
// that the contract requires further resolution, then another resolve is
// returned.
//
// NOTE: This function MUST be run as a goroutine.
func (c *commitSweepResolver) Resolve() (ContractResolver, error) {
// If we're already resolved, then we can exit early.
if c.resolved {
return nil, nil
}
confHeight, err := c.getCommitTxConfHeight()
if err != nil {
return nil, err
}
unlockHeight := confHeight + c.commitResolution.MaturityDelay
c.log.Debugf("commit conf_height=%v, unlock_height=%v",
confHeight, unlockHeight)
// Update report now that we learned the confirmation height.
c.reportLock.Lock()
c.currentReport.MaturityHeight = unlockHeight
c.reportLock.Unlock()
// If there is a csv delay, we'll wait for that.
if c.commitResolution.MaturityDelay > 0 {
c.log.Debugf("waiting for csv lock to expire at height %v",
unlockHeight)
// We only need to wait for the block before the block that
// unlocks the spend path.
err := c.waitForHeight(unlockHeight - 1)
if err != nil {
return nil, err
}
}
// We're dealing with our commitment transaction if the delay on the
// resolution isn't zero.
isLocalCommitTx := c.commitResolution.MaturityDelay != 0
// There're two types of commitments, those that have tweaks
// for the remote key (us in this case), and those that don't.
// We'll rely on the presence of the commitment tweak to to
// discern which type of commitment this is.
var witnessType input.WitnessType
switch {
case isLocalCommitTx:
witnessType = input.CommitmentTimeLock
case c.commitResolution.SelfOutputSignDesc.SingleTweak == nil:
witnessType = input.CommitSpendNoDelayTweakless
default:
witnessType = input.CommitmentNoDelay
}
// We'll craft an input with all the information required for
// the sweeper to create a fully valid sweeping transaction to
// recover these coins.
inp := input.NewCsvInput(
&c.commitResolution.SelfOutPoint,
witnessType,
&c.commitResolution.SelfOutputSignDesc,
c.broadcastHeight,
c.commitResolution.MaturityDelay,
)
// With our input constructed, we'll now offer it to the
// sweeper.
c.log.Infof("sweeping commit output")
feePref := sweep.FeePreference{ConfTarget: commitOutputConfTarget}
resultChan, err := c.Sweeper.SweepInput(inp, feePref)
if err != nil {
c.log.Errorf("unable to sweep input: %v", err)
return nil, err
}
// Sweeper is going to join this input with other inputs if
// possible and publish the sweep tx. When the sweep tx
// confirms, it signals us through the result channel with the
// outcome. Wait for this to happen.
select {
case sweepResult := <-resultChan:
if sweepResult.Err != nil {
c.log.Errorf("unable to sweep input: %v",
sweepResult.Err)
return nil, sweepResult.Err
}
c.log.Infof("commit tx fully resolved by sweep tx: %v",
sweepResult.Tx.TxHash())
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case <-c.quit:
return nil, errResolverShuttingDown
}
// Funds have been swept and balance is no longer in limbo.
c.reportLock.Lock()
c.currentReport.RecoveredBalance = c.currentReport.LimboBalance
c.currentReport.LimboBalance = 0
c.reportLock.Unlock()
c.resolved = true
return nil, c.Checkpoint(c)
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) Stop() {
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close(c.quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) IsResolved() bool {
return c.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (c *commitSweepResolver) Encode(w io.Writer) error {
if err := encodeCommitResolution(w, &c.commitResolution); err != nil {
return err
}
if err := binary.Write(w, endian, c.resolved); err != nil {
return err
}
if err := binary.Write(w, endian, c.broadcastHeight); err != nil {
return err
}
if _, err := w.Write(c.chanPoint.Hash[:]); err != nil {
return err
}
err := binary.Write(w, endian, c.chanPoint.Index)
if err != nil {
return err
}
// Previously a sweep tx was serialized at this point. Refactoring
// removed this, but keep in mind that this data may still be present in
// the database.
return nil
}
// newCommitSweepResolverFromReader attempts to decode an encoded
// ContractResolver from the passed Reader instance, returning an active
// ContractResolver instance.
func newCommitSweepResolverFromReader(r io.Reader, resCfg ResolverConfig) (
*commitSweepResolver, error) {
c := &commitSweepResolver{
contractResolverKit: *newContractResolverKit(resCfg),
}
if err := decodeCommitResolution(r, &c.commitResolution); err != nil {
return nil, err
}
if err := binary.Read(r, endian, &c.resolved); err != nil {
return nil, err
}
if err := binary.Read(r, endian, &c.broadcastHeight); err != nil {
return nil, err
}
_, err := io.ReadFull(r, c.chanPoint.Hash[:])
if err != nil {
return nil, err
}
err = binary.Read(r, endian, &c.chanPoint.Index)
if err != nil {
return nil, err
}
// Previously a sweep tx was deserialized at this point. Refactoring
// removed this, but keep in mind that this data may still be present in
// the database.
c.initLogger(c)
c.initReport()
return c, nil
}
// report returns a report on the resolution state of the contract.
func (c *commitSweepResolver) report() *ContractReport {
c.reportLock.Lock()
defer c.reportLock.Unlock()
copy := c.currentReport
return &copy
}
// initReport initializes the pending channels report for this resolver.
func (c *commitSweepResolver) initReport() {
amt := btcutil.Amount(
c.commitResolution.SelfOutputSignDesc.Output.Value,
)
// Set the initial report. All fields are filled in, except for the
// maturity height which remains 0 until Resolve() is executed.
//
// TODO(joostjager): Resolvers only activate after the commit tx
// confirms. With more refactoring in channel arbitrator, it would be
// possible to make the confirmation height part of ResolverConfig and
// populate MaturityHeight here.
c.currentReport = ContractReport{
Outpoint: c.commitResolution.SelfOutPoint,
Type: ReportOutputUnencumbered,
Amount: amt,
LimboBalance: amt,
RecoveredBalance: 0,
}
}
// A compile time assertion to ensure commitSweepResolver meets the
// ContractResolver interface.
var _ reportingContractResolver = (*commitSweepResolver)(nil)