lnd/contractcourt/anchor_resolver.go

package contractcourt

import (
	"errors"
	"io"
	"sync"

	"github.com/btcsuite/btcd/btcutil"
	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/wire"
	"github.com/lightningnetwork/lnd/channeldb"
	"github.com/lightningnetwork/lnd/input"
	"github.com/lightningnetwork/lnd/sweep"
)

// anchorResolver is a resolver that will attempt to sweep our anchor output.
type anchorResolver struct {
	// anchorSignDescriptor contains the information that is required to
	// sweep the anchor.
	anchorSignDescriptor input.SignDescriptor

	// anchor is the outpoint on the commitment transaction.
	anchor wire.OutPoint

	// 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

	// chanType denotes the type of channel the contract belongs to.
	chanType channeldb.ChannelType

	// 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
}

// newAnchorResolver instantiates a new anchor resolver.
func newAnchorResolver(anchorSignDescriptor input.SignDescriptor,
	anchor wire.OutPoint, broadcastHeight uint32,
	chanPoint wire.OutPoint, resCfg ResolverConfig) *anchorResolver {

	amt := btcutil.Amount(anchorSignDescriptor.Output.Value)

	report := ContractReport{
		Outpoint:         anchor,
		Type:             ReportOutputAnchor,
		Amount:           amt,
		LimboBalance:     amt,
		RecoveredBalance: 0,
	}

	r := &anchorResolver{
		contractResolverKit:  *newContractResolverKit(resCfg),
		anchorSignDescriptor: anchorSignDescriptor,
		anchor:               anchor,
		broadcastHeight:      broadcastHeight,
		chanPoint:            chanPoint,
		currentReport:        report,
	}

	r.initLogger(r)

	return r
}

// ResolverKey returns an identifier which should be globally unique for this
// particular resolver within the chain the original contract resides within.
func (c *anchorResolver) ResolverKey() []byte {
	// The anchor resolver is stateless and doesn't need a database key.
	return nil
}

// Resolve offers the anchor output to the sweeper and waits for it to be swept.
func (c *anchorResolver) Resolve() (ContractResolver, error) {
	// Attempt to update the sweep parameters to the post-confirmation
	// situation. We don't want to force sweep anymore, because the anchor
	// lost its special purpose to get the commitment confirmed. It is just
	// an output that we want to sweep only if it is economical to do so.
	//
	// An exclusive group is not necessary anymore, because we know that
	// this is the only anchor that can be swept.
	//
	// We also clear the parent tx information for cpfp, because the
	// commitment tx is confirmed.
	//
	// After a restart or when the remote force closes, the sweeper is not
	// yet aware of the anchor. In that case, it will be added as new input
	// to the sweeper.
	relayFeeRate := c.Sweeper.RelayFeePerKW()

	witnessType := input.CommitmentAnchor

	// For taproot channels, we need to use the proper witness type.
	if c.chanType.IsTaproot() {
		witnessType = input.TaprootAnchorSweepSpend
	}

	anchorInput := input.MakeBaseInput(
		&c.anchor, witnessType, &c.anchorSignDescriptor,
		c.broadcastHeight, nil,
	)

	resultChan, err := c.Sweeper.SweepInput(
		&anchorInput,
		sweep.Params{
			Fee: sweep.FeePreference{
				FeeRate: relayFeeRate,
			},
		},
	)
	if err != nil {
		return nil, err
	}

	var (
		outcome channeldb.ResolverOutcome
		spendTx *chainhash.Hash
	)

	select {
	case sweepRes := <-resultChan:
		switch sweepRes.Err {
		// Anchor was swept successfully.
		case nil:
			sweepTxID := sweepRes.Tx.TxHash()

			spendTx = &sweepTxID
			outcome = channeldb.ResolverOutcomeClaimed

		// Anchor was swept by someone else. This is possible after the
		// 16 block csv lock.
		case sweep.ErrRemoteSpend:
			c.log.Warnf("our anchor spent by someone else")
			outcome = channeldb.ResolverOutcomeUnclaimed

		// The sweeper gave up on sweeping the anchor. This happens
		// after the maximum number of sweep attempts has been reached.
		// See sweep.DefaultMaxSweepAttempts. Sweep attempts are
		// interspaced with random delays picked from a range that
		// increases exponentially.
		//
		// We consider the anchor as being lost.
		case sweep.ErrTooManyAttempts:
			c.log.Warnf("anchor sweep abandoned")
			outcome = channeldb.ResolverOutcomeUnclaimed

		// An unexpected error occurred.
		default:
			c.log.Errorf("unable to sweep anchor: %v", sweepRes.Err)

			return nil, sweepRes.Err
		}

	case <-c.quit:
		return nil, errResolverShuttingDown
	}

	// Update report to reflect that funds are no longer in limbo.
	c.reportLock.Lock()
	if outcome == channeldb.ResolverOutcomeClaimed {
		c.currentReport.RecoveredBalance = c.currentReport.LimboBalance
	}
	c.currentReport.LimboBalance = 0
	report := c.currentReport.resolverReport(
		spendTx, channeldb.ResolverTypeAnchor, outcome,
	)
	c.reportLock.Unlock()

	c.resolved = true
	return nil, c.PutResolverReport(nil, report)
}

// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (c *anchorResolver) Stop() {
	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 *anchorResolver) IsResolved() bool {
	return c.resolved
}

// SupplementState allows the user of a ContractResolver to supplement it with
// state required for the proper resolution of a contract.
//
// NOTE: Part of the ContractResolver interface.
func (c *anchorResolver) SupplementState(state *channeldb.OpenChannel) {
	c.chanType = state.ChanType
}

// report returns a report on the resolution state of the contract.
func (c *anchorResolver) report() *ContractReport {
	c.reportLock.Lock()
	defer c.reportLock.Unlock()

	reportCopy := c.currentReport
	return &reportCopy
}

func (c *anchorResolver) Encode(w io.Writer) error {
	return errors.New("serialization not supported")
}

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