package contractcourt import ( "encoding/binary" "fmt" "io" "sync" "github.com/btcsuite/btcd/txscript" "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 } // newCommitSweepResolver instantiates a new direct commit output resolver. func newCommitSweepResolver(res lnwallet.CommitOutputResolution, broadcastHeight uint32, chanPoint wire.OutPoint, resCfg ResolverConfig) *commitSweepResolver { r := &commitSweepResolver{ contractResolverKit: *newContractResolverKit(resCfg), commitResolution: res, broadcastHeight: broadcastHeight, chanPoint: chanPoint, } r.initLogger(r) r.initReport() 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 *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 } } // The output is on our local commitment if the script starts with // OP_IF for the revocation clause. On the remote commitment it will // either be a regular P2WKH or a simple sig spend with a CSV delay. isLocalCommitTx := c.commitResolution.SelfOutputSignDesc.WitnessScript[0] == txscript.OP_IF isDelayedOutput := c.commitResolution.MaturityDelay != 0 c.log.Debugf("isDelayedOutput=%v, isLocalCommitTx=%v", isDelayedOutput, isLocalCommitTx) // There're three types of commitments, those that have tweaks // for the remote key (us in this case), those that don't, and a third // where there is no tweak and the output is delayed. On the local // commitment our output will always be delayed. We'll rely on the // presence of the commitment tweak to to discern which type of // commitment this is. var witnessType input.WitnessType switch { // Delayed output to us on our local commitment. case isLocalCommitTx: witnessType = input.CommitmentTimeLock // A confirmed output to us on the remote commitment. case isDelayedOutput: witnessType = input.CommitmentToRemoteConfirmed // A non-delayed output on the remote commitment where the key is // tweakless. case c.commitResolution.SelfOutputSignDesc.SingleTweak == nil: witnessType = input.CommitSpendNoDelayTweakless // A non-delayed output on the remote commitment where the key is // tweaked. default: witnessType = input.CommitmentNoDelay } c.log.Infof("Sweeping with witness type: %v", witnessType) // 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, sweep.Params{Fee: 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()) 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() { 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 © } // 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)