package contractcourt import ( "fmt" "sync" "sync/atomic" "github.com/btcsuite/btcd/btcec" "github.com/btcsuite/btcd/chaincfg" "github.com/btcsuite/btcd/txscript" "github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcutil" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/chainntnfs" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/lnwallet" ) // LocalUnilateralCloseInfo encapsulates all the informnation we need to act // on a local force close that gets confirmed. type LocalUnilateralCloseInfo struct { *chainntnfs.SpendDetail *lnwallet.LocalForceCloseSummary *channeldb.ChannelCloseSummary } // CooperativeCloseInfo encapsulates all the informnation we need to act // on a cooperative close that gets confirmed. type CooperativeCloseInfo struct { *channeldb.ChannelCloseSummary } // ChainEventSubscription is a struct that houses a subscription to be notified // for any on-chain events related to a channel. There are three types of // possible on-chain events: a cooperative channel closure, a unilateral // channel closure, and a channel breach. The fourth type: a force close is // locally initiated, so we don't provide any event stream for said event. type ChainEventSubscription struct { // ChanPoint is that channel that chain events will be dispatched for. ChanPoint wire.OutPoint // RemoteUnilateralClosure is a channel that will be sent upon in the // event that the remote party's commitment transaction is confirmed. RemoteUnilateralClosure chan *lnwallet.UnilateralCloseSummary // LocalUnilateralClosure is a channel that will be sent upon in the // event that our commitment transaction is confirmed. LocalUnilateralClosure chan *LocalUnilateralCloseInfo // CooperativeClosure is a signal that will be sent upon once a // cooperative channel closure has been detected confirmed. CooperativeClosure chan *CooperativeCloseInfo // ContractBreach is a channel that will be sent upon if we detect a // contract breach. The struct sent across the channel contains all the // material required to bring the cheating channel peer to justice. ContractBreach chan *lnwallet.BreachRetribution // Cancel cancels the subscription to the event stream for a particular // channel. This method should be called once the caller no longer needs to // be notified of any on-chain events for a particular channel. Cancel func() } // chainWatcherConfig encapsulates all the necessary functions and interfaces // needed to watch and act on on-chain events for a particular channel. type chainWatcherConfig struct { // chanState is a snapshot of the persistent state of the channel that // we're watching. In the event of an on-chain event, we'll query the // database to ensure that we act using the most up to date state. chanState *channeldb.OpenChannel // notifier is a reference to the channel notifier that we'll use to be // notified of output spends and when transactions are confirmed. notifier chainntnfs.ChainNotifier // pCache is a reference to the shared preimage cache. We'll use this // to see if we can settle any incoming HTLC's during a remote // commitment close event. pCache WitnessBeacon // signer is the main signer instances that will be responsible for // signing any HTLC and commitment transaction generated by the state // machine. signer lnwallet.Signer // contractBreach is a method that will be called by the watcher if it // detects that a contract breach transaction has been confirmed. Only // when this method returns with a non-nil error it will be safe to mark // the channel as pending close in the database. contractBreach func(*lnwallet.BreachRetribution) error // isOurAddr is a function that returns true if the passed address is // known to us. isOurAddr func(btcutil.Address) bool } // chainWatcher is a system that's assigned to every active channel. The duty // of this system is to watch the chain for spends of the channels chan point. // If a spend is detected then with chain watcher will notify all subscribers // that the channel has been closed, and also give them the materials necessary // to sweep the funds of the channel on chain eventually. type chainWatcher struct { started int32 // To be used atomically. stopped int32 // To be used atomically. quit chan struct{} wg sync.WaitGroup cfg chainWatcherConfig // stateHintObfuscator is a 48-bit state hint that's used to obfuscate // the current state number on the commitment transactions. stateHintObfuscator [lnwallet.StateHintSize]byte // All the fields below are protected by this mutex. sync.Mutex // clientID is an ephemeral counter used to keep track of each // individual client subscription. clientID uint64 // clientSubscriptions is a map that keeps track of all the active // client subscriptions for events related to this channel. clientSubscriptions map[uint64]*ChainEventSubscription } // newChainWatcher returns a new instance of a chainWatcher for a channel given // the chan point to watch, and also a notifier instance that will allow us to // detect on chain events. func newChainWatcher(cfg chainWatcherConfig) (*chainWatcher, error) { // In order to be able to detect the nature of a potential channel // closure we'll need to reconstruct the state hint bytes used to // obfuscate the commitment state number encoded in the lock time and // sequence fields. var stateHint [lnwallet.StateHintSize]byte chanState := cfg.chanState if chanState.IsInitiator { stateHint = lnwallet.DeriveStateHintObfuscator( chanState.LocalChanCfg.PaymentBasePoint.PubKey, chanState.RemoteChanCfg.PaymentBasePoint.PubKey, ) } else { stateHint = lnwallet.DeriveStateHintObfuscator( chanState.RemoteChanCfg.PaymentBasePoint.PubKey, chanState.LocalChanCfg.PaymentBasePoint.PubKey, ) } return &chainWatcher{ cfg: cfg, stateHintObfuscator: stateHint, quit: make(chan struct{}), clientSubscriptions: make(map[uint64]*ChainEventSubscription), }, nil } // Start starts all goroutines that the chainWatcher needs to perform its // duties. func (c *chainWatcher) Start() error { if !atomic.CompareAndSwapInt32(&c.started, 0, 1) { return nil } chanState := c.cfg.chanState log.Debugf("Starting chain watcher for ChannelPoint(%v)", chanState.FundingOutpoint) // First, we'll register for a notification to be dispatched if the // funding output is spent. fundingOut := &chanState.FundingOutpoint // As a height hint, we'll try to use the opening height, but if the // channel isn't yet open, then we'll use the height it was broadcast // at. heightHint := c.cfg.chanState.ShortChanID().BlockHeight if heightHint == 0 { heightHint = chanState.FundingBroadcastHeight } localKey := chanState.LocalChanCfg.MultiSigKey.PubKey.SerializeCompressed() remoteKey := chanState.RemoteChanCfg.MultiSigKey.PubKey.SerializeCompressed() multiSigScript, err := lnwallet.GenMultiSigScript( localKey, remoteKey, ) if err != nil { return err } pkScript, err := lnwallet.WitnessScriptHash(multiSigScript) if err != nil { return err } spendNtfn, err := c.cfg.notifier.RegisterSpendNtfn( fundingOut, pkScript, heightHint, ) if err != nil { return err } // With the spend notification obtained, we'll now dispatch the // closeObserver which will properly react to any changes. c.wg.Add(1) go c.closeObserver(spendNtfn) return nil } // Stop signals the close observer to gracefully exit. func (c *chainWatcher) Stop() error { if !atomic.CompareAndSwapInt32(&c.stopped, 0, 1) { return nil } close(c.quit) c.wg.Wait() return nil } // SubscribeChannelEvents returns an active subscription to the set of channel // events for the channel watched by this chain watcher. Once clients no longer // require the subscription, they should call the Cancel() method to allow the // watcher to regain those committed resources. func (c *chainWatcher) SubscribeChannelEvents() *ChainEventSubscription { c.Lock() clientID := c.clientID c.clientID++ c.Unlock() log.Debugf("New ChainEventSubscription(id=%v) for ChannelPoint(%v)", clientID, c.cfg.chanState.FundingOutpoint) sub := &ChainEventSubscription{ ChanPoint: c.cfg.chanState.FundingOutpoint, RemoteUnilateralClosure: make(chan *lnwallet.UnilateralCloseSummary, 1), LocalUnilateralClosure: make(chan *LocalUnilateralCloseInfo, 1), CooperativeClosure: make(chan *CooperativeCloseInfo, 1), ContractBreach: make(chan *lnwallet.BreachRetribution, 1), Cancel: func() { c.Lock() delete(c.clientSubscriptions, clientID) c.Unlock() return }, } c.Lock() c.clientSubscriptions[clientID] = sub c.Unlock() return sub } // closeObserver is a dedicated goroutine that will watch for any closes of the // channel that it's watching on chain. In the event of an on-chain event, the // close observer will assembled the proper materials required to claim the // funds of the channel on-chain (if required), then dispatch these as // notifications to all subscribers. func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) { defer c.wg.Done() log.Infof("Close observer for ChannelPoint(%v) active", c.cfg.chanState.FundingOutpoint) select { // We've detected a spend of the channel onchain! Depending on // the type of spend, we'll act accordingly , so we'll examine // the spending transaction to determine what we should do. // // TODO(Roasbeef): need to be able to ensure this only triggers // on confirmation, to ensure if multiple txns are broadcast, we // act on the one that's timestamped case commitSpend, ok := <-spendNtfn.Spend: // If the channel was closed, then this means that the // notifier exited, so we will as well. if !ok { return } // Otherwise, the remote party might have broadcast a // prior revoked state...!!! commitTxBroadcast := commitSpend.SpendingTx localCommit, remoteCommit, err := c.cfg.chanState.LatestCommitments() if err != nil { log.Errorf("Unable to fetch channel state for "+ "chan_point=%v", c.cfg.chanState.FundingOutpoint) return } // We'll not retrieve the latest sate of the revocation // store so we can populate the information within the // channel state object that we have. // // TODO(roasbeef): mutation is bad mkay _, err = c.cfg.chanState.RemoteRevocationStore() if err != nil { log.Errorf("Unable to fetch revocation state for "+ "chan_point=%v", c.cfg.chanState.FundingOutpoint) return } // If this is our commitment transaction, then we can // exit here as we don't have any further processing we // need to do (we can't cheat ourselves :p). commitmentHash := localCommit.CommitTx.TxHash() isOurCommitment := commitSpend.SpenderTxHash.IsEqual( &commitmentHash, ) if isOurCommitment { if err := c.dispatchLocalForceClose( commitSpend, *localCommit, ); err != nil { log.Errorf("unable to handle local"+ "close for chan_point=%v: %v", c.cfg.chanState.FundingOutpoint, err) } return } // Next, we'll check to see if this is a cooperative // channel closure or not. This is characterized by // having an input sequence number that's finalized. // This won't happen with regular commitment // transactions due to the state hint encoding scheme. if commitTxBroadcast.TxIn[0].Sequence == wire.MaxTxInSequenceNum { err := c.dispatchCooperativeClose(commitSpend) if err != nil { log.Errorf("unable to handle co op close: %v", err) } return } log.Warnf("Unprompted commitment broadcast for "+ "ChannelPoint(%v) ", c.cfg.chanState.FundingOutpoint) // Decode the state hint encoded within the commitment // transaction to determine if this is a revoked state // or not. obfuscator := c.stateHintObfuscator broadcastStateNum := lnwallet.GetStateNumHint( commitTxBroadcast, obfuscator, ) remoteStateNum := remoteCommit.CommitHeight remoteChainTip, err := c.cfg.chanState.RemoteCommitChainTip() if err != nil && err != channeldb.ErrNoPendingCommit { log.Errorf("unable to obtain chain tip for "+ "ChannelPoint(%v): %v", c.cfg.chanState.FundingOutpoint, err) return } switch { // If state number spending transaction matches the // current latest state, then they've initiated a // unilateral close. So we'll trigger the unilateral // close signal so subscribers can clean up the state // as necessary. case broadcastStateNum == remoteStateNum: err := c.dispatchRemoteForceClose( commitSpend, *remoteCommit, c.cfg.chanState.RemoteCurrentRevocation, ) if err != nil { log.Errorf("unable to handle remote "+ "close for chan_point=%v: %v", c.cfg.chanState.FundingOutpoint, err) } // We'll also handle the case of the remote party // broadcasting their commitment transaction which is // one height above ours. This case can arise when we // initiate a state transition, but the remote party // has a fail crash _after_ accepting the new state, // but _before_ sending their signature to us. case broadcastStateNum == remoteStateNum+1 && remoteChainTip != nil: err := c.dispatchRemoteForceClose( commitSpend, remoteChainTip.Commitment, c.cfg.chanState.RemoteNextRevocation, ) if err != nil { log.Errorf("unable to handle remote "+ "close for chan_point=%v: %v", c.cfg.chanState.FundingOutpoint, err) } // This is the case that somehow the commitment broadcast is // actually greater than even one beyond our best known state // number. This should ONLY happen in case we experienced some // sort of data loss. case broadcastStateNum > remoteStateNum+1: log.Warnf("Remote node broadcast state #%v, "+ "which is more than 1 beyond best known "+ "state #%v!!! Attempting recovery...", broadcastStateNum, remoteStateNum) // If we are lucky, the remote peer sent us the correct // commitment point during channel sync, such that we // can sweep our funds. // TODO(halseth): must handle the case where we haven't // yet processed the chan sync message. commitPoint, err := c.cfg.chanState.DataLossCommitPoint() if err != nil { log.Errorf("Unable to retrieve commitment "+ "point for channel(%v) with lost "+ "state: %v", c.cfg.chanState.FundingOutpoint, err) return } log.Infof("Recovered commit point(%x) for "+ "channel(%v)! Now attempting to use it to "+ "sweep our funds...", commitPoint.SerializeCompressed(), c.cfg.chanState.FundingOutpoint) // Since we don't have the commitment stored for this // state, we'll just pass an empty commitment. Note // that this means we won't be able to recover any HTLC // funds. // TODO(halseth): can we try to recover some HTLCs? err = c.dispatchRemoteForceClose( commitSpend, channeldb.ChannelCommitment{}, commitPoint, ) if err != nil { log.Errorf("unable to handle remote "+ "close for chan_point=%v: %v", c.cfg.chanState.FundingOutpoint, err) } // If the state number broadcast is lower than the // remote node's current un-revoked height, then // THEY'RE ATTEMPTING TO VIOLATE THE CONTRACT LAID OUT // WITHIN THE PAYMENT CHANNEL. Therefore we close the // signal indicating a revoked broadcast to allow // subscribers to swiftly dispatch justice!!! case broadcastStateNum < remoteStateNum: err := c.dispatchContractBreach( commitSpend, remoteCommit, broadcastStateNum, ) if err != nil { log.Errorf("unable to handle channel "+ "breach for chan_point=%v: %v", c.cfg.chanState.FundingOutpoint, err) } } // Now that a spend has been detected, we've done our // job, so we'll exit immediately. return // The chainWatcher has been signalled to exit, so we'll do so now. case <-c.quit: return } } // toSelfAmount takes a transaction and returns the sum of all outputs that pay // to a script that the wallet controls. If no outputs pay to us, then we // return zero. This is possible as our output may have been trimmed due to // being dust. func (c *chainWatcher) toSelfAmount(tx *wire.MsgTx) btcutil.Amount { var selfAmt btcutil.Amount for _, txOut := range tx.TxOut { _, addrs, _, err := txscript.ExtractPkScriptAddrs( // Doesn't matter what net we actually pass in. txOut.PkScript, &chaincfg.TestNet3Params, ) if err != nil { continue } for _, addr := range addrs { if c.cfg.isOurAddr(addr) { selfAmt += btcutil.Amount(txOut.Value) } } } return selfAmt } // dispatchCooperativeClose processed a detect cooperative channel closure. // We'll use the spending transaction to locate our output within the // transaction, then clean up the database state. We'll also dispatch a // notification to all subscribers that the channel has been closed in this // manner. func (c *chainWatcher) dispatchCooperativeClose(commitSpend *chainntnfs.SpendDetail) error { broadcastTx := commitSpend.SpendingTx log.Infof("Cooperative closure for ChannelPoint(%v): %v", c.cfg.chanState.FundingOutpoint, spew.Sdump(broadcastTx)) // If the input *is* final, then we'll check to see which output is // ours. localAmt := c.toSelfAmount(broadcastTx) // Once this is known, we'll mark the state as fully closed in the // database. We can do this as a cooperatively closed channel has all // its outputs resolved after only one confirmation. closeSummary := &channeldb.ChannelCloseSummary{ ChanPoint: c.cfg.chanState.FundingOutpoint, ChainHash: c.cfg.chanState.ChainHash, ClosingTXID: *commitSpend.SpenderTxHash, RemotePub: c.cfg.chanState.IdentityPub, Capacity: c.cfg.chanState.Capacity, CloseHeight: uint32(commitSpend.SpendingHeight), SettledBalance: localAmt, CloseType: channeldb.CooperativeClose, ShortChanID: c.cfg.chanState.ShortChanID(), IsPending: true, RemoteCurrentRevocation: c.cfg.chanState.RemoteCurrentRevocation, RemoteNextRevocation: c.cfg.chanState.RemoteNextRevocation, LocalChanConfig: c.cfg.chanState.LocalChanCfg, } // Create a summary of all the information needed to handle the // cooperative closure. closeInfo := &CooperativeCloseInfo{ ChannelCloseSummary: closeSummary, } // With the event processed, we'll now notify all subscribers of the // event. c.Lock() for _, sub := range c.clientSubscriptions { select { case sub.CooperativeClosure <- closeInfo: case <-c.quit: c.Unlock() return fmt.Errorf("exiting") } } c.Unlock() return nil } // dispatchLocalForceClose processes a unilateral close by us being confirmed. func (c *chainWatcher) dispatchLocalForceClose( commitSpend *chainntnfs.SpendDetail, localCommit channeldb.ChannelCommitment) error { log.Infof("Local unilateral close of ChannelPoint(%v) "+ "detected", c.cfg.chanState.FundingOutpoint) forceClose, err := lnwallet.NewLocalForceCloseSummary( c.cfg.chanState, c.cfg.signer, c.cfg.pCache, commitSpend.SpendingTx, localCommit, ) if err != nil { return err } // As we've detected that the channel has been closed, immediately // creating a close summary for future usage by related sub-systems. chanSnapshot := forceClose.ChanSnapshot closeSummary := &channeldb.ChannelCloseSummary{ ChanPoint: chanSnapshot.ChannelPoint, ChainHash: chanSnapshot.ChainHash, ClosingTXID: forceClose.CloseTx.TxHash(), RemotePub: &chanSnapshot.RemoteIdentity, Capacity: chanSnapshot.Capacity, CloseType: channeldb.LocalForceClose, IsPending: true, ShortChanID: c.cfg.chanState.ShortChanID(), CloseHeight: uint32(commitSpend.SpendingHeight), RemoteCurrentRevocation: c.cfg.chanState.RemoteCurrentRevocation, RemoteNextRevocation: c.cfg.chanState.RemoteNextRevocation, LocalChanConfig: c.cfg.chanState.LocalChanCfg, } // If our commitment output isn't dust or we have active HTLC's on the // commitment transaction, then we'll populate the balances on the // close channel summary. if forceClose.CommitResolution != nil { closeSummary.SettledBalance = chanSnapshot.LocalBalance.ToSatoshis() closeSummary.TimeLockedBalance = chanSnapshot.LocalBalance.ToSatoshis() } for _, htlc := range forceClose.HtlcResolutions.OutgoingHTLCs { htlcValue := btcutil.Amount(htlc.SweepSignDesc.Output.Value) closeSummary.TimeLockedBalance += htlcValue } // With the event processed, we'll now notify all subscribers of the // event. closeInfo := &LocalUnilateralCloseInfo{ commitSpend, forceClose, closeSummary, } c.Lock() for _, sub := range c.clientSubscriptions { select { case sub.LocalUnilateralClosure <- closeInfo: case <-c.quit: c.Unlock() return fmt.Errorf("exiting") } } c.Unlock() return nil } // dispatchRemoteForceClose processes a detected unilateral channel closure by // the remote party. This function will prepare a UnilateralCloseSummary which // will then be sent to any subscribers allowing them to resolve all our funds // in the channel on chain. Once this close summary is prepared, all registered // subscribers will receive a notification of this event. The commitPoint // argument should be set to the per_commitment_point corresponding to the // spending commitment. // // NOTE: The remoteCommit argument should be set to the stored commitment for // this particular state. If we don't have the commitment stored (should only // happen in case we have lost state) it should be set to an empty struct, in // which case we will attempt to sweep the non-HTLC output using the passed // commitPoint. func (c *chainWatcher) dispatchRemoteForceClose( commitSpend *chainntnfs.SpendDetail, remoteCommit channeldb.ChannelCommitment, commitPoint *btcec.PublicKey) error { log.Infof("Unilateral close of ChannelPoint(%v) "+ "detected", c.cfg.chanState.FundingOutpoint) // First, we'll create a closure summary that contains all the // materials required to let each subscriber sweep the funds in the // channel on-chain. uniClose, err := lnwallet.NewUnilateralCloseSummary( c.cfg.chanState, c.cfg.signer, c.cfg.pCache, commitSpend, remoteCommit, commitPoint, ) if err != nil { return err } // With the event processed, we'll now notify all subscribers of the // event. c.Lock() for _, sub := range c.clientSubscriptions { select { case sub.RemoteUnilateralClosure <- uniClose: case <-c.quit: c.Unlock() return fmt.Errorf("exiting") } } c.Unlock() return nil } // dispatchContractBreach processes a detected contract breached by the remote // party. This method is to be called once we detect that the remote party has // broadcast a prior revoked commitment state. This method well prepare all the // materials required to bring the cheater to justice, then notify all // registered subscribers of this event. func (c *chainWatcher) dispatchContractBreach(spendEvent *chainntnfs.SpendDetail, remoteCommit *channeldb.ChannelCommitment, broadcastStateNum uint64) error { log.Warnf("Remote peer has breached the channel contract for "+ "ChannelPoint(%v). Revoked state #%v was broadcast!!!", c.cfg.chanState.FundingOutpoint, broadcastStateNum) if err := c.cfg.chanState.MarkBorked(); err != nil { return fmt.Errorf("unable to mark channel as borked: %v", err) } var ( commitTxBroadcast = spendEvent.SpendingTx spendHeight = uint32(spendEvent.SpendingHeight) ) // Create a new reach retribution struct which contains all the data // needed to swiftly bring the cheating peer to justice. // // TODO(roasbeef): move to same package retribution, err := lnwallet.NewBreachRetribution( c.cfg.chanState, broadcastStateNum, commitTxBroadcast, spendHeight, ) if err != nil { return fmt.Errorf("unable to create breach retribution: %v", err) } // Nil the curve before printing. if retribution.RemoteOutputSignDesc != nil && retribution.RemoteOutputSignDesc.DoubleTweak != nil { retribution.RemoteOutputSignDesc.DoubleTweak.Curve = nil } if retribution.LocalOutputSignDesc != nil && retribution.LocalOutputSignDesc.DoubleTweak != nil { retribution.LocalOutputSignDesc.DoubleTweak.Curve = nil } log.Debugf("Punishment breach retribution created: %v", newLogClosure(func() string { return spew.Sdump(retribution) })) // Hand the retribution info over to the breach arbiter. if err := c.cfg.contractBreach(retribution); err != nil { log.Errorf("unable to hand breached contract off to "+ "breachArbiter: %v", err) return err } // With the event processed, we'll now notify all subscribers of the // event. c.Lock() for _, sub := range c.clientSubscriptions { select { case sub.ContractBreach <- retribution: case <-c.quit: c.Unlock() return fmt.Errorf("quitting") } } c.Unlock() // At this point, we've successfully received an ack for the breach // close. We now construct and persist the close summary, marking the // channel as pending force closed. // // TODO(roasbeef): instead mark we got all the monies? // TODO(halseth): move responsibility to breach arbiter? settledBalance := remoteCommit.LocalBalance.ToSatoshis() closeSummary := channeldb.ChannelCloseSummary{ ChanPoint: c.cfg.chanState.FundingOutpoint, ChainHash: c.cfg.chanState.ChainHash, ClosingTXID: *spendEvent.SpenderTxHash, CloseHeight: spendHeight, RemotePub: c.cfg.chanState.IdentityPub, Capacity: c.cfg.chanState.Capacity, SettledBalance: settledBalance, CloseType: channeldb.BreachClose, IsPending: true, ShortChanID: c.cfg.chanState.ShortChanID(), RemoteCurrentRevocation: c.cfg.chanState.RemoteCurrentRevocation, RemoteNextRevocation: c.cfg.chanState.RemoteNextRevocation, LocalChanConfig: c.cfg.chanState.LocalChanCfg, } if err := c.cfg.chanState.CloseChannel(&closeSummary); err != nil { return err } log.Infof("Breached channel=%v marked pending-closed", c.cfg.chanState.FundingOutpoint) return nil }