diff --git a/contractcourt/chain_watcher.go b/contractcourt/chain_watcher.go index 1600aa2d7..234fc7c38 100644 --- a/contractcourt/chain_watcher.go +++ b/contractcourt/chain_watcher.go @@ -88,6 +88,38 @@ type BreachCloseInfo struct { CloseSummary channeldb.ChannelCloseSummary } +// spendConfirmationState represents the state of spend confirmation tracking +// in the closeObserver state machine. We wait for N confirmations before +// processing any spend to protect against shallow reorgs. +type spendConfirmationState uint8 + +const ( + // spendStateNone indicates no spend has been detected yet. + spendStateNone spendConfirmationState = iota + + // spendStatePending indicates a spend has been detected and we're + // waiting for the required number of confirmations. + spendStatePending + + // spendStateConfirmed indicates the spend has reached the required + // confirmations and has been processed. + spendStateConfirmed +) + +// String returns a human-readable representation of the state. +func (s spendConfirmationState) String() string { + switch s { + case spendStateNone: + return "None" + case spendStatePending: + return "Pending" + case spendStateConfirmed: + return "Confirmed" + default: + return "Unknown" + } +} + // CommitSet is a collection of the set of known valid commitments at a given // instant. If ConfCommitKey is set, then the commitment identified by the // HtlcSetKey has hit the chain. This struct will be used to examine all live @@ -652,51 +684,225 @@ func newChainSet(chanState *channeldb.OpenChannel) (*chainSet, error) { } // 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. +// channel that it's watching on chain. It implements a state machine to handle +// spend detection and confirmation with reorg protection. The states are: +// +// - None (confNtfn == nil): No spend detected yet, waiting for spend +// notification +// +// - Pending (confNtfn != nil): Spend detected, waiting for N confirmations +// +// - Confirmed: Spend confirmed with N blocks, close has been processed func (c *chainWatcher) closeObserver() { defer c.wg.Done() - defer c.fundingSpendNtfn.Cancel() + + registerForSpend := func() (*chainntnfs.SpendEvent, error) { + fundingPkScript, err := deriveFundingPkScript(c.cfg.chanState) + if err != nil { + return nil, err + } + + heightHint := c.cfg.chanState.DeriveHeightHint() + + return c.cfg.notifier.RegisterSpendNtfn( + &c.cfg.chanState.FundingOutpoint, + fundingPkScript, + heightHint, + ) + } + + spendNtfn := c.fundingSpendNtfn + defer spendNtfn.Cancel() + + // We use these variables to implement a state machine to track the + // state of the spend confirmation process: + // * When confNtfn is nil, we're in state "None" waiting for a spend. + // * When confNtfn is set, we're in state "Pending" waiting for + // confirmations. + // + // After confirmations, we transition to state "Confirmed" and clean up. + var ( + pendingSpend *chainntnfs.SpendDetail + confNtfn *chainntnfs.ConfirmationEvent + ) log.Infof("Close observer for ChannelPoint(%v) active", c.cfg.chanState.FundingOutpoint) + // handleSpendDetection processes a newly detected spend by registering + // for confirmations. Returns the new confNtfn or error. + handleSpendDetection := func( + spend *chainntnfs.SpendDetail, + ) (*chainntnfs.ConfirmationEvent, error) { + + // If we already have a pending spend, check if it's the same + // transaction. This can happen if both the spend notification + // and blockbeat detect the same spend. + if pendingSpend != nil { + if *pendingSpend.SpenderTxHash == *spend.SpenderTxHash { + log.Debugf("ChannelPoint(%v): ignoring "+ + "duplicate spend detection for tx %v", + c.cfg.chanState.FundingOutpoint, + spend.SpenderTxHash) + return confNtfn, nil + } + + // Different spend detected. Cancel existing confNtfn + // and replace with new one. + log.Warnf("ChannelPoint(%v): detected different "+ + "spend tx %v, replacing pending tx %v", + c.cfg.chanState.FundingOutpoint, + spend.SpenderTxHash, + pendingSpend.SpenderTxHash) + + if confNtfn != nil { + confNtfn.Cancel() + } + } + + numConfs := c.requiredConfsForSpend() + txid := spend.SpenderTxHash + + newConfNtfn, err := c.cfg.notifier.RegisterConfirmationsNtfn( + txid, spend.SpendingTx.TxOut[0].PkScript, + numConfs, uint32(spend.SpendingHeight), + ) + if err != nil { + return nil, fmt.Errorf("register confirmations: %w", + err) + } + + log.Infof("ChannelPoint(%v): waiting for %d confirmations "+ + "of spend tx %v", c.cfg.chanState.FundingOutpoint, + numConfs, txid) + + return newConfNtfn, nil + } + for { + // We only listen to confirmation channels when we have a + // pending spend. By setting these to nil when not needed, Go's + // select ignores those cases, effectively implementing our + // state machine. + var ( + confChan <-chan *chainntnfs.TxConfirmation + negativeConfChan <-chan int32 + ) + if confNtfn != nil { + confChan = confNtfn.Confirmed + negativeConfChan = confNtfn.NegativeConf + } + select { - // A new block is received, we will check whether this block - // contains a spending tx that we are interested in. case beat := <-c.BlockbeatChan: log.Debugf("ChainWatcher(%v) received blockbeat %v", c.cfg.chanState.FundingOutpoint, beat.Height()) - // Process the block. - c.handleBlockbeat(beat) + spend := c.handleBlockbeat(beat) + if spend == nil { + continue + } - // If the funding outpoint is spent, we now go ahead and handle - // it. Note that we cannot rely solely on the `block` event - // above to trigger a close event, as deep down, the receiving - // of block notifications and the receiving of spending - // notifications are done in two different goroutines, so the - // expected order: [receive block -> receive spend] is not - // guaranteed . - case spend, ok := <-c.fundingSpendNtfn.Spend: - // If the channel was closed, then this means that the - // notifier exited, so we will as well. + // STATE TRANSITION: None -> Pending (from blockbeat). + log.Infof("ChannelPoint(%v): detected spend from "+ + "blockbeat, transitioning to %v", + c.cfg.chanState.FundingOutpoint, + spendStatePending) + + newConfNtfn, err := handleSpendDetection(spend) + if err != nil { + log.Errorf("Unable to handle spend "+ + "detection: %v", err) + return + } + pendingSpend = spend + confNtfn = newConfNtfn + + // STATE TRANSITION: None -> Pending. + // We've detected a spend, but don't process it yet. Instead, + // register for confirmations to protect against shallow reorgs. + case spend, ok := <-spendNtfn.Spend: if !ok { return } - err := c.handleCommitSpend(spend) + log.Infof("ChannelPoint(%v): detected spend from "+ + "notification, transitioning to %v", + c.cfg.chanState.FundingOutpoint, + spendStatePending) + + newConfNtfn, err := handleSpendDetection(spend) if err != nil { - log.Errorf("Failed to handle commit spend: %v", - err) + log.Errorf("Unable to handle spend "+ + "detection: %v", err) + return } + pendingSpend = spend + confNtfn = newConfNtfn + + // STATE TRANSITION: Pending -> Confirmed + // The spend has reached required confirmations. It's now safe + // to process since we've protected against shallow reorgs. + case conf, ok := <-confChan: + if !ok { + log.Errorf("Confirmation channel closed " + + "unexpectedly") + return + } + + log.Infof("ChannelPoint(%v): spend confirmed at "+ + "height %d, transitioning to %v", + c.cfg.chanState.FundingOutpoint, + conf.BlockHeight, spendStateConfirmed) + + err := c.handleCommitSpend(pendingSpend) + if err != nil { + log.Errorf("Failed to handle confirmed "+ + "spend: %v", err) + } + + confNtfn.Cancel() + confNtfn = nil + pendingSpend = nil + + // STATE TRANSITION: Pending -> None + // A reorg removed the spend tx. We reset to initial state and + // wait for ANY new spend (could be the same tx re-mined, or a + // different tx like an RBF replacement). + case reorgDepth, ok := <-negativeConfChan: + if !ok { + log.Errorf("Negative conf channel closed " + + "unexpectedly") + return + } + + log.Infof("ChannelPoint(%v): spend reorged out at "+ + "depth %d, transitioning back to %v", + c.cfg.chanState.FundingOutpoint, reorgDepth, + spendStateNone) + + confNtfn.Cancel() + confNtfn = nil + pendingSpend = nil + + spendNtfn.Cancel() + var err error + spendNtfn, err = registerForSpend() + if err != nil { + log.Errorf("Unable to re-register for "+ + "spend: %v", err) + return + } + + log.Infof("ChannelPoint(%v): re-registered for spend "+ + "detection", c.cfg.chanState.FundingOutpoint) // The chainWatcher has been signalled to exit, so we'll do so // now. case <-c.quit: + if confNtfn != nil { + confNtfn.Cancel() + } return } } @@ -992,6 +1198,18 @@ func (c *chainWatcher) toSelfAmount(tx *wire.MsgTx) btcutil.Amount { return btcutil.Amount(fn.Sum(vals)) } +// requiredConfsForSpend determines the number of confirmations required before +// processing a spend of the funding output. Uses config override if set +// (typically for testing), otherwise scales with channel capacity to balance +// security vs user experience for channels of different sizes. +func (c *chainWatcher) requiredConfsForSpend() uint32 { + return c.cfg.chanCloseConfs.UnwrapOrFunc(func() uint32 { + return lnwallet.CloseConfsForCapacity( + c.cfg.chanState.Capacity, + ) + }) +} + // 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 @@ -1009,8 +1227,8 @@ func (c *chainWatcher) dispatchCooperativeClose(commitSpend *chainntnfs.SpendDet 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. + // database. For cooperative closes, we wait for a confirmation depth + // determined by channel capacity before dispatching this event. closeSummary := &channeldb.ChannelCloseSummary{ ChanPoint: c.cfg.chanState.FundingOutpoint, ChainHash: c.cfg.chanState.ChainHash, @@ -1419,9 +1637,10 @@ func (c *chainWatcher) handleCommitSpend( case wire.MaxTxInSequenceNum: fallthrough case mempool.MaxRBFSequence: - // TODO(roasbeef): rare but possible, need itest case for - err := c.dispatchCooperativeClose(commitSpend) - if err != nil { + // This is a cooperative close. Dispatch it directly - the + // confirmation waiting and reorg handling is done in the + // closeObserver state machine before we reach this point. + if err := c.dispatchCooperativeClose(commitSpend); err != nil { return fmt.Errorf("handle coop close: %w", err) } @@ -1526,9 +1745,9 @@ func (c *chainWatcher) chanPointConfirmed() bool { } // handleBlockbeat takes a blockbeat and queries for a spending tx for the -// funding output. If the spending tx is found, it will be handled based on the -// closure type. -func (c *chainWatcher) handleBlockbeat(beat chainio.Blockbeat) { +// funding output. If found, it returns the spend details so closeObserver can +// process it. Returns nil if no spend was detected. +func (c *chainWatcher) handleBlockbeat(beat chainio.Blockbeat) *chainntnfs.SpendDetail { // Notify the chain watcher has processed the block. defer c.NotifyBlockProcessed(beat, nil) @@ -1540,24 +1759,23 @@ func (c *chainWatcher) handleBlockbeat(beat chainio.Blockbeat) { // If the funding output hasn't confirmed in this block, we // will check it again in the next block. if !c.chanPointConfirmed() { - return + return nil } } // Perform a non-blocking read to check whether the funding output was - // spent. + // spent. The actual spend handling is done in closeObserver's state + // machine to avoid blocking the block processing pipeline. spend := c.checkFundingSpend() if spend == nil { log.Tracef("No spend found for ChannelPoint(%v) in block %v", c.cfg.chanState.FundingOutpoint, beat.Height()) - return + return nil } - // The funding output was spent, we now handle it by sending a close - // event to the channel arbitrator. - err := c.handleCommitSpend(spend) - if err != nil { - log.Errorf("Failed to handle commit spend: %v", err) - } + log.Debugf("Detected spend of ChannelPoint(%v) in block %v", + c.cfg.chanState.FundingOutpoint, beat.Height()) + + return spend }