package chainntnfs import ( "errors" "fmt" "sync" "github.com/btcsuite/btcd/chaincfg/chainhash" "github.com/btcsuite/btcutil" ) var ( // ErrTxConfNotifierExiting is an error returned when attempting to // interact with the TxConfNotifier but it been shut down. ErrTxConfNotifierExiting = errors.New("TxConfNotifier is exiting") ) // ConfNtfn represents a notifier client's request to receive a notification // once the target transaction gets sufficient confirmations. The client is // asynchronously notified via the ConfirmationEvent channels. type ConfNtfn struct { // ConfID uniquely identifies the confirmation notification request for // the specified transaction. ConfID uint64 // TxID is the hash of the transaction for which confirmation notifications // are requested. TxID *chainhash.Hash // NumConfirmations is the number of confirmations after which the // notification is to be sent. NumConfirmations uint32 // Event contains references to the channels that the notifications are to // be sent over. Event *ConfirmationEvent // details describes the transaction's position is the blockchain. May be // nil for unconfirmed transactions. details *TxConfirmation // dispatched is false if the confirmed notification has not been sent yet. dispatched bool } // NewConfirmationEvent constructs a new ConfirmationEvent with newly opened // channels. func NewConfirmationEvent(numConfs uint32) *ConfirmationEvent { return &ConfirmationEvent{ Confirmed: make(chan *TxConfirmation, 1), Updates: make(chan uint32, numConfs), NegativeConf: make(chan int32, 1), } } // TxConfNotifier is used to register transaction confirmation notifications and // dispatch them as the transactions confirm. A client can request to be // notified when a particular transaction has sufficient on-chain confirmations // (or be notified immediately if the tx already does), and the TxConfNotifier // will watch changes to the blockchain in order to satisfy these requests. type TxConfNotifier struct { // currentHeight is the height of the tracked blockchain. It is used to // determine the number of confirmations a tx has and ensure blocks are // connected and disconnected in order. currentHeight uint32 // reorgSafetyLimit is the chain depth beyond which it is assumed a block // will not be reorganized out of the chain. This is used to determine when // to prune old confirmation requests so that reorgs are handled correctly. // The coinbase maturity period is a reasonable value to use. reorgSafetyLimit uint32 // reorgDepth is the depth of a chain organization that this system is being // informed of. This is incremented as long as a sequence of blocks are // disconnected without being interrupted by a new block. reorgDepth uint32 // confNotifications is an index of notification requests by transaction // hash. confNotifications map[chainhash.Hash]map[uint64]*ConfNtfn // txsByInitialHeight is an index of watched transactions by the height // that they are included at in the blockchain. This is tracked so that // incorrect notifications are not sent if a transaction is reorganized // out of the chain and so that negative confirmations can be recognized. txsByInitialHeight map[uint32]map[chainhash.Hash]struct{} // ntfnsByConfirmHeight is an index of notification requests by the height // at which the transaction will have sufficient confirmations. ntfnsByConfirmHeight map[uint32]map[*ConfNtfn]struct{} // hintCache is a cache used to maintain the latest height hints for // transactions. Each height hint represents the earliest height at // which the transactions could have been confirmed within the chain. hintCache ConfirmHintCache // quit is closed in order to signal that the notifier is gracefully // exiting. quit chan struct{} sync.Mutex } // NewTxConfNotifier creates a TxConfNotifier. The current height of the // blockchain is accepted as a parameter. func NewTxConfNotifier(startHeight uint32, reorgSafetyLimit uint32, hintCache ConfirmHintCache) *TxConfNotifier { return &TxConfNotifier{ currentHeight: startHeight, reorgSafetyLimit: reorgSafetyLimit, confNotifications: make(map[chainhash.Hash]map[uint64]*ConfNtfn), txsByInitialHeight: make(map[uint32]map[chainhash.Hash]struct{}), ntfnsByConfirmHeight: make(map[uint32]map[*ConfNtfn]struct{}), hintCache: hintCache, quit: make(chan struct{}), } } // Register handles a new notification request. The client will be notified when // the transaction gets a sufficient number of confirmations on the blockchain. // // NOTE: If the transaction has already been included in a block on the chain, // the confirmation details must be provided with the UpdateConfDetails method, // otherwise we will wait for the transaction to confirm even though it already // has. func (tcn *TxConfNotifier) Register(ntfn *ConfNtfn) error { select { case <-tcn.quit: return ErrTxConfNotifierExiting default: } tcn.Lock() defer tcn.Unlock() ntfns, ok := tcn.confNotifications[*ntfn.TxID] if !ok { ntfns = make(map[uint64]*ConfNtfn) tcn.confNotifications[*ntfn.TxID] = ntfns err := tcn.hintCache.CommitConfirmHint( tcn.currentHeight, *ntfn.TxID, ) if err != nil { // The error is not fatal, so we should not return an // error to the caller. Log.Errorf("Unable to update confirm hint to %d for "+ "%v: %v", tcn.currentHeight, *ntfn.TxID, err) } } ntfns[ntfn.ConfID] = ntfn return nil } // UpdateConfDetails attempts to update the confirmation details for an active // notification within the notifier. This should only be used in the case of a // transaction that has confirmed before the notifier's current height. // // NOTE: The notification should be registered first to ensure notifications are // dispatched correctly. func (tcn *TxConfNotifier) UpdateConfDetails(txid chainhash.Hash, clientID uint64, details *TxConfirmation) error { select { case <-tcn.quit: return ErrTxConfNotifierExiting default: } // Ensure we hold the lock throughout handling the notification to // prevent the notifier from advancing its height underneath us. tcn.Lock() defer tcn.Unlock() // First, we'll determine whether we have an active notification for // this transaction with the given ID. ntfns, ok := tcn.confNotifications[txid] if !ok { return fmt.Errorf("no notifications found for txid %v", txid) } ntfn, ok := ntfns[clientID] if !ok { return fmt.Errorf("no notification found with ID %v", clientID) } // If the notification has already recognized that the transaction // confirmed, there's nothing left for us to do. if ntfn.details != nil { return nil } err := tcn.hintCache.CommitConfirmHint(details.BlockHeight, txid) if err != nil { // The error is not fatal, so we should not return an error to // the caller. Log.Errorf("Unable to update confirm hint to %d for %v: %v", details.BlockHeight, txid, err) } // The notifier has yet to reach the height at which the transaction was // included in a block, so we should defer until handling it then within // ConnectTip. if details == nil || details.BlockHeight > tcn.currentHeight { return nil } ntfn.details = details // Now, we'll examine whether the transaction of this notification // request has reched its required number of confirmations. If it has, // we'll disaptch a confirmation notification to the caller. confHeight := details.BlockHeight + ntfn.NumConfirmations - 1 if confHeight <= tcn.currentHeight { Log.Infof("Dispatching %v conf notification for %v", ntfn.NumConfirmations, ntfn.TxID) // We'll send a 0 value to the Updates channel, indicating that // the transaction has already been confirmed. select { case ntfn.Event.Updates <- 0: case <-tcn.quit: return ErrTxConfNotifierExiting } select { case ntfn.Event.Confirmed <- details: ntfn.dispatched = true case <-tcn.quit: return ErrTxConfNotifierExiting } } else { // Otherwise, we'll keep track of the notification request by // the height at which we should dispatch the confirmation // notification. ntfnSet, exists := tcn.ntfnsByConfirmHeight[confHeight] if !exists { ntfnSet = make(map[*ConfNtfn]struct{}) tcn.ntfnsByConfirmHeight[confHeight] = ntfnSet } ntfnSet[ntfn] = struct{}{} // We'll also send an update to the client of how many // confirmations are left for the transaction to be confirmed. numConfsLeft := confHeight - tcn.currentHeight select { case ntfn.Event.Updates <- numConfsLeft: case <-tcn.quit: return ErrTxConfNotifierExiting } } // As a final check, we'll also watch the transaction if it's still // possible for it to get reorged out of the chain. if details.BlockHeight+tcn.reorgSafetyLimit > tcn.currentHeight { txSet, exists := tcn.txsByInitialHeight[details.BlockHeight] if !exists { txSet = make(map[chainhash.Hash]struct{}) tcn.txsByInitialHeight[details.BlockHeight] = txSet } txSet[txid] = struct{}{} } return nil } // ConnectTip handles a new block extending the current chain. This checks each // transaction in the block to see if any watched transactions are included. // Also, if any watched transactions now have the required number of // confirmations as a result of this block being connected, this dispatches // notifications. func (tcn *TxConfNotifier) ConnectTip(blockHash *chainhash.Hash, blockHeight uint32, txns []*btcutil.Tx) error { select { case <-tcn.quit: return ErrTxConfNotifierExiting default: } tcn.Lock() defer tcn.Unlock() if blockHeight != tcn.currentHeight+1 { return fmt.Errorf("Received blocks out of order: "+ "current height=%d, new height=%d", tcn.currentHeight, blockHeight) } tcn.currentHeight++ tcn.reorgDepth = 0 // Record any newly confirmed transactions by their confirmed height so // that notifications get dispatched when the transactions reach their // required number of confirmations. We'll also watch these transactions // at the height they were included in the chain so reorgs can be // handled correctly. for _, tx := range txns { txHash := tx.Hash() for _, ntfn := range tcn.confNotifications[*txHash] { ntfn.details = &TxConfirmation{ BlockHash: blockHash, BlockHeight: blockHeight, TxIndex: uint32(tx.Index()), } confHeight := blockHeight + ntfn.NumConfirmations - 1 ntfnSet, exists := tcn.ntfnsByConfirmHeight[confHeight] if !exists { ntfnSet = make(map[*ConfNtfn]struct{}) tcn.ntfnsByConfirmHeight[confHeight] = ntfnSet } ntfnSet[ntfn] = struct{}{} txSet, exists := tcn.txsByInitialHeight[blockHeight] if !exists { txSet = make(map[chainhash.Hash]struct{}) tcn.txsByInitialHeight[blockHeight] = txSet } txSet[*txHash] = struct{}{} } } // In order to update the height hint for all the required transactions // under one database transaction, we'll gather the set of unconfirmed // transactions along with the ones that confirmed at the current // height. To do so, we'll iterate over the confNotifications map, which // contains the transactions we currently have notifications for. Since // this map doesn't tell us whether the transaction hsa confirmed or // not, we'll need to look at txsByInitialHeight to determine so. var txsToUpdateHints []chainhash.Hash for confirmedTx := range tcn.txsByInitialHeight[tcn.currentHeight] { txsToUpdateHints = append(txsToUpdateHints, confirmedTx) } out: for maybeUnconfirmedTx := range tcn.confNotifications { for height, confirmedTxs := range tcn.txsByInitialHeight { // Skip the transactions that confirmed at the new block // height as those have already been added. if height == blockHeight { continue } // If the transaction was found within the set of // confirmed transactions at this height, we'll skip it. if _, ok := confirmedTxs[maybeUnconfirmedTx]; ok { continue out } } txsToUpdateHints = append(txsToUpdateHints, maybeUnconfirmedTx) } if len(txsToUpdateHints) > 0 { err := tcn.hintCache.CommitConfirmHint( tcn.currentHeight, txsToUpdateHints..., ) if err != nil { // The error is not fatal, so we should not return an // error to the caller. Log.Errorf("Unable to update confirm hint to %d for "+ "%v: %v", tcn.currentHeight, txsToUpdateHints, err) } } // Next, we'll dispatch an update to all of the notification clients for // our watched transactions with the number of confirmations left at // this new height. for _, txHashes := range tcn.txsByInitialHeight { for txHash := range txHashes { for _, ntfn := range tcn.confNotifications[txHash] { // If the notification hasn't learned about the // confirmation of its transaction yet (in the // case of historical confirmations), we'll skip // it. if ntfn.details == nil { continue } txConfHeight := ntfn.details.BlockHeight + ntfn.NumConfirmations - 1 numConfsLeft := txConfHeight - blockHeight // Since we don't clear notifications until // transactions are no longer under the risk of // being reorganized out of the chain, we'll // skip sending updates for transactions that // have already been confirmed. if int32(numConfsLeft) < 0 { continue } select { case ntfn.Event.Updates <- numConfsLeft: case <-tcn.quit: return ErrTxConfNotifierExiting } } } } // Then, we'll dispatch notifications for all the transactions that have // become confirmed at this new block height. for ntfn := range tcn.ntfnsByConfirmHeight[tcn.currentHeight] { Log.Infof("Dispatching %v conf notification for %v", ntfn.NumConfirmations, ntfn.TxID) select { case ntfn.Event.Confirmed <- ntfn.details: ntfn.dispatched = true case <-tcn.quit: return ErrTxConfNotifierExiting } } delete(tcn.ntfnsByConfirmHeight, tcn.currentHeight) // Clear entries from confNotifications and confTxsByInitialHeight. We // assume that reorgs deeper than the reorg safety limit do not happen, // so we can clear out entries for the block that is now mature. if tcn.currentHeight >= tcn.reorgSafetyLimit { matureBlockHeight := tcn.currentHeight - tcn.reorgSafetyLimit for txHash := range tcn.txsByInitialHeight[matureBlockHeight] { delete(tcn.confNotifications, txHash) } delete(tcn.txsByInitialHeight, matureBlockHeight) } return nil } // DisconnectTip handles the tip of the current chain being disconnected during // a chain reorganization. If any watched transactions were included in this // block, internal structures are updated to ensure a confirmation notification // is not sent unless the transaction is included in the new chain. func (tcn *TxConfNotifier) DisconnectTip(blockHeight uint32) error { select { case <-tcn.quit: return ErrTxConfNotifierExiting default: } tcn.Lock() defer tcn.Unlock() if blockHeight != tcn.currentHeight { return fmt.Errorf("Received blocks out of order: "+ "current height=%d, disconnected height=%d", tcn.currentHeight, blockHeight) } tcn.currentHeight-- tcn.reorgDepth++ // We'll go through all of our watched transactions and attempt to drain // their notification channels to ensure sending notifications to the // clients is always non-blocking. for initialHeight, txHashes := range tcn.txsByInitialHeight { for txHash := range txHashes { for _, ntfn := range tcn.confNotifications[txHash] { // First, we'll attempt to drain an update // from each notification to ensure sends to the // Updates channel are always non-blocking. select { case <-ntfn.Event.Updates: case <-tcn.quit: return ErrTxConfNotifierExiting default: } // Then, we'll check if the current transaction // was included in the block currently being // disconnected. If it was, we'll need to take // some necessary precautions. if initialHeight == blockHeight { // If the transaction's confirmation notification // has already been dispatched, we'll attempt to // notify the client it was reorged out of the chain. if ntfn.dispatched { // Attempt to drain the confirmation notification // to ensure sends to the Confirmed channel are // always non-blocking. select { case <-ntfn.Event.Confirmed: case <-tcn.quit: return ErrTxConfNotifierExiting default: } ntfn.dispatched = false // Send a negative confirmation notification to the // client indicating how many blocks have been // disconnected successively. select { case ntfn.Event.NegativeConf <- int32(tcn.reorgDepth): case <-tcn.quit: return ErrTxConfNotifierExiting } continue } // Otherwise, since the transactions was reorged out // of the chain, we can safely remove its accompanying // confirmation notification. confHeight := blockHeight + ntfn.NumConfirmations - 1 ntfnSet, exists := tcn.ntfnsByConfirmHeight[confHeight] if !exists { continue } delete(ntfnSet, ntfn) } } } } // Rewind the height hint for all watched transactions. var txs []chainhash.Hash for tx := range tcn.confNotifications { txs = append(txs, tx) } err := tcn.hintCache.CommitConfirmHint(tcn.currentHeight, txs...) if err != nil { // The error is not fatal, so we should not return an error to // the caller. Log.Errorf("Unable to update confirm hint to %d for %v: %v", tcn.currentHeight, txs, err) } // Finally, we can remove the transactions we're currently watching that // were included in this block height. delete(tcn.txsByInitialHeight, blockHeight) return nil } // TearDown is to be called when the owner of the TxConfNotifier is exiting. // This closes the event channels of all registered notifications that have // not been dispatched yet. func (tcn *TxConfNotifier) TearDown() { tcn.Lock() defer tcn.Unlock() close(tcn.quit) for _, ntfns := range tcn.confNotifications { for _, ntfn := range ntfns { if ntfn.dispatched { continue } close(ntfn.Event.Confirmed) close(ntfn.Event.Updates) close(ntfn.Event.NegativeConf) } } }