package bitcoindnotify import ( "errors" "fmt" "sync" "sync/atomic" "time" "github.com/btcsuite/btcd/btcjson" "github.com/btcsuite/btcd/chaincfg/chainhash" "github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcutil" "github.com/btcsuite/btcwallet/chain" "github.com/btcsuite/btcwallet/wtxmgr" "github.com/lightningnetwork/lnd/chainntnfs" ) const ( // notifierType uniquely identifies this concrete implementation of the // ChainNotifier interface. notifierType = "bitcoind" // reorgSafetyLimit is assumed maximum depth of a chain reorganization. // After this many confirmation, transaction confirmation info will be // pruned. reorgSafetyLimit = 100 ) var ( // ErrChainNotifierShuttingDown is used when we are trying to // measure a spend notification when notifier is already stopped. ErrChainNotifierShuttingDown = errors.New("chainntnfs: system interrupt " + "while attempting to register for spend notification.") // ErrTransactionNotFound is an error returned when we attempt to find a // transaction by manually scanning the chain within a specific range // but it is not found. ErrTransactionNotFound = errors.New("transaction not found within range") ) // chainUpdate encapsulates an update to the current main chain. This struct is // used as an element within an unbounded queue in order to avoid blocking the // main rpc dispatch rule. type chainUpdate struct { blockHash *chainhash.Hash blockHeight int32 } // TODO(roasbeef): generalize struct below: // * move chans to config // * extract common code // * allow outside callers to handle send conditions // BitcoindNotifier implements the ChainNotifier interface using a bitcoind // chain client. Multiple concurrent clients are supported. All notifications // are achieved via non-blocking sends on client channels. type BitcoindNotifier struct { confClientCounter uint64 // To be used atomically. spendClientCounter uint64 // To be used atomically. epochClientCounter uint64 // To be used atomically. started int32 // To be used atomically. stopped int32 // To be used atomically. chainConn *chain.BitcoindClient notificationCancels chan interface{} notificationRegistry chan interface{} spendNotifications map[wire.OutPoint]map[uint64]*spendNotification txConfNotifier *chainntnfs.TxConfNotifier blockEpochClients map[uint64]*blockEpochRegistration bestBlock chainntnfs.BlockEpoch // spendHintCache is a cache used to query and update the latest height // hints for an outpoint. Each height hint represents the earliest // height at which the outpoint could have been spent within the chain. spendHintCache chainntnfs.SpendHintCache // confirmHintCache is a cache used to query the latest height hints for // a transaction. Each height hint represents the earliest height at // which the transaction could have confirmed within the chain. confirmHintCache chainntnfs.ConfirmHintCache wg sync.WaitGroup quit chan struct{} } // Ensure BitcoindNotifier implements the ChainNotifier interface at compile // time. var _ chainntnfs.ChainNotifier = (*BitcoindNotifier)(nil) // New returns a new BitcoindNotifier instance. This function assumes the // bitcoind node detailed in the passed configuration is already running, and // willing to accept RPC requests and new zmq clients. func New(chainConn *chain.BitcoindConn, spendHintCache chainntnfs.SpendHintCache, confirmHintCache chainntnfs.ConfirmHintCache) *BitcoindNotifier { notifier := &BitcoindNotifier{ notificationCancels: make(chan interface{}), notificationRegistry: make(chan interface{}), blockEpochClients: make(map[uint64]*blockEpochRegistration), spendNotifications: make(map[wire.OutPoint]map[uint64]*spendNotification), spendHintCache: spendHintCache, confirmHintCache: confirmHintCache, quit: make(chan struct{}), } notifier.chainConn = chainConn.NewBitcoindClient(time.Unix(0, 0)) return notifier } // Start connects to the running bitcoind node over websockets, registers for // block notifications, and finally launches all related helper goroutines. func (b *BitcoindNotifier) Start() error { // Already started? if atomic.AddInt32(&b.started, 1) != 1 { return nil } // Connect to bitcoind, and register for notifications on connected, // and disconnected blocks. if err := b.chainConn.Start(); err != nil { return err } if err := b.chainConn.NotifyBlocks(); err != nil { return err } currentHash, currentHeight, err := b.chainConn.GetBestBlock() if err != nil { return err } b.txConfNotifier = chainntnfs.NewTxConfNotifier( uint32(currentHeight), reorgSafetyLimit, b.confirmHintCache, ) b.bestBlock = chainntnfs.BlockEpoch{ Height: currentHeight, Hash: currentHash, } b.wg.Add(1) go b.notificationDispatcher() return nil } // Stop shutsdown the BitcoindNotifier. func (b *BitcoindNotifier) Stop() error { // Already shutting down? if atomic.AddInt32(&b.stopped, 1) != 1 { return nil } // Shutdown the rpc client, this gracefully disconnects from bitcoind, // and cleans up all related resources. b.chainConn.Stop() close(b.quit) b.wg.Wait() // Notify all pending clients of our shutdown by closing the related // notification channels. for _, spendClients := range b.spendNotifications { for _, spendClient := range spendClients { close(spendClient.spendChan) } } for _, epochClient := range b.blockEpochClients { close(epochClient.cancelChan) epochClient.wg.Wait() close(epochClient.epochChan) } b.txConfNotifier.TearDown() return nil } // blockNtfn packages a notification of a connected/disconnected block along // with its height at the time. type blockNtfn struct { sha *chainhash.Hash height int32 } // notificationDispatcher is the primary goroutine which handles client // notification registrations, as well as notification dispatches. func (b *BitcoindNotifier) notificationDispatcher() { out: for { select { case cancelMsg := <-b.notificationCancels: switch msg := cancelMsg.(type) { case *spendCancel: chainntnfs.Log.Infof("Cancelling spend "+ "notification for out_point=%v, "+ "spend_id=%v", msg.op, msg.spendID) // Before we attempt to close the spendChan, // ensure that the notification hasn't already // yet been dispatched. if outPointClients, ok := b.spendNotifications[msg.op]; ok { close(outPointClients[msg.spendID].spendChan) delete(b.spendNotifications[msg.op], msg.spendID) } case *epochCancel: chainntnfs.Log.Infof("Cancelling epoch "+ "notification, epoch_id=%v", msg.epochID) // First, we'll lookup the original // registration in order to stop the active // queue goroutine. reg := b.blockEpochClients[msg.epochID] reg.epochQueue.Stop() // Next, close the cancel channel for this // specific client, and wait for the client to // exit. close(b.blockEpochClients[msg.epochID].cancelChan) b.blockEpochClients[msg.epochID].wg.Wait() // Once the client has exited, we can then // safely close the channel used to send epoch // notifications, in order to notify any // listeners that the intent has been // cancelled. close(b.blockEpochClients[msg.epochID].epochChan) delete(b.blockEpochClients, msg.epochID) } case registerMsg := <-b.notificationRegistry: switch msg := registerMsg.(type) { case *spendNotification: chainntnfs.Log.Infof("New spend subscription: "+ "utxo=%v", msg.targetOutpoint) op := *msg.targetOutpoint if _, ok := b.spendNotifications[op]; !ok { b.spendNotifications[op] = make(map[uint64]*spendNotification) } b.spendNotifications[op][msg.spendID] = msg case *confirmationNotification: chainntnfs.Log.Infof("New confirmation "+ "subscription: txid=%v, numconfs=%v", msg.TxID, msg.NumConfirmations) currentHeight := uint32(b.bestBlock.Height) // Look up whether the transaction is already // included in the active chain. We'll do this // in a goroutine to prevent blocking // potentially long rescans. b.wg.Add(1) go func() { defer b.wg.Done() confDetails, err := b.historicalConfDetails( msg.TxID, msg.heightHint, currentHeight, ) if err != nil { chainntnfs.Log.Error(err) return } if confDetails != nil { err := b.txConfNotifier.UpdateConfDetails( *msg.TxID, msg.ConfID, confDetails, ) if err != nil { chainntnfs.Log.Error(err) } } }() case *blockEpochRegistration: chainntnfs.Log.Infof("New block epoch subscription") b.blockEpochClients[msg.epochID] = msg if msg.bestBlock != nil { missedBlocks, err := chainntnfs.GetClientMissedBlocks( b.chainConn, msg.bestBlock, b.bestBlock.Height, true, ) if err != nil { msg.errorChan <- err continue } for _, block := range missedBlocks { b.notifyBlockEpochClient(msg, block.Height, block.Hash) } } msg.errorChan <- nil case chain.RelevantTx: b.handleRelevantTx(msg, b.bestBlock.Height) } case ntfn := <-b.chainConn.Notifications(): switch item := ntfn.(type) { case chain.BlockConnected: blockHeader, err := b.chainConn.GetBlockHeader(&item.Hash) if err != nil { chainntnfs.Log.Errorf("Unable to fetch "+ "block header: %v", err) continue } if blockHeader.PrevBlock != *b.bestBlock.Hash { // Handle the case where the notifier // missed some blocks from its chain // backend. chainntnfs.Log.Infof("Missed blocks, " + "attempting to catch up") newBestBlock, missedBlocks, err := chainntnfs.HandleMissedBlocks( b.chainConn, b.txConfNotifier, b.bestBlock, item.Height, true, ) if err != nil { // Set the bestBlock here in case // a catch up partially completed. b.bestBlock = newBestBlock chainntnfs.Log.Error(err) continue } for _, block := range missedBlocks { err := b.handleBlockConnected(block) if err != nil { chainntnfs.Log.Error(err) continue out } } } newBlock := chainntnfs.BlockEpoch{ Height: item.Height, Hash: &item.Hash, } if err := b.handleBlockConnected(newBlock); err != nil { chainntnfs.Log.Error(err) } continue case chain.BlockDisconnected: if item.Height != b.bestBlock.Height { chainntnfs.Log.Infof("Missed disconnected" + "blocks, attempting to catch up") } newBestBlock, err := chainntnfs.RewindChain( b.chainConn, b.txConfNotifier, b.bestBlock, item.Height-1, ) if err != nil { chainntnfs.Log.Errorf("Unable to rewind chain "+ "from height %d to height %d: %v", b.bestBlock.Height, item.Height-1, err) } // Set the bestBlock here in case a chain // rewind partially completed. b.bestBlock = newBestBlock case chain.RelevantTx: b.handleRelevantTx(item, b.bestBlock.Height) } case <-b.quit: break out } } b.wg.Done() } // handleRelevantTx notifies any clients of a relevant transaction. func (b *BitcoindNotifier) handleRelevantTx(tx chain.RelevantTx, bestHeight int32) { msgTx := tx.TxRecord.MsgTx // We only care about notifying on confirmed spends, so in case this is // a mempool spend, we can continue, and wait for the spend to appear // in chain. if tx.Block == nil { return } // First, check if this transaction spends an output // that has an existing spend notification for it. for i, txIn := range msgTx.TxIn { prevOut := txIn.PreviousOutPoint // If this transaction indeed does spend an // output which we have a registered // notification for, then create a spend // summary, finally sending off the details to // the notification subscriber. if clients, ok := b.spendNotifications[prevOut]; ok { spenderSha := msgTx.TxHash() spendDetails := &chainntnfs.SpendDetail{ SpentOutPoint: &prevOut, SpenderTxHash: &spenderSha, SpendingTx: &msgTx, SpenderInputIndex: uint32(i), } spendDetails.SpendingHeight = tx.Block.Height for _, ntfn := range clients { chainntnfs.Log.Infof("Dispatching confirmed "+ "spend notification for outpoint=%v "+ "at height %v", ntfn.targetOutpoint, spendDetails.SpendingHeight) ntfn.spendChan <- spendDetails // Close spendChan to ensure that any calls to // Cancel will not block. This is safe to do // since the channel is buffered, and the // message can still be read by the receiver. close(ntfn.spendChan) } delete(b.spendNotifications, prevOut) } } } // historicalConfDetails looks up whether a transaction is already included in a // block in the active chain and, if so, returns details about the confirmation. func (b *BitcoindNotifier) historicalConfDetails(txid *chainhash.Hash, heightHint, currentHeight uint32) (*chainntnfs.TxConfirmation, error) { // First, we'll attempt to retrieve the transaction details using the // backend node's transaction index. txConf, err := b.confDetailsFromTxIndex(txid) if err != nil { return nil, err } if txConf != nil { return txConf, nil } // If the backend node's transaction index is not enabled, then we'll // fall back to manually scanning the chain's blocks, looking for the // block where the transaction was included in. return b.confDetailsManually(txid, heightHint, currentHeight) } // confDetailsFromTxIndex looks up whether a transaction is already included // in a block in the active chain by using the backend node's transaction index. // If the transaction is found, its confirmation details are returned. // Otherwise, nil is returned. func (b *BitcoindNotifier) confDetailsFromTxIndex(txid *chainhash.Hash, ) (*chainntnfs.TxConfirmation, error) { // If the transaction has some or all of its confirmations required, // then we may be able to dispatch it immediately. tx, err := b.chainConn.GetRawTransactionVerbose(txid) if err != nil { // Avoid returning an error if the transaction index is not // enabled to proceed with fallback methods. jsonErr, ok := err.(*btcjson.RPCError) if !ok || jsonErr.Code != btcjson.ErrRPCNoTxInfo { return nil, fmt.Errorf("unable to query for txid "+ "%v: %v", txid, err) } } // Make sure we actually retrieved a transaction that is included in a // block. Without this, we won't be able to retrieve its confirmation // details. if tx == nil || tx.BlockHash == "" { return nil, nil } // As we need to fully populate the returned TxConfirmation struct, // grab the block in which the transaction was confirmed so we can // locate its exact index within the block. blockHash, err := chainhash.NewHashFromStr(tx.BlockHash) if err != nil { return nil, fmt.Errorf("unable to get block hash %v for "+ "historical dispatch: %v", tx.BlockHash, err) } block, err := b.chainConn.GetBlockVerbose(blockHash) if err != nil { return nil, fmt.Errorf("unable to get block with hash %v for "+ "historical dispatch: %v", blockHash, err) } // If the block was obtained, locate the transaction's index within the // block so we can give the subscriber full confirmation details. targetTxidStr := txid.String() for txIndex, txHash := range block.Tx { if txHash == targetTxidStr { return &chainntnfs.TxConfirmation{ BlockHash: blockHash, BlockHeight: uint32(block.Height), TxIndex: uint32(txIndex), }, nil } } // We return an error because we should have found the transaction // within the block, but didn't. return nil, fmt.Errorf("unable to locate tx %v in block %v", txid, blockHash) } // confDetailsManually looks up whether a transaction is already included in a // block in the active chain by scanning the chain's blocks, starting from the // earliest height the transaction could have been included in, to the current // height in the chain. If the transaction is found, its confirmation details // are returned. Otherwise, nil is returned. func (b *BitcoindNotifier) confDetailsManually(txid *chainhash.Hash, heightHint, currentHeight uint32) (*chainntnfs.TxConfirmation, error) { targetTxidStr := txid.String() // Begin scanning blocks at every height to determine where the // transaction was included in. for height := heightHint; height <= currentHeight; height++ { // Ensure we haven't been requested to shut down before // processing the next height. select { case <-b.quit: return nil, ErrChainNotifierShuttingDown default: } blockHash, err := b.chainConn.GetBlockHash(int64(height)) if err != nil { return nil, fmt.Errorf("unable to get hash from block "+ "with height %d", height) } block, err := b.chainConn.GetBlockVerbose(blockHash) if err != nil { return nil, fmt.Errorf("unable to get block with hash "+ "%v: %v", blockHash, err) } for txIndex, txHash := range block.Tx { // If we're able to find the transaction in this block, // return its confirmation details. if txHash == targetTxidStr { return &chainntnfs.TxConfirmation{ BlockHash: blockHash, BlockHeight: height, TxIndex: uint32(txIndex), }, nil } } } // If we reach here, then we were not able to find the transaction // within a block, so we avoid returning an error. return nil, nil } // handleBlockConnected applies a chain update for a new block. Any watched // transactions included this block will processed to either send notifications // now or after numConfirmations confs. func (b *BitcoindNotifier) handleBlockConnected(block chainntnfs.BlockEpoch) error { rawBlock, err := b.chainConn.GetBlock(block.Hash) if err != nil { return fmt.Errorf("unable to get block: %v", err) } txns := btcutil.NewBlock(rawBlock).Transactions() err = b.txConfNotifier.ConnectTip( block.Hash, uint32(block.Height), txns) if err != nil { return fmt.Errorf("unable to connect tip: %v", err) } chainntnfs.Log.Infof("New block: height=%v, sha=%v", block.Height, block.Hash) // We want to set the best block before dispatching notifications so // if any subscribers make queries based on their received block epoch, // our state is fully updated in time. b.bestBlock = block b.notifyBlockEpochs(block.Height, block.Hash) // Finally, we'll update the spend height hint for all of our watched // outpoints that have not been spent yet. This is safe to do as we do // not watch already spent outpoints for spend notifications. ops := make([]wire.OutPoint, 0, len(b.spendNotifications)) for op := range b.spendNotifications { ops = append(ops, op) } if len(ops) > 0 { err := b.spendHintCache.CommitSpendHint( uint32(block.Height), ops..., ) if err != nil { // The error is not fatal, so we should not return an // error to the caller. chainntnfs.Log.Errorf("Unable to update spend hint to "+ "%d for %v: %v", block.Height, ops, err) } } return nil } // notifyBlockEpochs notifies all registered block epoch clients of the newly // connected block to the main chain. func (b *BitcoindNotifier) notifyBlockEpochs(newHeight int32, newSha *chainhash.Hash) { for _, client := range b.blockEpochClients { b.notifyBlockEpochClient(client, newHeight, newSha) } } // notifyBlockEpochClient sends a registered block epoch client a notification // about a specific block. func (b *BitcoindNotifier) notifyBlockEpochClient(epochClient *blockEpochRegistration, height int32, sha *chainhash.Hash) { epoch := &chainntnfs.BlockEpoch{ Height: height, Hash: sha, } select { case epochClient.epochQueue.ChanIn() <- epoch: case <-epochClient.cancelChan: case <-b.quit: } } // spendNotification couples a target outpoint along with the channel used for // notifications once a spend of the outpoint has been detected. type spendNotification struct { targetOutpoint *wire.OutPoint spendChan chan *chainntnfs.SpendDetail spendID uint64 heightHint uint32 } // spendCancel is a message sent to the BitcoindNotifier when a client wishes // to cancel an outstanding spend notification that has yet to be dispatched. type spendCancel struct { // op is the target outpoint of the notification to be cancelled. op wire.OutPoint // spendID the ID of the notification to cancel. spendID uint64 } // RegisterSpendNtfn registers an intent to be notified once the target // outpoint has been spent by a transaction on-chain. Once a spend of the target // outpoint has been detected, the details of the spending event will be sent // across the 'Spend' channel. The heightHint should represent the earliest // height in the chain where the transaction could have been spent in. func (b *BitcoindNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint, pkScript []byte, heightHint uint32) (*chainntnfs.SpendEvent, error) { // Before proceeding to register the notification, we'll query our // height hint cache to determine whether a better one exists. if hint, err := b.spendHintCache.QuerySpendHint(*outpoint); err == nil { if hint > heightHint { chainntnfs.Log.Debugf("Using height hint %d retrieved "+ "from cache for %v", hint, outpoint) heightHint = hint } } // Construct a notification request for the outpoint and send it to the // main event loop. ntfn := &spendNotification{ targetOutpoint: outpoint, spendChan: make(chan *chainntnfs.SpendDetail, 1), spendID: atomic.AddUint64(&b.spendClientCounter, 1), } select { case <-b.quit: return nil, ErrChainNotifierShuttingDown case b.notificationRegistry <- ntfn: } if err := b.chainConn.NotifySpent([]*wire.OutPoint{outpoint}); err != nil { return nil, err } // The following conditional checks to ensure that when a spend // notification is registered, the output hasn't already been spent. If // the output is no longer in the UTXO set, the chain will be rescanned // from the point where the output was added. The rescan will dispatch // the notification. txOut, err := b.chainConn.GetTxOut(&outpoint.Hash, outpoint.Index, true) if err != nil { return nil, err } // If the output is unspent, then we'll write it to the cache with the // given height hint. This allows us to increase the height hint as the // chain extends and the output remains unspent. if txOut != nil { err := b.spendHintCache.CommitSpendHint(heightHint, *outpoint) if err != nil { // The error is not fatal, so we should not return an // error to the caller. chainntnfs.Log.Error("Unable to update spend hint to "+ "%d for %v: %v", heightHint, *outpoint, err) } } else { // Otherwise, we'll determine when the output was spent. // // First, we'll attempt to retrieve the transaction's block hash // using the backend's transaction index. tx, err := b.chainConn.GetRawTransactionVerbose(&outpoint.Hash) if err != nil { // Avoid returning an error if the transaction was not // found to proceed with fallback methods. jsonErr, ok := err.(*btcjson.RPCError) if !ok || jsonErr.Code != btcjson.ErrRPCNoTxInfo { return nil, fmt.Errorf("unable to query for "+ "txid %v: %v", outpoint.Hash, err) } } var blockHash *chainhash.Hash if tx != nil && tx.BlockHash != "" { // If we're able to retrieve a valid block hash from the // transaction, then we'll use it as our rescan starting // point. blockHash, err = chainhash.NewHashFromStr(tx.BlockHash) if err != nil { return nil, err } } else { // Otherwise, we'll attempt to retrieve the hash for the // block at the heightHint. blockHash, err = b.chainConn.GetBlockHash( int64(heightHint), ) if err != nil { return nil, fmt.Errorf("unable to retrieve "+ "hash for block with height %d: %v", heightHint, err) } } // We'll only scan old blocks if the transaction has actually // been included within a block. Otherwise, we'll encounter an // error when scanning for blocks. This can happens in the case // of a race condition, wherein the output itself is unspent, // and only arrives in the mempool after the getxout call. if blockHash != nil { // Rescan all the blocks until the current one. startHeight, err := b.chainConn.GetBlockHeight( blockHash, ) if err != nil { return nil, err } _, endHeight, err := b.chainConn.GetBestBlock() if err != nil { return nil, err } // In order to ensure we don't block the caller on what // may be a long rescan, we'll launch a goroutine to do // so in the background. b.wg.Add(1) go func() { defer b.wg.Done() err := b.dispatchSpendDetailsManually( *outpoint, startHeight, endHeight, ) if err != nil { chainntnfs.Log.Errorf("Rescan for spend "+ "notification txout(%x) "+ "failed: %v", outpoint, err) } }() } } return &chainntnfs.SpendEvent{ Spend: ntfn.spendChan, Cancel: func() { cancel := &spendCancel{ op: *outpoint, spendID: ntfn.spendID, } // Submit spend cancellation to notification dispatcher. select { case b.notificationCancels <- cancel: // Cancellation is being handled, drain the // spend chan until it is closed before yielding // to the caller. for { select { case _, ok := <-ntfn.spendChan: if !ok { return } case <-b.quit: return } } case <-b.quit: } }, }, nil } // disaptchSpendDetailsManually attempts to manually scan the chain within the // given height range for a transaction that spends the given outpoint. If one // is found, it's spending details are sent to the notifier dispatcher, which // will then dispatch the notification to all of its clients. func (b *BitcoindNotifier) dispatchSpendDetailsManually(op wire.OutPoint, startHeight, endHeight int32) error { // Begin scanning blocks at every height to determine if the outpoint // was spent. for height := startHeight; height <= endHeight; height++ { // Ensure we haven't been requested to shut down before // processing the next height. select { case <-b.quit: return ErrChainNotifierShuttingDown default: } blockHash, err := b.chainConn.GetBlockHash(int64(height)) if err != nil { return fmt.Errorf("unable to retrieve hash for block "+ "with height %d: %v", height, err) } block, err := b.chainConn.GetBlock(blockHash) if err != nil { return fmt.Errorf("unable to retrieve block with hash "+ "%v: %v", blockHash, err) } for _, tx := range block.Transactions { for _, in := range tx.TxIn { if in.PreviousOutPoint != op { continue } // If this transaction input spends the // outpoint, we'll gather the details of the // spending transaction and dispatch a spend // notification to our clients. relTx := chain.RelevantTx{ TxRecord: &wtxmgr.TxRecord{ MsgTx: *tx, Hash: tx.TxHash(), Received: block.Header.Timestamp, }, Block: &wtxmgr.BlockMeta{ Block: wtxmgr.Block{ Hash: *blockHash, Height: height, }, Time: block.Header.Timestamp, }, } select { case b.notificationRegistry <- relTx: case <-b.quit: return ErrChainNotifierShuttingDown } return nil } } } return ErrTransactionNotFound } // confirmationNotification represents a client's intent to receive a // notification once the target txid reaches numConfirmations confirmations. type confirmationNotification struct { chainntnfs.ConfNtfn heightHint uint32 } // RegisterConfirmationsNtfn registers a notification with BitcoindNotifier // which will be triggered once the txid reaches numConfs number of // confirmations. func (b *BitcoindNotifier) RegisterConfirmationsNtfn(txid *chainhash.Hash, _ []byte, numConfs, heightHint uint32) (*chainntnfs.ConfirmationEvent, error) { // Before proceeding to register the notification, we'll query our // height hint cache to determine whether a better one exists. if hint, err := b.confirmHintCache.QueryConfirmHint(*txid); err == nil { if hint > heightHint { chainntnfs.Log.Debugf("Using height hint %d retrieved "+ "from cache for %v", hint, txid) heightHint = hint } } // Construct a notification request for the transaction and send it to // the main event loop. ntfn := &confirmationNotification{ ConfNtfn: chainntnfs.ConfNtfn{ ConfID: atomic.AddUint64(&b.confClientCounter, 1), TxID: txid, NumConfirmations: numConfs, Event: chainntnfs.NewConfirmationEvent(numConfs), }, heightHint: heightHint, } if err := b.txConfNotifier.Register(&ntfn.ConfNtfn); err != nil { return nil, err } select { case b.notificationRegistry <- ntfn: return ntfn.Event, nil case <-b.quit: return nil, ErrChainNotifierShuttingDown } } // blockEpochRegistration represents a client's intent to receive a // notification with each newly connected block. type blockEpochRegistration struct { epochID uint64 epochChan chan *chainntnfs.BlockEpoch epochQueue *chainntnfs.ConcurrentQueue bestBlock *chainntnfs.BlockEpoch errorChan chan error cancelChan chan struct{} wg sync.WaitGroup } // epochCancel is a message sent to the BitcoindNotifier when a client wishes // to cancel an outstanding epoch notification that has yet to be dispatched. type epochCancel struct { epochID uint64 } // RegisterBlockEpochNtfn returns a BlockEpochEvent which subscribes the // caller to receive notifications, of each new block connected to the main // chain. Clients have the option of passing in their best known block, which // the notifier uses to check if they are behind on blocks and catch them up. func (b *BitcoindNotifier) RegisterBlockEpochNtfn( bestBlock *chainntnfs.BlockEpoch) (*chainntnfs.BlockEpochEvent, error) { reg := &blockEpochRegistration{ epochQueue: chainntnfs.NewConcurrentQueue(20), epochChan: make(chan *chainntnfs.BlockEpoch, 20), cancelChan: make(chan struct{}), epochID: atomic.AddUint64(&b.epochClientCounter, 1), bestBlock: bestBlock, errorChan: make(chan error, 1), } reg.epochQueue.Start() // Before we send the request to the main goroutine, we'll launch a new // goroutine to proxy items added to our queue to the client itself. // This ensures that all notifications are received *in order*. reg.wg.Add(1) go func() { defer reg.wg.Done() for { select { case ntfn := <-reg.epochQueue.ChanOut(): blockNtfn := ntfn.(*chainntnfs.BlockEpoch) select { case reg.epochChan <- blockNtfn: case <-reg.cancelChan: return case <-b.quit: return } case <-reg.cancelChan: return case <-b.quit: return } } }() select { case <-b.quit: // As we're exiting before the registration could be sent, // we'll stop the queue now ourselves. reg.epochQueue.Stop() return nil, errors.New("chainntnfs: system interrupt while " + "attempting to register for block epoch notification.") case b.notificationRegistry <- reg: return &chainntnfs.BlockEpochEvent{ Epochs: reg.epochChan, Cancel: func() { cancel := &epochCancel{ epochID: reg.epochID, } // Submit epoch cancellation to notification dispatcher. select { case b.notificationCancels <- cancel: // Cancellation is being handled, drain the epoch channel until it is // closed before yielding to caller. for { select { case _, ok := <-reg.epochChan: if !ok { return } case <-b.quit: return } } case <-b.quit: } }, }, nil } }