lnd.xprv/chainntnfs/bitcoindnotify/bitcoind.go

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package bitcoindnotify
import (
"errors"
"fmt"
"sync"
"sync/atomic"
"time"
"github.com/btcsuite/btcd/btcjson"
"github.com/btcsuite/btcd/chaincfg"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/rpcclient"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcwallet/chain"
"github.com/btcsuite/btcwallet/wtxmgr"
"github.com/lightningnetwork/lnd/chainntnfs"
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)
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")
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)
// 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
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// 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.
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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
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(config *rpcclient.ConnConfig, zmqConnect string,
params chaincfg.Params) (*BitcoindNotifier, error) {
notifier := &BitcoindNotifier{
notificationCancels: make(chan interface{}),
notificationRegistry: make(chan interface{}),
blockEpochClients: make(map[uint64]*blockEpochRegistration),
spendNotifications: make(map[wire.OutPoint]map[uint64]*spendNotification),
quit: make(chan struct{}),
}
// Disable connecting to bitcoind within the rpcclient.New method. We
// defer establishing the connection to our .Start() method.
config.DisableConnectOnNew = true
config.DisableAutoReconnect = false
chainConn, err := chain.NewBitcoindClient(&params, config.Host,
config.User, config.Pass, zmqConnect, 100*time.Millisecond)
if err != nil {
return nil, err
}
notifier.chainConn = chainConn
return notifier, nil
}
// 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
}
_, currentHeight, err := b.chainConn.GetBestBlock()
if err != nil {
return err
}
b.txConfNotifier = chainntnfs.NewTxConfNotifier(
uint32(currentHeight), reorgSafetyLimit)
b.wg.Add(1)
go b.notificationDispatcher(currentHeight)
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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()
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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(bestHeight int32) {
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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
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// 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 "+
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"subscription: txid=%v, numconfs=%v",
msg.TxID, msg.NumConfirmations)
currentHeight := uint32(bestHeight)
// 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)
}
}
}()
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case *blockEpochRegistration:
chainntnfs.Log.Infof("New block epoch subscription")
b.blockEpochClients[msg.epochID] = msg
case chain.RelevantTx:
b.handleRelevantTx(msg, bestHeight)
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}
case ntfn := <-b.chainConn.Notifications():
switch item := ntfn.(type) {
case chain.BlockConnected:
if item.Height != bestHeight+1 {
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chainntnfs.Log.Warnf("Received blocks out of order: "+
"current height=%d, new height=%d",
bestHeight, item.Height)
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continue
}
bestHeight = item.Height
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rawBlock, err := b.chainConn.GetBlock(&item.Hash)
if err != nil {
chainntnfs.Log.Errorf("Unable to get block: %v", err)
continue
}
chainntnfs.Log.Infof("New block: height=%v, sha=%v",
item.Height, item.Hash)
b.notifyBlockEpochs(item.Height, &item.Hash)
txns := btcutil.NewBlock(rawBlock).Transactions()
err = b.txConfNotifier.ConnectTip(&item.Hash,
uint32(item.Height), txns)
if err != nil {
chainntnfs.Log.Error(err)
}
continue
case chain.BlockDisconnected:
if item.Height != bestHeight {
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chainntnfs.Log.Warnf("Received blocks "+
"out of order: current height="+
"%d, disconnected height=%d",
bestHeight, item.Height)
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continue
}
bestHeight = item.Height - 1
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chainntnfs.Log.Infof("Block disconnected from "+
"main chain: height=%v, sha=%v",
item.Height, item.Hash)
err := b.txConfNotifier.DisconnectTip(
uint32(item.Height))
if err != nil {
chainntnfs.Log.Error(err)
}
case chain.RelevantTx:
b.handleRelevantTx(item, bestHeight)
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}
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)
}
}
}
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// 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,
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) (*chainntnfs.TxConfirmation, error) {
// If the transaction has some or all of its confirmations required,
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// 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)
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}
}
// 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
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}
// 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)
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}
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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)
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}
// If the block was obtained, locate the transaction's index within the
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// block so we can give the subscriber full confirmation details.
targetTxidStr := txid.String()
for txIndex, txHash := range block.Tx {
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if txHash == targetTxidStr {
return &chainntnfs.TxConfirmation{
BlockHash: blockHash,
BlockHeight: uint32(block.Height),
TxIndex: uint32(txIndex),
}, nil
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}
}
// 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)
}
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// 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
}
}
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}
// 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
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}
// 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) {
epoch := &chainntnfs.BlockEpoch{
Height: newHeight,
Hash: newSha,
}
for _, epochClient := range b.blockEpochClients {
select {
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case epochClient.epochQueue.ChanIn() <- epoch:
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case <-epochClient.cancelChan:
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case <-b.quit:
}
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}
}
// 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
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}
// 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.
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func (b *BitcoindNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint,
pkScript []byte, heightHint uint32) (*chainntnfs.SpendEvent, error) {
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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)
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if err != nil {
return nil, err
}
if txOut == nil {
// First, we'll attempt to retrieve the transaction's block hash
// using the backend's transaction index.
tx, err := b.chainConn.GetRawTransactionVerbose(&outpoint.Hash)
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if err != nil {
// Avoid returning an error if the transaction was not
// found to proceed with fallback methods.
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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 {
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return nil, 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,
)
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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)
}
}()
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}
}
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.
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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 err
}
block, err := b.chainConn.GetBlock(blockHash)
if err != nil {
return 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
}
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// confirmationNotification represents a client's intent to receive a
// notification once the target txid reaches numConfirmations confirmations.
type confirmationNotification struct {
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chainntnfs.ConfNtfn
heightHint uint32
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}
// 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) {
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ntfn := &confirmationNotification{
ConfNtfn: chainntnfs.ConfNtfn{
ConfID: atomic.AddUint64(&b.confClientCounter, 1),
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TxID: txid,
NumConfirmations: numConfs,
Event: chainntnfs.NewConfirmationEvent(numConfs),
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},
heightHint: heightHint,
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}
if err := b.txConfNotifier.Register(&ntfn.ConfNtfn); err != nil {
return nil, err
}
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select {
case b.notificationRegistry <- ntfn:
return ntfn.Event, nil
case <-b.quit:
return nil, ErrChainNotifierShuttingDown
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}
}
// 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
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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.
func (b *BitcoindNotifier) RegisterBlockEpochNtfn() (*chainntnfs.BlockEpochEvent, error) {
reg := &blockEpochRegistration{
epochQueue: chainntnfs.NewConcurrentQueue(20),
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epochChan: make(chan *chainntnfs.BlockEpoch, 20),
cancelChan: make(chan struct{}),
epochID: atomic.AddUint64(&b.epochClientCounter, 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
}
}
}()
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select {
case <-b.quit:
// As we're exiting before the registration could be sent,
// we'll stop the queue now ourselves.
reg.epochQueue.Stop()
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return nil, errors.New("chainntnfs: system interrupt while " +
"attempting to register for block epoch notification.")
case b.notificationRegistry <- reg:
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return &chainntnfs.BlockEpochEvent{
Epochs: reg.epochChan,
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Cancel: func() {
cancel := &epochCancel{
epochID: reg.epochID,
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}
// 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:
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if !ok {
return
}
case <-b.quit:
return
}
}
case <-b.quit:
}
},
}, nil
}
}