lnd.xprv/chainntnfs/bitcoindnotify/bitcoind.go

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package bitcoindnotify
import (
"errors"
"fmt"
"sync"
"sync/atomic"
"github.com/btcsuite/btcd/btcjson"
"github.com/btcsuite/btcd/chaincfg"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcwallet/chain"
"github.com/lightningnetwork/lnd/chainntnfs"
"github.com/lightningnetwork/lnd/queue"
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)
const (
// notifierType uniquely identifies this concrete implementation of the
// ChainNotifier interface.
notifierType = "bitcoind"
)
// 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 {
epochClientCounter uint64 // To be used atomically.
started int32 // To be used atomically.
stopped int32 // To be used atomically.
chainConn *chain.BitcoindClient
chainParams *chaincfg.Params
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notificationCancels chan interface{}
notificationRegistry chan interface{}
txNotifier *chainntnfs.TxNotifier
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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
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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
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// willing to accept RPC requests and new zmq clients.
func New(chainConn *chain.BitcoindConn, chainParams *chaincfg.Params,
spendHintCache chainntnfs.SpendHintCache,
confirmHintCache chainntnfs.ConfirmHintCache) *BitcoindNotifier {
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notifier := &BitcoindNotifier{
chainParams: chainParams,
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notificationCancels: make(chan interface{}),
notificationRegistry: make(chan interface{}),
blockEpochClients: make(map[uint64]*blockEpochRegistration),
spendHintCache: spendHintCache,
confirmHintCache: confirmHintCache,
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quit: make(chan struct{}),
}
notifier.chainConn = chainConn.NewBitcoindClient()
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return notifier
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}
// 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()
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if err != nil {
return err
}
b.txNotifier = chainntnfs.NewTxNotifier(
uint32(currentHeight), chainntnfs.ReorgSafetyLimit,
b.confirmHintCache, b.spendHintCache,
)
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b.bestBlock = chainntnfs.BlockEpoch{
Height: currentHeight,
Hash: currentHash,
}
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b.wg.Add(1)
go b.notificationDispatcher()
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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 _, epochClient := range b.blockEpochClients {
close(epochClient.cancelChan)
epochClient.wg.Wait()
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close(epochClient.epochChan)
}
b.txNotifier.TearDown()
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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() {
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out:
for {
select {
case cancelMsg := <-b.notificationCancels:
switch msg := cancelMsg.(type) {
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 *chainntnfs.HistoricalConfDispatch:
// 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.
//
// TODO(wilmer): add retry logic if rescan fails?
b.wg.Add(1)
go func() {
defer b.wg.Done()
confDetails, _, err := b.historicalConfDetails(
msg.ConfRequest,
msg.StartHeight, msg.EndHeight,
)
if err != nil {
chainntnfs.Log.Errorf("Rescan to "+
"determine the conf "+
"details of %v within "+
"range %d-%d failed: %v",
msg.ConfRequest,
msg.StartHeight,
msg.EndHeight, err)
return
}
// If the historical dispatch finished
// without error, we will invoke
// UpdateConfDetails even if none were
// found. This allows the notifier to
// begin safely updating the height hint
// cache at tip, since any pending
// rescans have now completed.
err = b.txNotifier.UpdateConfDetails(
msg.ConfRequest, confDetails,
)
if err != nil {
chainntnfs.Log.Errorf("Unable "+
"to update conf "+
"details of %v: %v",
msg.ConfRequest, err)
}
}()
case *chainntnfs.HistoricalSpendDispatch:
// 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.
//
// TODO(wilmer): add retry logic if rescan fails?
b.wg.Add(1)
go func() {
defer b.wg.Done()
spendDetails, err := b.historicalSpendDetails(
msg.SpendRequest,
msg.StartHeight, msg.EndHeight,
)
if err != nil {
chainntnfs.Log.Errorf("Rescan to "+
"determine the spend "+
"details of %v within "+
"range %d-%d failed: %v",
msg.SpendRequest,
msg.StartHeight,
msg.EndHeight, err)
return
}
// If the historical dispatch finished
// without error, we will invoke
// UpdateSpendDetails even if none were
// found. This allows the notifier to
// begin safely updating the height hint
// cache at tip, since any pending
// rescans have now completed.
err = b.txNotifier.UpdateSpendDetails(
msg.SpendRequest, spendDetails,
)
if err != nil {
chainntnfs.Log.Errorf("Unable "+
"to update spend "+
"details of %v: %v",
msg.SpendRequest, err)
}
}()
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case *blockEpochRegistration:
chainntnfs.Log.Infof("New block epoch subscription")
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b.blockEpochClients[msg.epochID] = msg
// If the client did not provide their best
// known block, then we'll immediately dispatch
// a notification for the current tip.
if msg.bestBlock == nil {
b.notifyBlockEpochClient(
msg, b.bestBlock.Height,
b.bestBlock.Hash,
)
msg.errorChan <- nil
continue
}
// Otherwise, we'll attempt to deliver the
// backlog of notifications from their best
// known block.
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
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}
case ntfn := <-b.chainConn.Notifications():
switch item := ntfn.(type) {
case chain.BlockConnected:
blockHeader, err :=
b.chainConn.GetBlockHeader(&item.Hash)
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if err != nil {
chainntnfs.Log.Errorf("Unable to fetch "+
"block header: %v", err)
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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.txNotifier,
b.bestBlock, item.Height,
true,
)
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if err != nil {
// Set the bestBlock here in case
// a catch up partially completed.
b.bestBlock = newBestBlock
chainntnfs.Log.Error(err)
continue
}
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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 {
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chainntnfs.Log.Error(err)
}
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continue
case chain.BlockDisconnected:
if item.Height != b.bestBlock.Height {
chainntnfs.Log.Infof("Missed disconnected" +
"blocks, attempting to catch up")
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}
newBestBlock, err := chainntnfs.RewindChain(
b.chainConn, b.txNotifier,
b.bestBlock, item.Height-1,
)
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if err != nil {
chainntnfs.Log.Errorf("Unable to rewind chain "+
"from height %d to height %d: %v",
b.bestBlock.Height, item.Height-1, err)
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}
// Set the bestBlock here in case a chain
// rewind partially completed.
b.bestBlock = newBestBlock
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case chain.RelevantTx:
// We only care about notifying on confirmed
// spends, so if this is a mempool spend, we can
// ignore it and wait for the spend to appear in
// on-chain.
if item.Block == nil {
continue
}
tx := btcutil.NewTx(&item.TxRecord.MsgTx)
err := b.txNotifier.ProcessRelevantSpendTx(
tx, uint32(item.Block.Height),
)
if err != nil {
chainntnfs.Log.Errorf("Unable to "+
"process transaction %v: %v",
tx.Hash(), err)
}
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}
case <-b.quit:
break out
}
}
b.wg.Done()
}
// historicalConfDetails looks up whether a confirmation request (txid/output
// script) has already been included in a block in the active chain and, if so,
// returns details about said block.
func (b *BitcoindNotifier) historicalConfDetails(confRequest chainntnfs.ConfRequest,
startHeight, endHeight uint32) (*chainntnfs.TxConfirmation,
chainntnfs.TxConfStatus, error) {
// If a txid was not provided, then we should dispatch upon seeing the
// script on-chain, so we'll short-circuit straight to scanning manually
// as there doesn't exist a script index to query.
if confRequest.TxID == chainntnfs.ZeroHash {
return b.confDetailsManually(
confRequest, startHeight, endHeight,
)
}
// Otherwise, we'll dispatch upon seeing a transaction on-chain with the
// given hash.
//
// We'll first attempt to retrieve the transaction using the node's
// txindex.
txNotFoundErr := "No such mempool or blockchain transaction"
txConf, txStatus, err := chainntnfs.ConfDetailsFromTxIndex(
b.chainConn, confRequest, txNotFoundErr,
)
// We'll then check the status of the transaction lookup returned to
// determine whether we should proceed with any fallback methods.
switch {
// We failed querying the index for the transaction, fall back to
// scanning manually.
case err != nil:
chainntnfs.Log.Debugf("Failed getting conf details from "+
"index (%v), scanning manually", err)
return b.confDetailsManually(confRequest, startHeight, endHeight)
// The transaction was found within the node's mempool.
case txStatus == chainntnfs.TxFoundMempool:
// The transaction was found within the node's txindex.
case txStatus == chainntnfs.TxFoundIndex:
// The transaction was not found within the node's mempool or txindex.
case txStatus == chainntnfs.TxNotFoundIndex:
// Unexpected txStatus returned.
default:
return nil, txStatus,
fmt.Errorf("Got unexpected txConfStatus: %v", txStatus)
}
return txConf, txStatus, nil
}
// confDetailsManually looks up whether a transaction/output script has already
// been included in a block in the active chain by scanning the chain's blocks
// within the given range. If the transaction/output script is found, its
// confirmation details are returned. Otherwise, nil is returned.
func (b *BitcoindNotifier) confDetailsManually(confRequest chainntnfs.ConfRequest,
heightHint, currentHeight uint32) (*chainntnfs.TxConfirmation,
chainntnfs.TxConfStatus, error) {
// Begin scanning blocks at every height to determine where the
// transaction was included in.
for height := currentHeight; height >= heightHint && height > 0; height-- {
// Ensure we haven't been requested to shut down before
// processing the next height.
select {
case <-b.quit:
return nil, chainntnfs.TxNotFoundManually,
chainntnfs.ErrChainNotifierShuttingDown
default:
}
blockHash, err := b.chainConn.GetBlockHash(int64(height))
if err != nil {
return nil, chainntnfs.TxNotFoundManually,
fmt.Errorf("unable to get hash from block "+
"with height %d", height)
}
block, err := b.chainConn.GetBlock(blockHash)
if err != nil {
return nil, chainntnfs.TxNotFoundManually,
fmt.Errorf("unable to get block with hash "+
"%v: %v", blockHash, err)
}
// For every transaction in the block, check which one matches
// our request. If we find one that does, we can dispatch its
// confirmation details.
for txIndex, tx := range block.Transactions {
if !confRequest.MatchesTx(tx) {
continue
}
return &chainntnfs.TxConfirmation{
Tx: tx,
BlockHash: blockHash,
BlockHeight: height,
TxIndex: uint32(txIndex),
}, chainntnfs.TxFoundManually, 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, chainntnfs.TxNotFoundManually, nil
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}
// 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 {
// First, we'll fetch the raw block as we'll need to gather all the
// transactions to determine whether any are relevant to our registered
// clients.
rawBlock, err := b.chainConn.GetBlock(block.Hash)
if err != nil {
return fmt.Errorf("unable to get block: %v", err)
}
txns := btcutil.NewBlock(rawBlock).Transactions()
// We'll then extend the txNotifier's height with the information of
// this new block, which will handle all of the notification logic for
// us.
err = b.txNotifier.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)
// Now that we've guaranteed the new block extends the txNotifier's
// current tip, we'll proceed to dispatch notifications to all of our
// registered clients whom have had notifications fulfilled. Before
// doing so, we'll make sure update our in memory state in order to
// satisfy any client requests based upon the new block.
b.bestBlock = block
b.notifyBlockEpochs(block.Height, block.Hash)
return b.txNotifier.NotifyHeight(uint32(block.Height))
}
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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) {
for _, client := range b.blockEpochClients {
b.notifyBlockEpochClient(client, newHeight, newSha)
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}
}
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// notifyBlockEpochClient sends a registered block epoch client a notification
// about a specific block.
func (b *BitcoindNotifier) notifyBlockEpochClient(epochClient *blockEpochRegistration,
height int32, sha *chainhash.Hash) {
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epoch := &chainntnfs.BlockEpoch{
Height: height,
Hash: sha,
}
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select {
case epochClient.epochQueue.ChanIn() <- epoch:
case <-epochClient.cancelChan:
case <-b.quit:
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}
}
// RegisterSpendNtfn registers an intent to be notified once the target
// outpoint/output script has been spent by a transaction on-chain. When
// intending to be notified of the spend of an output script, a nil outpoint
// must be used. The heightHint should represent the earliest height in the
// chain of the transaction that spent the outpoint/output script.
//
// Once a spend of has been detected, the details of the spending event will be
// sent across the 'Spend' channel.
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func (b *BitcoindNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint,
pkScript []byte, heightHint uint32) (*chainntnfs.SpendEvent, error) {
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// Register the conf notification with the TxNotifier. A non-nil value
// for `dispatch` will be returned if we are required to perform a
// manual scan for the confirmation. Otherwise the notifier will begin
// watching at tip for the transaction to confirm.
ntfn, err := b.txNotifier.RegisterSpend(outpoint, pkScript, heightHint)
if err != nil {
return nil, err
}
// We'll then request the backend to notify us when it has detected the
// outpoint/output script as spent.
//
// TODO(wilmer): use LoadFilter API instead.
if outpoint == nil || *outpoint == chainntnfs.ZeroOutPoint {
_, addrs, _, err := txscript.ExtractPkScriptAddrs(
pkScript, b.chainParams,
)
if err != nil {
return nil, fmt.Errorf("unable to parse script: %v", err)
}
if err := b.chainConn.NotifyReceived(addrs); err != nil {
return nil, err
}
} else {
ops := []*wire.OutPoint{outpoint}
if err := b.chainConn.NotifySpent(ops); err != nil {
return nil, err
}
}
// If the txNotifier didn't return any details to perform a historical
// scan of the chain, then we can return early as there's nothing left
// for us to do.
if ntfn.HistoricalDispatch == nil {
return ntfn.Event, nil
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}
// Otherwise, we'll need to dispatch a historical rescan to determine if
// the outpoint was already spent at a previous height.
//
// We'll short-circuit the path when dispatching the spend of a script,
// rather than an outpoint, as there aren't any additional checks we can
// make for scripts.
if ntfn.HistoricalDispatch.OutPoint == chainntnfs.ZeroOutPoint {
select {
case b.notificationRegistry <- ntfn.HistoricalDispatch:
case <-b.quit:
return nil, chainntnfs.ErrChainNotifierShuttingDown
}
return ntfn.Event, nil
}
// When dispatching spends of outpoints, there are a number of checks we
// can make to start our rescan from a better height or completely avoid
// it.
//
// We'll start by checking the backend's UTXO set to determine whether
// the outpoint has been spent. If it hasn't, we can return to the
// caller as well.
txOut, err := b.chainConn.GetTxOut(&outpoint.Hash, outpoint.Index, true)
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if err != nil {
return nil, err
}
if txOut != nil {
// We'll let the txNotifier know the outpoint is still unspent
// in order to begin updating its spend hint.
err := b.txNotifier.UpdateSpendDetails(
ntfn.HistoricalDispatch.SpendRequest, nil,
)
if err != nil {
return nil, err
}
return ntfn.Event, nil
}
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// Since the outpoint was spent, as it no longer exists within the UTXO
// set, we'll determine when it happened by scanning the chain.
//
// As a minimal optimization, we'll query the backend's transaction
// index (if enabled) to determine if we have a better rescan starting
// height. We can do this as the GetRawTransaction call will return the
// hash of the block it was included in within the chain.
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)
}
}
// If the transaction index was enabled, we'll use the block's hash to
// retrieve its height and check whether it provides a better starting
// point for our rescan.
if tx != nil {
// If the transaction containing the outpoint hasn't confirmed
// on-chain, then there's no need to perform a rescan.
if tx.BlockHash == "" {
return ntfn.Event, nil
}
blockHash, err := chainhash.NewHashFromStr(tx.BlockHash)
if err != nil {
return nil, err
}
blockHeight, err := b.chainConn.GetBlockHeight(blockHash)
if err != nil {
return nil, err
}
if uint32(blockHeight) > ntfn.HistoricalDispatch.StartHeight {
ntfn.HistoricalDispatch.StartHeight = uint32(blockHeight)
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}
}
// Now that we've determined the starting point of our rescan, we can
// dispatch it and return.
select {
case b.notificationRegistry <- ntfn.HistoricalDispatch:
case <-b.quit:
return nil, chainntnfs.ErrChainNotifierShuttingDown
}
return ntfn.Event, nil
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}
// historicalSpendDetails attempts to manually scan the chain within the given
// height range for a transaction that spends the given outpoint/output script.
// If one is found, the spend details are assembled and returned to the caller.
// If the spend is not found, a nil spend detail will be returned.
func (b *BitcoindNotifier) historicalSpendDetails(
spendRequest chainntnfs.SpendRequest, startHeight, endHeight uint32) (
*chainntnfs.SpendDetail, error) {
// Begin scanning blocks at every height to determine if the outpoint
// was spent.
for height := endHeight; height >= startHeight && height > 0; height-- {
// Ensure we haven't been requested to shut down before
// processing the next height.
select {
case <-b.quit:
return nil, chainntnfs.ErrChainNotifierShuttingDown
default:
}
// First, we'll fetch the block for the current height.
blockHash, err := b.chainConn.GetBlockHash(int64(height))
if err != nil {
return nil, fmt.Errorf("unable to retrieve hash for "+
"block with height %d: %v", height, err)
}
block, err := b.chainConn.GetBlock(blockHash)
if err != nil {
return nil, fmt.Errorf("unable to retrieve block "+
"with hash %v: %v", blockHash, err)
}
// Then, we'll manually go over every input in every transaction
// in it and determine whether it spends the request in
// question. If we find one, we'll dispatch the spend details.
for _, tx := range block.Transactions {
matches, inputIdx, err := spendRequest.MatchesTx(tx)
if err != nil {
return nil, err
}
if !matches {
continue
}
txHash := tx.TxHash()
return &chainntnfs.SpendDetail{
SpentOutPoint: &tx.TxIn[inputIdx].PreviousOutPoint,
SpenderTxHash: &txHash,
SpendingTx: tx,
SpenderInputIndex: inputIdx,
SpendingHeight: int32(height),
}, nil
}
}
return nil, nil
}
// RegisterConfirmationsNtfn registers an intent to be notified once the target
// txid/output script has reached numConfs confirmations on-chain. When
// intending to be notified of the confirmation of an output script, a nil txid
// must be used. The heightHint should represent the earliest height at which
// the txid/output script could have been included in the chain.
//
// Progress on the number of confirmations left can be read from the 'Updates'
// channel. Once it has reached all of its confirmations, a notification will be
// sent across the 'Confirmed' channel.
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func (b *BitcoindNotifier) RegisterConfirmationsNtfn(txid *chainhash.Hash,
pkScript []byte,
numConfs, heightHint uint32) (*chainntnfs.ConfirmationEvent, error) {
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// Register the conf notification with the TxNotifier. A non-nil value
// for `dispatch` will be returned if we are required to perform a
// manual scan for the confirmation. Otherwise the notifier will begin
// watching at tip for the transaction to confirm.
ntfn, err := b.txNotifier.RegisterConf(
txid, pkScript, numConfs, heightHint,
)
if err != nil {
return nil, err
}
if ntfn.HistoricalDispatch == nil {
return ntfn.Event, nil
}
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select {
case b.notificationRegistry <- ntfn.HistoricalDispatch:
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return ntfn.Event, nil
case <-b.quit:
return nil, chainntnfs.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 *queue.ConcurrentQueue
bestBlock *chainntnfs.BlockEpoch
errorChan chan error
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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. 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. If
// they do not provide one, then a notification will be dispatched immediately
// for the current tip of the chain upon a successful registration.
func (b *BitcoindNotifier) RegisterBlockEpochNtfn(
bestBlock *chainntnfs.BlockEpoch) (*chainntnfs.BlockEpochEvent, error) {
reg := &blockEpochRegistration{
epochQueue: queue.NewConcurrentQueue(20),
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epochChan: make(chan *chainntnfs.BlockEpoch, 20),
cancelChan: make(chan struct{}),
epochID: atomic.AddUint64(&b.epochClientCounter, 1),
bestBlock: bestBlock,
errorChan: make(chan error, 1),
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}
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
}
}