9915780197

Committed 13 Jul 2024 12:30AM UTC coverage: 49.268% (-9.1%) from 58.413%

Build # 9915780197

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Merge pull request #8653 from ProofOfKeags/fn-prim

DynComms [0/n]: `fn` package additions

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/chainntnfs/neutrinonotify/neutrino.go

package neutrinonotify

import (
        "errors"
        "fmt"
        "strings"
        "sync"
        "sync/atomic"
        "time"

        "github.com/btcsuite/btcd/btcjson"
        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/btcutil/gcs/builder"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/rpcclient"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
        "github.com/lightninglabs/neutrino"
        "github.com/lightninglabs/neutrino/headerfs"
        "github.com/lightningnetwork/lnd/blockcache"
        "github.com/lightningnetwork/lnd/chainntnfs"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/queue"
)

const (
        // notifierType uniquely identifies this concrete implementation of the
        // ChainNotifier interface.
        notifierType = "neutrino"
)

// NeutrinoNotifier is a version of ChainNotifier that's backed by the neutrino
// Bitcoin light client. Unlike other implementations, this implementation
// speaks directly to the p2p network. As a result, this implementation of the
// ChainNotifier interface is much more light weight that other implementation
// which rely of receiving notification over an RPC interface backed by a
// running full node.
//
// TODO(roasbeef): heavily consolidate with NeutrinoNotifier code
//   - maybe combine into single package?
type NeutrinoNotifier struct {
        epochClientCounter uint64 // To be used atomically.

        start   sync.Once
        active  int32 // To be used atomically.
        stopped int32 // To be used atomically.

        bestBlockMtx sync.RWMutex
        bestBlock    chainntnfs.BlockEpoch

        p2pNode   *neutrino.ChainService
        chainView *neutrino.Rescan

        chainConn *NeutrinoChainConn

        notificationCancels  chan interface{}
        notificationRegistry chan interface{}

        txNotifier *chainntnfs.TxNotifier

        blockEpochClients map[uint64]*blockEpochRegistration

        rescanErr <-chan error

        chainUpdates chan *filteredBlock

        txUpdates *queue.ConcurrentQueue

        // 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

        // blockCache is an LRU block cache.
        blockCache *blockcache.BlockCache

        wg   sync.WaitGroup
        quit chan struct{}
}

// Ensure NeutrinoNotifier implements the ChainNotifier interface at compile time.
var _ chainntnfs.ChainNotifier = (*NeutrinoNotifier)(nil)

// New creates a new instance of the NeutrinoNotifier concrete implementation
// of the ChainNotifier interface.
//
// NOTE: The passed neutrino node should already be running and active before
// being passed into this function.
func New(node *neutrino.ChainService, spendHintCache chainntnfs.SpendHintCache,
        confirmHintCache chainntnfs.ConfirmHintCache,
        blockCache *blockcache.BlockCache) *NeutrinoNotifier {

        return &NeutrinoNotifier{
                notificationCancels:  make(chan interface{}),
                notificationRegistry: make(chan interface{}),

                blockEpochClients: make(map[uint64]*blockEpochRegistration),

                p2pNode:   node,
                chainConn: &NeutrinoChainConn{node},

                rescanErr: make(chan error),

                chainUpdates: make(chan *filteredBlock, 100),

                txUpdates: queue.NewConcurrentQueue(10),

                spendHintCache:   spendHintCache,
                confirmHintCache: confirmHintCache,

                blockCache: blockCache,

                quit: make(chan struct{}),
        }
}

// Start contacts the running neutrino light client and kicks off an initial
// empty rescan.
func (n *NeutrinoNotifier) Start() error {
        var startErr error
        n.start.Do(func() {
                startErr = n.startNotifier()
        })
        return startErr
}

// Stop shuts down the NeutrinoNotifier.
func (n *NeutrinoNotifier) Stop() error {
        // Already shutting down?
        if atomic.AddInt32(&n.stopped, 1) != 1 {
                return nil
        }

        chainntnfs.Log.Info("neutrino notifier shutting down...")
        defer chainntnfs.Log.Debug("neutrino notifier shutdown complete")

        close(n.quit)
        n.wg.Wait()

        n.txUpdates.Stop()

        // Notify all pending clients of our shutdown by closing the related
        // notification channels.
        for _, epochClient := range n.blockEpochClients {
                close(epochClient.cancelChan)
                epochClient.wg.Wait()

                close(epochClient.epochChan)
        }
        n.txNotifier.TearDown()

        return nil
}

// Started returns true if this instance has been started, and false otherwise.
func (n *NeutrinoNotifier) Started() bool {
        return atomic.LoadInt32(&n.active) != 0
}

func (n *NeutrinoNotifier) startNotifier() error {
        // Start our concurrent queues before starting the rescan, to ensure
        // onFilteredBlockConnected and onRelavantTx callbacks won't be
        // blocked.
        n.txUpdates.Start()

        // First, we'll obtain the latest block height of the p2p node. We'll
        // start the auto-rescan from this point. Once a caller actually wishes
        // to register a chain view, the rescan state will be rewound
        // accordingly.
        startingPoint, err := n.p2pNode.BestBlock()
        if err != nil {
                n.txUpdates.Stop()
                return err
        }
        startingHeader, err := n.p2pNode.GetBlockHeader(
                &startingPoint.Hash,
        )
        if err != nil {
                n.txUpdates.Stop()
                return err
        }

        n.bestBlock.Hash = &startingPoint.Hash
        n.bestBlock.Height = startingPoint.Height
        n.bestBlock.BlockHeader = startingHeader

        n.txNotifier = chainntnfs.NewTxNotifier(
                uint32(n.bestBlock.Height), chainntnfs.ReorgSafetyLimit,
                n.confirmHintCache, n.spendHintCache,
        )

        // Next, we'll create our set of rescan options. Currently it's
        // required that a user MUST set an addr/outpoint/txid when creating a
        // rescan. To get around this, we'll add a "zero" outpoint, that won't
        // actually be matched.
        var zeroInput neutrino.InputWithScript
        rescanOptions := []neutrino.RescanOption{
                neutrino.StartBlock(startingPoint),
                neutrino.QuitChan(n.quit),
                neutrino.NotificationHandlers(
                        rpcclient.NotificationHandlers{
                                OnFilteredBlockConnected:    n.onFilteredBlockConnected,
                                OnFilteredBlockDisconnected: n.onFilteredBlockDisconnected,
                                OnRedeemingTx:               n.onRelevantTx,
                        },
                ),
                neutrino.WatchInputs(zeroInput),
        }

        // Finally, we'll create our rescan struct, start it, and launch all
        // the goroutines we need to operate this ChainNotifier instance.
        n.chainView = neutrino.NewRescan(
                &neutrino.RescanChainSource{
                        ChainService: n.p2pNode,
                },
                rescanOptions...,
        )
        n.rescanErr = n.chainView.Start()

        n.wg.Add(1)
        go n.notificationDispatcher()

        // Set the active flag now that we've completed the full
        // startup.
        atomic.StoreInt32(&n.active, 1)

        return nil
}

// filteredBlock represents a new block which has been connected to the main
// chain. The slice of transactions will only be populated if the block
// includes a transaction that confirmed one of our watched txids, or spends
// one of the outputs currently being watched.
type filteredBlock struct {
        header *wire.BlockHeader
        hash   chainhash.Hash
        height uint32
        txns   []*btcutil.Tx

        // connected is true if this update is a new block and false if it is a
        // disconnected block.
        connect bool
}

// rescanFilterUpdate represents a request that will be sent to the
// notificaionRegistry in order to prevent race conditions between the filter
// update and new block notifications.
type rescanFilterUpdate struct {
        updateOptions []neutrino.UpdateOption
        errChan       chan error
}

// onFilteredBlockConnected is a callback which is executed each a new block is
// connected to the end of the main chain.
func (n *NeutrinoNotifier) onFilteredBlockConnected(height int32,
        header *wire.BlockHeader, txns []*btcutil.Tx) {

        // Append this new chain update to the end of the queue of new chain
        // updates.
        select {
        case n.chainUpdates <- &filteredBlock{
                hash:    header.BlockHash(),
                height:  uint32(height),
                txns:    txns,
                header:  header,
                connect: true,
        }:
        case <-n.quit:
        }
}

// onFilteredBlockDisconnected is a callback which is executed each time a new
// block has been disconnected from the end of the mainchain due to a re-org.
func (n *NeutrinoNotifier) onFilteredBlockDisconnected(height int32,
        header *wire.BlockHeader) {

        // Append this new chain update to the end of the queue of new chain
        // disconnects.
        select {
        case n.chainUpdates <- &filteredBlock{
                hash:    header.BlockHash(),
                height:  uint32(height),
                connect: false,
        }:
        case <-n.quit:
        }
}

// relevantTx represents a relevant transaction to the notifier that fulfills
// any outstanding spend requests.
type relevantTx struct {
        tx      *btcutil.Tx
        details *btcjson.BlockDetails
}

// onRelevantTx is a callback that proxies relevant transaction notifications
// from the backend to the notifier's main event handler.
func (n *NeutrinoNotifier) onRelevantTx(tx *btcutil.Tx, details *btcjson.BlockDetails) {
        select {
        case n.txUpdates.ChanIn() <- &relevantTx{tx, details}:
        case <-n.quit:
        }
}

// connectFilteredBlock is called when we receive a filteredBlock from the
// backend. If the block is ahead of what we're expecting, we'll attempt to
// catch up and then process the block.
func (n *NeutrinoNotifier) connectFilteredBlock(update *filteredBlock) {
        n.bestBlockMtx.Lock()
        defer n.bestBlockMtx.Unlock()

        if update.height != uint32(n.bestBlock.Height+1) {
                chainntnfs.Log.Infof("Missed blocks, attempting to catch up")

                _, missedBlocks, err := chainntnfs.HandleMissedBlocks(
                        n.chainConn, n.txNotifier, n.bestBlock,
                        int32(update.height), false,
                )
                if err != nil {
                        chainntnfs.Log.Error(err)
                        return
                }

                for _, block := range missedBlocks {
                        filteredBlock, err := n.getFilteredBlock(block)
                        if err != nil {
                                chainntnfs.Log.Error(err)
                                return
                        }
                        err = n.handleBlockConnected(filteredBlock)
                        if err != nil {
                                chainntnfs.Log.Error(err)
                                return
                        }
                }
        }

        err := n.handleBlockConnected(update)
        if err != nil {
                chainntnfs.Log.Error(err)
        }
}

// disconnectFilteredBlock is called when our disconnected filtered block
// callback is fired. It attempts to rewind the chain to before the
// disconnection and updates our best block.
func (n *NeutrinoNotifier) disconnectFilteredBlock(update *filteredBlock) {
        n.bestBlockMtx.Lock()
        defer n.bestBlockMtx.Unlock()

        if update.height != uint32(n.bestBlock.Height) {
                chainntnfs.Log.Infof("Missed disconnected blocks, attempting" +
                        " to catch up")
        }
        newBestBlock, err := chainntnfs.RewindChain(n.chainConn, n.txNotifier,
                n.bestBlock, int32(update.height-1),
        )
        if err != nil {
                chainntnfs.Log.Errorf("Unable to rewind chain from height %d"+
                        "to height %d: %v", n.bestBlock.Height,
                        update.height-1, err,
                )
        }

        n.bestBlock = newBestBlock
}

// drainChainUpdates is called after updating the filter. It reads every
// buffered item off the chan and returns when no more are available. It is
// used to ensure that callers performing a historical scan properly update
// their EndHeight to scan blocks that did not have the filter applied at
// processing time. Without this, a race condition exists that could allow a
// spend or confirmation notification to be missed. It is unlikely this would
// occur in a real-world scenario, and instead would manifest itself in tests.
func (n *NeutrinoNotifier) drainChainUpdates() {
        for {
                select {
                case update := <-n.chainUpdates:
                        if update.connect {
                                n.connectFilteredBlock(update)
                                break
                        }
                        n.disconnectFilteredBlock(update)
                default:
                        return
                }
        }
}

// notificationDispatcher is the primary goroutine which handles client
// notification registrations, as well as notification dispatches.
func (n *NeutrinoNotifier) notificationDispatcher() {
        defer n.wg.Done()

        for {
                select {
                case cancelMsg := <-n.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 := n.blockEpochClients[msg.epochID]
                                reg.epochQueue.Stop()

                                // Next, close the cancel channel for this
                                // specific client, and wait for the client to
                                // exit.
                                close(n.blockEpochClients[msg.epochID].cancelChan)
                                n.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
                                // canceled.
                                close(n.blockEpochClients[msg.epochID].epochChan)
                                delete(n.blockEpochClients, msg.epochID)
                        }

                case registerMsg := <-n.notificationRegistry:
                        switch msg := registerMsg.(type) {
                        case *chainntnfs.HistoricalConfDispatch:
                                // We'll start a historical rescan chain of the
                                // chain asynchronously to prevent blocking
                                // potentially long rescans.
                                n.wg.Add(1)

                                //nolint:lll
                                go func(msg *chainntnfs.HistoricalConfDispatch) {
                                        defer n.wg.Done()

                                        confDetails, err := n.historicalConfDetails(
                                                msg.ConfRequest,
                                                msg.StartHeight, msg.EndHeight,
                                        )
                                        if err != nil {
                                                chainntnfs.Log.Error(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 = n.txNotifier.UpdateConfDetails(
                                                msg.ConfRequest, confDetails,
                                        )
                                        if err != nil {
                                                chainntnfs.Log.Error(err)
                                        }
                                }(msg)

                        case *blockEpochRegistration:
                                chainntnfs.Log.Infof("New block epoch subscription")

                                n.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 {
                                        n.notifyBlockEpochClient(
                                                msg, n.bestBlock.Height,
                                                n.bestBlock.Hash,
                                                n.bestBlock.BlockHeader,
                                        )

                                        msg.errorChan <- nil
                                        continue
                                }

                                // Otherwise, we'll attempt to deliver the
                                // backlog of notifications from their best
                                // known block.
                                n.bestBlockMtx.Lock()
                                bestHeight := n.bestBlock.Height
                                n.bestBlockMtx.Unlock()

                                missedBlocks, err := chainntnfs.GetClientMissedBlocks(
                                        n.chainConn, msg.bestBlock, bestHeight,
                                        false,
                                )
                                if err != nil {
                                        msg.errorChan <- err
                                        continue
                                }

                                for _, block := range missedBlocks {
                                        n.notifyBlockEpochClient(
                                                msg, block.Height, block.Hash,
                                                block.BlockHeader,
                                        )
                                }

                                msg.errorChan <- nil

                        case *rescanFilterUpdate:
                                err := n.chainView.Update(msg.updateOptions...)
                                if err != nil {
                                        chainntnfs.Log.Errorf("Unable to "+
                                                "update rescan filter: %v", err)
                                }

                                // Drain the chainUpdates chan so the caller
                                // listening on errChan can be sure that
                                // updates after receiving the error will have
                                // the filter applied. This allows the caller
                                // to update their EndHeight if they're
                                // performing a historical scan.
                                n.drainChainUpdates()

                                // After draining, send the error to the
                                // caller.
                                msg.errChan <- err
                        }

                case item := <-n.chainUpdates:
                        update := item
                        if update.connect {
                                n.connectFilteredBlock(update)
                                continue
                        }

                        n.disconnectFilteredBlock(update)

                case txUpdate := <-n.txUpdates.ChanOut():
                        // A new relevant transaction notification has been
                        // received from the backend. We'll attempt to process
                        // it to determine if it fulfills any outstanding
                        // confirmation and/or spend requests and dispatch
                        // notifications for them.
                        update := txUpdate.(*relevantTx)
                        err := n.txNotifier.ProcessRelevantSpendTx(
                                update.tx, uint32(update.details.Height),
                        )
                        if err != nil {
                                chainntnfs.Log.Errorf("Unable to process "+
                                        "transaction %v: %v", update.tx.Hash(),
                                        err)
                        }

                case err := <-n.rescanErr:
                        chainntnfs.Log.Errorf("Error during rescan: %v", err)

                case <-n.quit:
                        return

                }
        }
}

// 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 (n *NeutrinoNotifier) historicalConfDetails(confRequest chainntnfs.ConfRequest,
        startHeight, endHeight uint32) (*chainntnfs.TxConfirmation, error) {

        // Starting from the height hint, we'll walk forwards in the chain to
        // see if this transaction/output script has already been confirmed.
        for scanHeight := endHeight; scanHeight >= startHeight && scanHeight > 0; scanHeight-- {
                // Ensure we haven't been requested to shut down before
                // processing the next height.
                select {
                case <-n.quit:
                        return nil, chainntnfs.ErrChainNotifierShuttingDown
                default:
                }

                // First, we'll fetch the block header for this height so we
                // can compute the current block hash.
                blockHash, err := n.p2pNode.GetBlockHash(int64(scanHeight))
                if err != nil {
                        return nil, fmt.Errorf("unable to get header for "+
                                "height=%v: %w", scanHeight, err)
                }

                // With the hash computed, we can now fetch the basic filter for this
                // height. Since the range of required items is known we avoid
                // roundtrips by requesting a batched response and save bandwidth by
                // limiting the max number of items per batch. Since neutrino populates
                // its underline filters cache with the batch response, the next call
                // will execute a network query only once per batch and not on every
                // iteration.
                regFilter, err := n.p2pNode.GetCFilter(
                        *blockHash, wire.GCSFilterRegular,
                        neutrino.NumRetries(5),
                        neutrino.OptimisticReverseBatch(),
                        neutrino.MaxBatchSize(int64(scanHeight-startHeight+1)),
                )
                if err != nil {
                        return nil, fmt.Errorf("unable to retrieve regular "+
                                "filter for height=%v: %w", scanHeight, err)
                }

                // In the case that the filter exists, we'll attempt to see if
                // any element in it matches our target public key script.
                key := builder.DeriveKey(blockHash)
                match, err := regFilter.Match(key, confRequest.PkScript.Script())
                if err != nil {
                        return nil, fmt.Errorf("unable to query filter: %w",
                                err)
                }

                // If there's no match, then we can continue forward to the
                // next block.
                if !match {
                        continue
                }

                // In the case that we do have a match, we'll fetch the block
                // from the network so we can find the positional data required
                // to send the proper response.
                block, err := n.GetBlock(*blockHash)
                if err != nil {
                        return nil, fmt.Errorf("unable to get block from "+
                                "network: %w", 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 i, tx := range block.Transactions() {
                        if !confRequest.MatchesTx(tx.MsgTx()) {
                                continue
                        }

                        return &chainntnfs.TxConfirmation{
                                Tx:          tx.MsgTx().Copy(),
                                BlockHash:   blockHash,
                                BlockHeight: scanHeight,
                                TxIndex:     uint32(i),
                                Block:       block.MsgBlock(),
                        }, nil
                }
        }

        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.
//
// NOTE: This method must be called with the bestBlockMtx lock held.
func (n *NeutrinoNotifier) handleBlockConnected(newBlock *filteredBlock) error {
        // We'll extend the txNotifier's height with the information of this
        // new block, which will handle all of the notification logic for us.
        //
        // We actually need the _full_ block here as well in order to be able
        // to send the full block back up to the client. The neutrino client
        // itself will only dispatch a block if one of the items we're looking
        // for matches, so ultimately passing it the full block will still only
        // result in the items we care about being dispatched.
        rawBlock, err := n.GetBlock(newBlock.hash)
        if err != nil {
                return fmt.Errorf("unable to get full block: %w", err)
        }
        err = n.txNotifier.ConnectTip(rawBlock, newBlock.height)
        if err != nil {
                return fmt.Errorf("unable to connect tip: %w", err)
        }

        chainntnfs.Log.Infof("New block: height=%v, sha=%v", newBlock.height,
                newBlock.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.
        n.bestBlock.Hash = &newBlock.hash
        n.bestBlock.Height = int32(newBlock.height)
        n.bestBlock.BlockHeader = newBlock.header

        n.notifyBlockEpochs(
                int32(newBlock.height), &newBlock.hash, newBlock.header,
        )
        return n.txNotifier.NotifyHeight(newBlock.height)
}

// getFilteredBlock is a utility to retrieve the full filtered block from a block epoch.
func (n *NeutrinoNotifier) getFilteredBlock(epoch chainntnfs.BlockEpoch) (*filteredBlock, error) {
        rawBlock, err := n.GetBlock(*epoch.Hash)
        if err != nil {
                return nil, fmt.Errorf("unable to get block: %w", err)
        }

        txns := rawBlock.Transactions()

        block := &filteredBlock{
                hash:    *epoch.Hash,
                height:  uint32(epoch.Height),
                header:  &rawBlock.MsgBlock().Header,
                txns:    txns,
                connect: true,
        }
        return block, nil
}

// notifyBlockEpochs notifies all registered block epoch clients of the newly
// connected block to the main chain.
func (n *NeutrinoNotifier) notifyBlockEpochs(newHeight int32, newSha *chainhash.Hash,
        blockHeader *wire.BlockHeader) {

        for _, client := range n.blockEpochClients {
                n.notifyBlockEpochClient(client, newHeight, newSha, blockHeader)
        }
}

// notifyBlockEpochClient sends a registered block epoch client a notification
// about a specific block.
func (n *NeutrinoNotifier) notifyBlockEpochClient(epochClient *blockEpochRegistration,
        height int32, sha *chainhash.Hash, blockHeader *wire.BlockHeader) {

        epoch := &chainntnfs.BlockEpoch{
                Height:      height,
                Hash:        sha,
                BlockHeader: blockHeader,
        }

        select {
        case epochClient.epochQueue.ChanIn() <- epoch:
        case <-epochClient.cancelChan:
        case <-n.quit:
        }
}

// 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.
func (n *NeutrinoNotifier) RegisterSpendNtfn(outpoint *wire.OutPoint,
        pkScript []byte, heightHint uint32) (*chainntnfs.SpendEvent, error) {

        // 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 := n.txNotifier.RegisterSpend(outpoint, pkScript, heightHint)
        if err != nil {
                return nil, err
        }

        // To determine whether this outpoint has been spent on-chain, we'll
        // update our filter to watch for the transaction at tip and we'll also
        // dispatch a historical rescan to determine if it has been spent in the
        // past.
        //
        // We'll update our filter first to ensure we can immediately detect the
        // spend at tip.
        if outpoint == nil {
                outpoint = &chainntnfs.ZeroOutPoint
        }
        inputToWatch := neutrino.InputWithScript{
                OutPoint: *outpoint,
                PkScript: pkScript,
        }
        updateOptions := []neutrino.UpdateOption{
                neutrino.AddInputs(inputToWatch),
                neutrino.DisableDisconnectedNtfns(true),
        }

        // We'll use the txNotifier's tip as the starting point of our filter
        // update. In the case of an output script spend request, we'll check if
        // we should perform a historical rescan and start from there, as we
        // cannot do so with GetUtxo since it matches outpoints.
        rewindHeight := ntfn.Height
        if ntfn.HistoricalDispatch != nil && *outpoint == chainntnfs.ZeroOutPoint {
                rewindHeight = ntfn.HistoricalDispatch.StartHeight
        }
        updateOptions = append(updateOptions, neutrino.Rewind(rewindHeight))

        errChan := make(chan error, 1)
        select {
        case n.notificationRegistry <- &rescanFilterUpdate{
                updateOptions: updateOptions,
                errChan:       errChan,
        }:
        case <-n.quit:
                return nil, chainntnfs.ErrChainNotifierShuttingDown
        }

        select {
        case err = <-errChan:
        case <-n.quit:
                return nil, chainntnfs.ErrChainNotifierShuttingDown
        }
        if err != nil {
                return nil, fmt.Errorf("unable to update filter: %w", err)
        }

        // If the txNotifier didn't return any details to perform a historical
        // scan of the chain, or if we already performed one like in the case of
        // output script spend requests, then we can return early as there's
        // nothing left for us to do.
        if ntfn.HistoricalDispatch == nil || *outpoint == chainntnfs.ZeroOutPoint {
                return ntfn.Event, nil
        }

        // Grab the current best height as the height may have been updated
        // while we were draining the chainUpdates queue.
        n.bestBlockMtx.RLock()
        currentHeight := uint32(n.bestBlock.Height)
        n.bestBlockMtx.RUnlock()

        ntfn.HistoricalDispatch.EndHeight = currentHeight

        // With the filter updated, we'll dispatch our historical rescan to
        // ensure we detect the spend if it happened in the past.
        n.wg.Add(1)
        go func() {
                defer n.wg.Done()

                // We'll ensure that neutrino is caught up to the starting
                // height before we attempt to fetch the UTXO from the chain.
                // If we're behind, then we may miss a notification dispatch.
                for {
                        n.bestBlockMtx.RLock()
                        currentHeight := uint32(n.bestBlock.Height)
                        n.bestBlockMtx.RUnlock()

                        if currentHeight >= ntfn.HistoricalDispatch.StartHeight {
                                break
                        }

                        select {
                        case <-time.After(time.Millisecond * 200):
                        case <-n.quit:
                                return
                        }
                }

                spendReport, err := n.p2pNode.GetUtxo(
                        neutrino.WatchInputs(inputToWatch),
                        neutrino.StartBlock(&headerfs.BlockStamp{
                                Height: int32(ntfn.HistoricalDispatch.StartHeight),
                        }),
                        neutrino.EndBlock(&headerfs.BlockStamp{
                                Height: int32(ntfn.HistoricalDispatch.EndHeight),
                        }),
                        neutrino.ProgressHandler(func(processedHeight uint32) {
                                // We persist the rescan progress to achieve incremental
                                // behavior across restarts, otherwise long rescans may
                                // start from the beginning with every restart.
                                err := n.spendHintCache.CommitSpendHint(
                                        processedHeight,
                                        ntfn.HistoricalDispatch.SpendRequest)
                                if err != nil {
                                        chainntnfs.Log.Errorf("Failed to update rescan "+
                                                "progress: %v", err)
                                }
                        }),
                        neutrino.QuitChan(n.quit),
                )
                if err != nil && !strings.Contains(err.Error(), "not found") {
                        chainntnfs.Log.Errorf("Failed getting UTXO: %v", err)
                        return
                }

                // If a spend report was returned, and the transaction is present, then
                // this means that the output is already spent.
                var spendDetails *chainntnfs.SpendDetail
                if spendReport != nil && spendReport.SpendingTx != nil {
                        spendingTxHash := spendReport.SpendingTx.TxHash()
                        spendDetails = &chainntnfs.SpendDetail{
                                SpentOutPoint:     outpoint,
                                SpenderTxHash:     &spendingTxHash,
                                SpendingTx:        spendReport.SpendingTx,
                                SpenderInputIndex: spendReport.SpendingInputIndex,
                                SpendingHeight:    int32(spendReport.SpendingTxHeight),
                        }
                }

                // Finally, no matter whether the rescan found a spend in the past or
                // not, we'll mark our historical rescan as complete to ensure the
                // outpoint's spend hint gets updated upon connected/disconnected
                // blocks.
                err = n.txNotifier.UpdateSpendDetails(
                        ntfn.HistoricalDispatch.SpendRequest, spendDetails,
                )
                if err != nil {
                        chainntnfs.Log.Errorf("Failed to update spend details: %v", err)
                        return
                }
        }()

        return ntfn.Event, 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.
func (n *NeutrinoNotifier) RegisterConfirmationsNtfn(txid *chainhash.Hash,
        pkScript []byte, numConfs, heightHint uint32,
        opts ...chainntnfs.NotifierOption) (*chainntnfs.ConfirmationEvent, error) {

        // 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 := n.txNotifier.RegisterConf(
                txid, pkScript, numConfs, heightHint, opts...,
        )
        if err != nil {
                return nil, err
        }

        // To determine whether this transaction has confirmed on-chain, we'll
        // update our filter to watch for the transaction at tip and we'll also
        // dispatch a historical rescan to determine if it has confirmed in the
        // past.
        //
        // We'll update our filter first to ensure we can immediately detect the
        // confirmation at tip. To do so, we'll map the script into an address
        // type so we can instruct neutrino to match if the transaction
        // containing the script is found in a block.
        params := n.p2pNode.ChainParams()
        _, addrs, _, err := txscript.ExtractPkScriptAddrs(pkScript, &params)
        if err != nil {
                return nil, fmt.Errorf("unable to extract script: %w", err)
        }

        // We'll send the filter update request to the notifier's main event
        // handler and wait for its response.
        errChan := make(chan error, 1)
        select {
        case n.notificationRegistry <- &rescanFilterUpdate{
                updateOptions: []neutrino.UpdateOption{
                        neutrino.AddAddrs(addrs...),
                        neutrino.Rewind(ntfn.Height),
                        neutrino.DisableDisconnectedNtfns(true),
                },
                errChan: errChan,
        }:
        case <-n.quit:
                return nil, chainntnfs.ErrChainNotifierShuttingDown
        }

        select {
        case err = <-errChan:
        case <-n.quit:
                return nil, chainntnfs.ErrChainNotifierShuttingDown
        }
        if err != nil {
                return nil, fmt.Errorf("unable to update filter: %w", err)
        }

        // If a historical rescan was not requested by the txNotifier, then we
        // can return to the caller.
        if ntfn.HistoricalDispatch == nil {
                return ntfn.Event, nil
        }

        // Grab the current best height as the height may have been updated
        // while we were draining the chainUpdates queue.
        n.bestBlockMtx.RLock()
        currentHeight := uint32(n.bestBlock.Height)
        n.bestBlockMtx.RUnlock()

        ntfn.HistoricalDispatch.EndHeight = currentHeight

        // Finally, with the filter updated, we can dispatch the historical
        // rescan to ensure we can detect if the event happened in the past.
        select {
        case n.notificationRegistry <- ntfn.HistoricalDispatch:
        case <-n.quit:
                return nil, chainntnfs.ErrChainNotifierShuttingDown
        }

        return ntfn.Event, nil
}

// GetBlock is used to retrieve the block with the given hash. Since the block
// cache used by neutrino will be the same as that used by LND (since it is
// passed to neutrino on initialisation), the neutrino GetBlock method can be
// called directly since it already uses the block cache. However, neutrino
// does not lock the block cache mutex for the given block hash and so that is
// done here.
func (n *NeutrinoNotifier) GetBlock(hash chainhash.Hash) (
        *btcutil.Block, error) {

        n.blockCache.HashMutex.Lock(lntypes.Hash(hash))
        defer n.blockCache.HashMutex.Unlock(lntypes.Hash(hash))

        return n.p2pNode.GetBlock(hash)
}

// 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

        cancelChan chan struct{}

        bestBlock *chainntnfs.BlockEpoch

        errorChan chan error

        wg sync.WaitGroup
}

// epochCancel is a message sent to the NeutrinoNotifier 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 (n *NeutrinoNotifier) RegisterBlockEpochNtfn(
        bestBlock *chainntnfs.BlockEpoch) (*chainntnfs.BlockEpochEvent, error) {

        reg := &blockEpochRegistration{
                epochQueue: queue.NewConcurrentQueue(20),
                epochChan:  make(chan *chainntnfs.BlockEpoch, 20),
                cancelChan: make(chan struct{}),
                epochID:    atomic.AddUint64(&n.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 <-n.quit:
                                        return
                                }

                        case <-reg.cancelChan:
                                return

                        case <-n.quit:
                                return
                        }
                }
        }()

        select {
        case <-n.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 n.notificationRegistry <- reg:
                return &chainntnfs.BlockEpochEvent{
                        Epochs: reg.epochChan,
                        Cancel: func() {
                                cancel := &epochCancel{
                                        epochID: reg.epochID,
                                }

                                // Submit epoch cancellation to notification dispatcher.
                                select {
                                case n.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 <-n.quit:
                                                        return
                                                }
                                        }
                                case <-n.quit:
                                }
                        },
                }, nil
        }
}

// NeutrinoChainConn is a wrapper around neutrino's chain backend in order
// to satisfy the chainntnfs.ChainConn interface.
type NeutrinoChainConn struct {
        p2pNode *neutrino.ChainService
}

// GetBlockHeader returns the block header for a hash.
func (n *NeutrinoChainConn) GetBlockHeader(blockHash *chainhash.Hash) (*wire.BlockHeader, error) {
        return n.p2pNode.GetBlockHeader(blockHash)
}

// GetBlockHeaderVerbose returns a verbose block header result for a hash. This
// result only contains the height with a nil hash.
func (n *NeutrinoChainConn) GetBlockHeaderVerbose(blockHash *chainhash.Hash) (
        *btcjson.GetBlockHeaderVerboseResult, error) {

        height, err := n.p2pNode.GetBlockHeight(blockHash)
        if err != nil {
                return nil, err
        }
        // Since only the height is used from the result, leave the hash nil.
        return &btcjson.GetBlockHeaderVerboseResult{Height: int32(height)}, nil
}

// GetBlockHash returns the hash from a block height.
func (n *NeutrinoChainConn) GetBlockHash(blockHeight int64) (*chainhash.Hash, error) {
        return n.p2pNode.GetBlockHash(blockHeight)
}

lightningnetwork / lnd / 9915780197

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