12428593038

Committed 20 Dec 2024 09:02AM UTC coverage: 58.33% (-0.2%) from 58.576%

Build # 12428593038

Build Type

Pull #9382

github

Committed by

guggero

Commit Message

.golangci.yml: speed up linter by updating start commit

With this we allow the linter to only look at recent changes, since
everything between that old commit and this most recent one has been
linted correctly anyway.

Pull Request Pull Request #9382: lint: deprecate old linters, use new ref commit

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88.42

/chainntnfs/txnotifier.go

package chainntnfs

import (
        "bytes"
        "errors"
        "fmt"
        "sync"
        "sync/atomic"

        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
)

const (
        // ReorgSafetyLimit is the chain depth beyond which it is assumed a
        // block will not be reorganized out of the chain. This is used to
        // determine when to prune old confirmation requests so that reorgs are
        // handled correctly. The average number of blocks in a day is a
        // reasonable value to use.
        ReorgSafetyLimit = 144

        // MaxNumConfs is the maximum number of confirmations that can be
        // requested on a transaction.
        MaxNumConfs = ReorgSafetyLimit
)

var (
        // ZeroHash is the value that should be used as the txid when
        // registering for the confirmation of a script on-chain. This allows
        // the notifier to match _and_ dispatch upon the inclusion of the script
        // on-chain, rather than the txid.
        ZeroHash chainhash.Hash

        // ZeroOutPoint is the value that should be used as the outpoint when
        // registering for the spend of a script on-chain. This allows the
        // notifier to match _and_ dispatch upon detecting the spend of the
        // script on-chain, rather than the outpoint.
        ZeroOutPoint wire.OutPoint

        // zeroV1KeyPush is a pkScript that pushes an all-zero 32-byte Taproot
        // SegWit v1 key to the stack.
        zeroV1KeyPush = [34]byte{
                txscript.OP_1, txscript.OP_DATA_32, // 32 byte of zeroes here
        }

        // ZeroTaprootPkScript is the parsed txscript.PkScript of an empty
        // Taproot SegWit v1 key being pushed to the stack. This allows the
        // notifier to match _and_ dispatch upon detecting the spend of the
        // outpoint on-chain, rather than the pkScript (which cannot be derived
        // from the witness alone in the SegWit v1 case).
        ZeroTaprootPkScript, _ = txscript.ParsePkScript(zeroV1KeyPush[:])
)

var (
        // ErrTxNotifierExiting is an error returned when attempting to interact
        // with the TxNotifier but it been shut down.
        ErrTxNotifierExiting = errors.New("TxNotifier is exiting")

        // ErrNoScript is an error returned when a confirmation/spend
        // registration is attempted without providing an accompanying output
        // script.
        ErrNoScript = errors.New("an output script must be provided")

        // ErrNoHeightHint is an error returned when a confirmation/spend
        // registration is attempted without providing an accompanying height
        // hint.
        ErrNoHeightHint = errors.New("a height hint greater than 0 must be " +
                "provided")

        // ErrNumConfsOutOfRange is an error returned when a confirmation/spend
        // registration is attempted and the number of confirmations provided is
        // out of range.
        ErrNumConfsOutOfRange = fmt.Errorf("number of confirmations must be "+
                "between %d and %d", 1, MaxNumConfs)

        // ErrEmptyWitnessStack is returned when a spending transaction has an
        // empty witness stack. More details in,
        // - https://github.com/bitcoin/bitcoin/issues/28730
        ErrEmptyWitnessStack = errors.New("witness stack is empty")
)

// rescanState indicates the progression of a registration before the notifier
// can begin dispatching confirmations at tip.
type rescanState byte

const (
        // rescanNotStarted is the initial state, denoting that a historical
        // dispatch may be required.
        rescanNotStarted rescanState = iota

        // rescanPending indicates that a dispatch has already been made, and we
        // are waiting for its completion. No other rescans should be dispatched
        // while in this state.
        rescanPending

        // rescanComplete signals either that a rescan was dispatched and has
        // completed, or that we began watching at tip immediately. In either
        // case, the notifier can only dispatch notifications from tip when in
        // this state.
        rescanComplete
)

// confNtfnSet holds all known, registered confirmation notifications for a
// txid/output script. If duplicates notifications are requested, only one
// historical dispatch will be spawned to ensure redundant scans are not
// permitted. A single conf detail will be constructed and dispatched to all
// interested
// clients.
type confNtfnSet struct {
        // ntfns keeps tracks of all the active client notification requests for
        // a transaction/output script
        ntfns map[uint64]*ConfNtfn

        // rescanStatus represents the current rescan state for the
        // transaction/output script.
        rescanStatus rescanState

        // details serves as a cache of the confirmation details of a
        // transaction that we'll use to determine if a transaction/output
        // script has already confirmed at the time of registration.
        // details is also used to make sure that in case of an address reuse
        // (funds sent to a previously confirmed script) no additional
        // notification is registered which would lead to an inconsistent state.
        details *TxConfirmation
}

// newConfNtfnSet constructs a fresh confNtfnSet for a group of clients
// interested in a notification for a particular txid.
func newConfNtfnSet() *confNtfnSet {
        return &confNtfnSet{
                ntfns:        make(map[uint64]*ConfNtfn),
                rescanStatus: rescanNotStarted,
        }
}

// spendNtfnSet holds all known, registered spend notifications for a spend
// request (outpoint/output script). If duplicate notifications are requested,
// only one historical dispatch will be spawned to ensure redundant scans are
// not permitted.
type spendNtfnSet struct {
        // ntfns keeps tracks of all the active client notification requests for
        // an outpoint/output script.
        ntfns map[uint64]*SpendNtfn

        // rescanStatus represents the current rescan state for the spend
        // request (outpoint/output script).
        rescanStatus rescanState

        // details serves as a cache of the spend details for an outpoint/output
        // script that we'll use to determine if it has already been spent at
        // the time of registration.
        details *SpendDetail
}

// newSpendNtfnSet constructs a new spend notification set.
func newSpendNtfnSet() *spendNtfnSet {
        return &spendNtfnSet{
                ntfns:        make(map[uint64]*SpendNtfn),
                rescanStatus: rescanNotStarted,
        }
}

// ConfRequest encapsulates a request for a confirmation notification of either
// a txid or output script.
type ConfRequest struct {
        // TxID is the hash of the transaction for which confirmation
        // notifications are requested. If set to a zero hash, then a
        // confirmation notification will be dispatched upon inclusion of the
        // _script_, rather than the txid.
        TxID chainhash.Hash

        // PkScript is the public key script of an outpoint created in this
        // transaction.
        PkScript txscript.PkScript
}

// NewConfRequest creates a request for a confirmation notification of either a
// txid or output script. A nil txid or an allocated ZeroHash can be used to
// dispatch the confirmation notification on the script.
func NewConfRequest(txid *chainhash.Hash, pkScript []byte) (ConfRequest, error) {
        var r ConfRequest
        outputScript, err := txscript.ParsePkScript(pkScript)
        if err != nil {
                return r, err
        }

        // We'll only set a txid for which we'll dispatch a confirmation
        // notification on this request if one was provided. Otherwise, we'll
        // default to dispatching on the confirmation of the script instead.
        if txid != nil {
                r.TxID = *txid
        }
        r.PkScript = outputScript

        return r, nil
}

// String returns the string representation of the ConfRequest.
func (r ConfRequest) String() string {
        if r.TxID != ZeroHash {
                return fmt.Sprintf("txid=%v", r.TxID)
        }
        return fmt.Sprintf("script=%v", r.PkScript)
}

// MatchesTx determines whether the given transaction satisfies the confirmation
// request. If the confirmation request is for a script, then we'll check all of
// the outputs of the transaction to determine if it matches. Otherwise, we'll
// match on the txid.
func (r ConfRequest) MatchesTx(tx *wire.MsgTx) bool {
        scriptMatches := func() bool {
                pkScript := r.PkScript.Script()
                for _, txOut := range tx.TxOut {
                        if bytes.Equal(txOut.PkScript, pkScript) {
                                return true
                        }
                }

                return false
        }

        if r.TxID != ZeroHash {
                return r.TxID == tx.TxHash() && scriptMatches()
        }

        return scriptMatches()
}

// ConfNtfn represents a notifier client's request to receive a notification
// once the target transaction/output script gets sufficient confirmations. The
// client is asynchronously notified via the ConfirmationEvent channels.
type ConfNtfn struct {
        // ConfID uniquely identifies the confirmation notification request for
        // the specified transaction/output script.
        ConfID uint64

        // ConfRequest represents either the txid or script we should detect
        // inclusion of within the chain.
        ConfRequest

        // NumConfirmations is the number of confirmations after which the
        // notification is to be sent.
        NumConfirmations uint32

        // Event contains references to the channels that the notifications are
        // to be sent over.
        Event *ConfirmationEvent

        // HeightHint is the minimum height in the chain that we expect to find
        // this txid.
        HeightHint uint32

        // dispatched is false if the confirmed notification has not been sent
        // yet.
        dispatched bool

        // includeBlock is true if the dispatched notification should also have
        // the block included with it.
        includeBlock bool

        // numConfsLeft is the number of confirmations left to be sent to the
        // subscriber.
        numConfsLeft uint32
}

// HistoricalConfDispatch parametrizes a manual rescan for a particular
// transaction/output script. The parameters include the start and end block
// heights specifying the range of blocks to scan.
type HistoricalConfDispatch struct {
        // ConfRequest represents either the txid or script we should detect
        // inclusion of within the chain.
        ConfRequest

        // StartHeight specifies the block height at which to begin the
        // historical rescan.
        StartHeight uint32

        // EndHeight specifies the last block height (inclusive) that the
        // historical scan should consider.
        EndHeight uint32
}

// ConfRegistration encompasses all of the information required for callers to
// retrieve details about a confirmation event.
type ConfRegistration struct {
        // Event contains references to the channels that the notifications are
        // to be sent over.
        Event *ConfirmationEvent

        // HistoricalDispatch, if non-nil, signals to the client who registered
        // the notification that they are responsible for attempting to manually
        // rescan blocks for the txid/output script between the start and end
        // heights.
        HistoricalDispatch *HistoricalConfDispatch

        // Height is the height of the TxNotifier at the time the confirmation
        // notification was registered. This can be used so that backends can
        // request to be notified of confirmations from this point forwards.
        Height uint32
}

// SpendRequest encapsulates a request for a spend notification of either an
// outpoint or output script.
type SpendRequest struct {
        // OutPoint is the outpoint for which a client has requested a spend
        // notification for. If set to a zero outpoint, then a spend
        // notification will be dispatched upon detecting the spend of the
        // _script_, rather than the outpoint.
        OutPoint wire.OutPoint

        // PkScript is the script of the outpoint. If a zero outpoint is set,
        // then this can be an arbitrary script.
        PkScript txscript.PkScript
}

// NewSpendRequest creates a request for a spend notification of either an
// outpoint or output script. A nil outpoint or an allocated ZeroOutPoint can be
// used to dispatch the confirmation notification on the script.
func NewSpendRequest(op *wire.OutPoint, pkScript []byte) (SpendRequest, error) {
        var r SpendRequest
        outputScript, err := txscript.ParsePkScript(pkScript)
        if err != nil {
                return r, err
        }

        // We'll only set an outpoint for which we'll dispatch a spend
        // notification on this request if one was provided. Otherwise, we'll
        // default to dispatching on the spend of the script instead.
        if op != nil {
                r.OutPoint = *op
        }
        r.PkScript = outputScript

        // For Taproot spends we have the main problem that for the key spend
        // path we cannot derive the pkScript from only looking at the input's
        // witness. So we need to rely on the outpoint information alone.
        //
        // TODO(guggero): For script path spends we can derive the pkScript from
        // the witness, since we have the full control block and the spent
        // script available.
        if outputScript.Class() == txscript.WitnessV1TaprootTy {
                if op == nil {
                        return r, fmt.Errorf("cannot register witness v1 " +
                                "spend request without outpoint")
                }

                // We have an outpoint, so we can set the pkScript to an all
                // zero Taproot key that we'll compare this spend request to.
                r.PkScript = ZeroTaprootPkScript
        }

        return r, nil
}

// String returns the string representation of the SpendRequest.
func (r SpendRequest) String() string {
        if r.OutPoint != ZeroOutPoint {
                return fmt.Sprintf("outpoint=%v, script=%v", r.OutPoint,
                        r.PkScript)
        }
        return fmt.Sprintf("outpoint=<zero>, script=%v", r.PkScript)
}

// MatchesTx determines whether the given transaction satisfies the spend
// request. If the spend request is for an outpoint, then we'll check all of
// the outputs being spent by the inputs of the transaction to determine if it
// matches. Otherwise, we'll need to match on the output script being spent, so
// we'll recompute it for each input of the transaction to determine if it
// matches.
func (r SpendRequest) MatchesTx(tx *wire.MsgTx) (bool, uint32, error) {
        if r.OutPoint != ZeroOutPoint {
                for i, txIn := range tx.TxIn {
                        if txIn.PreviousOutPoint == r.OutPoint {
                                return true, uint32(i), nil
                        }
                }

                return false, 0, nil
        }

        for i, txIn := range tx.TxIn {
                pkScript, err := txscript.ComputePkScript(
                        txIn.SignatureScript, txIn.Witness,
                )
                if err == txscript.ErrUnsupportedScriptType {
                        continue
                }
                if err != nil {
                        return false, 0, err
                }

                if bytes.Equal(pkScript.Script(), r.PkScript.Script()) {
                        return true, uint32(i), nil
                }
        }

        return false, 0, nil
}

// SpendNtfn represents a client's request to receive a notification once an
// outpoint/output script has been spent on-chain. The client is asynchronously
// notified via the SpendEvent channels.
type SpendNtfn struct {
        // SpendID uniquely identies the spend notification request for the
        // specified outpoint/output script.
        SpendID uint64

        // SpendRequest represents either the outpoint or script we should
        // detect the spend of.
        SpendRequest

        // Event contains references to the channels that the notifications are
        // to be sent over.
        Event *SpendEvent

        // HeightHint is the earliest height in the chain that we expect to find
        // the spending transaction of the specified outpoint/output script.
        // This value will be overridden by the spend hint cache if it contains
        // an entry for it.
        HeightHint uint32

        // dispatched signals whether a spend notification has been dispatched
        // to the client.
        dispatched bool
}

// HistoricalSpendDispatch parametrizes a manual rescan to determine the
// spending details (if any) of an outpoint/output script. The parameters
// include the start and end block heights specifying the range of blocks to
// scan.
type HistoricalSpendDispatch struct {
        // SpendRequest represents either the outpoint or script we should
        // detect the spend of.
        SpendRequest

        // StartHeight specified the block height at which to begin the
        // historical rescan.
        StartHeight uint32

        // EndHeight specifies the last block height (inclusive) that the
        // historical rescan should consider.
        EndHeight uint32
}

// SpendRegistration encompasses all of the information required for callers to
// retrieve details about a spend event.
type SpendRegistration struct {
        // Event contains references to the channels that the notifications are
        // to be sent over.
        Event *SpendEvent

        // HistoricalDispatch, if non-nil, signals to the client who registered
        // the notification that they are responsible for attempting to manually
        // rescan blocks for the txid/output script between the start and end
        // heights.
        HistoricalDispatch *HistoricalSpendDispatch

        // Height is the height of the TxNotifier at the time the spend
        // notification was registered. This can be used so that backends can
        // request to be notified of spends from this point forwards.
        Height uint32
}

// TxNotifier is a struct responsible for delivering transaction notifications
// to subscribers. These notifications can be of two different types:
// transaction/output script confirmations and/or outpoint/output script spends.
// The TxNotifier will watch the blockchain as new blocks come in, in order to
// satisfy its client requests.
type TxNotifier struct {
        confClientCounter  uint64 // To be used atomically.
        spendClientCounter uint64 // To be used atomically.

        // currentHeight is the height of the tracked blockchain. It is used to
        // determine the number of confirmations a tx has and ensure blocks are
        // connected and disconnected in order.
        currentHeight uint32

        // reorgSafetyLimit is the chain depth beyond which it is assumed a
        // block will not be reorganized out of the chain. This is used to
        // determine when to prune old notification requests so that reorgs are
        // handled correctly. The coinbase maturity period is a reasonable value
        // to use.
        reorgSafetyLimit uint32

        // reorgDepth is the depth of a chain organization that this system is
        // being informed of. This is incremented as long as a sequence of
        // blocks are disconnected without being interrupted by a new block.
        reorgDepth uint32

        // confNotifications is an index of confirmation notification requests
        // by transaction hash/output script.
        confNotifications map[ConfRequest]*confNtfnSet

        // confsByInitialHeight is an index of watched transactions/output
        // scripts by the height that they are included at in the chain. This
        // is tracked so that incorrect notifications are not sent if a
        // transaction/output script is reorged out of the chain and so that
        // negative confirmations can be recognized.
        confsByInitialHeight map[uint32]map[ConfRequest]struct{}

        // ntfnsByConfirmHeight is an index of notification requests by the
        // height at which the transaction/output script will have sufficient
        // confirmations.
        ntfnsByConfirmHeight map[uint32]map[*ConfNtfn]struct{}

        // spendNotifications is an index of all active notification requests
        // per outpoint/output script.
        spendNotifications map[SpendRequest]*spendNtfnSet

        // spendsByHeight is an index that keeps tracks of the spending height
        // of outpoints/output scripts we are currently tracking notifications
        // for. This is used in order to recover from spending transactions
        // being reorged out of the chain.
        spendsByHeight map[uint32]map[SpendRequest]struct{}

        // confirmHintCache is a cache used to maintain the latest height hints
        // for transactions/output scripts. Each height hint represents the
        // earliest height at which they scripts could have been confirmed
        // within the chain.
        confirmHintCache ConfirmHintCache

        // spendHintCache is a cache used to maintain the latest height hints
        // for outpoints/output scripts. Each height hint represents the
        // earliest height at which they could have been spent within the chain.
        spendHintCache SpendHintCache

        // quit is closed in order to signal that the notifier is gracefully
        // exiting.
        quit chan struct{}

        sync.Mutex
}

// NewTxNotifier creates a TxNotifier. The current height of the blockchain is
// accepted as a parameter. The different hint caches (confirm and spend) are
// used as an optimization in order to retrieve a better starting point when
// dispatching a rescan for a historical event in the chain.
func NewTxNotifier(startHeight uint32, reorgSafetyLimit uint32,
        confirmHintCache ConfirmHintCache,
        spendHintCache SpendHintCache) *TxNotifier {

        return &TxNotifier{
                currentHeight:        startHeight,
                reorgSafetyLimit:     reorgSafetyLimit,
                confNotifications:    make(map[ConfRequest]*confNtfnSet),
                confsByInitialHeight: make(map[uint32]map[ConfRequest]struct{}),
                ntfnsByConfirmHeight: make(map[uint32]map[*ConfNtfn]struct{}),
                spendNotifications:   make(map[SpendRequest]*spendNtfnSet),
                spendsByHeight:       make(map[uint32]map[SpendRequest]struct{}),
                confirmHintCache:     confirmHintCache,
                spendHintCache:       spendHintCache,
                quit:                 make(chan struct{}),
        }
}

// newConfNtfn validates all of the parameters required to successfully create
// and register a confirmation notification.
func (n *TxNotifier) newConfNtfn(txid *chainhash.Hash,
        pkScript []byte, numConfs, heightHint uint32,
        opts *notifierOptions) (*ConfNtfn, error) {

        // An accompanying output script must always be provided.
        if len(pkScript) == 0 {
                return nil, ErrNoScript
        }

        // Enforce that we will not dispatch confirmations beyond the reorg
        // safety limit.
        if numConfs == 0 || numConfs > n.reorgSafetyLimit {
                return nil, ErrNumConfsOutOfRange
        }

        // A height hint must be provided to prevent scanning from the genesis
        // block.
        if heightHint == 0 {
                return nil, ErrNoHeightHint
        }

        // Ensure the output script is of a supported type.
        confRequest, err := NewConfRequest(txid, pkScript)
        if err != nil {
                return nil, err
        }

        confID := atomic.AddUint64(&n.confClientCounter, 1)
        return &ConfNtfn{
                ConfID:           confID,
                ConfRequest:      confRequest,
                NumConfirmations: numConfs,
                Event: NewConfirmationEvent(numConfs, func() {
                        n.CancelConf(confRequest, confID)
                }),
                HeightHint:   heightHint,
                includeBlock: opts.includeBlock,
                numConfsLeft: numConfs,
        }, nil
}

// RegisterConf handles a new confirmation notification request. The client will
// be notified when the transaction/output script gets a sufficient number of
// confirmations in the blockchain.
//
// NOTE: If the transaction/output script has already been included in a block
// on the chain, the confirmation details must be provided with the
// UpdateConfDetails method, otherwise we will wait for the transaction/output
// script to confirm even though it already has.
func (n *TxNotifier) RegisterConf(txid *chainhash.Hash, pkScript []byte,
        numConfs, heightHint uint32,
        optFuncs ...NotifierOption) (*ConfRegistration, error) {

        select {
        case <-n.quit:
                return nil, ErrTxNotifierExiting
        default:
        }

        opts := defaultNotifierOptions()
        for _, optFunc := range optFuncs {
                optFunc(opts)
        }

        // We'll start by performing a series of validation checks.
        ntfn, err := n.newConfNtfn(txid, pkScript, numConfs, heightHint, opts)
        if err != nil {
                return nil, err
        }

        // Before proceeding to register the notification, we'll query our
        // height hint cache to determine whether a better one exists.
        //
        // TODO(conner): verify that all submitted height hints are identical.
        startHeight := ntfn.HeightHint
        hint, err := n.confirmHintCache.QueryConfirmHint(ntfn.ConfRequest)
        if err == nil {
                if hint > startHeight {
                        Log.Debugf("Using height hint %d retrieved from cache "+
                                "for %v instead of %d for conf subscription",
                                hint, ntfn.ConfRequest, startHeight)
                        startHeight = hint
                }
        } else if err != ErrConfirmHintNotFound {
                Log.Errorf("Unable to query confirm hint for %v: %v",
                        ntfn.ConfRequest, err)
        }

        Log.Infof("New confirmation subscription: conf_id=%d, %v, "+
                "num_confs=%v height_hint=%d", ntfn.ConfID, ntfn.ConfRequest,
                numConfs, startHeight)

        n.Lock()
        defer n.Unlock()

        confSet, ok := n.confNotifications[ntfn.ConfRequest]
        if !ok {
                // If this is the first registration for this request, construct
                // a confSet to coalesce all notifications for the same request.
                confSet = newConfNtfnSet()
                n.confNotifications[ntfn.ConfRequest] = confSet
        }
        confSet.ntfns[ntfn.ConfID] = ntfn

        switch confSet.rescanStatus {

        // A prior rescan has already completed and we are actively watching at
        // tip for this request.
        case rescanComplete:
                // If the confirmation details for this set of notifications has
                // already been found, we'll attempt to deliver them immediately
                // to this client.
                Log.Debugf("Attempting to dispatch confirmation for %v on "+
                        "registration since rescan has finished, conf_id=%v",
                        ntfn.ConfRequest, ntfn.ConfID)

                // The default notification we assigned above includes the
                // block along with the rest of the details. However not all
                // clients want the block, so we make a copy here w/o the block
                // if needed so we can give clients only what they ask for.
                confDetails := confSet.details
                if !ntfn.includeBlock && confDetails != nil {
                        confDetailsCopy := *confDetails
                        confDetailsCopy.Block = nil

                        confDetails = &confDetailsCopy
                }

                // Deliver the details to the whole conf set where this ntfn
                // lives in.
                for _, subscriber := range confSet.ntfns {
                        err := n.dispatchConfDetails(subscriber, confDetails)
                        if err != nil {
                                return nil, err
                        }
                }

                return &ConfRegistration{
                        Event:              ntfn.Event,
                        HistoricalDispatch: nil,
                        Height:             n.currentHeight,
                }, nil

        // A rescan is already in progress, return here to prevent dispatching
        // another. When the rescan returns, this notification's details will be
        // updated as well.
        case rescanPending:
                Log.Debugf("Waiting for pending rescan to finish before "+
                        "notifying %v at tip", ntfn.ConfRequest)

                return &ConfRegistration{
                        Event:              ntfn.Event,
                        HistoricalDispatch: nil,
                        Height:             n.currentHeight,
                }, nil

        // If no rescan has been dispatched, attempt to do so now.
        case rescanNotStarted:
        }

        // If the provided or cached height hint indicates that the
        // transaction with the given txid/output script is to be confirmed at a
        // height greater than the notifier's current height, we'll refrain from
        // spawning a historical dispatch.
        if startHeight > n.currentHeight {
                Log.Debugf("Height hint is above current height, not "+
                        "dispatching historical confirmation rescan for %v",
                        ntfn.ConfRequest)

                // Set the rescan status to complete, which will allow the
                // notifier to start delivering messages for this set
                // immediately.
                confSet.rescanStatus = rescanComplete
                return &ConfRegistration{
                        Event:              ntfn.Event,
                        HistoricalDispatch: nil,
                        Height:             n.currentHeight,
                }, nil
        }

        Log.Debugf("Dispatching historical confirmation rescan for %v",
                ntfn.ConfRequest)

        // Construct the parameters for historical dispatch, scanning the range
        // of blocks between our best known height hint and the notifier's
        // current height. The notifier will begin also watching for
        // confirmations at tip starting with the next block.
        dispatch := &HistoricalConfDispatch{
                ConfRequest: ntfn.ConfRequest,
                StartHeight: startHeight,
                EndHeight:   n.currentHeight,
        }

        // Set this confSet's status to pending, ensuring subsequent
        // registrations don't also attempt a dispatch.
        confSet.rescanStatus = rescanPending

        return &ConfRegistration{
                Event:              ntfn.Event,
                HistoricalDispatch: dispatch,
                Height:             n.currentHeight,
        }, nil
}

// CancelConf cancels an existing request for a spend notification of an
// outpoint/output script. The request is identified by its spend ID.
func (n *TxNotifier) CancelConf(confRequest ConfRequest, confID uint64) {
        select {
        case <-n.quit:
                return
        default:
        }

        n.Lock()
        defer n.Unlock()

        confSet, ok := n.confNotifications[confRequest]
        if !ok {
                return
        }
        ntfn, ok := confSet.ntfns[confID]
        if !ok {
                return
        }

        Log.Debugf("Canceling confirmation notification: conf_id=%d, %v",
                confID, confRequest)

        // We'll close all the notification channels to let the client know
        // their cancel request has been fulfilled.
        close(ntfn.Event.Confirmed)
        close(ntfn.Event.Updates)
        close(ntfn.Event.NegativeConf)

        // Finally, we'll clean up any lingering references to this
        // notification.
        delete(confSet.ntfns, confID)

        // Remove the queued confirmation notification if the transaction has
        // already confirmed, but hasn't met its required number of
        // confirmations.
        if confSet.details != nil {
                confHeight := confSet.details.BlockHeight +
                        ntfn.NumConfirmations - 1
                delete(n.ntfnsByConfirmHeight[confHeight], ntfn)
        }
}

// UpdateConfDetails attempts to update the confirmation details for an active
// notification within the notifier. This should only be used in the case of a
// transaction/output script that has confirmed before the notifier's current
// height.
//
// NOTE: The notification should be registered first to ensure notifications are
// dispatched correctly.
func (n *TxNotifier) UpdateConfDetails(confRequest ConfRequest,
        details *TxConfirmation) error {

        select {
        case <-n.quit:
                return ErrTxNotifierExiting
        default:
        }

        // Ensure we hold the lock throughout handling the notification to
        // prevent the notifier from advancing its height underneath us.
        n.Lock()
        defer n.Unlock()

        // First, we'll determine whether we have an active confirmation
        // notification for the given txid/script.
        confSet, ok := n.confNotifications[confRequest]
        if !ok {
                return fmt.Errorf("confirmation notification for %v not found",
                        confRequest)
        }

        // If the confirmation details were already found at tip, all existing
        // notifications will have been dispatched or queued for dispatch. We
        // can exit early to avoid sending too many notifications on the
        // buffered channels.
        if confSet.details != nil {
                return nil
        }

        // The historical dispatch has been completed for this confSet. We'll
        // update the rescan status and cache any details that were found. If
        // the details are nil, that implies we did not find them and will
        // continue to watch for them at tip.
        confSet.rescanStatus = rescanComplete

        // The notifier has yet to reach the height at which the
        // transaction/output script was included in a block, so we should defer
        // until handling it then within ConnectTip.
        if details == nil {
                Log.Debugf("Confirmation details for %v not found during "+
                        "historical dispatch, waiting to dispatch at tip",
                        confRequest)

                // We'll commit the current height as the confirm hint to
                // prevent another potentially long rescan if we restart before
                // a new block comes in.
                err := n.confirmHintCache.CommitConfirmHint(
                        n.currentHeight, confRequest,
                )
                if err != nil {
                        // The error is not fatal as this is an optimistic
                        // optimization, so we'll avoid returning an error.
                        Log.Debugf("Unable to update confirm hint to %d for "+
                                "%v: %v", n.currentHeight, confRequest, err)
                }

                return nil
        }

        if details.BlockHeight > n.currentHeight {
                Log.Debugf("Confirmation details for %v found above current "+
                        "height, waiting to dispatch at tip", confRequest)

                return nil
        }

        Log.Debugf("Updating confirmation details for %v", confRequest)

        err := n.confirmHintCache.CommitConfirmHint(
                details.BlockHeight, confRequest,
        )
        if err != nil {
                // The error is not fatal, so we should not return an error to
                // the caller.
                Log.Errorf("Unable to update confirm hint to %d for %v: %v",
                        details.BlockHeight, confRequest, err)
        }

        // Cache the details found in the rescan and attempt to dispatch any
        // notifications that have not yet been delivered.
        confSet.details = details
        for _, ntfn := range confSet.ntfns {
                // The default notification we assigned above includes the
                // block along with the rest of the details. However not all
                // clients want the block, so we make a copy here w/o the block
                // if needed so we can give clients only what they ask for.
                confDetails := *details
                if !ntfn.includeBlock {
                        confDetails.Block = nil
                }

                err = n.dispatchConfDetails(ntfn, &confDetails)
                if err != nil {
                        return err
                }
        }

        return nil
}

// dispatchConfDetails attempts to cache and dispatch details to a particular
// client if the transaction/output script has sufficiently confirmed. If the
// provided details are nil, this method will be a no-op.
func (n *TxNotifier) dispatchConfDetails(
        ntfn *ConfNtfn, details *TxConfirmation) error {

        // If there are no conf details to dispatch or if the notification has
        // already been dispatched, then we can skip dispatching to this
        // client.
        if details == nil {
                Log.Debugf("Skipped dispatching nil conf details for request "+
                        "%v, conf_id=%v", ntfn.ConfRequest, ntfn.ConfID)

                return nil
        }

        if ntfn.dispatched {
                Log.Debugf("Skipped dispatched conf details for request %v "+
                        "conf_id=%v", ntfn.ConfRequest, ntfn.ConfID)

                return nil
        }

        // Now, we'll examine whether the transaction/output script of this
        // request has reached its required number of confirmations. If it has,
        // we'll dispatch a confirmation notification to the caller.
        confHeight := details.BlockHeight + ntfn.NumConfirmations - 1
        if confHeight <= n.currentHeight {
                Log.Debugf("Dispatching %v confirmation notification for "+
                        "conf_id=%v, %v", ntfn.NumConfirmations, ntfn.ConfID,
                        ntfn.ConfRequest)

                // We'll send a 0 value to the Updates channel,
                // indicating that the transaction/output script has already
                // been confirmed.
                err := n.notifyNumConfsLeft(ntfn, 0)
                if err != nil {
                        return err
                }

                select {
                case ntfn.Event.Confirmed <- details:
                        ntfn.dispatched = true
                case <-n.quit:
                        return ErrTxNotifierExiting
                }
        } else {
                Log.Debugf("Queueing %v confirmation notification for %v at "+
                        "tip", ntfn.NumConfirmations, ntfn.ConfRequest)

                // Otherwise, we'll keep track of the notification
                // request by the height at which we should dispatch the
                // confirmation notification.
                ntfnSet, exists := n.ntfnsByConfirmHeight[confHeight]
                if !exists {
                        ntfnSet = make(map[*ConfNtfn]struct{})
                        n.ntfnsByConfirmHeight[confHeight] = ntfnSet
                }
                ntfnSet[ntfn] = struct{}{}

                // We'll also send an update to the client of how many
                // confirmations are left for the transaction/output script to
                // be confirmed.
                numConfsLeft := confHeight - n.currentHeight
                err := n.notifyNumConfsLeft(ntfn, numConfsLeft)
                if err != nil {
                        return err
                }
        }

        // As a final check, we'll also watch the transaction/output script if
        // it's still possible for it to get reorged out of the chain.
        reorgSafeHeight := details.BlockHeight + n.reorgSafetyLimit
        if reorgSafeHeight > n.currentHeight {
                txSet, exists := n.confsByInitialHeight[details.BlockHeight]
                if !exists {
                        txSet = make(map[ConfRequest]struct{})
                        n.confsByInitialHeight[details.BlockHeight] = txSet
                }
                txSet[ntfn.ConfRequest] = struct{}{}
        }

        return nil
}

// newSpendNtfn validates all of the parameters required to successfully create
// and register a spend notification.
func (n *TxNotifier) newSpendNtfn(outpoint *wire.OutPoint,
        pkScript []byte, heightHint uint32) (*SpendNtfn, error) {

        // An accompanying output script must always be provided.
        if len(pkScript) == 0 {
                return nil, ErrNoScript
        }

        // A height hint must be provided to prevent scanning from the genesis
        // block.
        if heightHint == 0 {
                return nil, ErrNoHeightHint
        }

        // Ensure the output script is of a supported type.
        spendRequest, err := NewSpendRequest(outpoint, pkScript)
        if err != nil {
                return nil, err
        }

        spendID := atomic.AddUint64(&n.spendClientCounter, 1)
        return &SpendNtfn{
                SpendID:      spendID,
                SpendRequest: spendRequest,
                Event: NewSpendEvent(func() {
                        n.CancelSpend(spendRequest, spendID)
                }),
                HeightHint: heightHint,
        }, nil
}

// RegisterSpend handles a new spend notification request. The client will be
// notified once the outpoint/output script is detected as spent within the
// chain.
//
// NOTE: If the outpoint/output script has already been spent within the chain
// before the notifier's current tip, the spend details must be provided with
// the UpdateSpendDetails method, otherwise we will wait for the outpoint/output
// script to be spent at tip, even though it already has.
func (n *TxNotifier) RegisterSpend(outpoint *wire.OutPoint, pkScript []byte,
        heightHint uint32) (*SpendRegistration, error) {

        select {
        case <-n.quit:
                return nil, ErrTxNotifierExiting
        default:
        }

        // We'll start by performing a series of validation checks.
        ntfn, err := n.newSpendNtfn(outpoint, pkScript, heightHint)
        if err != nil {
                return nil, err
        }

        // Before proceeding to register the notification, we'll query our spend
        // hint cache to determine whether a better one exists.
        startHeight := ntfn.HeightHint
        hint, err := n.spendHintCache.QuerySpendHint(ntfn.SpendRequest)
        if err == nil {
                if hint > startHeight {
                        Log.Debugf("Using height hint %d retrieved from cache "+
                                "for %v instead of %d for spend subscription",
                                hint, ntfn.SpendRequest, startHeight)
                        startHeight = hint
                }
        } else if err != ErrSpendHintNotFound {
                Log.Errorf("Unable to query spend hint for %v: %v",
                        ntfn.SpendRequest, err)
        }

        n.Lock()
        defer n.Unlock()

        Log.Debugf("New spend subscription: spend_id=%d, %v, height_hint=%d",
                ntfn.SpendID, ntfn.SpendRequest, startHeight)

        // Keep track of the notification request so that we can properly
        // dispatch a spend notification later on.
        spendSet, ok := n.spendNotifications[ntfn.SpendRequest]
        if !ok {
                // If this is the first registration for the request, we'll
                // construct a spendNtfnSet to coalesce all notifications.
                spendSet = newSpendNtfnSet()
                n.spendNotifications[ntfn.SpendRequest] = spendSet
        }
        spendSet.ntfns[ntfn.SpendID] = ntfn

        // We'll now let the caller know whether a historical rescan is needed
        // depending on the current rescan status.
        switch spendSet.rescanStatus {

        // If the spending details for this request have already been determined
        // and cached, then we can use them to immediately dispatch the spend
        // notification to the client.
        case rescanComplete:
                Log.Debugf("Attempting to dispatch spend for %v on "+
                        "registration since rescan has finished",
                        ntfn.SpendRequest)

                err := n.dispatchSpendDetails(ntfn, spendSet.details)
                if err != nil {
                        return nil, err
                }

                return &SpendRegistration{
                        Event:              ntfn.Event,
                        HistoricalDispatch: nil,
                        Height:             n.currentHeight,
                }, nil

        // If there is an active rescan to determine whether the request has
        // been spent, then we won't trigger another one.
        case rescanPending:
                Log.Debugf("Waiting for pending rescan to finish before "+
                        "notifying %v at tip", ntfn.SpendRequest)

                return &SpendRegistration{
                        Event:              ntfn.Event,
                        HistoricalDispatch: nil,
                        Height:             n.currentHeight,
                }, nil

        // Otherwise, we'll fall through and let the caller know that a rescan
        // should be dispatched to determine whether the request has already
        // been spent.
        case rescanNotStarted:
        }

        // However, if the spend hint, either provided by the caller or
        // retrieved from the cache, is found to be at a later height than the
        // TxNotifier is aware of, then we'll refrain from dispatching a
        // historical rescan and wait for the spend to come in at tip.
        if startHeight > n.currentHeight {
                Log.Debugf("Spend hint of %d for %v is above current height %d",
                        startHeight, ntfn.SpendRequest, n.currentHeight)

                // We'll also set the rescan status as complete to ensure that
                // spend hints for this request get updated upon
                // connected/disconnected blocks.
                spendSet.rescanStatus = rescanComplete
                return &SpendRegistration{
                        Event:              ntfn.Event,
                        HistoricalDispatch: nil,
                        Height:             n.currentHeight,
                }, nil
        }

        // We'll set the rescan status to pending to ensure subsequent
        // notifications don't also attempt a historical dispatch.
        spendSet.rescanStatus = rescanPending

        Log.Debugf("Dispatching historical spend rescan for %v, start=%d, "+
                "end=%d", ntfn.SpendRequest, startHeight, n.currentHeight)

        return &SpendRegistration{
                Event: ntfn.Event,
                HistoricalDispatch: &HistoricalSpendDispatch{
                        SpendRequest: ntfn.SpendRequest,
                        StartHeight:  startHeight,
                        EndHeight:    n.currentHeight,
                },
                Height: n.currentHeight,
        }, nil
}

// CancelSpend cancels an existing request for a spend notification of an
// outpoint/output script. The request is identified by its spend ID.
func (n *TxNotifier) CancelSpend(spendRequest SpendRequest, spendID uint64) {
        select {
        case <-n.quit:
                return
        default:
        }

        n.Lock()
        defer n.Unlock()

        spendSet, ok := n.spendNotifications[spendRequest]
        if !ok {
                return
        }
        ntfn, ok := spendSet.ntfns[spendID]
        if !ok {
                return
        }

        Log.Debugf("Canceling spend notification: spend_id=%d, %v", spendID,
                spendRequest)

        // We'll close all the notification channels to let the client know
        // their cancel request has been fulfilled.
        close(ntfn.Event.Spend)
        close(ntfn.Event.Reorg)
        close(ntfn.Event.Done)
        delete(spendSet.ntfns, spendID)
}

// ProcessRelevantSpendTx processes a transaction provided externally. This will
// check whether the transaction is relevant to the notifier if it spends any
// outpoints/output scripts for which we currently have registered notifications
// for. If it is relevant, spend notifications will be dispatched to the caller.
func (n *TxNotifier) ProcessRelevantSpendTx(tx *btcutil.Tx,
        blockHeight uint32) error {

        select {
        case <-n.quit:
                return ErrTxNotifierExiting
        default:
        }

        // Ensure we hold the lock throughout handling the notification to
        // prevent the notifier from advancing its height underneath us.
        n.Lock()
        defer n.Unlock()

        // We'll use a channel to coalesce all the spend requests that this
        // transaction fulfills.
        type spend struct {
                request *SpendRequest
                details *SpendDetail
        }

        // We'll set up the onSpend filter callback to gather all the fulfilled
        // spends requests within this transaction.
        var spends []spend
        onSpend := func(request SpendRequest, details *SpendDetail) {
                spends = append(spends, spend{&request, details})
        }
        n.filterTx(nil, tx, blockHeight, nil, onSpend)

        // After the transaction has been filtered, we can finally dispatch
        // notifications for each request.
        for _, spend := range spends {
                err := n.updateSpendDetails(*spend.request, spend.details)
                if err != nil {
                        return err
                }
        }

        return nil
}

// UpdateSpendDetails attempts to update the spend details for all active spend
// notification requests for an outpoint/output script. This method should be
// used once a historical scan of the chain has finished. If the historical scan
// did not find a spending transaction for it, the spend details may be nil.
//
// NOTE: A notification request for the outpoint/output script must be
// registered first to ensure notifications are delivered.
func (n *TxNotifier) UpdateSpendDetails(spendRequest SpendRequest,
        details *SpendDetail) error {

        select {
        case <-n.quit:
                return ErrTxNotifierExiting
        default:
        }

        // Ensure we hold the lock throughout handling the notification to
        // prevent the notifier from advancing its height underneath us.
        n.Lock()
        defer n.Unlock()

        return n.updateSpendDetails(spendRequest, details)
}

// updateSpendDetails attempts to update the spend details for all active spend
// notification requests for an outpoint/output script. This method should be
// used once a historical scan of the chain has finished. If the historical scan
// did not find a spending transaction for it, the spend details may be nil.
//
// NOTE: This method must be called with the TxNotifier's lock held.
func (n *TxNotifier) updateSpendDetails(spendRequest SpendRequest,
        details *SpendDetail) error {

        // Mark the ongoing historical rescan for this request as finished. This
        // will allow us to update the spend hints for it at tip.
        spendSet, ok := n.spendNotifications[spendRequest]
        if !ok {
                return fmt.Errorf("spend notification for %v not found",
                        spendRequest)
        }

        // If the spend details have already been found either at tip, then the
        // notifications should have already been dispatched, so we can exit
        // early to prevent sending duplicate notifications.
        if spendSet.details != nil {
                return nil
        }

        // Since the historical rescan has completed for this request, we'll
        // mark its rescan status as complete in order to ensure that the
        // TxNotifier can properly update its spend hints upon
        // connected/disconnected blocks.
        spendSet.rescanStatus = rescanComplete

        // If the historical rescan was not able to find a spending transaction
        // for this request, then we can track the spend at tip.
        if details == nil {
                // We'll commit the current height as the spend hint to prevent
                // another potentially long rescan if we restart before a new
                // block comes in.
                err := n.spendHintCache.CommitSpendHint(
                        n.currentHeight, spendRequest,
                )
                if err != nil {
                        // The error is not fatal as this is an optimistic
                        // optimization, so we'll avoid returning an error.
                        Log.Debugf("Unable to update spend hint to %d for %v: %v",
                                n.currentHeight, spendRequest, err)
                }

                Log.Debugf("Updated spend hint to height=%v for unconfirmed "+
                        "spend request %v", n.currentHeight, spendRequest)
                return nil
        }

        // Return an error if the witness data is not present in the spending
        // transaction.
        //
        // NOTE: if the witness stack is empty, we will do a critical log which
        // shuts down the node.
        if !details.HasSpenderWitness() {
                Log.Criticalf("Found spending tx for outpoint=%v, but the "+
                        "transaction %v does not have witness",
                        spendRequest.OutPoint, details.SpendingTx.TxHash())

                return ErrEmptyWitnessStack
        }

        // If the historical rescan found the spending transaction for this
        // request, but it's at a later height than the notifier (this can
        // happen due to latency with the backend during a reorg), then we'll
        // defer handling the notification until the notifier has caught up to
        // such height.
        if uint32(details.SpendingHeight) > n.currentHeight {
                return nil
        }

        // Now that we've determined the request has been spent, we'll commit
        // its spending height as its hint in the cache and dispatch
        // notifications to all of its respective clients.
        err := n.spendHintCache.CommitSpendHint(
                uint32(details.SpendingHeight), spendRequest,
        )
        if err != nil {
                // The error is not fatal as this is an optimistic optimization,
                // so we'll avoid returning an error.
                Log.Debugf("Unable to update spend hint to %d for %v: %v",
                        details.SpendingHeight, spendRequest, err)
        }

        Log.Debugf("Updated spend hint to height=%v for confirmed spend "+
                "request %v", details.SpendingHeight, spendRequest)

        spendSet.details = details
        for _, ntfn := range spendSet.ntfns {
                err := n.dispatchSpendDetails(ntfn, spendSet.details)
                if err != nil {
                        return err
                }
        }

        return nil
}

// dispatchSpendDetails dispatches a spend notification to the client.
//
// NOTE: This must be called with the TxNotifier's lock held.
func (n *TxNotifier) dispatchSpendDetails(ntfn *SpendNtfn, details *SpendDetail) error {
        // If there are no spend details to dispatch or if the notification has
        // already been dispatched, then we can skip dispatching to this client.
        if details == nil || ntfn.dispatched {
                Log.Debugf("Skipping dispatch of spend details(%v) for "+
                        "request %v, dispatched=%v", details, ntfn.SpendRequest,
                        ntfn.dispatched)
                return nil
        }

        Log.Debugf("Dispatching confirmed spend notification for %v at "+
                "current height=%d: %v", ntfn.SpendRequest, n.currentHeight,
                details)

        select {
        case ntfn.Event.Spend <- details:
                ntfn.dispatched = true
        case <-n.quit:
                return ErrTxNotifierExiting
        }

        spendHeight := uint32(details.SpendingHeight)

        // We also add to spendsByHeight to notify on chain reorgs.
        reorgSafeHeight := spendHeight + n.reorgSafetyLimit
        if reorgSafeHeight > n.currentHeight {
                txSet, exists := n.spendsByHeight[spendHeight]
                if !exists {
                        txSet = make(map[SpendRequest]struct{})
                        n.spendsByHeight[spendHeight] = txSet
                }
                txSet[ntfn.SpendRequest] = struct{}{}
        }

        return nil
}

// ConnectTip handles a new block extending the current chain. It will go
// through every transaction and determine if it is relevant to any of its
// clients. A transaction can be relevant in either of the following two ways:
//
//  1. One of the inputs in the transaction spends an outpoint/output script
//     for which we currently have an active spend registration for.
//
//  2. The transaction has a txid or output script for which we currently have
//     an active confirmation registration for.
//
// In the event that the transaction is relevant, a confirmation/spend
// notification will be queued for dispatch to the relevant clients.
// Confirmation notifications will only be dispatched for transactions/output
// scripts that have met the required number of confirmations required by the
// client.
//
// NOTE: In order to actually dispatch the relevant transaction notifications to
// clients, NotifyHeight must be called with the same block height in order to
// maintain correctness.
func (n *TxNotifier) ConnectTip(block *btcutil.Block,
        blockHeight uint32) error {

        select {
        case <-n.quit:
                return ErrTxNotifierExiting
        default:
        }

        n.Lock()
        defer n.Unlock()

        if blockHeight != n.currentHeight+1 {
                return fmt.Errorf("received blocks out of order: "+
                        "current height=%d, new height=%d",
                        n.currentHeight, blockHeight)
        }
        n.currentHeight++
        n.reorgDepth = 0

        // First, we'll iterate over all the transactions found in this block to
        // determine if it includes any relevant transactions to the TxNotifier.
        if block != nil {
                Log.Debugf("Filtering %d txns for %d spend requests at "+
                        "height %d", len(block.Transactions()),
                        len(n.spendNotifications), blockHeight)

                for _, tx := range block.Transactions() {
                        n.filterTx(
                                block, tx, blockHeight,
                                n.handleConfDetailsAtTip,
                                n.handleSpendDetailsAtTip,
                        )
                }
        }

        // Now that we've determined which requests were confirmed and spent
        // within the new block, we can update their entries in their respective
        // caches, along with all of our unconfirmed and unspent requests.
        n.updateHints(blockHeight)

        // Finally, we'll clear the entries from our set of notifications for
        // requests that are no longer under the risk of being reorged out of
        // the chain.
        if blockHeight >= n.reorgSafetyLimit {
                matureBlockHeight := blockHeight - n.reorgSafetyLimit
                for confRequest := range n.confsByInitialHeight[matureBlockHeight] {
                        confSet := n.confNotifications[confRequest]
                        for _, ntfn := range confSet.ntfns {
                                select {
                                case ntfn.Event.Done <- struct{}{}:
                                case <-n.quit:
                                        return ErrTxNotifierExiting
                                }
                        }

                        delete(n.confNotifications, confRequest)
                }
                delete(n.confsByInitialHeight, matureBlockHeight)

                for spendRequest := range n.spendsByHeight[matureBlockHeight] {
                        spendSet := n.spendNotifications[spendRequest]
                        for _, ntfn := range spendSet.ntfns {
                                select {
                                case ntfn.Event.Done <- struct{}{}:
                                case <-n.quit:
                                        return ErrTxNotifierExiting
                                }
                        }

                        Log.Debugf("Deleting mature spend request %v at "+
                                "height=%d", spendRequest, blockHeight)
                        delete(n.spendNotifications, spendRequest)
                }
                delete(n.spendsByHeight, matureBlockHeight)
        }

        return nil
}

// filterTx determines whether the transaction spends or confirms any
// outstanding pending requests. The onConf and onSpend callbacks can be used to
// retrieve all the requests fulfilled by this transaction as they occur.
func (n *TxNotifier) filterTx(block *btcutil.Block, tx *btcutil.Tx,
        blockHeight uint32, onConf func(ConfRequest, *TxConfirmation),
        onSpend func(SpendRequest, *SpendDetail)) {

        // In order to determine if this transaction is relevant to the
        // notifier, we'll check its inputs for any outstanding spend
        // requests.
        txHash := tx.Hash()
        if onSpend != nil {
                // notifyDetails is a helper closure that will construct the
                // spend details of a request and hand them off to the onSpend
                // callback.
                notifyDetails := func(spendRequest SpendRequest,
                        prevOut wire.OutPoint, inputIdx uint32) {

                        Log.Debugf("Found spend of %v: spend_tx=%v, "+
                                "block_height=%d", spendRequest, txHash,
                                blockHeight)

                        onSpend(spendRequest, &SpendDetail{
                                SpentOutPoint:     &prevOut,
                                SpenderTxHash:     txHash,
                                SpendingTx:        tx.MsgTx(),
                                SpenderInputIndex: inputIdx,
                                SpendingHeight:    int32(blockHeight),
                        })
                }

                for i, txIn := range tx.MsgTx().TxIn {
                        // We'll re-derive the script of the output being spent
                        // to determine if the inputs spends any registered
                        // requests.
                        prevOut := txIn.PreviousOutPoint
                        pkScript, err := txscript.ComputePkScript(
                                txIn.SignatureScript, txIn.Witness,
                        )
                        if err != nil {
                                continue
                        }
                        spendRequest := SpendRequest{
                                OutPoint: prevOut,
                                PkScript: pkScript,
                        }

                        // If we have any, we'll record their spend height so
                        // that notifications get dispatched to the respective
                        // clients.
                        if _, ok := n.spendNotifications[spendRequest]; ok {
                                notifyDetails(spendRequest, prevOut, uint32(i))
                        }

                        // Now try with an empty taproot key pkScript, since we
                        // cannot derive the spent pkScript directly from the
                        // witness. But we have the outpoint, which should be
                        // enough.
                        spendRequest.PkScript = ZeroTaprootPkScript
                        if _, ok := n.spendNotifications[spendRequest]; ok {
                                notifyDetails(spendRequest, prevOut, uint32(i))
                        }

                        // Restore the pkScript but try with a zero outpoint
                        // instead (won't be possible for Taproot).
                        spendRequest.PkScript = pkScript
                        spendRequest.OutPoint = ZeroOutPoint
                        if _, ok := n.spendNotifications[spendRequest]; ok {
                                notifyDetails(spendRequest, prevOut, uint32(i))
                        }
                }
        }

        // We'll also check its outputs to determine if there are any
        // outstanding confirmation requests.
        if onConf != nil {
                // notifyDetails is a helper closure that will construct the
                // confirmation details of a request and hand them off to the
                // onConf callback.
                notifyDetails := func(confRequest ConfRequest) {
                        Log.Debugf("Found initial confirmation of %v: "+
                                "height=%d, hash=%v", confRequest,
                                blockHeight, block.Hash())

                        details := &TxConfirmation{
                                Tx:          tx.MsgTx(),
                                BlockHash:   block.Hash(),
                                BlockHeight: blockHeight,
                                TxIndex:     uint32(tx.Index()),
                                Block:       block.MsgBlock(),
                        }

                        onConf(confRequest, details)
                }

                for _, txOut := range tx.MsgTx().TxOut {
                        // We'll parse the script of the output to determine if
                        // we have any registered requests for it or the
                        // transaction itself.
                        pkScript, err := txscript.ParsePkScript(txOut.PkScript)
                        if err != nil {
                                continue
                        }
                        confRequest := ConfRequest{
                                TxID:     *txHash,
                                PkScript: pkScript,
                        }

                        // If we have any, we'll record their confirmed height
                        // so that notifications get dispatched when they
                        // reaches the clients' desired number of confirmations.
                        if _, ok := n.confNotifications[confRequest]; ok {
                                notifyDetails(confRequest)
                        }
                        confRequest.TxID = ZeroHash
                        if _, ok := n.confNotifications[confRequest]; ok {
                                notifyDetails(confRequest)
                        }
                }
        }
}

// handleConfDetailsAtTip tracks the confirmation height of the txid/output
// script in order to properly dispatch a confirmation notification after
// meeting each request's desired number of confirmations for all current and
// future registered clients.
func (n *TxNotifier) handleConfDetailsAtTip(confRequest ConfRequest,
        details *TxConfirmation) {

        // TODO(wilmer): cancel pending historical rescans if any?
        confSet := n.confNotifications[confRequest]

        // If we already have details for this request, we don't want to add it
        // again since we have already dispatched notifications for it.
        if confSet.details != nil {
                Log.Warnf("Ignoring address reuse for %s at height %d.",
                        confRequest, details.BlockHeight)
                return
        }

        confSet.rescanStatus = rescanComplete
        confSet.details = details

        for _, ntfn := range confSet.ntfns {
                // In the event that this notification was aware that the
                // transaction/output script was reorged out of the chain, we'll
                // consume the reorg notification if it hasn't been done yet
                // already.
                select {
                case <-ntfn.Event.NegativeConf:
                default:
                }

                // We'll note this client's required number of confirmations so
                // that we can notify them when expected.
                confHeight := details.BlockHeight + ntfn.NumConfirmations - 1
                ntfnSet, exists := n.ntfnsByConfirmHeight[confHeight]
                if !exists {
                        ntfnSet = make(map[*ConfNtfn]struct{})
                        n.ntfnsByConfirmHeight[confHeight] = ntfnSet
                }
                ntfnSet[ntfn] = struct{}{}
        }

        // We'll also note the initial confirmation height in order to correctly
        // handle dispatching notifications when the transaction/output script
        // gets reorged out of the chain.
        txSet, exists := n.confsByInitialHeight[details.BlockHeight]
        if !exists {
                txSet = make(map[ConfRequest]struct{})
                n.confsByInitialHeight[details.BlockHeight] = txSet
        }
        txSet[confRequest] = struct{}{}
}

// handleSpendDetailsAtTip tracks the spend height of the outpoint/output script
// in order to properly dispatch a spend notification for all current and future
// registered clients.
func (n *TxNotifier) handleSpendDetailsAtTip(spendRequest SpendRequest,
        details *SpendDetail) {

        // TODO(wilmer): cancel pending historical rescans if any?
        spendSet := n.spendNotifications[spendRequest]
        spendSet.rescanStatus = rescanComplete
        spendSet.details = details

        for _, ntfn := range spendSet.ntfns {
                // In the event that this notification was aware that the
                // spending transaction of its outpoint/output script was
                // reorged out of the chain, we'll consume the reorg
                // notification if it hasn't been done yet already.
                select {
                case <-ntfn.Event.Reorg:
                default:
                }
        }

        // We'll note the spending height of the request in order to correctly
        // handle dispatching notifications when the spending transactions gets
        // reorged out of the chain.
        spendHeight := uint32(details.SpendingHeight)
        opSet, exists := n.spendsByHeight[spendHeight]
        if !exists {
                opSet = make(map[SpendRequest]struct{})
                n.spendsByHeight[spendHeight] = opSet
        }
        opSet[spendRequest] = struct{}{}

        Log.Debugf("Spend request %v spent at tip=%d", spendRequest,
                spendHeight)
}

// NotifyHeight dispatches confirmation and spend notifications to the clients
// who registered for a notification which has been fulfilled at the passed
// height.
func (n *TxNotifier) NotifyHeight(height uint32) error {
        n.Lock()
        defer n.Unlock()

        // First, we'll dispatch an update to all of the notification clients
        // for our watched requests with the number of confirmations left at
        // this new height.
        for _, confRequests := range n.confsByInitialHeight {
                for confRequest := range confRequests {
                        confSet := n.confNotifications[confRequest]
                        for _, ntfn := range confSet.ntfns {
                                txConfHeight := confSet.details.BlockHeight +
                                        ntfn.NumConfirmations - 1
                                numConfsLeft := txConfHeight - height

                                // Since we don't clear notifications until
                                // transactions/output scripts are no longer
                                // under the risk of being reorganized out of
                                // the chain, we'll skip sending updates for
                                // those that have already been confirmed.
                                if int32(numConfsLeft) < 0 {
                                        continue
                                }

                                err := n.notifyNumConfsLeft(ntfn, numConfsLeft)
                                if err != nil {
                                        return err
                                }
                        }
                }
        }

        // Then, we'll dispatch notifications for all the requests that have
        // become confirmed at this new block height.
        for ntfn := range n.ntfnsByConfirmHeight[height] {
                confSet := n.confNotifications[ntfn.ConfRequest]

                Log.Debugf("Dispatching %v confirmation notification for "+
                        "conf_id=%v, %v", ntfn.NumConfirmations, ntfn.ConfID,
                        ntfn.ConfRequest)

                // The default notification we assigned above includes the
                // block along with the rest of the details. However not all
                // clients want the block, so we make a copy here w/o the block
                // if needed so we can give clients only what they ask for.
                confDetails := *confSet.details
                if !ntfn.includeBlock {
                        confDetails.Block = nil
                }

                select {
                case ntfn.Event.Confirmed <- &confDetails:
                        ntfn.dispatched = true
                case <-n.quit:
                        return ErrTxNotifierExiting
                }
        }
        delete(n.ntfnsByConfirmHeight, height)

        // Finally, we'll dispatch spend notifications for all the requests that
        // were spent at this new block height.
        for spendRequest := range n.spendsByHeight[height] {
                spendSet := n.spendNotifications[spendRequest]
                for _, ntfn := range spendSet.ntfns {
                        err := n.dispatchSpendDetails(ntfn, spendSet.details)
                        if err != nil {
                                return err
                        }
                }
        }

        return nil
}

// DisconnectTip handles the tip of the current chain being disconnected during
// a chain reorganization. If any watched requests were included in this block,
// internal structures are updated to ensure confirmation/spend notifications
// are consumed (if not already), and reorg notifications are dispatched
// instead. Confirmation/spend notifications will be dispatched again upon block
// inclusion.
func (n *TxNotifier) DisconnectTip(blockHeight uint32) error {
        select {
        case <-n.quit:
                return ErrTxNotifierExiting
        default:
        }

        n.Lock()
        defer n.Unlock()

        if blockHeight != n.currentHeight {
                return fmt.Errorf("received blocks out of order: "+
                        "current height=%d, disconnected height=%d",
                        n.currentHeight, blockHeight)
        }
        n.currentHeight--
        n.reorgDepth++

        // With the block disconnected, we'll update the confirm and spend hints
        // for our notification requests to reflect the new height, except for
        // those that have confirmed/spent at previous heights.
        n.updateHints(blockHeight)

        // We'll go through all of our watched confirmation requests and attempt
        // to drain their notification channels to ensure sending notifications
        // to the clients is always non-blocking.
        for initialHeight, txHashes := range n.confsByInitialHeight {
                for txHash := range txHashes {
                        // If the transaction/output script has been reorged out
                        // of the chain, we'll make sure to remove the cached
                        // confirmation details to prevent notifying clients
                        // with old information.
                        confSet := n.confNotifications[txHash]
                        if initialHeight == blockHeight {
                                confSet.details = nil
                        }

                        for _, ntfn := range confSet.ntfns {
                                // First, we'll attempt to drain an update
                                // from each notification to ensure sends to the
                                // Updates channel are always non-blocking.
                                select {
                                case <-ntfn.Event.Updates:
                                case <-n.quit:
                                        return ErrTxNotifierExiting
                                default:
                                }

                                // We also reset the num of confs update.
                                ntfn.numConfsLeft = ntfn.NumConfirmations

                                // Then, we'll check if the current
                                // transaction/output script was included in the
                                // block currently being disconnected. If it
                                // was, we'll need to dispatch a reorg
                                // notification to the client.
                                if initialHeight == blockHeight {
                                        err := n.dispatchConfReorg(
                                                ntfn, blockHeight,
                                        )
                                        if err != nil {
                                                return err
                                        }
                                }
                        }
                }
        }

        // We'll also go through our watched spend requests and attempt to drain
        // their dispatched notifications to ensure dispatching notifications to
        // clients later on is always non-blocking. We're only interested in
        // requests whose spending transaction was included at the height being
        // disconnected.
        for op := range n.spendsByHeight[blockHeight] {
                // Since the spending transaction is being reorged out of the
                // chain, we'll need to clear out the spending details of the
                // request.
                spendSet := n.spendNotifications[op]
                spendSet.details = nil

                // For all requests which have had a spend notification
                // dispatched, we'll attempt to drain it and send a reorg
                // notification instead.
                for _, ntfn := range spendSet.ntfns {
                        if err := n.dispatchSpendReorg(ntfn); err != nil {
                                return err
                        }
                }
        }

        // Finally, we can remove the requests that were confirmed and/or spent
        // at the height being disconnected. We'll still continue to track them
        // until they have been confirmed/spent and are no longer under the risk
        // of being reorged out of the chain again.
        delete(n.confsByInitialHeight, blockHeight)
        delete(n.spendsByHeight, blockHeight)

        return nil
}

// updateHints attempts to update the confirm and spend hints for all relevant
// requests respectively. The height parameter is used to determine which
// requests we should update based on whether a new block is being
// connected/disconnected.
//
// NOTE: This must be called with the TxNotifier's lock held and after its
// height has already been reflected by a block being connected/disconnected.
func (n *TxNotifier) updateHints(height uint32) {
        // TODO(wilmer): update under one database transaction.
        //
        // To update the height hint for all the required confirmation requests
        // under one database transaction, we'll gather the set of unconfirmed
        // requests along with the ones that confirmed at the height being
        // connected/disconnected.
        confRequests := n.unconfirmedRequests()
        for confRequest := range n.confsByInitialHeight[height] {
                confRequests = append(confRequests, confRequest)
        }
        err := n.confirmHintCache.CommitConfirmHint(
                n.currentHeight, confRequests...,
        )
        if err != nil {
                // The error is not fatal as this is an optimistic optimization,
                // so we'll avoid returning an error.
                Log.Debugf("Unable to update confirm hints to %d for "+
                        "%v: %v", n.currentHeight, confRequests, err)
        }

        // Similarly, to update the height hint for all the required spend
        // requests under one database transaction, we'll gather the set of
        // unspent requests along with the ones that were spent at the height
        // being connected/disconnected.
        spendRequests := n.unspentRequests()
        for spendRequest := range n.spendsByHeight[height] {
                spendRequests = append(spendRequests, spendRequest)
        }
        err = n.spendHintCache.CommitSpendHint(n.currentHeight, spendRequests...)
        if err != nil {
                // The error is not fatal as this is an optimistic optimization,
                // so we'll avoid returning an error.
                Log.Debugf("Unable to update spend hints to %d for "+
                        "%v: %v", n.currentHeight, spendRequests, err)
        }
}

// unconfirmedRequests returns the set of confirmation requests that are
// still seen as unconfirmed by the TxNotifier.
//
// NOTE: This method must be called with the TxNotifier's lock held.
func (n *TxNotifier) unconfirmedRequests() []ConfRequest {
        var unconfirmed []ConfRequest
        for confRequest, confNtfnSet := range n.confNotifications {
                // If the notification is already aware of its confirmation
                // details, or it's in the process of learning them, we'll skip
                // it as we can't yet determine if it's confirmed or not.
                if confNtfnSet.rescanStatus != rescanComplete ||
                        confNtfnSet.details != nil {
                        continue
                }

                unconfirmed = append(unconfirmed, confRequest)
        }

        return unconfirmed
}

// unspentRequests returns the set of spend requests that are still seen as
// unspent by the TxNotifier.
//
// NOTE: This method must be called with the TxNotifier's lock held.
func (n *TxNotifier) unspentRequests() []SpendRequest {
        var unspent []SpendRequest
        for spendRequest, spendNtfnSet := range n.spendNotifications {
                // If the notification is already aware of its spend details, or
                // it's in the process of learning them, we'll skip it as we
                // can't yet determine if it's unspent or not.
                if spendNtfnSet.rescanStatus != rescanComplete ||
                        spendNtfnSet.details != nil {
                        continue
                }

                unspent = append(unspent, spendRequest)
        }

        return unspent
}

// dispatchConfReorg dispatches a reorg notification to the client if the
// confirmation notification was already delivered.
//
// NOTE: This must be called with the TxNotifier's lock held.
func (n *TxNotifier) dispatchConfReorg(ntfn *ConfNtfn,
        heightDisconnected uint32) error {

        // If the request's confirmation notification has yet to be dispatched,
        // we'll need to clear its entry within the ntfnsByConfirmHeight index
        // to prevent from notifying the client once the notifier reaches the
        // confirmation height.
        if !ntfn.dispatched {
                confHeight := heightDisconnected + ntfn.NumConfirmations - 1
                ntfnSet, exists := n.ntfnsByConfirmHeight[confHeight]
                if exists {
                        delete(ntfnSet, ntfn)
                }
                return nil
        }

        // Otherwise, the entry within the ntfnsByConfirmHeight has already been
        // deleted, so we'll attempt to drain the confirmation notification to
        // ensure sends to the Confirmed channel are always non-blocking.
        select {
        case <-ntfn.Event.Confirmed:
        case <-n.quit:
                return ErrTxNotifierExiting
        default:
        }

        ntfn.dispatched = false

        // Send a negative confirmation notification to the client indicating
        // how many blocks have been disconnected successively.
        select {
        case ntfn.Event.NegativeConf <- int32(n.reorgDepth):
        case <-n.quit:
                return ErrTxNotifierExiting
        }

        return nil
}

// dispatchSpendReorg dispatches a reorg notification to the client if a spend
// notiification was already delivered.
//
// NOTE: This must be called with the TxNotifier's lock held.
func (n *TxNotifier) dispatchSpendReorg(ntfn *SpendNtfn) error {
        if !ntfn.dispatched {
                return nil
        }

        // Attempt to drain the spend notification to ensure sends to the Spend
        // channel are always non-blocking.
        select {
        case <-ntfn.Event.Spend:
        default:
        }

        // Send a reorg notification to the client in order for them to
        // correctly handle reorgs.
        select {
        case ntfn.Event.Reorg <- struct{}{}:
        case <-n.quit:
                return ErrTxNotifierExiting
        }

        ntfn.dispatched = false

        return nil
}

// TearDown is to be called when the owner of the TxNotifier is exiting. This
// closes the event channels of all registered notifications that have not been
// dispatched yet.
func (n *TxNotifier) TearDown() {
        close(n.quit)

        n.Lock()
        defer n.Unlock()

        for _, confSet := range n.confNotifications {
                for confID, ntfn := range confSet.ntfns {
                        close(ntfn.Event.Confirmed)
                        close(ntfn.Event.Updates)
                        close(ntfn.Event.NegativeConf)
                        close(ntfn.Event.Done)
                        delete(confSet.ntfns, confID)
                }
        }

        for _, spendSet := range n.spendNotifications {
                for spendID, ntfn := range spendSet.ntfns {
                        close(ntfn.Event.Spend)
                        close(ntfn.Event.Reorg)
                        close(ntfn.Event.Done)
                        delete(spendSet.ntfns, spendID)
                }
        }
}

// notifyNumConfsLeft sends the number of confirmations left to the
// notification subscriber through the Event.Updates channel.
//
// NOTE: must be used with the TxNotifier's lock held.
func (n *TxNotifier) notifyNumConfsLeft(ntfn *ConfNtfn, num uint32) error {
        // If the number left is no less than the recorded value, we can skip
        // sending it as it means this same value has already been sent before.
        if num >= ntfn.numConfsLeft {
                Log.Debugf("Skipped dispatched update (numConfsLeft=%v) for "+
                        "request %v conf_id=%v", num, ntfn.ConfRequest,
                        ntfn.ConfID)

                return nil
        }

        // Update the number of confirmations left to the notification.
        ntfn.numConfsLeft = num

        select {
        case ntfn.Event.Updates <- num:
        case <-n.quit:
                return ErrTxNotifierExiting
        }

        return nil
}

lightningnetwork / lnd / 12428593038

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