9840691252

Committed 08 Jul 2024 01:34PM UTC coverage: 58.404% (+0.08%) from 58.325%

Build # 9840691252

Build Type

Pull #8900

github

Committed by

guggero

Commit Message

Makefile: add GOCC variable

Pull Request Pull Request #8900: Makefile: add GOCC variable

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85.67

/invoices/invoiceregistry.go

package invoices

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

        "github.com/lightningnetwork/lnd/clock"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/queue"
        "github.com/lightningnetwork/lnd/record"
)

var (
        // ErrInvoiceExpiryTooSoon is returned when an invoice is attempted to
        // be accepted or settled with not enough blocks remaining.
        ErrInvoiceExpiryTooSoon = errors.New("invoice expiry too soon")

        // ErrInvoiceAmountTooLow is returned  when an invoice is attempted to
        // be accepted or settled with an amount that is too low.
        ErrInvoiceAmountTooLow = errors.New(
                "paid amount less than invoice amount",
        )

        // ErrShuttingDown is returned when an operation failed because the
        // invoice registry is shutting down.
        ErrShuttingDown = errors.New("invoice registry shutting down")
)

const (
        // DefaultHtlcHoldDuration defines the default for how long mpp htlcs
        // are held while waiting for the other set members to arrive.
        DefaultHtlcHoldDuration = 120 * time.Second
)

// RegistryConfig contains the configuration parameters for invoice registry.
type RegistryConfig struct {
        // FinalCltvRejectDelta defines the number of blocks before the expiry
        // of the htlc where we no longer settle it as an exit hop and instead
        // cancel it back. Normally this value should be lower than the cltv
        // expiry of any invoice we create and the code effectuating this should
        // not be hit.
        FinalCltvRejectDelta int32

        // HtlcHoldDuration defines for how long mpp htlcs are held while
        // waiting for the other set members to arrive.
        HtlcHoldDuration time.Duration

        // Clock holds the clock implementation that is used to provide
        // Now() and TickAfter() and is useful to stub out the clock functions
        // during testing.
        Clock clock.Clock

        // AcceptKeySend indicates whether we want to accept spontaneous key
        // send payments.
        AcceptKeySend bool

        // AcceptAMP indicates whether we want to accept spontaneous AMP
        // payments.
        AcceptAMP bool

        // GcCanceledInvoicesOnStartup if set, we'll attempt to garbage collect
        // all canceled invoices upon start.
        GcCanceledInvoicesOnStartup bool

        // GcCanceledInvoicesOnTheFly if set, we'll garbage collect all newly
        // canceled invoices on the fly.
        GcCanceledInvoicesOnTheFly bool

        // KeysendHoldTime indicates for how long we want to accept and hold
        // spontaneous keysend payments.
        KeysendHoldTime time.Duration
}

// htlcReleaseEvent describes an htlc auto-release event. It is used to release
// mpp htlcs for which the complete set didn't arrive in time.
type htlcReleaseEvent struct {
        // invoiceRef identifiers the invoice this htlc belongs to.
        invoiceRef InvoiceRef

        // key is the circuit key of the htlc to release.
        key CircuitKey

        // releaseTime is the time at which to release the htlc.
        releaseTime time.Time
}

// Less is used to order PriorityQueueItem's by their release time such that
// items with the older release time are at the top of the queue.
//
// NOTE: Part of the queue.PriorityQueueItem interface.
func (r *htlcReleaseEvent) Less(other queue.PriorityQueueItem) bool {
        return r.releaseTime.Before(other.(*htlcReleaseEvent).releaseTime)
}

// InvoiceRegistry is a central registry of all the outstanding invoices
// created by the daemon. The registry is a thin wrapper around a map in order
// to ensure that all updates/reads are thread safe.
type InvoiceRegistry struct {
        sync.RWMutex

        nextClientID uint32 // must be used atomically

        idb InvoiceDB

        // cfg contains the registry's configuration parameters.
        cfg *RegistryConfig

        // notificationClientMux locks notificationClients and
        // singleNotificationClients. Using a separate mutex for these maps is
        // necessary to avoid deadlocks in the registry when processing invoice
        // events.
        notificationClientMux sync.RWMutex

        notificationClients map[uint32]*InvoiceSubscription

        // TODO(yy): use map[lntypes.Hash]*SingleInvoiceSubscription for better
        // performance.
        singleNotificationClients map[uint32]*SingleInvoiceSubscription

        // invoiceEvents is a single channel over which invoice updates are
        // carried.
        invoiceEvents chan *invoiceEvent

        // hodlSubscriptionsMux locks the hodlSubscriptions and
        // hodlReverseSubscriptions. Using a separate mutex for these maps is
        // necessary to avoid deadlocks in the registry when processing invoice
        // events.
        hodlSubscriptionsMux sync.RWMutex

        // hodlSubscriptions is a map from a circuit key to a list of
        // subscribers. It is used for efficient notification of links.
        hodlSubscriptions map[CircuitKey]map[chan<- interface{}]struct{}

        // reverseSubscriptions tracks circuit keys subscribed to per
        // subscriber. This is used to unsubscribe from all hashes efficiently.
        hodlReverseSubscriptions map[chan<- interface{}]map[CircuitKey]struct{}

        // htlcAutoReleaseChan contains the new htlcs that need to be
        // auto-released.
        htlcAutoReleaseChan chan *htlcReleaseEvent

        expiryWatcher *InvoiceExpiryWatcher

        wg   sync.WaitGroup
        quit chan struct{}
}

// NewRegistry creates a new invoice registry. The invoice registry
// wraps the persistent on-disk invoice storage with an additional in-memory
// layer. The in-memory layer is in place such that debug invoices can be added
// which are volatile yet available system wide within the daemon.
func NewRegistry(idb InvoiceDB, expiryWatcher *InvoiceExpiryWatcher,
        cfg *RegistryConfig) *InvoiceRegistry {

        notificationClients := make(map[uint32]*InvoiceSubscription)
        singleNotificationClients := make(map[uint32]*SingleInvoiceSubscription)
        return &InvoiceRegistry{
                idb:                       idb,
                notificationClients:       notificationClients,
                singleNotificationClients: singleNotificationClients,
                invoiceEvents:             make(chan *invoiceEvent, 100),
                hodlSubscriptions: make(
                        map[CircuitKey]map[chan<- interface{}]struct{},
                ),
                hodlReverseSubscriptions: make(
                        map[chan<- interface{}]map[CircuitKey]struct{},
                ),
                cfg:                 cfg,
                htlcAutoReleaseChan: make(chan *htlcReleaseEvent),
                expiryWatcher:       expiryWatcher,
                quit:                make(chan struct{}),
        }
}

// scanInvoicesOnStart will scan all invoices on start and add active invoices
// to the invoice expiry watcher while also attempting to delete all canceled
// invoices.
func (i *InvoiceRegistry) scanInvoicesOnStart(ctx context.Context) error {
        pendingInvoices, err := i.idb.FetchPendingInvoices(ctx)
        if err != nil {
                return err
        }

        var pending []invoiceExpiry
        for paymentHash, invoice := range pendingInvoices {
                invoice := invoice
                expiryRef := makeInvoiceExpiry(paymentHash, &invoice)
                if expiryRef != nil {
                        pending = append(pending, expiryRef)
                }
        }

        log.Debugf("Adding %d pending invoices to the expiry watcher",
                len(pending))
        i.expiryWatcher.AddInvoices(pending...)

        if i.cfg.GcCanceledInvoicesOnStartup {
                log.Infof("Deleting canceled invoices")
                err = i.idb.DeleteCanceledInvoices(ctx)
                if err != nil {
                        log.Warnf("Deleting canceled invoices failed: %v", err)
                        return err
                }
        }

        return nil
}

// Start starts the registry and all goroutines it needs to carry out its task.
func (i *InvoiceRegistry) Start() error {
        // Start InvoiceExpiryWatcher and prepopulate it with existing active
        // invoices.
        err := i.expiryWatcher.Start(func(hash lntypes.Hash, force bool) error {
                return i.cancelInvoiceImpl(context.Background(), hash, force)
        })
        if err != nil {
                return err
        }

        log.Info("InvoiceRegistry starting")

        i.wg.Add(1)
        go i.invoiceEventLoop()

        // Now scan all pending and removable invoices to the expiry watcher or
        // delete them.
        err = i.scanInvoicesOnStart(context.Background())
        if err != nil {
                _ = i.Stop()
                return err
        }

        return nil
}

// Stop signals the registry for a graceful shutdown.
func (i *InvoiceRegistry) Stop() error {
        log.Info("InvoiceRegistry shutting down...")
        defer log.Debug("InvoiceRegistry shutdown complete")

        i.expiryWatcher.Stop()

        close(i.quit)

        i.wg.Wait()
        return nil
}

// invoiceEvent represents a new event that has modified on invoice on disk.
// Only two event types are currently supported: newly created invoices, and
// instance where invoices are settled.
type invoiceEvent struct {
        hash    lntypes.Hash
        invoice *Invoice
        setID   *[32]byte
}

// tickAt returns a channel that ticks at the specified time. If the time has
// already passed, it will tick immediately.
func (i *InvoiceRegistry) tickAt(t time.Time) <-chan time.Time {
        now := i.cfg.Clock.Now()
        return i.cfg.Clock.TickAfter(t.Sub(now))
}

// invoiceEventLoop is the dedicated goroutine responsible for accepting
// new notification subscriptions, cancelling old subscriptions, and
// dispatching new invoice events.
func (i *InvoiceRegistry) invoiceEventLoop() {
        defer i.wg.Done()

        // Set up a heap for htlc auto-releases.
        autoReleaseHeap := &queue.PriorityQueue{}

        for {
                // If there is something to release, set up a release tick
                // channel.
                var nextReleaseTick <-chan time.Time
                if autoReleaseHeap.Len() > 0 {
                        head := autoReleaseHeap.Top().(*htlcReleaseEvent)
                        nextReleaseTick = i.tickAt(head.releaseTime)
                }

                select {
                // A sub-systems has just modified the invoice state, so we'll
                // dispatch notifications to all registered clients.
                case event := <-i.invoiceEvents:
                        // For backwards compatibility, do not notify all
                        // invoice subscribers of cancel and accept events.
                        state := event.invoice.State
                        if state != ContractCanceled &&
                                state != ContractAccepted {

                                i.dispatchToClients(event)
                        }
                        i.dispatchToSingleClients(event)

                // A new htlc came in for auto-release.
                case event := <-i.htlcAutoReleaseChan:
                        log.Debugf("Scheduling auto-release for htlc: "+
                                "ref=%v, key=%v at %v",
                                event.invoiceRef, event.key, event.releaseTime)

                        // We use an independent timer for every htlc rather
                        // than a set timer that is reset with every htlc coming
                        // in. Otherwise the sender could keep resetting the
                        // timer until the broadcast window is entered and our
                        // channel is force closed.
                        autoReleaseHeap.Push(event)

                // The htlc at the top of the heap needs to be auto-released.
                case <-nextReleaseTick:
                        event := autoReleaseHeap.Pop().(*htlcReleaseEvent)
                        err := i.cancelSingleHtlc(
                                event.invoiceRef, event.key, ResultMppTimeout,
                        )
                        if err != nil {
                                log.Errorf("HTLC timer: %v", err)
                        }

                case <-i.quit:
                        return
                }
        }
}

// dispatchToSingleClients passes the supplied event to all notification
// clients that subscribed to all the invoice this event applies to.
func (i *InvoiceRegistry) dispatchToSingleClients(event *invoiceEvent) {
        // Dispatch to single invoice subscribers.
        clients := i.copySingleClients()
        for _, client := range clients {
                payHash := client.invoiceRef.PayHash()

                if payHash == nil || *payHash != event.hash {
                        continue
                }

                select {
                case <-client.backlogDelivered:
                        // We won't deliver any events until the backlog has
                        // went through first.
                case <-i.quit:
                        return
                }

                client.notify(event)
        }
}

// dispatchToClients passes the supplied event to all notification clients that
// subscribed to all invoices. Add and settle indices are used to make sure
// that clients don't receive duplicate or unwanted events.
func (i *InvoiceRegistry) dispatchToClients(event *invoiceEvent) {
        invoice := event.invoice

        clients := i.copyClients()
        for clientID, client := range clients {
                // Before we dispatch this event, we'll check
                // to ensure that this client hasn't already
                // received this notification in order to
                // ensure we don't duplicate any events.

                // TODO(joostjager): Refactor switches.
                state := event.invoice.State
                switch {
                // If we've already sent this settle event to
                // the client, then we can skip this.
                case state == ContractSettled &&
                        client.settleIndex >= invoice.SettleIndex:
                        continue

                // Similarly, if we've already sent this add to
                // the client then we can skip this one, but only if this isn't
                // an AMP invoice. AMP invoices always remain in the settle
                // state as a base invoice.
                case event.setID == nil && state == ContractOpen &&
                        client.addIndex >= invoice.AddIndex:
                        continue

                // These two states should never happen, but we
                // log them just in case so we can detect this
                // instance.
                case state == ContractOpen &&
                        client.addIndex+1 != invoice.AddIndex:
                        log.Warnf("client=%v for invoice "+
                                "notifications missed an update, "+
                                "add_index=%v, new add event index=%v",
                                clientID, client.addIndex,
                                invoice.AddIndex)

                case state == ContractSettled &&
                        client.settleIndex+1 != invoice.SettleIndex:
                        log.Warnf("client=%v for invoice "+
                                "notifications missed an update, "+
                                "settle_index=%v, new settle event index=%v",
                                clientID, client.settleIndex,
                                invoice.SettleIndex)
                }

                select {
                case <-client.backlogDelivered:
                        // We won't deliver any events until the backlog has
                        // been processed.
                case <-i.quit:
                        return
                }

                err := client.notify(&invoiceEvent{
                        invoice: invoice,
                        setID:   event.setID,
                })
                if err != nil {
                        log.Errorf("Failed dispatching to client: %v", err)
                        return
                }

                // Each time we send a notification to a client, we'll record
                // the latest add/settle index it has. We'll use this to ensure
                // we don't send a notification twice, which can happen if a new
                // event is added while we're catching up a new client.
                invState := event.invoice.State
                switch {
                case invState == ContractSettled:
                        client.settleIndex = invoice.SettleIndex

                case invState == ContractOpen && event.setID == nil:
                        client.addIndex = invoice.AddIndex

                // If this is an AMP invoice, then we'll need to use the set ID
                // to keep track of the settle index of the client. AMP
                // invoices never go to the open state, but if a setID is
                // passed, then we know it was just settled and will track the
                // highest settle index so far.
                case invState == ContractOpen && event.setID != nil:
                        setID := *event.setID
                        client.settleIndex = invoice.AMPState[setID].SettleIndex

                default:
                        log.Errorf("unexpected invoice state: %v",
                                event.invoice.State)
                }
        }
}

// deliverBacklogEvents will attempts to query the invoice database for any
// notifications that the client has missed since it reconnected last.
func (i *InvoiceRegistry) deliverBacklogEvents(ctx context.Context,
        client *InvoiceSubscription) error {

        addEvents, err := i.idb.InvoicesAddedSince(ctx, client.addIndex)
        if err != nil {
                return err
        }

        settleEvents, err := i.idb.InvoicesSettledSince(ctx, client.settleIndex)
        if err != nil {
                return err
        }

        // If we have any to deliver, then we'll append them to the end of the
        // notification queue in order to catch up the client before delivering
        // any new notifications.
        for _, addEvent := range addEvents {
                // We re-bind the loop variable to ensure we don't hold onto
                // the loop reference causing is to point to the same item.
                addEvent := addEvent

                select {
                case client.ntfnQueue.ChanIn() <- &invoiceEvent{
                        invoice: &addEvent,
                }:
                case <-i.quit:
                        return ErrShuttingDown
                }
        }

        for _, settleEvent := range settleEvents {
                // We re-bind the loop variable to ensure we don't hold onto
                // the loop reference causing is to point to the same item.
                settleEvent := settleEvent

                select {
                case client.ntfnQueue.ChanIn() <- &invoiceEvent{
                        invoice: &settleEvent,
                }:
                case <-i.quit:
                        return ErrShuttingDown
                }
        }

        return nil
}

// deliverSingleBacklogEvents will attempt to query the invoice database to
// retrieve the current invoice state and deliver this to the subscriber. Single
// invoice subscribers will always receive the current state right after
// subscribing. Only in case the invoice does not yet exist, nothing is sent
// yet.
func (i *InvoiceRegistry) deliverSingleBacklogEvents(ctx context.Context,
        client *SingleInvoiceSubscription) error {

        invoice, err := i.idb.LookupInvoice(ctx, client.invoiceRef)

        // It is possible that the invoice does not exist yet, but the client is
        // already watching it in anticipation.
        isNotFound := errors.Is(err, ErrInvoiceNotFound)
        isNotCreated := errors.Is(err, ErrNoInvoicesCreated)
        if isNotFound || isNotCreated {
                return nil
        }
        if err != nil {
                return err
        }

        payHash := client.invoiceRef.PayHash()
        if payHash == nil {
                return nil
        }

        err = client.notify(&invoiceEvent{
                hash:    *payHash,
                invoice: &invoice,
        })
        if err != nil {
                return err
        }

        log.Debugf("Client(id=%v) delivered single backlog event: payHash=%v",
                client.id, payHash)

        return nil
}

// AddInvoice adds a regular invoice for the specified amount, identified by
// the passed preimage. Additionally, any memo or receipt data provided will
// also be stored on-disk. Once this invoice is added, subsystems within the
// daemon add/forward HTLCs are able to obtain the proper preimage required for
// redemption in the case that we're the final destination. We also return the
// addIndex of the newly created invoice which monotonically increases for each
// new invoice added.  A side effect of this function is that it also sets
// AddIndex on the invoice argument.
func (i *InvoiceRegistry) AddInvoice(ctx context.Context, invoice *Invoice,
        paymentHash lntypes.Hash) (uint64, error) {

        i.Lock()

        ref := InvoiceRefByHash(paymentHash)
        log.Debugf("Invoice%v: added with terms %v", ref, invoice.Terms)

        addIndex, err := i.idb.AddInvoice(ctx, invoice, paymentHash)
        if err != nil {
                i.Unlock()
                return 0, err
        }

        // Now that we've added the invoice, we'll send dispatch a message to
        // notify the clients of this new invoice.
        i.notifyClients(paymentHash, invoice, nil)
        i.Unlock()

        // InvoiceExpiryWatcher.AddInvoice must not be locked by InvoiceRegistry
        // to avoid deadlock when a new invoice is added while an other is being
        // canceled.
        invoiceExpiryRef := makeInvoiceExpiry(paymentHash, invoice)
        if invoiceExpiryRef != nil {
                i.expiryWatcher.AddInvoices(invoiceExpiryRef)
        }

        return addIndex, nil
}

// LookupInvoice looks up an invoice by its payment hash (R-Hash), if found
// then we're able to pull the funds pending within an HTLC.
//
// TODO(roasbeef): ignore if settled?
func (i *InvoiceRegistry) LookupInvoice(ctx context.Context,
        rHash lntypes.Hash) (Invoice, error) {

        // We'll check the database to see if there's an existing matching
        // invoice.
        ref := InvoiceRefByHash(rHash)
        return i.idb.LookupInvoice(ctx, ref)
}

// LookupInvoiceByRef looks up an invoice by the given reference, if found
// then we're able to pull the funds pending within an HTLC.
func (i *InvoiceRegistry) LookupInvoiceByRef(ctx context.Context,
        ref InvoiceRef) (Invoice, error) {

        return i.idb.LookupInvoice(ctx, ref)
}

// startHtlcTimer starts a new timer via the invoice registry main loop that
// cancels a single htlc on an invoice when the htlc hold duration has passed.
func (i *InvoiceRegistry) startHtlcTimer(invoiceRef InvoiceRef,
        key CircuitKey, acceptTime time.Time) error {

        releaseTime := acceptTime.Add(i.cfg.HtlcHoldDuration)
        event := &htlcReleaseEvent{
                invoiceRef:  invoiceRef,
                key:         key,
                releaseTime: releaseTime,
        }

        select {
        case i.htlcAutoReleaseChan <- event:
                return nil

        case <-i.quit:
                return ErrShuttingDown
        }
}

// cancelSingleHtlc cancels a single accepted htlc on an invoice. It takes
// a resolution result which will be used to notify subscribed links and
// resolvers of the details of the htlc cancellation.
func (i *InvoiceRegistry) cancelSingleHtlc(invoiceRef InvoiceRef,
        key CircuitKey, result FailResolutionResult) error {

        updateInvoice := func(invoice *Invoice) (*InvoiceUpdateDesc, error) {
                // Only allow individual htlc cancellation on open invoices.
                if invoice.State != ContractOpen {
                        log.Debugf("cancelSingleHtlc: invoice %v no longer "+
                                "open", invoiceRef)

                        return nil, nil
                }

                // Lookup the current status of the htlc in the database.
                var (
                        htlcState HtlcState
                        setID     *SetID
                )
                htlc, ok := invoice.Htlcs[key]
                if !ok {
                        // If this is an AMP invoice, then all the HTLCs won't
                        // be read out, so we'll consult the other mapping to
                        // try to find the HTLC state in question here.
                        var found bool
                        for ampSetID, htlcSet := range invoice.AMPState {
                                ampSetID := ampSetID
                                for htlcKey := range htlcSet.InvoiceKeys {
                                        if htlcKey == key {
                                                htlcState = htlcSet.State
                                                setID = &ampSetID

                                                found = true
                                                break
                                        }
                                }
                        }

                        if !found {
                                return nil, fmt.Errorf("htlc %v not found", key)
                        }
                } else {
                        htlcState = htlc.State
                }

                // Cancellation is only possible if the htlc wasn't already
                // resolved.
                if htlcState != HtlcStateAccepted {
                        log.Debugf("cancelSingleHtlc: htlc %v on invoice %v "+
                                "is already resolved", key, invoiceRef)

                        return nil, nil
                }

                log.Debugf("cancelSingleHtlc: cancelling htlc %v on invoice %v",
                        key, invoiceRef)

                // Return an update descriptor that cancels htlc and keeps
                // invoice open.
                canceledHtlcs := map[CircuitKey]struct{}{
                        key: {},
                }

                return &InvoiceUpdateDesc{
                        UpdateType:  CancelHTLCsUpdate,
                        CancelHtlcs: canceledHtlcs,
                        SetID:       setID,
                }, nil
        }

        // Try to mark the specified htlc as canceled in the invoice database.
        // Intercept the update descriptor to set the local updated variable. If
        // no invoice update is performed, we can return early.
        setID := (*SetID)(invoiceRef.SetID())
        var updated bool
        invoice, err := i.idb.UpdateInvoice(
                context.Background(), invoiceRef, setID,
                func(invoice *Invoice) (
                        *InvoiceUpdateDesc, error) {

                        updateDesc, err := updateInvoice(invoice)
                        if err != nil {
                                return nil, err
                        }
                        updated = updateDesc != nil

                        return updateDesc, err
                },
        )
        if err != nil {
                return err
        }
        if !updated {
                return nil
        }

        // The invoice has been updated. Notify subscribers of the htlc
        // resolution.
        htlc, ok := invoice.Htlcs[key]
        if !ok {
                return fmt.Errorf("htlc %v not found", key)
        }
        if htlc.State == HtlcStateCanceled {
                resolution := NewFailResolution(
                        key, int32(htlc.AcceptHeight), result,
                )

                i.notifyHodlSubscribers(resolution)
        }
        return nil
}

// processKeySend just-in-time inserts an invoice if this htlc is a keysend
// htlc.
func (i *InvoiceRegistry) processKeySend(ctx invoiceUpdateCtx) error {
        // Retrieve keysend record if present.
        preimageSlice, ok := ctx.customRecords[record.KeySendType]
        if !ok {
                return nil
        }

        // Cancel htlc is preimage is invalid.
        preimage, err := lntypes.MakePreimage(preimageSlice)
        if err != nil {
                return err
        }
        if preimage.Hash() != ctx.hash {
                return fmt.Errorf("invalid keysend preimage %v for hash %v",
                        preimage, ctx.hash)
        }

        // Only allow keysend for non-mpp payments.
        if ctx.mpp != nil {
                return errors.New("no mpp keysend supported")
        }

        // Create an invoice for the htlc amount.
        amt := ctx.amtPaid

        // Set tlv required feature vector on the invoice. Otherwise we wouldn't
        // be able to pay to it with keysend.
        rawFeatures := lnwire.NewRawFeatureVector(
                lnwire.TLVOnionPayloadRequired,
        )
        features := lnwire.NewFeatureVector(rawFeatures, lnwire.Features)

        // Use the minimum block delta that we require for settling htlcs.
        finalCltvDelta := i.cfg.FinalCltvRejectDelta

        // Pre-check expiry here to prevent inserting an invoice that will not
        // be settled.
        if ctx.expiry < uint32(ctx.currentHeight+finalCltvDelta) {
                return errors.New("final expiry too soon")
        }

        // The invoice database indexes all invoices by payment address, however
        // legacy keysend payment do not have one. In order to avoid a new
        // payment type on-disk wrt. to indexing, we'll continue to insert a
        // blank payment address which is special cased in the insertion logic
        // to not be indexed. In the future, once AMP is merged, this should be
        // replaced by generating a random payment address on the behalf of the
        // sender.
        payAddr := BlankPayAddr

        // Create placeholder invoice.
        invoice := &Invoice{
                CreationDate: i.cfg.Clock.Now(),
                Terms: ContractTerm{
                        FinalCltvDelta:  finalCltvDelta,
                        Value:           amt,
                        PaymentPreimage: &preimage,
                        PaymentAddr:     payAddr,
                        Features:        features,
                },
        }

        if i.cfg.KeysendHoldTime != 0 {
                invoice.HodlInvoice = true
                invoice.Terms.Expiry = i.cfg.KeysendHoldTime
        }

        // Insert invoice into database. Ignore duplicates, because this
        // may be a replay.
        _, err = i.AddInvoice(context.Background(), invoice, ctx.hash)
        if err != nil && !errors.Is(err, ErrDuplicateInvoice) {
                return err
        }

        return nil
}

// processAMP just-in-time inserts an invoice if this htlc is a keysend
// htlc.
func (i *InvoiceRegistry) processAMP(ctx invoiceUpdateCtx) error {
        // AMP payments MUST also include an MPP record.
        if ctx.mpp == nil {
                return errors.New("no MPP record for AMP")
        }

        // Create an invoice for the total amount expected, provided in the MPP
        // record.
        amt := ctx.mpp.TotalMsat()

        // Set the TLV required and MPP optional features on the invoice. We'll
        // also make the AMP features required so that it can't be paid by
        // legacy or MPP htlcs.
        rawFeatures := lnwire.NewRawFeatureVector(
                lnwire.TLVOnionPayloadRequired,
                lnwire.PaymentAddrOptional,
                lnwire.AMPRequired,
        )
        features := lnwire.NewFeatureVector(rawFeatures, lnwire.Features)

        // Use the minimum block delta that we require for settling htlcs.
        finalCltvDelta := i.cfg.FinalCltvRejectDelta

        // Pre-check expiry here to prevent inserting an invoice that will not
        // be settled.
        if ctx.expiry < uint32(ctx.currentHeight+finalCltvDelta) {
                return errors.New("final expiry too soon")
        }

        // We'll use the sender-generated payment address provided in the HTLC
        // to create our AMP invoice.
        payAddr := ctx.mpp.PaymentAddr()

        // Create placeholder invoice.
        invoice := &Invoice{
                CreationDate: i.cfg.Clock.Now(),
                Terms: ContractTerm{
                        FinalCltvDelta:  finalCltvDelta,
                        Value:           amt,
                        PaymentPreimage: nil,
                        PaymentAddr:     payAddr,
                        Features:        features,
                },
        }

        // Insert invoice into database. Ignore duplicates payment hashes and
        // payment addrs, this may be a replay or a different HTLC for the AMP
        // invoice.
        _, err := i.AddInvoice(context.Background(), invoice, ctx.hash)
        isDuplicatedInvoice := errors.Is(err, ErrDuplicateInvoice)
        isDuplicatedPayAddr := errors.Is(err, ErrDuplicatePayAddr)
        switch {
        case isDuplicatedInvoice || isDuplicatedPayAddr:
                return nil
        default:
                return err
        }
}

// NotifyExitHopHtlc attempts to mark an invoice as settled. The return value
// describes how the htlc should be resolved.
//
// When the preimage of the invoice is not yet known (hodl invoice), this
// function moves the invoice to the accepted state. When SettleHoldInvoice is
// called later, a resolution message will be send back to the caller via the
// provided hodlChan. Invoice registry sends on this channel what action needs
// to be taken on the htlc (settle or cancel). The caller needs to ensure that
// the channel is either buffered or received on from another goroutine to
// prevent deadlock.
//
// In the case that the htlc is part of a larger set of htlcs that pay to the
// same invoice (multi-path payment), the htlc is held until the set is
// complete. If the set doesn't fully arrive in time, a timer will cancel the
// held htlc.
func (i *InvoiceRegistry) NotifyExitHopHtlc(rHash lntypes.Hash,
        amtPaid lnwire.MilliSatoshi, expiry uint32, currentHeight int32,
        circuitKey CircuitKey, hodlChan chan<- interface{},
        payload Payload) (HtlcResolution, error) {

        // Create the update context containing the relevant details of the
        // incoming htlc.
        ctx := invoiceUpdateCtx{
                hash:                 rHash,
                circuitKey:           circuitKey,
                amtPaid:              amtPaid,
                expiry:               expiry,
                currentHeight:        currentHeight,
                finalCltvRejectDelta: i.cfg.FinalCltvRejectDelta,
                customRecords:        payload.CustomRecords(),
                mpp:                  payload.MultiPath(),
                amp:                  payload.AMPRecord(),
                metadata:             payload.Metadata(),
        }

        switch {
        // If we are accepting spontaneous AMP payments and this payload
        // contains an AMP record, create an AMP invoice that will be settled
        // below.
        case i.cfg.AcceptAMP && ctx.amp != nil:
                err := i.processAMP(ctx)
                if err != nil {
                        ctx.log(fmt.Sprintf("amp error: %v", err))

                        return NewFailResolution(
                                circuitKey, currentHeight, ResultAmpError,
                        ), nil
                }

        // If we are accepting spontaneous keysend payments, create a regular
        // invoice that will be settled below. We also enforce that this is only
        // done when no AMP payload is present since it will only be settle-able
        // by regular HTLCs.
        case i.cfg.AcceptKeySend && ctx.amp == nil:
                err := i.processKeySend(ctx)
                if err != nil {
                        ctx.log(fmt.Sprintf("keysend error: %v", err))

                        return NewFailResolution(
                                circuitKey, currentHeight, ResultKeySendError,
                        ), nil
                }
        }

        // Execute locked notify exit hop logic.
        i.Lock()
        resolution, invoiceToExpire, err := i.notifyExitHopHtlcLocked(
                &ctx, hodlChan,
        )
        i.Unlock()
        if err != nil {
                return nil, err
        }

        if invoiceToExpire != nil {
                i.expiryWatcher.AddInvoices(invoiceToExpire)
        }

        switch r := resolution.(type) {
        // The htlc is held. Start a timer outside the lock if the htlc should
        // be auto-released, because otherwise a deadlock may happen with the
        // main event loop.
        case *htlcAcceptResolution:
                if r.autoRelease {
                        var invRef InvoiceRef
                        if ctx.amp != nil {
                                invRef = InvoiceRefBySetID(*ctx.setID())
                        } else {
                                invRef = ctx.invoiceRef()
                        }

                        err := i.startHtlcTimer(
                                invRef, circuitKey, r.acceptTime,
                        )
                        if err != nil {
                                return nil, err
                        }
                }

                // We return a nil resolution because htlc acceptances are
                // represented as nil resolutions externally.
                // TODO(carla) update calling code to handle accept resolutions.
                return nil, nil

        // A direct resolution was received for this htlc.
        case HtlcResolution:
                return r, nil

        // Fail if an unknown resolution type was received.
        default:
                return nil, errors.New("invalid resolution type")
        }
}

// notifyExitHopHtlcLocked is the internal implementation of NotifyExitHopHtlc
// that should be executed inside the registry lock. The returned invoiceExpiry
// (if not nil) needs to be added to the expiry watcher outside of the lock.
func (i *InvoiceRegistry) notifyExitHopHtlcLocked(
        ctx *invoiceUpdateCtx, hodlChan chan<- interface{}) (
        HtlcResolution, invoiceExpiry, error) {

        // We'll attempt to settle an invoice matching this rHash on disk (if
        // one exists). The callback will update the invoice state and/or htlcs.
        var (
                resolution        HtlcResolution
                updateSubscribers bool
        )

        callback := func(inv *Invoice) (*InvoiceUpdateDesc, error) {
                updateDesc, res, err := updateInvoice(ctx, inv)
                if err != nil {
                        return nil, err
                }

                // Only send an update if the invoice state was changed.
                updateSubscribers = updateDesc != nil &&
                        updateDesc.State != nil

                // Assign resolution to outer scope variable.
                resolution = res

                return updateDesc, nil
        }

        invoiceRef := ctx.invoiceRef()
        setID := (*SetID)(ctx.setID())
        invoice, err := i.idb.UpdateInvoice(
                context.Background(), invoiceRef, setID, callback,
        )

        var duplicateSetIDErr ErrDuplicateSetID
        if errors.As(err, &duplicateSetIDErr) {
                return NewFailResolution(
                        ctx.circuitKey, ctx.currentHeight,
                        ResultInvoiceNotFound,
                ), nil, nil
        }

        switch err {
        case ErrInvoiceNotFound:
                // If the invoice was not found, return a failure resolution
                // with an invoice not found result.
                return NewFailResolution(
                        ctx.circuitKey, ctx.currentHeight,
                        ResultInvoiceNotFound,
                ), nil, nil

        case ErrInvRefEquivocation:
                return NewFailResolution(
                        ctx.circuitKey, ctx.currentHeight,
                        ResultInvoiceNotFound,
                ), nil, nil

        case nil:

        default:
                ctx.log(err.Error())
                return nil, nil, err
        }

        var invoiceToExpire invoiceExpiry

        switch res := resolution.(type) {
        case *HtlcFailResolution:
                // Inspect latest htlc state on the invoice. If it is found,
                // we will update the accept height as it was recorded in the
                // invoice database (which occurs in the case where the htlc
                // reached the database in a previous call). If the htlc was
                // not found on the invoice, it was immediately failed so we
                // send the failure resolution as is, which has the current
                // height set as the accept height.
                invoiceHtlc, ok := invoice.Htlcs[ctx.circuitKey]
                if ok {
                        res.AcceptHeight = int32(invoiceHtlc.AcceptHeight)
                }

                ctx.log(fmt.Sprintf("failure resolution result "+
                        "outcome: %v, at accept height: %v",
                        res.Outcome, res.AcceptHeight))

                // Some failures apply to the entire HTLC set. Break here if
                // this isn't one of them.
                if !res.Outcome.IsSetFailure() {
                        break
                }

                // Also cancel any HTLCs in the HTLC set that are also in the
                // canceled state with the same failure result.
                setID := ctx.setID()
                canceledHtlcSet := invoice.HTLCSet(setID, HtlcStateCanceled)
                for key, htlc := range canceledHtlcSet {
                        htlcFailResolution := NewFailResolution(
                                key, int32(htlc.AcceptHeight), res.Outcome,
                        )

                        i.notifyHodlSubscribers(htlcFailResolution)
                }

        // If the htlc was settled, we will settle any previously accepted
        // htlcs and notify our peer to settle them.
        case *HtlcSettleResolution:
                ctx.log(fmt.Sprintf("settle resolution result "+
                        "outcome: %v, at accept height: %v",
                        res.Outcome, res.AcceptHeight))

                // Also settle any previously accepted htlcs. If a htlc is
                // marked as settled, we should follow now and settle the htlc
                // with our peer.
                setID := ctx.setID()
                settledHtlcSet := invoice.HTLCSet(setID, HtlcStateSettled)
                for key, htlc := range settledHtlcSet {
                        preimage := res.Preimage
                        if htlc.AMP != nil && htlc.AMP.Preimage != nil {
                                preimage = *htlc.AMP.Preimage
                        }

                        // Notify subscribers that the htlcs should be settled
                        // with our peer. Note that the outcome of the
                        // resolution is set based on the outcome of the single
                        // htlc that we just settled, so may not be accurate
                        // for all htlcs.
                        htlcSettleResolution := NewSettleResolution(
                                preimage, key,
                                int32(htlc.AcceptHeight), res.Outcome,
                        )

                        // Notify subscribers that the htlc should be settled
                        // with our peer.
                        i.notifyHodlSubscribers(htlcSettleResolution)
                }

                // If concurrent payments were attempted to this invoice before
                // the current one was ultimately settled, cancel back any of
                // the HTLCs immediately. As a result of the settle, the HTLCs
                // in other HTLC sets are automatically converted to a canceled
                // state when updating the invoice.
                //
                // TODO(roasbeef): can remove now??
                canceledHtlcSet := invoice.HTLCSetCompliment(
                        setID, HtlcStateCanceled,
                )
                for key, htlc := range canceledHtlcSet {
                        htlcFailResolution := NewFailResolution(
                                key, int32(htlc.AcceptHeight),
                                ResultInvoiceAlreadySettled,
                        )

                        i.notifyHodlSubscribers(htlcFailResolution)
                }

        // If we accepted the htlc, subscribe to the hodl invoice and return
        // an accept resolution with the htlc's accept time on it.
        case *htlcAcceptResolution:
                invoiceHtlc, ok := invoice.Htlcs[ctx.circuitKey]
                if !ok {
                        return nil, nil, fmt.Errorf("accepted htlc: %v not"+
                                " present on invoice: %x", ctx.circuitKey,
                                ctx.hash[:])
                }

                // Determine accepted height of this htlc. If the htlc reached
                // the invoice database (possibly in a previous call to the
                // invoice registry), we'll take the original accepted height
                // as it was recorded in the database.
                acceptHeight := int32(invoiceHtlc.AcceptHeight)

                ctx.log(fmt.Sprintf("accept resolution result "+
                        "outcome: %v, at accept height: %v",
                        res.outcome, acceptHeight))

                // Auto-release the htlc if the invoice is still open. It can
                // only happen for mpp payments that there are htlcs in state
                // Accepted while the invoice is Open.
                if invoice.State == ContractOpen {
                        res.acceptTime = invoiceHtlc.AcceptTime
                        res.autoRelease = true
                }

                // If we have fully accepted the set of htlcs for this invoice,
                // we can now add it to our invoice expiry watcher. We do not
                // add invoices before they are fully accepted, because it is
                // possible that we MppTimeout the htlcs, and then our relevant
                // expiry height could change.
                if res.outcome == resultAccepted {
                        invoiceToExpire = makeInvoiceExpiry(ctx.hash, invoice)
                }

                i.hodlSubscribe(hodlChan, ctx.circuitKey)

        default:
                panic("unknown action")
        }

        // Now that the links have been notified of any state changes to their
        // HTLCs, we'll go ahead and notify any clients wiaiting on the invoice
        // state changes.
        if updateSubscribers {
                // We'll add a setID onto the notification, but only if this is
                // an AMP invoice being settled.
                var setID *[32]byte
                if _, ok := resolution.(*HtlcSettleResolution); ok {
                        setID = ctx.setID()
                }

                i.notifyClients(ctx.hash, invoice, setID)
        }

        return resolution, invoiceToExpire, nil
}

// SettleHodlInvoice sets the preimage of a hodl invoice.
func (i *InvoiceRegistry) SettleHodlInvoice(ctx context.Context,
        preimage lntypes.Preimage) error {

        i.Lock()
        defer i.Unlock()

        updateInvoice := func(invoice *Invoice) (*InvoiceUpdateDesc, error) {
                switch invoice.State {
                case ContractOpen:
                        return nil, ErrInvoiceStillOpen

                case ContractCanceled:
                        return nil, ErrInvoiceAlreadyCanceled

                case ContractSettled:
                        return nil, ErrInvoiceAlreadySettled
                }

                return &InvoiceUpdateDesc{
                        UpdateType: SettleHodlInvoiceUpdate,
                        State: &InvoiceStateUpdateDesc{
                                NewState: ContractSettled,
                                Preimage: &preimage,
                        },
                }, nil
        }

        hash := preimage.Hash()
        invoiceRef := InvoiceRefByHash(hash)
        invoice, err := i.idb.UpdateInvoice(ctx, invoiceRef, nil, updateInvoice)
        if err != nil {
                log.Errorf("SettleHodlInvoice with preimage %v: %v",
                        preimage, err)

                return err
        }

        log.Debugf("Invoice%v: settled with preimage %v", invoiceRef,
                invoice.Terms.PaymentPreimage)

        // In the callback, we marked the invoice as settled. UpdateInvoice will
        // have seen this and should have moved all htlcs that were accepted to
        // the settled state. In the loop below, we go through all of these and
        // notify links and resolvers that are waiting for resolution. Any htlcs
        // that were already settled before, will be notified again. This isn't
        // necessary but doesn't hurt either.
        for key, htlc := range invoice.Htlcs {
                if htlc.State != HtlcStateSettled {
                        continue
                }

                resolution := NewSettleResolution(
                        preimage, key, int32(htlc.AcceptHeight), ResultSettled,
                )

                i.notifyHodlSubscribers(resolution)
        }
        i.notifyClients(hash, invoice, nil)

        return nil
}

// CancelInvoice attempts to cancel the invoice corresponding to the passed
// payment hash.
func (i *InvoiceRegistry) CancelInvoice(ctx context.Context,
        payHash lntypes.Hash) error {

        return i.cancelInvoiceImpl(ctx, payHash, true)
}

// shouldCancel examines the state of an invoice and whether we want to
// cancel already accepted invoices, taking our force cancel boolean into
// account. This is pulled out into its own function so that tests that mock
// cancelInvoiceImpl can reuse this logic.
func shouldCancel(state ContractState, cancelAccepted bool) bool {
        if state != ContractAccepted {
                return true
        }

        // If the invoice is accepted, we should only cancel if we want to
        // force cancellation of accepted invoices.
        return cancelAccepted
}

// cancelInvoice attempts to cancel the invoice corresponding to the passed
// payment hash. Accepted invoices will only be canceled if explicitly
// requested to do so. It notifies subscribing links and resolvers that
// the associated htlcs were canceled if they change state.
func (i *InvoiceRegistry) cancelInvoiceImpl(ctx context.Context,
        payHash lntypes.Hash, cancelAccepted bool) error {

        i.Lock()
        defer i.Unlock()

        ref := InvoiceRefByHash(payHash)
        log.Debugf("Invoice%v: canceling invoice", ref)

        updateInvoice := func(invoice *Invoice) (*InvoiceUpdateDesc, error) {
                if !shouldCancel(invoice.State, cancelAccepted) {
                        return nil, nil
                }

                // Move invoice to the canceled state. Rely on validation in
                // channeldb to return an error if the invoice is already
                // settled or canceled.
                return &InvoiceUpdateDesc{
                        UpdateType: CancelInvoiceUpdate,
                        State: &InvoiceStateUpdateDesc{
                                NewState: ContractCanceled,
                        },
                }, nil
        }

        invoiceRef := InvoiceRefByHash(payHash)
        invoice, err := i.idb.UpdateInvoice(ctx, invoiceRef, nil, updateInvoice)

        // Implement idempotency by returning success if the invoice was already
        // canceled.
        if errors.Is(err, ErrInvoiceAlreadyCanceled) {
                log.Debugf("Invoice%v: already canceled", ref)
                return nil
        }
        if err != nil {
                return err
        }

        // Return without cancellation if the invoice state is ContractAccepted.
        if invoice.State == ContractAccepted {
                log.Debugf("Invoice%v: remains accepted as cancel wasn't"+
                        "explicitly requested.", ref)
                return nil
        }

        log.Debugf("Invoice%v: canceled", ref)

        // In the callback, some htlcs may have been moved to the canceled
        // state. We now go through all of these and notify links and resolvers
        // that are waiting for resolution. Any htlcs that were already canceled
        // before, will be notified again. This isn't necessary but doesn't hurt
        // either.
        for key, htlc := range invoice.Htlcs {
                if htlc.State != HtlcStateCanceled {
                        continue
                }

                i.notifyHodlSubscribers(
                        NewFailResolution(
                                key, int32(htlc.AcceptHeight), ResultCanceled,
                        ),
                )
        }
        i.notifyClients(payHash, invoice, nil)

        // Attempt to also delete the invoice if requested through the registry
        // config.
        if i.cfg.GcCanceledInvoicesOnTheFly {
                // Assemble the delete reference and attempt to delete through
                // the invocice from the DB.
                deleteRef := InvoiceDeleteRef{
                        PayHash:     payHash,
                        AddIndex:    invoice.AddIndex,
                        SettleIndex: invoice.SettleIndex,
                }
                if invoice.Terms.PaymentAddr != BlankPayAddr {
                        deleteRef.PayAddr = &invoice.Terms.PaymentAddr
                }

                err = i.idb.DeleteInvoice(ctx, []InvoiceDeleteRef{deleteRef})
                // If by any chance deletion failed, then log it instead of
                // returning the error, as the invoice itself has already been
                // canceled.
                if err != nil {
                        log.Warnf("Invoice %v could not be deleted: %v", ref,
                                err)
                }
        }

        return nil
}

// notifyClients notifies all currently registered invoice notification clients
// of a newly added/settled invoice.
func (i *InvoiceRegistry) notifyClients(hash lntypes.Hash,
        invoice *Invoice, setID *[32]byte) {

        event := &invoiceEvent{
                invoice: invoice,
                hash:    hash,
                setID:   setID,
        }

        select {
        case i.invoiceEvents <- event:
        case <-i.quit:
        }
}

// invoiceSubscriptionKit defines that are common to both all invoice
// subscribers and single invoice subscribers.
type invoiceSubscriptionKit struct {
        id uint32 // nolint:structcheck

        // quit is a chan mouted to InvoiceRegistry that signals a shutdown.
        quit chan struct{}

        ntfnQueue *queue.ConcurrentQueue

        canceled   uint32 // To be used atomically.
        cancelChan chan struct{}

        // backlogDelivered is closed when the backlog events have been
        // delivered.
        backlogDelivered chan struct{}
}

// InvoiceSubscription represents an intent to receive updates for newly added
// or settled invoices. For each newly added invoice, a copy of the invoice
// will be sent over the NewInvoices channel. Similarly, for each newly settled
// invoice, a copy of the invoice will be sent over the SettledInvoices
// channel.
type InvoiceSubscription struct {
        invoiceSubscriptionKit

        // NewInvoices is a channel that we'll use to send all newly created
        // invoices with an invoice index greater than the specified
        // StartingInvoiceIndex field.
        NewInvoices chan *Invoice

        // SettledInvoices is a channel that we'll use to send all settled
        // invoices with an invoices index greater than the specified
        // StartingInvoiceIndex field.
        SettledInvoices chan *Invoice

        // addIndex is the highest add index the caller knows of. We'll use
        // this information to send out an event backlog to the notifications
        // subscriber. Any new add events with an index greater than this will
        // be dispatched before any new notifications are sent out.
        addIndex uint64

        // settleIndex is the highest settle index the caller knows of. We'll
        // use this information to send out an event backlog to the
        // notifications subscriber. Any new settle events with an index
        // greater than this will be dispatched before any new notifications
        // are sent out.
        settleIndex uint64
}

// SingleInvoiceSubscription represents an intent to receive updates for a
// specific invoice.
type SingleInvoiceSubscription struct {
        invoiceSubscriptionKit

        invoiceRef InvoiceRef

        // Updates is a channel that we'll use to send all invoice events for
        // the invoice that is subscribed to.
        Updates chan *Invoice
}

// PayHash returns the optional payment hash of the target invoice.
//
// TODO(positiveblue): This method is only supposed to be used in tests. It will
// be deleted as soon as invoiceregistery_test is in the same module.
func (s *SingleInvoiceSubscription) PayHash() *lntypes.Hash {
        return s.invoiceRef.PayHash()
}

// Cancel unregisters the InvoiceSubscription, freeing any previously allocated
// resources.
func (i *invoiceSubscriptionKit) Cancel() {
        if !atomic.CompareAndSwapUint32(&i.canceled, 0, 1) {
                return
        }

        i.ntfnQueue.Stop()
        close(i.cancelChan)
}

func (i *invoiceSubscriptionKit) notify(event *invoiceEvent) error {
        select {
        case i.ntfnQueue.ChanIn() <- event:

        case <-i.cancelChan:
                // This can only be triggered by delivery of non-backlog
                // events.
                return ErrShuttingDown
        case <-i.quit:
                return ErrShuttingDown
        }

        return nil
}

// SubscribeNotifications returns an InvoiceSubscription which allows the
// caller to receive async notifications when any invoices are settled or
// added. The invoiceIndex parameter is a streaming "checkpoint". We'll start
// by first sending out all new events with an invoice index _greater_ than
// this value. Afterwards, we'll send out real-time notifications.
func (i *InvoiceRegistry) SubscribeNotifications(ctx context.Context,
        addIndex, settleIndex uint64) (*InvoiceSubscription, error) {

        client := &InvoiceSubscription{
                NewInvoices:     make(chan *Invoice),
                SettledInvoices: make(chan *Invoice),
                addIndex:        addIndex,
                settleIndex:     settleIndex,
                invoiceSubscriptionKit: invoiceSubscriptionKit{
                        quit:             i.quit,
                        ntfnQueue:        queue.NewConcurrentQueue(20),
                        cancelChan:       make(chan struct{}),
                        backlogDelivered: make(chan struct{}),
                },
        }
        client.ntfnQueue.Start()

        // This notifies other goroutines that the backlog phase is over.
        defer close(client.backlogDelivered)

        // Always increment by 1 first, and our client ID will start with 1,
        // not 0.
        client.id = atomic.AddUint32(&i.nextClientID, 1)

        // Before we register this new invoice subscription, we'll launch a new
        // goroutine that will proxy all notifications appended to the end of
        // the concurrent queue to the two client-side channels the caller will
        // feed off of.
        i.wg.Add(1)
        go func() {
                defer i.wg.Done()
                defer i.deleteClient(client.id)

                for {
                        select {
                        // A new invoice event has been sent by the
                        // invoiceRegistry! We'll figure out if this is an add
                        // event or a settle event, then dispatch the event to
                        // the client.
                        case ntfn := <-client.ntfnQueue.ChanOut():
                                invoiceEvent := ntfn.(*invoiceEvent)

                                var targetChan chan *Invoice
                                state := invoiceEvent.invoice.State
                                switch {
                                // AMP invoices never move to settled, but will
                                // be sent with a set ID if an HTLC set is
                                // being settled.
                                case state == ContractOpen &&
                                        invoiceEvent.setID != nil:
                                        fallthrough

                                case state == ContractSettled:
                                        targetChan = client.SettledInvoices

                                case state == ContractOpen:
                                        targetChan = client.NewInvoices

                                default:
                                        log.Errorf("unknown invoice state: %v",
                                                state)

                                        continue
                                }

                                select {
                                case targetChan <- invoiceEvent.invoice:

                                case <-client.cancelChan:
                                        return

                                case <-i.quit:
                                        return
                                }

                        case <-client.cancelChan:
                                return

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

        i.notificationClientMux.Lock()
        i.notificationClients[client.id] = client
        i.notificationClientMux.Unlock()

        // Query the database to see if based on the provided addIndex and
        // settledIndex we need to deliver any backlog notifications.
        err := i.deliverBacklogEvents(ctx, client)
        if err != nil {
                return nil, err
        }

        log.Infof("New invoice subscription client: id=%v", client.id)

        return client, nil
}

// SubscribeSingleInvoice returns an SingleInvoiceSubscription which allows the
// caller to receive async notifications for a specific invoice.
func (i *InvoiceRegistry) SubscribeSingleInvoice(ctx context.Context,
        hash lntypes.Hash) (*SingleInvoiceSubscription, error) {

        client := &SingleInvoiceSubscription{
                Updates: make(chan *Invoice),
                invoiceSubscriptionKit: invoiceSubscriptionKit{
                        quit:             i.quit,
                        ntfnQueue:        queue.NewConcurrentQueue(20),
                        cancelChan:       make(chan struct{}),
                        backlogDelivered: make(chan struct{}),
                },
                invoiceRef: InvoiceRefByHash(hash),
        }
        client.ntfnQueue.Start()

        // This notifies other goroutines that the backlog phase is done.
        defer close(client.backlogDelivered)

        // Always increment by 1 first, and our client ID will start with 1,
        // not 0.
        client.id = atomic.AddUint32(&i.nextClientID, 1)

        // Before we register this new invoice subscription, we'll launch a new
        // goroutine that will proxy all notifications appended to the end of
        // the concurrent queue to the two client-side channels the caller will
        // feed off of.
        i.wg.Add(1)
        go func() {
                defer i.wg.Done()
                defer i.deleteClient(client.id)

                for {
                        select {
                        // A new invoice event has been sent by the
                        // invoiceRegistry. We will dispatch the event to the
                        // client.
                        case ntfn := <-client.ntfnQueue.ChanOut():
                                invoiceEvent := ntfn.(*invoiceEvent)

                                select {
                                case client.Updates <- invoiceEvent.invoice:

                                case <-client.cancelChan:
                                        return

                                case <-i.quit:
                                        return
                                }

                        case <-client.cancelChan:
                                return

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

        i.notificationClientMux.Lock()
        i.singleNotificationClients[client.id] = client
        i.notificationClientMux.Unlock()

        err := i.deliverSingleBacklogEvents(ctx, client)
        if err != nil {
                return nil, err
        }

        log.Infof("New single invoice subscription client: id=%v, ref=%v",
                client.id, client.invoiceRef)

        return client, nil
}

// notifyHodlSubscribers sends out the htlc resolution to all current
// subscribers.
func (i *InvoiceRegistry) notifyHodlSubscribers(htlcResolution HtlcResolution) {
        i.hodlSubscriptionsMux.Lock()
        defer i.hodlSubscriptionsMux.Unlock()

        subscribers, ok := i.hodlSubscriptions[htlcResolution.CircuitKey()]
        if !ok {
                return
        }

        // Notify all interested subscribers and remove subscription from both
        // maps. The subscription can be removed as there only ever will be a
        // single resolution for each hash.
        for subscriber := range subscribers {
                select {
                case subscriber <- htlcResolution:
                case <-i.quit:
                        return
                }

                delete(
                        i.hodlReverseSubscriptions[subscriber],
                        htlcResolution.CircuitKey(),
                )
        }

        delete(i.hodlSubscriptions, htlcResolution.CircuitKey())
}

// hodlSubscribe adds a new invoice subscription.
func (i *InvoiceRegistry) hodlSubscribe(subscriber chan<- interface{},
        circuitKey CircuitKey) {

        i.hodlSubscriptionsMux.Lock()
        defer i.hodlSubscriptionsMux.Unlock()

        log.Debugf("Hodl subscribe for %v", circuitKey)

        subscriptions, ok := i.hodlSubscriptions[circuitKey]
        if !ok {
                subscriptions = make(map[chan<- interface{}]struct{})
                i.hodlSubscriptions[circuitKey] = subscriptions
        }
        subscriptions[subscriber] = struct{}{}

        reverseSubscriptions, ok := i.hodlReverseSubscriptions[subscriber]
        if !ok {
                reverseSubscriptions = make(map[CircuitKey]struct{})
                i.hodlReverseSubscriptions[subscriber] = reverseSubscriptions
        }
        reverseSubscriptions[circuitKey] = struct{}{}
}

// HodlUnsubscribeAll cancels the subscription.
func (i *InvoiceRegistry) HodlUnsubscribeAll(subscriber chan<- interface{}) {
        i.hodlSubscriptionsMux.Lock()
        defer i.hodlSubscriptionsMux.Unlock()

        hashes := i.hodlReverseSubscriptions[subscriber]
        for hash := range hashes {
                delete(i.hodlSubscriptions[hash], subscriber)
        }

        delete(i.hodlReverseSubscriptions, subscriber)
}

// copySingleClients copies i.SingleInvoiceSubscription inside a lock. This is
// useful when we need to iterate the map to send notifications.
func (i *InvoiceRegistry) copySingleClients() map[uint32]*SingleInvoiceSubscription { //nolint:lll
        i.notificationClientMux.RLock()
        defer i.notificationClientMux.RUnlock()

        clients := make(map[uint32]*SingleInvoiceSubscription)
        for k, v := range i.singleNotificationClients {
                clients[k] = v
        }
        return clients
}

// copyClients copies i.notificationClients inside a lock. This is useful when
// we need to iterate the map to send notifications.
func (i *InvoiceRegistry) copyClients() map[uint32]*InvoiceSubscription {
        i.notificationClientMux.RLock()
        defer i.notificationClientMux.RUnlock()

        clients := make(map[uint32]*InvoiceSubscription)
        for k, v := range i.notificationClients {
                clients[k] = v
        }
        return clients
}

// deleteClient removes a client by its ID inside a lock. Noop if the client is
// not found.
func (i *InvoiceRegistry) deleteClient(clientID uint32) {
        i.notificationClientMux.Lock()
        defer i.notificationClientMux.Unlock()

        log.Infof("Cancelling invoice subscription for client=%v", clientID)
        delete(i.notificationClients, clientID)
        delete(i.singleNotificationClients, clientID)
}

lightningnetwork / lnd / 9840691252

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