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control_tower.go
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control_tower.go
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package routing
import (
"sync"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/lntypes"
"github.com/lightningnetwork/lnd/multimutex"
"github.com/lightningnetwork/lnd/queue"
)
// ControlTower tracks all outgoing payments made, whose primary purpose is to
// prevent duplicate payments to the same payment hash. In production, a
// persistent implementation is preferred so that tracking can survive across
// restarts. Payments are transitioned through various payment states, and the
// ControlTower interface provides access to driving the state transitions.
type ControlTower interface {
// This method checks that no suceeded payment exist for this payment
// hash.
InitPayment(lntypes.Hash, *channeldb.PaymentCreationInfo) error
// RegisterAttempt atomically records the provided HTLCAttemptInfo.
RegisterAttempt(lntypes.Hash, *channeldb.HTLCAttemptInfo) error
// SettleAttempt marks the given attempt settled with the preimage. If
// this is a multi shard payment, this might implicitly mean the the
// full payment succeeded.
//
// After invoking this method, InitPayment should always return an
// error to prevent us from making duplicate payments to the same
// payment hash. The provided preimage is atomically saved to the DB
// for record keeping.
SettleAttempt(lntypes.Hash, uint64, *channeldb.HTLCSettleInfo) error
// FailAttempt marks the given payment attempt failed.
FailAttempt(lntypes.Hash, uint64, *channeldb.HTLCFailInfo) error
// FetchPayment fetches the payment corresponding to the given payment
// hash.
FetchPayment(paymentHash lntypes.Hash) (*channeldb.MPPayment, error)
// Fail transitions a payment into the Failed state, and records the
// ultimate reason the payment failed. Note that this should only be
// called when all active active attempts are already failed. After
// invoking this method, InitPayment should return nil on its next call
// for this payment hash, allowing the user to make a subsequent
// payment.
Fail(lntypes.Hash, channeldb.FailureReason) error
// FetchInFlightPayments returns all payments with status InFlight.
FetchInFlightPayments() ([]*channeldb.InFlightPayment, error)
// SubscribePayment subscribes to updates for the payment with the given
// hash. A first update with the current state of the payment is always
// sent out immediately.
SubscribePayment(paymentHash lntypes.Hash) (*ControlTowerSubscriber,
error)
}
// ControlTowerSubscriber contains the state for a payment update subscriber.
type ControlTowerSubscriber struct {
// Updates is the channel over which *channeldb.MPPayment updates can be
// received.
Updates <-chan interface{}
queue *queue.ConcurrentQueue
quit chan struct{}
}
// newControlTowerSubscriber instantiates a new subscriber state object.
func newControlTowerSubscriber() *ControlTowerSubscriber {
// Create a queue for payment updates.
queue := queue.NewConcurrentQueue(20)
queue.Start()
return &ControlTowerSubscriber{
Updates: queue.ChanOut(),
queue: queue,
quit: make(chan struct{}),
}
}
// Close signals that the subscriber is no longer interested in updates.
func (s *ControlTowerSubscriber) Close() {
// Close quit channel so that any pending writes to the queue are
// cancelled.
close(s.quit)
// Stop the queue goroutine so that it won't leak.
s.queue.Stop()
}
// controlTower is persistent implementation of ControlTower to restrict
// double payment sending.
type controlTower struct {
db *channeldb.PaymentControl
subscribers map[lntypes.Hash][]*ControlTowerSubscriber
subscribersMtx sync.Mutex
// paymentsMtx provides synchronization on the payment level to ensure
// that no race conditions occur in between updating the database and
// sending a notification.
paymentsMtx *multimutex.HashMutex
}
// NewControlTower creates a new instance of the controlTower.
func NewControlTower(db *channeldb.PaymentControl) ControlTower {
return &controlTower{
db: db,
subscribers: make(map[lntypes.Hash][]*ControlTowerSubscriber),
paymentsMtx: multimutex.NewHashMutex(),
}
}
// InitPayment checks or records the given PaymentCreationInfo with the DB,
// making sure it does not already exist as an in-flight payment. Then this
// method returns successfully, the payment is guranteeed to be in the InFlight
// state.
func (p *controlTower) InitPayment(paymentHash lntypes.Hash,
info *channeldb.PaymentCreationInfo) error {
return p.db.InitPayment(paymentHash, info)
}
// RegisterAttempt atomically records the provided HTLCAttemptInfo to the
// DB.
func (p *controlTower) RegisterAttempt(paymentHash lntypes.Hash,
attempt *channeldb.HTLCAttemptInfo) error {
p.paymentsMtx.Lock(paymentHash)
defer p.paymentsMtx.Unlock(paymentHash)
payment, err := p.db.RegisterAttempt(paymentHash, attempt)
if err != nil {
return err
}
// Notify subscribers of the attempt registration.
p.notifySubscribers(paymentHash, payment)
return nil
}
// SettleAttempt marks the given attempt settled with the preimage. If
// this is a multi shard payment, this might implicitly mean the the
// full payment succeeded.
func (p *controlTower) SettleAttempt(paymentHash lntypes.Hash,
attemptID uint64, settleInfo *channeldb.HTLCSettleInfo) error {
p.paymentsMtx.Lock(paymentHash)
defer p.paymentsMtx.Unlock(paymentHash)
payment, err := p.db.SettleAttempt(paymentHash, attemptID, settleInfo)
if err != nil {
return err
}
// Notify subscribers of success event.
p.notifySubscribers(paymentHash, payment)
return nil
}
// FailAttempt marks the given payment attempt failed.
func (p *controlTower) FailAttempt(paymentHash lntypes.Hash,
attemptID uint64, failInfo *channeldb.HTLCFailInfo) error {
p.paymentsMtx.Lock(paymentHash)
defer p.paymentsMtx.Unlock(paymentHash)
payment, err := p.db.FailAttempt(paymentHash, attemptID, failInfo)
if err != nil {
return err
}
// Notify subscribers of failed attempt.
p.notifySubscribers(paymentHash, payment)
return nil
}
// FetchPayment fetches the payment corresponding to the given payment hash.
func (p *controlTower) FetchPayment(paymentHash lntypes.Hash) (
*channeldb.MPPayment, error) {
return p.db.FetchPayment(paymentHash)
}
// Fail transitions a payment into the Failed state, and records the reason the
// payment failed. After invoking this method, InitPayment should return nil on
// its next call for this payment hash, allowing the switch to make a
// subsequent payment.
func (p *controlTower) Fail(paymentHash lntypes.Hash,
reason channeldb.FailureReason) error {
p.paymentsMtx.Lock(paymentHash)
defer p.paymentsMtx.Unlock(paymentHash)
payment, err := p.db.Fail(paymentHash, reason)
if err != nil {
return err
}
// Notify subscribers of fail event.
p.notifySubscribers(paymentHash, payment)
return nil
}
// FetchInFlightPayments returns all payments with status InFlight.
func (p *controlTower) FetchInFlightPayments() ([]*channeldb.InFlightPayment, error) {
return p.db.FetchInFlightPayments()
}
// SubscribePayment subscribes to updates for the payment with the given hash. A
// first update with the current state of the payment is always sent out
// immediately.
func (p *controlTower) SubscribePayment(paymentHash lntypes.Hash) (
*ControlTowerSubscriber, error) {
// Take lock before querying the db to prevent missing or duplicating an
// update.
p.paymentsMtx.Lock(paymentHash)
defer p.paymentsMtx.Unlock(paymentHash)
payment, err := p.db.FetchPayment(paymentHash)
if err != nil {
return nil, err
}
subscriber := newControlTowerSubscriber()
// Always write current payment state to the channel.
subscriber.queue.ChanIn() <- payment
// Payment is currently in flight. Register this subscriber for further
// updates. Otherwise this update is the final update and the incoming
// channel can be closed. This will close the queue's outgoing channel
// when all updates have been written.
if payment.Status == channeldb.StatusInFlight {
p.subscribersMtx.Lock()
p.subscribers[paymentHash] = append(
p.subscribers[paymentHash], subscriber,
)
p.subscribersMtx.Unlock()
} else {
close(subscriber.queue.ChanIn())
}
return subscriber, nil
}
// notifySubscribers sends a final payment event to all subscribers of this
// payment. The channel will be closed after this. Note that this function must
// be executed atomically (by means of a lock) with the database update to
// guarantuee consistency of the notifications.
func (p *controlTower) notifySubscribers(paymentHash lntypes.Hash,
event *channeldb.MPPayment) {
// Get all subscribers for this payment.
p.subscribersMtx.Lock()
list, ok := p.subscribers[paymentHash]
if !ok {
p.subscribersMtx.Unlock()
return
}
// If the payment reached a terminal state, the subscriber list can be
// cleared. There won't be any more updates.
terminal := event.Status != channeldb.StatusInFlight
if terminal {
delete(p.subscribers, paymentHash)
}
p.subscribersMtx.Unlock()
// Notify all subscribers of the event.
for _, subscriber := range list {
select {
case subscriber.queue.ChanIn() <- event:
// If this event is the last, close the incoming channel
// of the queue. This will signal the subscriber that
// there won't be any more updates.
if terminal {
close(subscriber.queue.ChanIn())
}
// If subscriber disappeared, skip notification. For further
// notifications, we'll keep skipping over this subscriber.
case <-subscriber.quit:
}
}
}