lnd.xprv/routing/control_tower.go

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package routing
import (
"errors"
"sync"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/lntypes"
)
// 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. It returns a boolean indicating whether the payment is still in
// flight and a channel that provides the final outcome of the payment.
SubscribePayment(paymentHash lntypes.Hash) (bool, chan PaymentResult,
error)
}
// PaymentResult is the struct describing the events received by payment
// subscribers.
type PaymentResult struct {
// Success indicates whether the payment was successful.
Success bool
// Preimage is the preimage of a successful payment. This serves as a
// proof of payment. It is only set for successful payments.
Preimage lntypes.Preimage
// FailureReason is a failure reason code indicating the reason the
// payment failed. It is only set for failed payments.
FailureReason channeldb.FailureReason
// HTLCs is a list of HTLCs that have been attempted in order to settle
// the payment.
HTLCs []channeldb.HTLCAttempt
}
// controlTower is persistent implementation of ControlTower to restrict
// double payment sending.
type controlTower struct {
db *channeldb.PaymentControl
subscribers map[lntypes.Hash][]chan PaymentResult
subscribersMtx sync.Mutex
}
// NewControlTower creates a new instance of the controlTower.
func NewControlTower(db *channeldb.PaymentControl) ControlTower {
return &controlTower{
db: db,
subscribers: make(map[lntypes.Hash][]chan PaymentResult),
}
}
// 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 {
return p.db.RegisterAttempt(paymentHash, attempt)
}
// 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 {
payment, err := p.db.SettleAttempt(paymentHash, attemptID, settleInfo)
if err != nil {
return err
}
// Notify subscribers of success event.
p.notifyFinalEvent(
paymentHash, createSuccessResult(payment.HTLCs),
)
return nil
}
// FailAttempt marks the given payment attempt failed.
func (p *controlTower) FailAttempt(paymentHash lntypes.Hash,
attemptID uint64, failInfo *channeldb.HTLCFailInfo) error {
return p.db.FailAttempt(paymentHash, attemptID, failInfo)
}
// 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)
}
// createSuccessResult creates a success result to send to subscribers.
func createSuccessResult(htlcs []channeldb.HTLCAttempt) *PaymentResult {
// Extract any preimage from the list of HTLCs.
var preimage lntypes.Preimage
for _, htlc := range htlcs {
if htlc.Settle != nil {
preimage = htlc.Settle.Preimage
break
}
}
return &PaymentResult{
Success: true,
Preimage: preimage,
HTLCs: htlcs,
}
}
// createFailResult creates a failed result to send to subscribers.
func createFailedResult(htlcs []channeldb.HTLCAttempt,
reason channeldb.FailureReason) *PaymentResult {
return &PaymentResult{
Success: false,
FailureReason: reason,
HTLCs: htlcs,
}
}
// 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 {
payment, err := p.db.Fail(paymentHash, reason)
if err != nil {
return err
}
// Notify subscribers of fail event.
p.notifyFinalEvent(
paymentHash, createFailedResult(
payment.HTLCs, reason,
),
)
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.
// It returns a boolean indicating whether the payment is still in flight and a
// channel that provides the final outcome of the payment.
func (p *controlTower) SubscribePayment(paymentHash lntypes.Hash) (
bool, chan PaymentResult, error) {
// Create a channel with buffer size 1. For every payment there will be
// exactly one event sent.
c := make(chan PaymentResult, 1)
// Take lock before querying the db to prevent this scenario:
// FetchPayment returns us an in-flight state -> payment succeeds, but
// there is no subscriber to notify yet -> we add ourselves as a
// subscriber -> ... we will never receive a notification.
p.subscribersMtx.Lock()
defer p.subscribersMtx.Unlock()
payment, err := p.db.FetchPayment(paymentHash)
if err != nil {
return false, nil, err
}
var event PaymentResult
switch payment.Status {
// Payment is currently in flight. Register this subscriber and
// return without writing a result to the channel yet.
case channeldb.StatusInFlight:
p.subscribers[paymentHash] = append(
p.subscribers[paymentHash], c,
)
return true, c, nil
// Payment already succeeded. It is not necessary to register as
// a subscriber, because we can send the result on the channel
// immediately.
case channeldb.StatusSucceeded:
event = *createSuccessResult(payment.HTLCs)
// Payment already failed. It is not necessary to register as a
// subscriber, because we can send the result on the channel
// immediately.
case channeldb.StatusFailed:
event = *createFailedResult(
payment.HTLCs, *payment.FailureReason,
)
default:
return false, nil, errors.New("unknown payment status")
}
// Write immediate result to the channel.
c <- event
close(c)
return false, c, nil
}
// notifyFinalEvent sends a final payment event to all subscribers of this
// payment. The channel will be closed after this.
func (p *controlTower) notifyFinalEvent(paymentHash lntypes.Hash,
event *PaymentResult) {
// Get all subscribers for this hash. As there is only a single outcome,
// the subscriber list can be cleared.
p.subscribersMtx.Lock()
list, ok := p.subscribers[paymentHash]
if !ok {
p.subscribersMtx.Unlock()
return
}
delete(p.subscribers, paymentHash)
p.subscribersMtx.Unlock()
// Notify all subscribers of the event. The subscriber channel is
// buffered, so it cannot block here.
for _, subscriber := range list {
subscriber <- *event
close(subscriber)
}
}