12312390362

Committed 13 Dec 2024 08:44AM UTC coverage: 57.458% (+8.5%) from 48.92%

Build # 12312390362

Build Type

Pull #9343

github

Committed by

ellemouton

Commit Message

fn: rework the ContextGuard and add tests

In this commit, the ContextGuard struct is re-worked such that the
context that its new main WithCtx method provides is cancelled in sync
with a parent context being cancelled or with it's quit channel being
cancelled. Tests are added to assert the behaviour. In order for the
close of the quit channel to be consistent with the cancelling of the
derived context, the quit channel _must_ be contained internal to the
ContextGuard so that callers are only able to close the channel via the
exposed Quit method which will then take care to first cancel any
derived context that depend on the quit channel before returning.

Pull Request Pull Request #9343: fn: expand the ContextGuard and add tests

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87.88

/routing/payment_lifecycle.go

package routing

import (
        "context"
        "errors"
        "fmt"
        "time"

        "github.com/btcsuite/btcd/btcec/v2"
        "github.com/davecgh/go-spew/spew"
        sphinx "github.com/lightningnetwork/lightning-onion"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/fn/v2"
        "github.com/lightningnetwork/lnd/graph/db/models"
        "github.com/lightningnetwork/lnd/htlcswitch"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/routing/route"
        "github.com/lightningnetwork/lnd/routing/shards"
        "github.com/lightningnetwork/lnd/tlv"
)

// ErrPaymentLifecycleExiting is used when waiting for htlc attempt result, but
// the payment lifecycle is exiting .
var ErrPaymentLifecycleExiting = errors.New("payment lifecycle exiting")

// paymentLifecycle holds all information about the current state of a payment
// needed to resume if from any point.
type paymentLifecycle struct {
        router                *ChannelRouter
        feeLimit              lnwire.MilliSatoshi
        identifier            lntypes.Hash
        paySession            PaymentSession
        shardTracker          shards.ShardTracker
        currentHeight         int32
        firstHopCustomRecords lnwire.CustomRecords

        // quit is closed to signal the sub goroutines of the payment lifecycle
        // to stop.
        quit chan struct{}

        // resultCollected is used to signal that the result of an attempt has
        // been collected. A nil error means the attempt is either successful
        // or failed with temporary error. Otherwise, we should exit the
        // lifecycle loop as a terminal error has occurred.
        resultCollected chan error

        // resultCollector is a function that is used to collect the result of
        // an HTLC attempt, which is always mounted to `p.collectResultAsync`
        // except in unit test, where we use a much simpler resultCollector to
        // decouple the test flow for the payment lifecycle.
        resultCollector func(attempt *channeldb.HTLCAttempt)
}

// newPaymentLifecycle initiates a new payment lifecycle and returns it.
func newPaymentLifecycle(r *ChannelRouter, feeLimit lnwire.MilliSatoshi,
        identifier lntypes.Hash, paySession PaymentSession,
        shardTracker shards.ShardTracker, currentHeight int32,
        firstHopCustomRecords lnwire.CustomRecords) *paymentLifecycle {

        p := &paymentLifecycle{
                router:                r,
                feeLimit:              feeLimit,
                identifier:            identifier,
                paySession:            paySession,
                shardTracker:          shardTracker,
                currentHeight:         currentHeight,
                quit:                  make(chan struct{}),
                resultCollected:       make(chan error, 1),
                firstHopCustomRecords: firstHopCustomRecords,
        }

        // Mount the result collector.
        p.resultCollector = p.collectResultAsync

        return p
}

// calcFeeBudget returns the available fee to be used for sending HTLC
// attempts.
func (p *paymentLifecycle) calcFeeBudget(
        feesPaid lnwire.MilliSatoshi) lnwire.MilliSatoshi {

        budget := p.feeLimit

        // We'll subtract the used fee from our fee budget. In case of
        // overflow, we need to check whether feesPaid exceeds our budget
        // already.
        if feesPaid <= budget {
                budget -= feesPaid
        } else {
                budget = 0
        }

        return budget
}

// stateStep defines an action to be taken in our payment lifecycle. We either
// quit, continue, or exit the lifecycle, see details below.
type stateStep uint8

const (
        // stepSkip is used when we need to skip the current lifecycle and jump
        // to the next one.
        stepSkip stateStep = iota

        // stepProceed is used when we can proceed the current lifecycle.
        stepProceed

        // stepExit is used when we need to quit the current lifecycle.
        stepExit
)

// decideNextStep is used to determine the next step in the payment lifecycle.
func (p *paymentLifecycle) decideNextStep(
        payment DBMPPayment) (stateStep, error) {

        // Check whether we could make new HTLC attempts.
        allow, err := payment.AllowMoreAttempts()
        if err != nil {
                return stepExit, err
        }

        if !allow {
                // Check whether we need to wait for results.
                wait, err := payment.NeedWaitAttempts()
                if err != nil {
                        return stepExit, err
                }

                // If we are not allowed to make new HTLC attempts and there's
                // no need to wait, the lifecycle is done and we can exit.
                if !wait {
                        return stepExit, nil
                }

                log.Tracef("Waiting for attempt results for payment %v",
                        p.identifier)

                // Otherwise we wait for one HTLC attempt then continue
                // the lifecycle.
                //
                // NOTE: we don't check `p.quit` since `decideNextStep` is
                // running in the same goroutine as `resumePayment`.
                select {
                case err := <-p.resultCollected:
                        // If an error is returned, exit with it.
                        if err != nil {
                                return stepExit, err
                        }

                        log.Tracef("Received attempt result for payment %v",
                                p.identifier)

                case <-p.router.quit:
                        return stepExit, ErrRouterShuttingDown
                }

                return stepSkip, nil
        }

        // Otherwise we need to make more attempts.
        return stepProceed, nil
}

// resumePayment resumes the paymentLifecycle from the current state.
func (p *paymentLifecycle) resumePayment(ctx context.Context) ([32]byte,
        *route.Route, error) {

        // When the payment lifecycle loop exits, we make sure to signal any
        // sub goroutine of the HTLC attempt to exit, then wait for them to
        // return.
        defer p.stop()

        // If we had any existing attempts outstanding, we'll start by spinning
        // up goroutines that'll collect their results and deliver them to the
        // lifecycle loop below.
        payment, err := p.router.cfg.Control.FetchPayment(p.identifier)
        if err != nil {
                return [32]byte{}, nil, err
        }

        for _, a := range payment.InFlightHTLCs() {
                a := a

                log.Infof("Resuming HTLC attempt %v for payment %v",
                        a.AttemptID, p.identifier)

                p.resultCollector(&a)
        }

        // exitWithErr is a helper closure that logs and returns an error.
        exitWithErr := func(err error) ([32]byte, *route.Route, error) {
                log.Errorf("Payment %v with status=%v failed: %v",
                        p.identifier, payment.GetStatus(), err)
                return [32]byte{}, nil, err
        }

        // We'll continue until either our payment succeeds, or we encounter a
        // critical error during path finding.
lifecycle:
        for {
                // We update the payment state on every iteration. Since the
                // payment state is affected by multiple goroutines (ie,
                // collectResultAsync), it is NOT guaranteed that we always
                // have the latest state here. This is fine as long as the
                // state is consistent as a whole.
                payment, err = p.router.cfg.Control.FetchPayment(p.identifier)
                if err != nil {
                        return exitWithErr(err)
                }

                ps := payment.GetState()
                remainingFees := p.calcFeeBudget(ps.FeesPaid)

                log.Debugf("Payment %v: status=%v, active_shards=%v, "+
                        "rem_value=%v, fee_limit=%v", p.identifier,
                        payment.GetStatus(), ps.NumAttemptsInFlight,
                        ps.RemainingAmt, remainingFees)

                // We now proceed our lifecycle with the following tasks in
                // order,
                //   1. check context.
                //   2. request route.
                //   3. create HTLC attempt.
                //   4. send HTLC attempt.
                //   5. collect HTLC attempt result.
                //
                // Before we attempt any new shard, we'll check to see if we've
                // gone past the payment attempt timeout, or if the context was
                // cancelled, or the router is exiting. In any of these cases,
                // we'll stop this payment attempt short.
                if err := p.checkContext(ctx); err != nil {
                        return exitWithErr(err)
                }

                // Now decide the next step of the current lifecycle.
                step, err := p.decideNextStep(payment)
                if err != nil {
                        return exitWithErr(err)
                }

                switch step {
                // Exit the for loop and return below.
                case stepExit:
                        break lifecycle

                // Continue the for loop and skip the rest.
                case stepSkip:
                        continue lifecycle

                // Continue the for loop and proceed the rest.
                case stepProceed:

                // Unknown step received, exit with an error.
                default:
                        err = fmt.Errorf("unknown step: %v", step)
                        return exitWithErr(err)
                }

                // Now request a route to be used to create our HTLC attempt.
                rt, err := p.requestRoute(ps)
                if err != nil {
                        return exitWithErr(err)
                }

                // We may not be able to find a route for current attempt. In
                // that case, we continue the loop and move straight to the
                // next iteration in case there are results for inflight HTLCs
                // that still need to be collected.
                if rt == nil {
                        log.Errorf("No route found for payment %v",
                                p.identifier)

                        continue lifecycle
                }

                log.Tracef("Found route: %s", spew.Sdump(rt.Hops))

                // Allow the traffic shaper to add custom records to the
                // outgoing HTLC and also adjust the amount if needed.
                err = p.amendFirstHopData(rt)
                if err != nil {
                        return exitWithErr(err)
                }

                // We found a route to try, create a new HTLC attempt to try.
                attempt, err := p.registerAttempt(rt, ps.RemainingAmt)
                if err != nil {
                        return exitWithErr(err)
                }

                // Once the attempt is created, send it to the htlcswitch.
                result, err := p.sendAttempt(attempt)
                if err != nil {
                        return exitWithErr(err)
                }

                // Now that the shard was successfully sent, launch a go
                // routine that will handle its result when its back.
                if result.err == nil {
                        p.resultCollector(attempt)
                }
        }

        // Once we are out the lifecycle loop, it means we've reached a
        // terminal condition. We either return the settled preimage or the
        // payment's failure reason.
        //
        // Optionally delete the failed attempts from the database.
        err = p.router.cfg.Control.DeleteFailedAttempts(p.identifier)
        if err != nil {
                log.Errorf("Error deleting failed htlc attempts for payment "+
                        "%v: %v", p.identifier, err)
        }

        htlc, failure := payment.TerminalInfo()
        if htlc != nil {
                return htlc.Settle.Preimage, &htlc.Route, nil
        }

        // Otherwise return the payment failure reason.
        return [32]byte{}, nil, *failure
}

// checkContext checks whether the payment context has been canceled.
// Cancellation occurs manually or if the context times out.
func (p *paymentLifecycle) checkContext(ctx context.Context) error {
        select {
        case <-ctx.Done():
                // If the context was canceled, we'll mark the payment as
                // failed. There are two cases to distinguish here: Either a
                // user-provided timeout was reached, or the context was
                // canceled, either to a manual cancellation or due to an
                // unknown error.
                var reason channeldb.FailureReason
                if errors.Is(ctx.Err(), context.DeadlineExceeded) {
                        reason = channeldb.FailureReasonTimeout
                        log.Warnf("Payment attempt not completed before "+
                                "timeout, id=%s", p.identifier.String())
                } else {
                        reason = channeldb.FailureReasonCanceled
                        log.Warnf("Payment attempt context canceled, id=%s",
                                p.identifier.String())
                }

                // By marking the payment failed, depending on whether it has
                // inflight HTLCs or not, its status will now either be
                // `StatusInflight` or `StatusFailed`. In either case, no more
                // HTLCs will be attempted.
                err := p.router.cfg.Control.FailPayment(p.identifier, reason)
                if err != nil {
                        return fmt.Errorf("FailPayment got %w", err)
                }

        case <-p.router.quit:
                return fmt.Errorf("check payment timeout got: %w",
                        ErrRouterShuttingDown)

        // Fall through if we haven't hit our time limit.
        default:
        }

        return nil
}

// requestRoute is responsible for finding a route to be used to create an HTLC
// attempt.
func (p *paymentLifecycle) requestRoute(
        ps *channeldb.MPPaymentState) (*route.Route, error) {

        remainingFees := p.calcFeeBudget(ps.FeesPaid)

        // Query our payment session to construct a route.
        rt, err := p.paySession.RequestRoute(
                ps.RemainingAmt, remainingFees,
                uint32(ps.NumAttemptsInFlight), uint32(p.currentHeight),
                p.firstHopCustomRecords,
        )

        // Exit early if there's no error.
        if err == nil {
                return rt, nil
        }

        // Otherwise we need to handle the error.
        log.Warnf("Failed to find route for payment %v: %v", p.identifier, err)

        // If the error belongs to `noRouteError` set, it means a non-critical
        // error has happened during path finding, and we will mark the payment
        // failed with this reason. Otherwise, we'll return the critical error
        // found to abort the lifecycle.
        var routeErr noRouteError
        if !errors.As(err, &routeErr) {
                return nil, fmt.Errorf("requestRoute got: %w", err)
        }

        // It's the `paymentSession`'s responsibility to find a route for us
        // with the best effort. When it cannot find a path, we need to treat it
        // as a terminal condition and fail the payment no matter it has
        // inflight HTLCs or not.
        failureCode := routeErr.FailureReason()
        log.Warnf("Marking payment %v permanently failed with no route: %v",
                p.identifier, failureCode)

        err = p.router.cfg.Control.FailPayment(p.identifier, failureCode)
        if err != nil {
                return nil, fmt.Errorf("FailPayment got: %w", err)
        }

        // NOTE: we decide to not return the non-critical noRouteError here to
        // avoid terminating the payment lifecycle as there might be other
        // inflight HTLCs which we must wait for their results.
        return nil, nil
}

// stop signals any active shard goroutine to exit.
func (p *paymentLifecycle) stop() {
        close(p.quit)
}

// attemptResult holds the HTLC attempt and a possible error returned from
// sending it.
type attemptResult struct {
        // err is non-nil if a non-critical error was encountered when trying
        // to send the attempt, and we successfully updated the control tower
        // to reflect this error. This can be errors like not enough local
        // balance for the given route etc.
        err error

        // attempt is the attempt structure as recorded in the database.
        attempt *channeldb.HTLCAttempt
}

// collectResultAsync launches a goroutine that will wait for the result of the
// given HTLC attempt to be available then handle its result. Once received, it
// will send a nil error to channel `resultCollected` to indicate there's a
// result.
func (p *paymentLifecycle) collectResultAsync(attempt *channeldb.HTLCAttempt) {
        log.Debugf("Collecting result for attempt %v in payment %v",
                attempt.AttemptID, p.identifier)

        go func() {
                // Block until the result is available.
                _, err := p.collectResult(attempt)
                if err != nil {
                        log.Errorf("Error collecting result for attempt %v "+
                                "in payment %v: %v", attempt.AttemptID,
                                p.identifier, err)
                }

                log.Debugf("Result collected for attempt %v in payment %v",
                        attempt.AttemptID, p.identifier)

                // Once the result is collected, we signal it by writing the
                // error to `resultCollected`.
                select {
                // Send the signal or quit.
                case p.resultCollected <- err:

                case <-p.quit:
                        log.Debugf("Lifecycle exiting while collecting "+
                                "result for payment %v", p.identifier)

                case <-p.router.quit:
                        return
                }
        }()
}

// collectResult waits for the result for the given attempt to be available
// from the Switch, then records the attempt outcome with the control tower.
// An attemptResult is returned, indicating the final outcome of this HTLC
// attempt.
func (p *paymentLifecycle) collectResult(attempt *channeldb.HTLCAttempt) (
        *attemptResult, error) {

        log.Tracef("Collecting result for attempt %v", spew.Sdump(attempt))

        // We'll retrieve the hash specific to this shard from the
        // shardTracker, since it will be needed to regenerate the circuit
        // below.
        hash, err := p.shardTracker.GetHash(attempt.AttemptID)
        if err != nil {
                return p.failAttempt(attempt.AttemptID, err)
        }

        // Regenerate the circuit for this attempt.
        _, circuit, err := generateSphinxPacket(
                &attempt.Route, hash[:], attempt.SessionKey(),
        )
        // TODO(yy): We generate this circuit to create the error decryptor,
        // which is then used in htlcswitch as the deobfuscator to decode the
        // error from `UpdateFailHTLC`. However, suppose it's an
        // `UpdateFulfillHTLC` message yet for some reason the sphinx packet is
        // failed to be generated, we'd miss settling it. This means we should
        // give it a second chance to try the settlement path in case
        // `GetAttemptResult` gives us back the preimage. And move the circuit
        // creation into htlcswitch so it's only constructed when there's a
        // failure message we need to decode.
        if err != nil {
                log.Debugf("Unable to generate circuit for attempt %v: %v",
                        attempt.AttemptID, err)

                return p.failAttempt(attempt.AttemptID, err)
        }

        // Using the created circuit, initialize the error decrypter, so we can
        // parse+decode any failures incurred by this payment within the
        // switch.
        errorDecryptor := &htlcswitch.SphinxErrorDecrypter{
                OnionErrorDecrypter: sphinx.NewOnionErrorDecrypter(circuit),
        }

        // Now ask the switch to return the result of the payment when
        // available.
        //
        // TODO(yy): consider using htlcswitch to create the `errorDecryptor`
        // since the htlc is already in db. This will also make the interface
        // `PaymentAttemptDispatcher` deeper and easier to use. Moreover, we'd
        // only create the decryptor when received a failure, further saving us
        // a few CPU cycles.
        resultChan, err := p.router.cfg.Payer.GetAttemptResult(
                attempt.AttemptID, p.identifier, errorDecryptor,
        )
        // Handle the switch error.
        if err != nil {
                log.Errorf("Failed getting result for attemptID %d "+
                        "from switch: %v", attempt.AttemptID, err)

                return p.handleSwitchErr(attempt, err)
        }

        // The switch knows about this payment, we'll wait for a result to be
        // available.
        var (
                result *htlcswitch.PaymentResult
                ok     bool
        )

        select {
        case result, ok = <-resultChan:
                if !ok {
                        return nil, htlcswitch.ErrSwitchExiting
                }

        case <-p.quit:
                return nil, ErrPaymentLifecycleExiting

        case <-p.router.quit:
                return nil, ErrRouterShuttingDown
        }

        // In case of a payment failure, fail the attempt with the control
        // tower and return.
        if result.Error != nil {
                return p.handleSwitchErr(attempt, result.Error)
        }

        // We successfully got a payment result back from the switch.
        log.Debugf("Payment %v succeeded with pid=%v",
                p.identifier, attempt.AttemptID)

        // Report success to mission control.
        err = p.router.cfg.MissionControl.ReportPaymentSuccess(
                attempt.AttemptID, &attempt.Route,
        )
        if err != nil {
                log.Errorf("Error reporting payment success to mc: %v", err)
        }

        // In case of success we atomically store settle result to the DB move
        // the shard to the settled state.
        htlcAttempt, err := p.router.cfg.Control.SettleAttempt(
                p.identifier, attempt.AttemptID,
                &channeldb.HTLCSettleInfo{
                        Preimage:   result.Preimage,
                        SettleTime: p.router.cfg.Clock.Now(),
                },
        )
        if err != nil {
                log.Errorf("Error settling attempt %v for payment %v with "+
                        "preimage %v: %v", attempt.AttemptID, p.identifier,
                        result.Preimage, err)

                // We won't mark the attempt as failed since we already have
                // the preimage.
                return nil, err
        }

        return &attemptResult{
                attempt: htlcAttempt,
        }, nil
}

// registerAttempt is responsible for creating and saving an HTLC attempt in db
// by using the route info provided. The `remainingAmt` is used to decide
// whether this is the last attempt.
func (p *paymentLifecycle) registerAttempt(rt *route.Route,
        remainingAmt lnwire.MilliSatoshi) (*channeldb.HTLCAttempt, error) {

        // If this route will consume the last remaining amount to send
        // to the receiver, this will be our last shard (for now).
        isLastAttempt := rt.ReceiverAmt() == remainingAmt

        // Using the route received from the payment session, create a new
        // shard to send.
        attempt, err := p.createNewPaymentAttempt(rt, isLastAttempt)
        if err != nil {
                return nil, err
        }

        // Before sending this HTLC to the switch, we checkpoint the fresh
        // paymentID and route to the DB. This lets us know on startup the ID
        // of the payment that we attempted to send, such that we can query the
        // Switch for its whereabouts. The route is needed to handle the result
        // when it eventually comes back.
        err = p.router.cfg.Control.RegisterAttempt(
                p.identifier, &attempt.HTLCAttemptInfo,
        )

        return attempt, err
}

// createNewPaymentAttempt creates a new payment attempt from the given route.
func (p *paymentLifecycle) createNewPaymentAttempt(rt *route.Route,
        lastShard bool) (*channeldb.HTLCAttempt, error) {

        // Generate a new key to be used for this attempt.
        sessionKey, err := generateNewSessionKey()
        if err != nil {
                return nil, err
        }

        // We generate a new, unique payment ID that we will use for
        // this HTLC.
        attemptID, err := p.router.cfg.NextPaymentID()
        if err != nil {
                return nil, err
        }

        // Request a new shard from the ShardTracker. If this is an AMP
        // payment, and this is the last shard, the outstanding shards together
        // with this one will be enough for the receiver to derive all HTLC
        // preimages. If this a non-AMP payment, the ShardTracker will return a
        // simple shard with the payment's static payment hash.
        shard, err := p.shardTracker.NewShard(attemptID, lastShard)
        if err != nil {
                return nil, err
        }

        // If this shard carries MPP or AMP options, add them to the last hop
        // on the route.
        hop := rt.Hops[len(rt.Hops)-1]
        if shard.MPP() != nil {
                hop.MPP = shard.MPP()
        }

        if shard.AMP() != nil {
                hop.AMP = shard.AMP()
        }

        hash := shard.Hash()

        // We now have all the information needed to populate the current
        // attempt information.
        attempt := channeldb.NewHtlcAttempt(
                attemptID, sessionKey, *rt, p.router.cfg.Clock.Now(), &hash,
        )

        return attempt, nil
}

// sendAttempt attempts to send the current attempt to the switch to complete
// the payment. If this attempt fails, then we'll continue on to the next
// available route.
func (p *paymentLifecycle) sendAttempt(
        attempt *channeldb.HTLCAttempt) (*attemptResult, error) {

        log.Debugf("Sending HTLC attempt(id=%v, total_amt=%v, first_hop_amt=%d"+
                ") for payment %v", attempt.AttemptID,
                attempt.Route.TotalAmount, attempt.Route.FirstHopAmount.Val,
                p.identifier)

        rt := attempt.Route

        // Construct the first hop.
        firstHop := lnwire.NewShortChanIDFromInt(rt.Hops[0].ChannelID)

        // Craft an HTLC packet to send to the htlcswitch. The metadata within
        // this packet will be used to route the payment through the network,
        // starting with the first-hop.
        htlcAdd := &lnwire.UpdateAddHTLC{
                Amount:        rt.FirstHopAmount.Val.Int(),
                Expiry:        rt.TotalTimeLock,
                PaymentHash:   *attempt.Hash,
                CustomRecords: rt.FirstHopWireCustomRecords,
        }

        // Generate the raw encoded sphinx packet to be included along
        // with the htlcAdd message that we send directly to the
        // switch.
        onionBlob, _, err := generateSphinxPacket(
                &rt, attempt.Hash[:], attempt.SessionKey(),
        )
        if err != nil {
                log.Errorf("Failed to create onion blob: attempt=%d in "+
                        "payment=%v, err:%v", attempt.AttemptID,
                        p.identifier, err)

                return p.failAttempt(attempt.AttemptID, err)
        }

        copy(htlcAdd.OnionBlob[:], onionBlob)

        // Send it to the Switch. When this method returns we assume
        // the Switch successfully has persisted the payment attempt,
        // such that we can resume waiting for the result after a
        // restart.
        err = p.router.cfg.Payer.SendHTLC(firstHop, attempt.AttemptID, htlcAdd)
        if err != nil {
                log.Errorf("Failed sending attempt %d for payment %v to "+
                        "switch: %v", attempt.AttemptID, p.identifier, err)

                return p.handleSwitchErr(attempt, err)
        }

        log.Debugf("Attempt %v for payment %v successfully sent to switch, "+
                "route: %v", attempt.AttemptID, p.identifier, &attempt.Route)

        return &attemptResult{
                attempt: attempt,
        }, nil
}

// amendFirstHopData is a function that calls the traffic shaper to allow it to
// add custom records to the outgoing HTLC and also adjust the amount if
// needed.
func (p *paymentLifecycle) amendFirstHopData(rt *route.Route) error {
        // The first hop amount on the route is the full route amount if not
        // overwritten by the traffic shaper. So we set the initial value now
        // and potentially overwrite it later.
        rt.FirstHopAmount = tlv.NewRecordT[tlv.TlvType0](
                tlv.NewBigSizeT(rt.TotalAmount),
        )

        // By default, we set the first hop custom records to the initial
        // value requested by the RPC. The traffic shaper may overwrite this
        // value.
        rt.FirstHopWireCustomRecords = p.firstHopCustomRecords

        // extraDataRequest is a helper struct to pass the custom records and
        // amount back from the traffic shaper.
        type extraDataRequest struct {
                customRecords fn.Option[lnwire.CustomRecords]

                amount fn.Option[lnwire.MilliSatoshi]
        }

        // If a hook exists that may affect our outgoing message, we call it now
        // and apply its side effects to the UpdateAddHTLC message.
        result, err := fn.MapOptionZ(
                p.router.cfg.TrafficShaper,
                //nolint:ll
                func(ts htlcswitch.AuxTrafficShaper) fn.Result[extraDataRequest] {
                        newAmt, newRecords, err := ts.ProduceHtlcExtraData(
                                rt.TotalAmount, p.firstHopCustomRecords,
                        )
                        if err != nil {
                                return fn.Err[extraDataRequest](err)
                        }

                        // Make sure we only received valid records.
                        if err := newRecords.Validate(); err != nil {
                                return fn.Err[extraDataRequest](err)
                        }

                        log.Debugf("Aux traffic shaper returned custom "+
                                "records %v and amount %d msat for HTLC",
                                spew.Sdump(newRecords), newAmt)

                        return fn.Ok(extraDataRequest{
                                customRecords: fn.Some(newRecords),
                                amount:        fn.Some(newAmt),
                        })
                },
        ).Unpack()
        if err != nil {
                return fmt.Errorf("traffic shaper failed to produce extra "+
                        "data: %w", err)
        }

        // Apply the side effects to the UpdateAddHTLC message.
        result.customRecords.WhenSome(func(records lnwire.CustomRecords) {
                rt.FirstHopWireCustomRecords = records
        })
        result.amount.WhenSome(func(amount lnwire.MilliSatoshi) {
                rt.FirstHopAmount = tlv.NewRecordT[tlv.TlvType0](
                        tlv.NewBigSizeT(amount),
                )
        })

        return nil
}

// failAttemptAndPayment fails both the payment and its attempt via the
// router's control tower, which marks the payment as failed in db.
func (p *paymentLifecycle) failPaymentAndAttempt(
        attemptID uint64, reason *channeldb.FailureReason,
        sendErr error) (*attemptResult, error) {

        log.Errorf("Payment %v failed: final_outcome=%v, raw_err=%v",
                p.identifier, *reason, sendErr)

        // Fail the payment via control tower.
        //
        // NOTE: we must fail the payment first before failing the attempt.
        // Otherwise, once the attempt is marked as failed, another goroutine
        // might make another attempt while we are failing the payment.
        err := p.router.cfg.Control.FailPayment(p.identifier, *reason)
        if err != nil {
                log.Errorf("Unable to fail payment: %v", err)
                return nil, err
        }

        // Fail the attempt.
        return p.failAttempt(attemptID, sendErr)
}

// handleSwitchErr inspects the given error from the Switch and determines
// whether we should make another payment attempt, or if it should be
// considered a terminal error. Terminal errors will be recorded with the
// control tower. It analyzes the sendErr for the payment attempt received from
// the switch and updates mission control and/or channel policies. Depending on
// the error type, the error is either the final outcome of the payment or we
// need to continue with an alternative route. A final outcome is indicated by
// a non-nil reason value.
func (p *paymentLifecycle) handleSwitchErr(attempt *channeldb.HTLCAttempt,
        sendErr error) (*attemptResult, error) {

        internalErrorReason := channeldb.FailureReasonError
        attemptID := attempt.AttemptID

        // reportAndFail is a helper closure that reports the failure to the
        // mission control, which helps us to decide whether we want to retry
        // the payment or not. If a non nil reason is returned from mission
        // control, it will further fail the payment via control tower.
        reportAndFail := func(srcIdx *int,
                msg lnwire.FailureMessage) (*attemptResult, error) {

                // Report outcome to mission control.
                reason, err := p.router.cfg.MissionControl.ReportPaymentFail(
                        attemptID, &attempt.Route, srcIdx, msg,
                )
                if err != nil {
                        log.Errorf("Error reporting payment result to mc: %v",
                                err)

                        reason = &internalErrorReason
                }

                // Fail the attempt only if there's no reason.
                if reason == nil {
                        // Fail the attempt.
                        return p.failAttempt(attemptID, sendErr)
                }

                // Otherwise fail both the payment and the attempt.
                return p.failPaymentAndAttempt(attemptID, reason, sendErr)
        }

        // If this attempt ID is unknown to the Switch, it means it was never
        // checkpointed and forwarded by the switch before a restart. In this
        // case we can safely send a new payment attempt, and wait for its
        // result to be available.
        if errors.Is(sendErr, htlcswitch.ErrPaymentIDNotFound) {
                log.Debugf("Attempt ID %v for payment %v not found in the "+
                        "Switch, retrying.", attempt.AttemptID, p.identifier)

                return p.failAttempt(attemptID, sendErr)
        }

        if errors.Is(sendErr, htlcswitch.ErrUnreadableFailureMessage) {
                log.Warn("Unreadable failure when sending htlc: id=%v, hash=%v",
                        attempt.AttemptID, attempt.Hash)

                // Since this error message cannot be decrypted, we will send a
                // nil error message to our mission controller and fail the
                // payment.
                return reportAndFail(nil, nil)
        }

        // If the error is a ClearTextError, we have received a valid wire
        // failure message, either from our own outgoing link or from a node
        // down the route. If the error is not related to the propagation of
        // our payment, we can stop trying because an internal error has
        // occurred.
        var rtErr htlcswitch.ClearTextError
        ok := errors.As(sendErr, &rtErr)
        if !ok {
                return p.failPaymentAndAttempt(
                        attemptID, &internalErrorReason, sendErr,
                )
        }

        // failureSourceIdx is the index of the node that the failure occurred
        // at. If the ClearTextError received is not a ForwardingError the
        // payment error occurred at our node, so we leave this value as 0
        // to indicate that the failure occurred locally. If the error is a
        // ForwardingError, it did not originate at our node, so we set
        // failureSourceIdx to the index of the node where the failure occurred.
        failureSourceIdx := 0
        var source *htlcswitch.ForwardingError
        ok = errors.As(rtErr, &source)
        if ok {
                failureSourceIdx = source.FailureSourceIdx
        }

        // Extract the wire failure and apply channel update if it contains one.
        // If we received an unknown failure message from a node along the
        // route, the failure message will be nil.
        failureMessage := rtErr.WireMessage()
        err := p.handleFailureMessage(
                &attempt.Route, failureSourceIdx, failureMessage,
        )
        if err != nil {
                return p.failPaymentAndAttempt(
                        attemptID, &internalErrorReason, sendErr,
                )
        }

        log.Tracef("Node=%v reported failure when sending htlc",
                failureSourceIdx)

        return reportAndFail(&failureSourceIdx, failureMessage)
}

// handleFailureMessage tries to apply a channel update present in the failure
// message if any.
func (p *paymentLifecycle) handleFailureMessage(rt *route.Route,
        errorSourceIdx int, failure lnwire.FailureMessage) error {

        if failure == nil {
                return nil
        }

        // It makes no sense to apply our own channel updates.
        if errorSourceIdx == 0 {
                log.Errorf("Channel update of ourselves received")

                return nil
        }

        // Extract channel update if the error contains one.
        update := p.router.extractChannelUpdate(failure)
        if update == nil {
                return nil
        }

        // Parse pubkey to allow validation of the channel update. This should
        // always succeed, otherwise there is something wrong in our
        // implementation. Therefore, return an error.
        errVertex := rt.Hops[errorSourceIdx-1].PubKeyBytes
        errSource, err := btcec.ParsePubKey(errVertex[:])
        if err != nil {
                log.Errorf("Cannot parse pubkey: idx=%v, pubkey=%v",
                        errorSourceIdx, errVertex)

                return err
        }

        var (
                isAdditionalEdge bool
                policy           *models.CachedEdgePolicy
        )

        // Before we apply the channel update, we need to decide whether the
        // update is for additional (ephemeral) edge or normal edge stored in
        // db.
        //
        // Note: the p.paySession might be nil here if it's called inside
        // SendToRoute where there's no payment lifecycle.
        if p.paySession != nil {
                policy = p.paySession.GetAdditionalEdgePolicy(
                        errSource, update.ShortChannelID.ToUint64(),
                )
                if policy != nil {
                        isAdditionalEdge = true
                }
        }

        // Apply channel update to additional edge policy.
        if isAdditionalEdge {
                if !p.paySession.UpdateAdditionalEdge(
                        update, errSource, policy) {

                        log.Debugf("Invalid channel update received: node=%v",
                                errVertex)
                }
                return nil
        }

        // Apply channel update to the channel edge policy in our db.
        if !p.router.cfg.ApplyChannelUpdate(update) {
                log.Debugf("Invalid channel update received: node=%v",
                        errVertex)
        }
        return nil
}

// failAttempt calls control tower to fail the current payment attempt.
func (p *paymentLifecycle) failAttempt(attemptID uint64,
        sendError error) (*attemptResult, error) {

        log.Warnf("Attempt %v for payment %v failed: %v", attemptID,
                p.identifier, sendError)

        failInfo := marshallError(
                sendError,
                p.router.cfg.Clock.Now(),
        )

        // Now that we are failing this payment attempt, cancel the shard with
        // the ShardTracker such that it can derive the correct hash for the
        // next attempt.
        if err := p.shardTracker.CancelShard(attemptID); err != nil {
                return nil, err
        }

        attempt, err := p.router.cfg.Control.FailAttempt(
                p.identifier, attemptID, failInfo,
        )
        if err != nil {
                return nil, err
        }

        return &attemptResult{
                attempt: attempt,
                err:     sendError,
        }, nil
}

// marshallError marshall an error as received from the switch to a structure
// that is suitable for database storage.
func marshallError(sendError error, time time.Time) *channeldb.HTLCFailInfo {
        response := &channeldb.HTLCFailInfo{
                FailTime: time,
        }

        switch {
        case errors.Is(sendError, htlcswitch.ErrPaymentIDNotFound):
                response.Reason = channeldb.HTLCFailInternal
                return response

        case errors.Is(sendError, htlcswitch.ErrUnreadableFailureMessage):
                response.Reason = channeldb.HTLCFailUnreadable
                return response
        }

        var rtErr htlcswitch.ClearTextError
        ok := errors.As(sendError, &rtErr)
        if !ok {
                response.Reason = channeldb.HTLCFailInternal
                return response
        }

        message := rtErr.WireMessage()
        if message != nil {
                response.Reason = channeldb.HTLCFailMessage
                response.Message = message
        } else {
                response.Reason = channeldb.HTLCFailUnknown
        }

        // If the ClearTextError received is a ForwardingError, the error
        // originated from a node along the route, not locally on our outgoing
        // link. We set failureSourceIdx to the index of the node where the
        // failure occurred. If the error is not a ForwardingError, the failure
        // occurred at our node, so we leave the index as 0 to indicate that
        // we failed locally.
        var fErr *htlcswitch.ForwardingError
        ok = errors.As(rtErr, &fErr)
        if ok {
                response.FailureSourceIndex = uint32(fErr.FailureSourceIdx)
        }

        return response
}

lightningnetwork / lnd / 12312390362

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