package routing import ( "fmt" "sync" "time" "github.com/davecgh/go-spew/spew" sphinx "github.com/lightningnetwork/lightning-onion" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/htlcswitch" "github.com/lightningnetwork/lnd/lntypes" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/routing/route" ) // paymentLifecycle holds all information about the current state of a payment // needed to resume if from any point. type paymentLifecycle struct { router *ChannelRouter totalAmount lnwire.MilliSatoshi feeLimit lnwire.MilliSatoshi paymentHash lntypes.Hash paySession PaymentSession timeoutChan <-chan time.Time currentHeight int32 } // payemntState holds a number of key insights learned from a given MPPayment // that we use to determine what to do on each payment loop iteration. type paymentState struct { numShardsInFlight int remainingAmt lnwire.MilliSatoshi remainingFees lnwire.MilliSatoshi terminate bool } // paymentState uses the passed payment to find the latest information we need // to act on every iteration of the payment loop. func (p *paymentLifecycle) paymentState(payment *channeldb.MPPayment) ( *paymentState, error) { // Fetch the total amount and fees that has already been sent in // settled and still in-flight shards. sentAmt, fees := payment.SentAmt() // Sanity check we haven't sent a value larger than the payment amount. if sentAmt > p.totalAmount { return nil, fmt.Errorf("amount sent %v exceeds "+ "total amount %v", sentAmt, p.totalAmount) } // We'll subtract the used fee from our fee budget, but allow the fees // of the already sent shards to exceed our budget (can happen after // restarts). feeBudget := p.feeLimit if fees <= feeBudget { feeBudget -= fees } else { feeBudget = 0 } // Get any terminal info for this payment. settle, failure := payment.TerminalInfo() // If either an HTLC settled, or the payment has a payment level // failure recorded, it means we should terminate the moment all shards // have returned with a result. terminate := settle != nil || failure != nil activeShards := payment.InFlightHTLCs() return &paymentState{ numShardsInFlight: len(activeShards), remainingAmt: p.totalAmount - sentAmt, remainingFees: feeBudget, terminate: terminate, }, nil } // resumePayment resumes the paymentLifecycle from the current state. func (p *paymentLifecycle) resumePayment() ([32]byte, *route.Route, error) { shardHandler := &shardHandler{ router: p.router, paymentHash: p.paymentHash, shardErrors: make(chan error), quit: make(chan struct{}), } // When the payment lifecycle loop exits, we make sure to signal any // sub goroutine of the shardHandler to exit, then wait for them to // return. defer shardHandler.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.paymentHash, ) if err != nil { return [32]byte{}, nil, err } for _, a := range payment.InFlightHTLCs() { a := a log.Debugf("Resuming payment shard %v for hash %v", a.AttemptID, p.paymentHash) shardHandler.collectResultAsync(&a.HTLCAttemptInfo) } // We'll continue until either our payment succeeds, or we encounter a // critical error during path finding. for { // Start by quickly checking if there are any outcomes already // available to handle before we reevaluate our state. if err := shardHandler.checkShards(); err != nil { return [32]byte{}, nil, err } // We start every iteration by fetching the lastest state of // the payment from the ControlTower. This ensures that we will // act on the latest available information, whether we are // resuming an existing payment or just sent a new attempt. payment, err := p.router.cfg.Control.FetchPayment( p.paymentHash, ) if err != nil { return [32]byte{}, nil, err } // Using this latest state of the payment, calculate // information about our active shards and terminal conditions. state, err := p.paymentState(payment) if err != nil { return [32]byte{}, nil, err } log.Debugf("Payment %v in state terminate=%v, "+ "active_shards=%v, rem_value=%v, fee_limit=%v", p.paymentHash, state.terminate, state.numShardsInFlight, state.remainingAmt, state.remainingFees) switch { // We have a terminal condition and no active shards, we are // ready to exit. case state.terminate && state.numShardsInFlight == 0: // Find the first successful shard and return // the preimage and route. for _, a := range payment.HTLCs { if a.Settle != nil { return a.Settle.Preimage, &a.Route, nil } } // Payment failed. return [32]byte{}, nil, *payment.FailureReason // If we either reached a terminal error condition (but had // active shards still) or there is no remaining value to send, // we'll wait for a shard outcome. case state.terminate || state.remainingAmt == 0: // We still have outstanding shards, so wait for a new // outcome to be available before re-evaluating our // state. if err := shardHandler.waitForShard(); err != nil { return [32]byte{}, nil, err } continue } // Before we attempt any new shard, we'll check to see if // either we've gone past the payment attempt timeout, or the // router is exiting. In either case, we'll stop this payment // attempt short. If a timeout is not applicable, timeoutChan // will be nil. select { case <-p.timeoutChan: log.Warnf("payment attempt not completed before " + "timeout") // By marking the payment failed with the control // tower, no further shards will be launched and we'll // return with an error the moment all active shards // have finished. saveErr := p.router.cfg.Control.Fail( p.paymentHash, channeldb.FailureReasonTimeout, ) if saveErr != nil { return [32]byte{}, nil, saveErr } continue case <-p.router.quit: return [32]byte{}, nil, ErrRouterShuttingDown // Fall through if we haven't hit our time limit. default: } // Create a new payment attempt from the given payment session. rt, err := p.paySession.RequestRoute( state.remainingAmt, state.remainingFees, uint32(state.numShardsInFlight), uint32(p.currentHeight), ) if err != nil { log.Warnf("Failed to find route for payment %v: %v", p.paymentHash, err) routeErr, ok := err.(noRouteError) if !ok { return [32]byte{}, nil, err } // There is no route to try, and we have no active // shards. This means that there is no way for us to // send the payment, so mark it failed with no route. if state.numShardsInFlight == 0 { failureCode := routeErr.FailureReason() log.Debugf("Marking payment %v permanently "+ "failed with no route: %v", p.paymentHash, failureCode) saveErr := p.router.cfg.Control.Fail( p.paymentHash, failureCode, ) if saveErr != nil { return [32]byte{}, nil, saveErr } continue } // We still have active shards, we'll wait for an // outcome to be available before retrying. if err := shardHandler.waitForShard(); err != nil { return [32]byte{}, nil, err } continue } // We found a route to try, launch a new shard. attempt, outcome, err := shardHandler.launchShard(rt) if err != nil { return [32]byte{}, nil, err } // If we encountered a non-critical error when launching the // shard, handle it. if outcome.err != nil { log.Warnf("Failed to launch shard %v for "+ "payment %v: %v", attempt.AttemptID, p.paymentHash, outcome.err) // We must inspect the error to know whether it was // critical or not, to decide whether we should // continue trying. err := shardHandler.handleSendError( attempt, outcome.err, ) if err != nil { return [32]byte{}, nil, err } // Error was handled successfully, continue to make a // new attempt. continue } // Now that the shard was successfully sent, launch a go // routine that will handle its result when its back. shardHandler.collectResultAsync(attempt) } } // shardHandler holds what is necessary to send and collect the result of // shards. type shardHandler struct { paymentHash lntypes.Hash router *ChannelRouter // shardErrors is a channel where errors collected by calling // collectResultAsync will be delivered. These results are meant to be // inspected by calling waitForShard or checkShards, and the channel // doesn't need to be initiated if the caller is using the sync // collectResult directly. shardErrors chan error // quit is closed to signal the sub goroutines of the payment lifecycle // to stop. quit chan struct{} wg sync.WaitGroup } // stop signals any active shard goroutine to exit and waits for them to exit. func (p *shardHandler) stop() { close(p.quit) p.wg.Wait() } // waitForShard blocks until any of the outstanding shards return. func (p *shardHandler) waitForShard() error { select { case err := <-p.shardErrors: return err case <-p.quit: return fmt.Errorf("shard handler quitting") case <-p.router.quit: return ErrRouterShuttingDown } } // checkShards is a non-blocking method that check if any shards has finished // their execution. func (p *shardHandler) checkShards() error { for { select { case err := <-p.shardErrors: if err != nil { return err } case <-p.quit: return fmt.Errorf("shard handler quitting") case <-p.router.quit: return ErrRouterShuttingDown default: return nil } } } // launchOutcome is a type returned from launchShard that indicates whether the // shard was successfully send onto the network. type launchOutcome struct { // err is non-nil if a non-critical error was encountered when trying // to send the shard, 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 } // launchShard creates and sends an HTLC attempt along the given route, // registering it with the control tower before sending it. It returns the // HTLCAttemptInfo that was created for the shard, along with a launchOutcome. // The launchOutcome is used to indicate whether the attempt was successfully // sent. If the launchOutcome wraps a non-nil error, it means that the attempt // was not sent onto the network, so no result will be available in the future // for it. func (p *shardHandler) launchShard(rt *route.Route) (*channeldb.HTLCAttemptInfo, *launchOutcome, error) { // Using the route received from the payment session, create a new // shard to send. firstHop, htlcAdd, attempt, err := p.createNewPaymentAttempt( rt, ) if err != nil { return nil, 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.paymentHash, attempt) if err != nil { return nil, nil, err } // Now that the attempt is created and checkpointed to the DB, we send // it. sendErr := p.sendPaymentAttempt(attempt, firstHop, htlcAdd) if sendErr != nil { // TODO(joostjager): Distinguish unexpected internal errors // from real send errors. htlcAttempt, err := p.failAttempt(attempt, sendErr) if err != nil { return nil, nil, err } // Return a launchOutcome indicating the shard failed. return attempt, &launchOutcome{ attempt: htlcAttempt, err: sendErr, }, nil } return attempt, &launchOutcome{}, nil } // shardResult holds the resulting outcome of a shard sent. type shardResult struct { // attempt is the attempt structure as recorded in the database. attempt *channeldb.HTLCAttempt // err indicates that the shard failed. err error } // collectResultAsync launches a goroutine that will wait for the result of the // given HTLC attempt to be available then handle its result. Note that it will // fail the payment with the control tower if a terminal error is encountered. func (p *shardHandler) collectResultAsync(attempt *channeldb.HTLCAttemptInfo) { p.wg.Add(1) go func() { defer p.wg.Done() // Block until the result is available. result, err := p.collectResult(attempt) if err != nil { if err != ErrRouterShuttingDown && err != htlcswitch.ErrSwitchExiting { log.Errorf("Error collecting result for "+ "shard %v for payment %v: %v", attempt.AttemptID, p.paymentHash, err) } select { case p.shardErrors <- err: case <-p.router.quit: case <-p.quit: } return } // If a non-critical error was encountered handle it and mark // the payment failed if the failure was terminal. if result.err != nil { err := p.handleSendError(attempt, result.err) if err != nil { select { case p.shardErrors <- err: case <-p.router.quit: case <-p.quit: } return } } select { case p.shardErrors <- nil: case <-p.router.quit: case <-p.quit: } }() } // collectResult waits for the result for the given attempt to be available // from the Switch, then records the attempt outcome with the control tower. A // shardResult is returned, indicating the final outcome of this HTLC attempt. func (p *shardHandler) collectResult(attempt *channeldb.HTLCAttemptInfo) ( *shardResult, error) { // Regenerate the circuit for this attempt. _, circuit, err := generateSphinxPacket( &attempt.Route, p.paymentHash[:], attempt.SessionKey, ) if err != nil { return nil, 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. resultChan, err := p.router.cfg.Payer.GetPaymentResult( attempt.AttemptID, p.paymentHash, errorDecryptor, ) switch { // 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. case err == htlcswitch.ErrPaymentIDNotFound: log.Debugf("Payment ID %v for hash %v not found in "+ "the Switch, retrying.", attempt.AttemptID, p.paymentHash) attempt, cErr := p.failAttempt(attempt, err) if cErr != nil { return nil, cErr } return &shardResult{ attempt: attempt, err: err, }, nil // A critical, unexpected error was encountered. case err != nil: log.Errorf("Failed getting result for attemptID %d "+ "from switch: %v", attempt.AttemptID, err) return nil, 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.router.quit: return nil, ErrRouterShuttingDown case <-p.quit: return nil, fmt.Errorf("shard handler exiting") } // In case of a payment failure, fail the attempt with the control // tower and return. if result.Error != nil { attempt, err := p.failAttempt(attempt, result.Error) if err != nil { return nil, err } return &shardResult{ attempt: attempt, err: result.Error, }, nil } // We successfully got a payment result back from the switch. log.Debugf("Payment %v succeeded with pid=%v", p.paymentHash, 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.paymentHash, attempt.AttemptID, &channeldb.HTLCSettleInfo{ Preimage: result.Preimage, SettleTime: p.router.cfg.Clock.Now(), }, ) if err != nil { log.Errorf("Unable to succeed payment attempt: %v", err) return nil, err } return &shardResult{ attempt: htlcAttempt, }, nil } // createNewPaymentAttempt creates a new payment attempt from the given route. func (p *shardHandler) createNewPaymentAttempt(rt *route.Route) ( lnwire.ShortChannelID, *lnwire.UpdateAddHTLC, *channeldb.HTLCAttemptInfo, error) { // Generate a new key to be used for this attempt. sessionKey, err := generateNewSessionKey() if err != nil { return lnwire.ShortChannelID{}, nil, nil, err } // 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, p.paymentHash[:], sessionKey, ) if err != nil { return lnwire.ShortChannelID{}, nil, nil, err } // Craft an HTLC packet to send to the layer 2 switch. 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.TotalAmount, Expiry: rt.TotalTimeLock, PaymentHash: p.paymentHash, } copy(htlcAdd.OnionBlob[:], onionBlob) // Attempt to send this payment through the network to complete // the payment. If this attempt fails, then we'll continue on // to the next available route. firstHop := lnwire.NewShortChanIDFromInt( rt.Hops[0].ChannelID, ) // We generate a new, unique payment ID that we will use for // this HTLC. attemptID, err := p.router.cfg.NextPaymentID() if err != nil { return lnwire.ShortChannelID{}, nil, nil, err } // We now have all the information needed to populate // the current attempt information. attempt := &channeldb.HTLCAttemptInfo{ AttemptID: attemptID, AttemptTime: p.router.cfg.Clock.Now(), SessionKey: sessionKey, Route: *rt, } return firstHop, htlcAdd, attempt, nil } // sendPaymentAttempt attempts to send the current attempt to the switch. func (p *shardHandler) sendPaymentAttempt( attempt *channeldb.HTLCAttemptInfo, firstHop lnwire.ShortChannelID, htlcAdd *lnwire.UpdateAddHTLC) error { log.Tracef("Attempting to send payment %v (pid=%v), "+ "using route: %v", p.paymentHash, attempt.AttemptID, newLogClosure(func() string { return spew.Sdump(attempt.Route) }), ) // 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.paymentHash, err) return err } log.Debugf("Payment %v (pid=%v) successfully sent to switch, route: %v", p.paymentHash, attempt.AttemptID, &attempt.Route) return nil } // handleSendError 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. func (p *shardHandler) handleSendError(attempt *channeldb.HTLCAttemptInfo, sendErr error) error { reason := p.router.processSendError( attempt.AttemptID, &attempt.Route, sendErr, ) if reason == nil { return nil } log.Debugf("Payment %v failed: final_outcome=%v, raw_err=%v", p.paymentHash, *reason, sendErr) err := p.router.cfg.Control.Fail(p.paymentHash, *reason) if err != nil { return err } return nil } // failAttempt calls control tower to fail the current payment attempt. func (p *shardHandler) failAttempt(attempt *channeldb.HTLCAttemptInfo, sendError error) (*channeldb.HTLCAttempt, error) { log.Warnf("Attempt %v for payment %v failed: %v", attempt.AttemptID, p.paymentHash, sendError) failInfo := marshallError( sendError, p.router.cfg.Clock.Now(), ) return p.router.cfg.Control.FailAttempt( p.paymentHash, attempt.AttemptID, failInfo, ) } // 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 sendError { case htlcswitch.ErrPaymentIDNotFound: response.Reason = channeldb.HTLCFailInternal return response case htlcswitch.ErrUnreadableFailureMessage: response.Reason = channeldb.HTLCFailUnreadable return response } rtErr, ok := sendError.(htlcswitch.ClearTextError) 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. fErr, ok := rtErr.(*htlcswitch.ForwardingError) if ok { response.FailureSourceIndex = uint32(fErr.FailureSourceIdx) } return response }