package routing import ( "fmt" "github.com/btcsuite/btclog" "github.com/lightningnetwork/lnd/build" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/routing/route" ) // BlockPadding is used to increment the finalCltvDelta value for the last hop // to prevent an HTLC being failed if some blocks are mined while it's in-flight. const BlockPadding uint16 = 3 // noRouteError encodes a non-critical error encountered during path finding. type noRouteError uint8 const ( // errNoTlvPayload is returned when the destination hop does not support // a tlv payload. errNoTlvPayload noRouteError = iota // errNoPaymentAddr is returned when the destination hop does not // support payment addresses. errNoPaymentAddr // errNoPathFound is returned when a path to the target destination does // not exist in the graph. errNoPathFound // errInsufficientLocalBalance is returned when none of the local // channels have enough balance for the payment. errInsufficientBalance // errEmptyPaySession is returned when the empty payment session is // queried for a route. errEmptyPaySession ) var ( // DefaultShardMinAmt is the default amount beyond which we won't try to // further split the payment if no route is found. It is the minimum // amount that we use as the shard size when splitting. DefaultShardMinAmt = lnwire.NewMSatFromSatoshis(10000) ) // Error returns the string representation of the noRouteError func (e noRouteError) Error() string { switch e { case errNoTlvPayload: return "destination hop doesn't understand new TLV payloads" case errNoPaymentAddr: return "destination hop doesn't understand payment addresses" case errNoPathFound: return "unable to find a path to destination" case errEmptyPaySession: return "empty payment session" case errInsufficientBalance: return "insufficient local balance" default: return "unknown no-route error" } } // FailureReason converts a path finding error into a payment-level failure. func (e noRouteError) FailureReason() channeldb.FailureReason { switch e { case errNoTlvPayload, errNoPaymentAddr, errNoPathFound, errEmptyPaySession: return channeldb.FailureReasonNoRoute case errInsufficientBalance: return channeldb.FailureReasonInsufficientBalance default: return channeldb.FailureReasonError } } // PaymentSession is used during SendPayment attempts to provide routes to // attempt. It also defines methods to give the PaymentSession additional // information learned during the previous attempts. type PaymentSession interface { // RequestRoute returns the next route to attempt for routing the // specified HTLC payment to the target node. The returned route should // carry at most maxAmt to the target node, and pay at most feeLimit in // fees. It can carry less if the payment is MPP. The activeShards // argument should be set to instruct the payment session about the // number of in flight HTLCS for the payment, such that it can choose // splitting strategy accordingly. // // A noRouteError is returned if a non-critical error is encountered // during path finding. RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi, activeShards, height uint32) (*route.Route, error) } // paymentSession is used during an HTLC routings session to prune the local // chain view in response to failures, and also report those failures back to // MissionControl. The snapshot copied for this session will only ever grow, // and will now be pruned after a decay like the main view within mission // control. We do this as we want to avoid the case where we continually try a // bad edge or route multiple times in a session. This can lead to an infinite // loop if payment attempts take long enough. An additional set of edges can // also be provided to assist in reaching the payment's destination. type paymentSession struct { additionalEdges map[route.Vertex][]*channeldb.ChannelEdgePolicy getBandwidthHints func() (map[uint64]lnwire.MilliSatoshi, error) payment *LightningPayment empty bool pathFinder pathFinder getRoutingGraph func() (routingGraph, func(), error) // pathFindingConfig defines global parameters that control the // trade-off in path finding between fees and probabiity. pathFindingConfig PathFindingConfig missionControl MissionController // minShardAmt is the amount beyond which we won't try to further split // the payment if no route is found. If the maximum number of htlcs // specified in the payment is one, under no circumstances splitting // will happen and this value remains unused. minShardAmt lnwire.MilliSatoshi // log is a payment session-specific logger. log btclog.Logger } // newPaymentSession instantiates a new payment session. func newPaymentSession(p *LightningPayment, getBandwidthHints func() (map[uint64]lnwire.MilliSatoshi, error), getRoutingGraph func() (routingGraph, func(), error), missionControl MissionController, pathFindingConfig PathFindingConfig) ( *paymentSession, error) { edges, err := RouteHintsToEdges(p.RouteHints, p.Target) if err != nil { return nil, err } logPrefix := fmt.Sprintf("PaymentSession(%x):", p.PaymentHash) return &paymentSession{ additionalEdges: edges, getBandwidthHints: getBandwidthHints, payment: p, pathFinder: findPath, getRoutingGraph: getRoutingGraph, pathFindingConfig: pathFindingConfig, missionControl: missionControl, minShardAmt: DefaultShardMinAmt, log: build.NewPrefixLog(logPrefix, log), }, nil } // RequestRoute returns a route which is likely to be capable for successfully // routing the specified HTLC payment to the target node. Initially the first // set of paths returned from this method may encounter routing failure along // the way, however as more payments are sent, mission control will start to // build an up to date view of the network itself. With each payment a new area // will be explored, which feeds into the recommendations made for routing. // // NOTE: This function is safe for concurrent access. // NOTE: Part of the PaymentSession interface. func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi, activeShards, height uint32) (*route.Route, error) { if p.empty { return nil, errEmptyPaySession } // Add BlockPadding to the finalCltvDelta so that the receiving node // does not reject the HTLC if some blocks are mined while it's in-flight. finalCltvDelta := p.payment.FinalCLTVDelta finalCltvDelta += BlockPadding // We need to subtract the final delta before passing it into path // finding. The optimal path is independent of the final cltv delta and // the path finding algorithm is unaware of this value. cltvLimit := p.payment.CltvLimit - uint32(finalCltvDelta) // TODO(roasbeef): sync logic amongst dist sys // Taking into account this prune view, we'll attempt to locate a path // to our destination, respecting the recommendations from // MissionControl. restrictions := &RestrictParams{ ProbabilitySource: p.missionControl.GetProbability, FeeLimit: feeLimit, OutgoingChannelIDs: p.payment.OutgoingChannelIDs, LastHop: p.payment.LastHop, CltvLimit: cltvLimit, DestCustomRecords: p.payment.DestCustomRecords, DestFeatures: p.payment.DestFeatures, PaymentAddr: p.payment.PaymentAddr, } finalHtlcExpiry := int32(height) + int32(finalCltvDelta) for { // We'll also obtain a set of bandwidthHints from the lower // layer for each of our outbound channels. This will allow the // path finding to skip any links that aren't active or just // don't have enough bandwidth to carry the payment. New // bandwidth hints are queried for every new path finding // attempt, because concurrent payments may change balances. bandwidthHints, err := p.getBandwidthHints() if err != nil { return nil, err } p.log.Debugf("pathfinding for amt=%v", maxAmt) // Get a routing graph. routingGraph, cleanup, err := p.getRoutingGraph() if err != nil { return nil, err } sourceVertex := routingGraph.sourceNode() // Find a route for the current amount. path, err := p.pathFinder( &graphParams{ additionalEdges: p.additionalEdges, bandwidthHints: bandwidthHints, graph: routingGraph, }, restrictions, &p.pathFindingConfig, sourceVertex, p.payment.Target, maxAmt, finalHtlcExpiry, ) // Close routing graph. cleanup() switch { case err == errNoPathFound: // Don't split if this is a legacy payment without mpp // record. if p.payment.PaymentAddr == nil { p.log.Debugf("not splitting because payment " + "address is unspecified") return nil, errNoPathFound } // No splitting if this is the last shard. isLastShard := activeShards+1 >= p.payment.MaxParts if isLastShard { p.log.Debugf("not splitting because shard "+ "limit %v has been reached", p.payment.MaxParts) return nil, errNoPathFound } // This is where the magic happens. If we can't find a // route, try it for half the amount. maxAmt /= 2 // Put a lower bound on the minimum shard size. if maxAmt < p.minShardAmt { p.log.Debugf("not splitting because minimum "+ "shard amount %v has been reached", p.minShardAmt) return nil, errNoPathFound } // Go pathfinding. continue // If there isn't enough local bandwidth, there is no point in // splitting. It won't be possible to create a complete set in // any case, but the sent out partial payments would be held by // the receiver until the mpp timeout. case err == errInsufficientBalance: p.log.Debug("not splitting because local balance " + "is insufficient") return nil, err case err != nil: return nil, err } // With the next candidate path found, we'll attempt to turn // this into a route by applying the time-lock and fee // requirements. route, err := newRoute( sourceVertex, path, height, finalHopParams{ amt: maxAmt, totalAmt: p.payment.Amount, cltvDelta: finalCltvDelta, records: p.payment.DestCustomRecords, paymentAddr: p.payment.PaymentAddr, }, ) if err != nil { return nil, err } return route, err } }