lnd.xprv/routing/payment_session.go

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package routing
import (
"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
// 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"
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
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
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// 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
}
// 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
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// MissionControl.
restrictions := &RestrictParams{
ProbabilitySource: p.missionControl.GetProbability,
FeeLimit: feeLimit,
OutgoingChannelID: p.payment.OutgoingChannelID,
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
}
log.Debugf("PaymentSession for %x: trying pathfinding with %v",
p.payment.PaymentHash, 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:
// No splitting if this is the last shard.
isLastShard := activeShards+1 >= p.payment.MaxHtlcs
if isLastShard {
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 {
return nil, errNoPathFound
}
// Go pathfinding.
continue
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
}
}