lnd.xprv/routing/payment_session.go
Wilmer Paulino 0fc401de19
routing+routerrpc: take max cltv limit into account within path finding
With the introduction of the max CLTV limit parameter, nodes are able to
reject HTLCs that exceed it. This should also be applied to path
finding, otherwise HTLCs crafted by the same node that exceed it never
left the switch. This wasn't a big deal since the previous max CLTV
limit was ~5000 blocks. Once it was lowered to 1008, the issue became
more apparent. Therefore, all of our path finding attempts now have a
restriction of said limit in in order to properly carry out HTLCs to the
network.
2019-10-11 18:04:49 -04:00

135 lines
4.7 KiB
Go

package routing
import (
"fmt"
"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
// 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.
RequestRoute(payment *LightningPayment,
height uint32, finalCltvDelta uint16) (*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)
sessionSource *SessionSource
preBuiltRoute *route.Route
preBuiltRouteTried bool
pathFinder pathFinder
}
// 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(payment *LightningPayment,
height uint32, finalCltvDelta uint16) (*route.Route, error) {
switch {
// If we have a pre-built route, use that directly.
case p.preBuiltRoute != nil && !p.preBuiltRouteTried:
p.preBuiltRouteTried = true
return p.preBuiltRoute, nil
// If the pre-built route has been tried already, the payment session is
// over.
case p.preBuiltRoute != nil:
return nil, fmt.Errorf("pre-built route already tried")
}
// 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 += 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 := 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.
ss := p.sessionSource
restrictions := &RestrictParams{
ProbabilitySource: ss.MissionControl.GetProbability,
FeeLimit: payment.FeeLimit,
OutgoingChannelID: payment.OutgoingChannelID,
CltvLimit: cltvLimit,
}
// 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
}
path, err := p.pathFinder(
&graphParams{
graph: ss.Graph,
additionalEdges: p.additionalEdges,
bandwidthHints: bandwidthHints,
},
restrictions, &ss.PathFindingConfig,
ss.SelfNode.PubKeyBytes, payment.Target,
payment.Amount,
)
if 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.
sourceVertex := route.Vertex(ss.SelfNode.PubKeyBytes)
route, err := newRoute(
payment.Amount, sourceVertex, path, height, finalCltvDelta,
payment.FinalDestRecords,
)
if err != nil {
// TODO(roasbeef): return which edge/vertex didn't work
// out
return nil, err
}
return route, err
}