lnd.xprv/routing/payment_session.go

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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
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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)
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
// If a route cltv limit was specified, 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.
var cltvLimit *uint32
if payment.CltvLimit != nil {
limit := *payment.CltvLimit - uint32(finalCltvDelta)
cltvLimit = &limit
}
// 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.
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
}
// nodeChannel is a combination of the node pubkey and one of its channels.
type nodeChannel struct {
node route.Vertex
channel uint64
}