136 lines
4.7 KiB
Go
136 lines
4.7 KiB
Go
package routing
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import (
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"fmt"
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"github.com/lightningnetwork/lnd/channeldb"
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"github.com/lightningnetwork/lnd/lnwire"
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"github.com/lightningnetwork/lnd/routing/route"
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)
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// BlockPadding is used to increment the finalCltvDelta value for the last hop
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// to prevent an HTLC being failed if some blocks are mined while it's in-flight.
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const BlockPadding uint16 = 3
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// PaymentSession is used during SendPayment attempts to provide routes to
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// attempt. It also defines methods to give the PaymentSession additional
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// information learned during the previous attempts.
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type PaymentSession interface {
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// RequestRoute returns the next route to attempt for routing the
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// specified HTLC payment to the target node.
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RequestRoute(payment *LightningPayment,
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height uint32, finalCltvDelta uint16) (*route.Route, error)
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}
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// paymentSession is used during an HTLC routings session to prune the local
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// 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,
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// and will now be pruned after a decay like the main view within mission
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// control. We do this as we want to avoid the case where we continually try a
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// bad edge or route multiple times in a session. This can lead to an infinite
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// loop if payment attempts take long enough. An additional set of edges can
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// also be provided to assist in reaching the payment's destination.
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type paymentSession struct {
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additionalEdges map[route.Vertex][]*channeldb.ChannelEdgePolicy
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getBandwidthHints func() (map[uint64]lnwire.MilliSatoshi, error)
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sessionSource *SessionSource
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preBuiltRoute *route.Route
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preBuiltRouteTried bool
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pathFinder pathFinder
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}
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// RequestRoute returns a route which is likely to be capable for successfully
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// routing the specified HTLC payment to the target node. Initially the first
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// set of paths returned from this method may encounter routing failure along
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// the way, however as more payments are sent, mission control will start to
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// build an up to date view of the network itself. With each payment a new area
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// will be explored, which feeds into the recommendations made for routing.
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//
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// NOTE: This function is safe for concurrent access.
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// NOTE: Part of the PaymentSession interface.
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func (p *paymentSession) RequestRoute(payment *LightningPayment,
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height uint32, finalCltvDelta uint16) (*route.Route, error) {
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switch {
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// If we have a pre-built route, use that directly.
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case p.preBuiltRoute != nil && !p.preBuiltRouteTried:
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p.preBuiltRouteTried = true
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return p.preBuiltRoute, nil
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// If the pre-built route has been tried already, the payment session is
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// over.
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case p.preBuiltRoute != nil:
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return nil, fmt.Errorf("pre-built route already tried")
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}
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// Add BlockPadding to the finalCltvDelta so that the receiving node
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// does not reject the HTLC if some blocks are mined while it's in-flight.
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finalCltvDelta += BlockPadding
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// We need to subtract the final delta before passing it into path
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// finding. The optimal path is independent of the final cltv delta and
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// the path finding algorithm is unaware of this value.
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cltvLimit := payment.CltvLimit - uint32(finalCltvDelta)
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// TODO(roasbeef): sync logic amongst dist sys
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// Taking into account this prune view, we'll attempt to locate a path
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// to our destination, respecting the recommendations from
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// MissionControl.
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ss := p.sessionSource
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restrictions := &RestrictParams{
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ProbabilitySource: ss.MissionControl.GetProbability,
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FeeLimit: payment.FeeLimit,
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OutgoingChannelID: payment.OutgoingChannelID,
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LastHop: payment.LastHop,
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CltvLimit: cltvLimit,
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}
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// We'll also obtain a set of bandwidthHints from the lower layer for
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// each of our outbound channels. This will allow the path finding to
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// skip any links that aren't active or just don't have enough bandwidth
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// to carry the payment. New bandwidth hints are queried for every new
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// path finding attempt, because concurrent payments may change
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// balances.
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bandwidthHints, err := p.getBandwidthHints()
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if err != nil {
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return nil, err
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}
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path, err := p.pathFinder(
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&graphParams{
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graph: ss.Graph,
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additionalEdges: p.additionalEdges,
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bandwidthHints: bandwidthHints,
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},
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restrictions, &ss.PathFindingConfig,
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ss.SelfNode.PubKeyBytes, payment.Target,
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payment.Amount,
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)
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if err != nil {
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return nil, err
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}
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// With the next candidate path found, we'll attempt to turn this into
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// a route by applying the time-lock and fee requirements.
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sourceVertex := route.Vertex(ss.SelfNode.PubKeyBytes)
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route, err := newRoute(
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payment.Amount, sourceVertex, path, height, finalCltvDelta,
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payment.FinalDestRecords,
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)
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if err != nil {
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// TODO(roasbeef): return which edge/vertex didn't work
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// out
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return nil, err
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}
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return route, err
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}
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