lnd.xprv/routing/pathfind.go
2019-04-29 14:52:33 +02:00

796 lines
28 KiB
Go

package routing
import (
"container/heap"
"math"
"github.com/coreos/bbolt"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/routing/route"
)
const (
// HopLimit is the maximum number hops that is permissible as a route.
// Any potential paths found that lie above this limit will be rejected
// with an error. This value is computed using the current fixed-size
// packet length of the Sphinx construction.
HopLimit = 20
// infinity is used as a starting distance in our shortest path search.
infinity = math.MaxInt64
// RiskFactorBillionths controls the influence of time lock delta
// of a channel on route selection. It is expressed as billionths
// of msat per msat sent through the channel per time lock delta
// block. See edgeWeight function below for more details.
// The chosen value is based on the previous incorrect weight function
// 1 + timelock + fee * fee. In this function, the fee penalty
// diminishes the time lock penalty for all but the smallest amounts.
// To not change the behaviour of path finding too drastically, a
// relatively small value is chosen which is still big enough to give
// some effect with smaller time lock values. The value may need
// tweaking and/or be made configurable in the future.
RiskFactorBillionths = 15
)
// pathFinder defines the interface of a path finding algorithm.
type pathFinder = func(g *graphParams, r *RestrictParams,
source, target route.Vertex, amt lnwire.MilliSatoshi) (
[]*channeldb.ChannelEdgePolicy, error)
// edgePolicyWithSource is a helper struct to keep track of the source node
// of a channel edge. ChannelEdgePolicy only contains to destination node
// of the edge.
type edgePolicyWithSource struct {
sourceNode *channeldb.LightningNode
edge *channeldb.ChannelEdgePolicy
}
// computeFee computes the fee to forward an HTLC of `amt` milli-satoshis over
// the passed active payment channel. This value is currently computed as
// specified in BOLT07, but will likely change in the near future.
func computeFee(amt lnwire.MilliSatoshi,
edge *channeldb.ChannelEdgePolicy) lnwire.MilliSatoshi {
return edge.FeeBaseMSat + (amt*edge.FeeProportionalMillionths)/1000000
}
// isSamePath returns true if path1 and path2 travel through the exact same
// edges, and false otherwise.
func isSamePath(path1, path2 []*channeldb.ChannelEdgePolicy) bool {
if len(path1) != len(path2) {
return false
}
for i := 0; i < len(path1); i++ {
if path1[i].ChannelID != path2[i].ChannelID {
return false
}
}
return true
}
// newRoute returns a fully valid route between the source and target that's
// capable of supporting a payment of `amtToSend` after fees are fully
// computed. If the route is too long, or the selected path cannot support the
// fully payment including fees, then a non-nil error is returned.
//
// NOTE: The passed slice of ChannelHops MUST be sorted in forward order: from
// the source to the target node of the path finding attempt.
func newRoute(amtToSend lnwire.MilliSatoshi, sourceVertex route.Vertex,
pathEdges []*channeldb.ChannelEdgePolicy, currentHeight uint32,
finalCLTVDelta uint16) (*route.Route, error) {
var (
hops []*route.Hop
// totalTimeLock will accumulate the cumulative time lock
// across the entire route. This value represents how long the
// sender will need to wait in the *worst* case.
totalTimeLock = currentHeight
// nextIncomingAmount is the amount that will need to flow into
// the *next* hop. Since we're going to be walking the route
// backwards below, this next hop gets closer and closer to the
// sender of the payment.
nextIncomingAmount lnwire.MilliSatoshi
)
pathLength := len(pathEdges)
for i := pathLength - 1; i >= 0; i-- {
// Now we'll start to calculate the items within the per-hop
// payload for the hop this edge is leading to.
edge := pathEdges[i]
// If this is the last hop, then the hop payload will contain
// the exact amount. In BOLT #4: Onion Routing
// Protocol / "Payload for the Last Node", this is detailed.
amtToForward := amtToSend
// Fee is not part of the hop payload, but only used for
// reporting through RPC. Set to zero for the final hop.
fee := lnwire.MilliSatoshi(0)
// If the current hop isn't the last hop, then add enough funds
// to pay for transit over the next link.
if i != len(pathEdges)-1 {
// The amount that the current hop needs to forward is
// equal to the incoming amount of the next hop.
amtToForward = nextIncomingAmount
// The fee that needs to be paid to the current hop is
// based on the amount that this hop needs to forward
// and its policy for the outgoing channel. This policy
// is stored as part of the incoming channel of
// the next hop.
fee = computeFee(amtToForward, pathEdges[i+1])
}
// If this is the last hop, then for verification purposes, the
// value of the outgoing time-lock should be _exactly_ the
// absolute time out they'd expect in the HTLC.
var outgoingTimeLock uint32
if i == len(pathEdges)-1 {
// As this is the last hop, we'll use the specified
// final CLTV delta value instead of the value from the
// last link in the route.
totalTimeLock += uint32(finalCLTVDelta)
outgoingTimeLock = currentHeight + uint32(finalCLTVDelta)
} else {
// Next, increment the total timelock of the entire
// route such that each hops time lock increases as we
// walk backwards in the route, using the delta of the
// previous hop.
delta := uint32(pathEdges[i+1].TimeLockDelta)
totalTimeLock += delta
// Otherwise, the value of the outgoing time-lock will
// be the value of the time-lock for the _outgoing_
// HTLC, so we factor in their specified grace period
// (time lock delta).
outgoingTimeLock = totalTimeLock - delta
}
// Since we're traversing the path backwards atm, we prepend
// each new hop such that, the final slice of hops will be in
// the forwards order.
currentHop := &route.Hop{
PubKeyBytes: edge.Node.PubKeyBytes,
ChannelID: edge.ChannelID,
AmtToForward: amtToForward,
OutgoingTimeLock: outgoingTimeLock,
}
hops = append([]*route.Hop{currentHop}, hops...)
// Finally, we update the amount that needs to flow into the
// *next* hop, which is the amount this hop needs to forward,
// accounting for the fee that it takes.
nextIncomingAmount = amtToForward + fee
}
// With the base routing data expressed as hops, build the full route
newRoute, err := route.NewRouteFromHops(
nextIncomingAmount, totalTimeLock, route.Vertex(sourceVertex), hops,
)
if err != nil {
return nil, err
}
return newRoute, nil
}
// edgeWeight computes the weight of an edge. This value is used when searching
// for the shortest path within the channel graph between two nodes. Weight is
// is the fee itself plus a time lock penalty added to it. This benefits
// channels with shorter time lock deltas and shorter (hops) routes in general.
// RiskFactor controls the influence of time lock on route selection. This is
// currently a fixed value, but might be configurable in the future.
func edgeWeight(lockedAmt lnwire.MilliSatoshi, fee lnwire.MilliSatoshi,
timeLockDelta uint16) int64 {
// timeLockPenalty is the penalty for the time lock delta of this channel.
// It is controlled by RiskFactorBillionths and scales proportional
// to the amount that will pass through channel. Rationale is that it if
// a twice as large amount gets locked up, it is twice as bad.
timeLockPenalty := int64(lockedAmt) * int64(timeLockDelta) *
RiskFactorBillionths / 1000000000
return int64(fee) + timeLockPenalty
}
// graphParams wraps the set of graph parameters passed to findPath.
type graphParams struct {
// tx can be set to an existing db transaction. If not set, a new
// transaction will be started.
tx *bbolt.Tx
// graph is the ChannelGraph to be used during path finding.
graph *channeldb.ChannelGraph
// additionalEdges is an optional set of edges that should be
// considered during path finding, that is not already found in the
// channel graph.
additionalEdges map[route.Vertex][]*channeldb.ChannelEdgePolicy
// bandwidthHints is an optional map from channels to bandwidths that
// can be populated if the caller has a better estimate of the current
// channel bandwidth than what is found in the graph. If set, it will
// override the capacities and disabled flags found in the graph for
// local channels when doing path finding. In particular, it should be
// set to the current available sending bandwidth for active local
// channels, and 0 for inactive channels.
bandwidthHints map[uint64]lnwire.MilliSatoshi
}
// RestrictParams wraps the set of restrictions passed to findPath that the
// found path must adhere to.
type RestrictParams struct {
// IgnoredNodes is an optional set of nodes that should be ignored if
// encountered during path finding.
IgnoredNodes map[route.Vertex]struct{}
// IgnoredEdges is an optional set of edges that should be ignored if
// encountered during path finding.
IgnoredEdges map[EdgeLocator]struct{}
// FeeLimit is a maximum fee amount allowed to be used on the path from
// the source to the target.
FeeLimit lnwire.MilliSatoshi
// OutgoingChannelID is the channel that needs to be taken to the first
// hop. If nil, any channel may be used.
OutgoingChannelID *uint64
// CltvLimit is the maximum time lock of the route excluding the final
// ctlv. After path finding is complete, the caller needs to increase
// all cltv expiry heights with the required final cltv delta.
CltvLimit *uint32
}
// findPath attempts to find a path from the source node within the
// ChannelGraph to the target node that's capable of supporting a payment of
// `amt` value. The current approach implemented is modified version of
// Dijkstra's algorithm to find a single shortest path between the source node
// and the destination. The distance metric used for edges is related to the
// time-lock+fee costs along a particular edge. If a path is found, this
// function returns a slice of ChannelHop structs which encoded the chosen path
// from the target to the source. The search is performed backwards from
// destination node back to source. This is to properly accumulate fees
// that need to be paid along the path and accurately check the amount
// to forward at every node against the available bandwidth.
func findPath(g *graphParams, r *RestrictParams, source, target route.Vertex,
amt lnwire.MilliSatoshi) ([]*channeldb.ChannelEdgePolicy, error) {
var err error
tx := g.tx
if tx == nil {
tx, err = g.graph.Database().Begin(false)
if err != nil {
return nil, err
}
defer tx.Rollback()
}
// First we'll initialize an empty heap which'll help us to quickly
// locate the next edge we should visit next during our graph
// traversal.
var nodeHeap distanceHeap
// For each node in the graph, we create an entry in the distance map
// for the node set with a distance of "infinity". graph.ForEachNode
// also returns the source node, so there is no need to add the source
// node explicitly.
distance := make(map[route.Vertex]nodeWithDist)
if err := g.graph.ForEachNode(tx, func(_ *bbolt.Tx,
node *channeldb.LightningNode) error {
// TODO(roasbeef): with larger graph can just use disk seeks
// with a visited map
distance[route.Vertex(node.PubKeyBytes)] = nodeWithDist{
dist: infinity,
node: node,
}
return nil
}); err != nil {
return nil, err
}
additionalEdgesWithSrc := make(map[route.Vertex][]*edgePolicyWithSource)
for vertex, outgoingEdgePolicies := range g.additionalEdges {
// We'll also include all the nodes found within the additional
// edges that are not known to us yet in the distance map.
node := &channeldb.LightningNode{PubKeyBytes: vertex}
distance[vertex] = nodeWithDist{
dist: infinity,
node: node,
}
// Build reverse lookup to find incoming edges. Needed because
// search is taken place from target to source.
for _, outgoingEdgePolicy := range outgoingEdgePolicies {
toVertex := outgoingEdgePolicy.Node.PubKeyBytes
incomingEdgePolicy := &edgePolicyWithSource{
sourceNode: node,
edge: outgoingEdgePolicy,
}
additionalEdgesWithSrc[toVertex] =
append(additionalEdgesWithSrc[toVertex],
incomingEdgePolicy)
}
}
// We can't always assume that the end destination is publicly
// advertised to the network and included in the graph.ForEachNode call
// above, so we'll manually include the target node. The target node
// charges no fee. Distance is set to 0, because this is the starting
// point of the graph traversal. We are searching backwards to get the
// fees first time right and correctly match channel bandwidth.
targetNode := &channeldb.LightningNode{PubKeyBytes: target}
distance[target] = nodeWithDist{
dist: 0,
node: targetNode,
amountToReceive: amt,
fee: 0,
incomingCltv: 0,
}
// We'll use this map as a series of "next" hop pointers. So to get
// from `Vertex` to the target node, we'll take the edge that it's
// mapped to within `next`.
next := make(map[route.Vertex]*channeldb.ChannelEdgePolicy)
ignoredEdges := r.IgnoredEdges
if ignoredEdges == nil {
ignoredEdges = make(map[EdgeLocator]struct{})
}
ignoredNodes := r.IgnoredNodes
if ignoredNodes == nil {
ignoredNodes = make(map[route.Vertex]struct{})
}
// processEdge is a helper closure that will be used to make sure edges
// satisfy our specific requirements.
processEdge := func(fromNode *channeldb.LightningNode,
edge *channeldb.ChannelEdgePolicy,
bandwidth lnwire.MilliSatoshi, toNode route.Vertex) {
fromVertex := route.Vertex(fromNode.PubKeyBytes)
// If this is not a local channel and it is disabled, we will
// skip it.
// TODO(halseth): also ignore disable flags for non-local
// channels if bandwidth hint is set?
isSourceChan := fromVertex == source
edgeFlags := edge.ChannelFlags
isDisabled := edgeFlags&lnwire.ChanUpdateDisabled != 0
if !isSourceChan && isDisabled {
return
}
// If we have an outgoing channel restriction and this is not
// the specified channel, skip it.
if isSourceChan && r.OutgoingChannelID != nil &&
*r.OutgoingChannelID != edge.ChannelID {
return
}
// If this vertex or edge has been black listed, then we'll
// skip exploring this edge.
if _, ok := ignoredNodes[fromVertex]; ok {
return
}
locator := newEdgeLocator(edge)
if _, ok := ignoredEdges[*locator]; ok {
return
}
toNodeDist := distance[toNode]
amountToSend := toNodeDist.amountToReceive
// If the estimated bandwidth of the channel edge is not able
// to carry the amount that needs to be send, return.
if bandwidth < amountToSend {
return
}
// If the amountToSend is less than the minimum required
// amount, return.
if amountToSend < edge.MinHTLC {
return
}
// If this edge was constructed from a hop hint, we won't have access to
// its max HTLC. Therefore, only consider discarding this edge here if
// the field is set.
if edge.MaxHTLC != 0 && edge.MaxHTLC < amountToSend {
return
}
// Compute fee that fromNode is charging. It is based on the
// amount that needs to be sent to the next node in the route.
//
// Source node has no predecessor to pay a fee. Therefore set
// fee to zero, because it should not be included in the fee
// limit check and edge weight.
//
// Also determine the time lock delta that will be added to the
// route if fromNode is selected. If fromNode is the source
// node, no additional timelock is required.
var fee lnwire.MilliSatoshi
var timeLockDelta uint16
if fromVertex != source {
fee = computeFee(amountToSend, edge)
timeLockDelta = edge.TimeLockDelta
}
incomingCltv := toNodeDist.incomingCltv +
uint32(timeLockDelta)
// Check that we have cltv limit and that we are within it.
if r.CltvLimit != nil && incomingCltv > *r.CltvLimit {
return
}
// amountToReceive is the amount that the node that is added to
// the distance map needs to receive from a (to be found)
// previous node in the route. That previous node will need to
// pay the amount that this node forwards plus the fee it
// charges.
amountToReceive := amountToSend + fee
// Check if accumulated fees would exceed fee limit when this
// node would be added to the path.
totalFee := amountToReceive - amt
if totalFee > r.FeeLimit {
return
}
// By adding fromNode in the route, there will be an extra
// weight composed of the fee that this node will charge and
// the amount that will be locked for timeLockDelta blocks in
// the HTLC that is handed out to fromNode.
weight := edgeWeight(amountToReceive, fee, timeLockDelta)
// Compute the tentative distance to this new channel/edge
// which is the distance from our toNode to the target node
// plus the weight of this edge.
tempDist := toNodeDist.dist + weight
// If this new tentative distance is not better than the current
// best known distance to this node, return.
if tempDist >= distance[fromVertex].dist {
return
}
// Every edge should have a positive time lock delta. If we
// encounter a zero delta, log a warning line.
if edge.TimeLockDelta == 0 {
log.Warnf("Channel %v has zero cltv delta",
edge.ChannelID)
}
// All conditions are met and this new tentative distance is
// better than the current best known distance to this node.
// The new better distance is recorded, and also our "next hop"
// map is populated with this edge.
distance[fromVertex] = nodeWithDist{
dist: tempDist,
node: fromNode,
amountToReceive: amountToReceive,
fee: fee,
incomingCltv: incomingCltv,
}
next[fromVertex] = edge
// Add this new node to our heap as we'd like to further
// explore backwards through this edge.
heap.Push(&nodeHeap, distance[fromVertex])
}
// TODO(roasbeef): also add path caching
// * similar to route caching, but doesn't factor in the amount
// To start, our target node will the sole item within our distance
// heap.
heap.Push(&nodeHeap, distance[target])
for nodeHeap.Len() != 0 {
// Fetch the node within the smallest distance from our source
// from the heap.
partialPath := heap.Pop(&nodeHeap).(nodeWithDist)
bestNode := partialPath.node
// If we've reached our source (or we don't have any incoming
// edges), then we're done here and can exit the graph
// traversal early.
if bestNode.PubKeyBytes == source {
break
}
// Now that we've found the next potential step to take we'll
// examine all the incoming edges (channels) from this node to
// further our graph traversal.
pivot := route.Vertex(bestNode.PubKeyBytes)
err := bestNode.ForEachChannel(tx, func(tx *bbolt.Tx,
edgeInfo *channeldb.ChannelEdgeInfo,
_, inEdge *channeldb.ChannelEdgePolicy) error {
// If there is no edge policy for this candidate
// node, skip. Note that we are searching backwards
// so this node would have come prior to the pivot
// node in the route.
if inEdge == nil {
return nil
}
// We'll query the lower layer to see if we can obtain
// any more up to date information concerning the
// bandwidth of this edge.
edgeBandwidth, ok := g.bandwidthHints[edgeInfo.ChannelID]
if !ok {
// If we don't have a hint for this edge, then
// we'll just use the known Capacity/MaxHTLC as
// the available bandwidth. It's possible for
// the capacity to be unknown when operating
// under a light client.
edgeBandwidth = inEdge.MaxHTLC
if edgeBandwidth == 0 {
edgeBandwidth = lnwire.NewMSatFromSatoshis(
edgeInfo.Capacity,
)
}
}
// Before we can process the edge, we'll need to fetch
// the node on the _other_ end of this channel as we
// may later need to iterate over the incoming edges of
// this node if we explore it further.
channelSource, err := edgeInfo.FetchOtherNode(
tx, pivot[:],
)
if err != nil {
return err
}
// Check if this candidate node is better than what we
// already have.
processEdge(channelSource, inEdge, edgeBandwidth, pivot)
return nil
})
if err != nil {
return nil, err
}
// Then, we'll examine all the additional edges from the node
// we're currently visiting. Since we don't know the capacity
// of the private channel, we'll assume it was selected as a
// routing hint due to having enough capacity for the payment
// and use the payment amount as its capacity.
bandWidth := partialPath.amountToReceive
for _, reverseEdge := range additionalEdgesWithSrc[bestNode.PubKeyBytes] {
processEdge(reverseEdge.sourceNode, reverseEdge.edge,
bandWidth, pivot)
}
}
// If the source node isn't found in the next hop map, then a path
// doesn't exist, so we terminate in an error.
if _, ok := next[source]; !ok {
return nil, newErrf(ErrNoPathFound, "unable to find a path to "+
"destination")
}
// Use the nextHop map to unravel the forward path from source to
// target.
pathEdges := make([]*channeldb.ChannelEdgePolicy, 0, len(next))
currentNode := source
for currentNode != target { // TODO(roasbeef): assumes no cycles
// Determine the next hop forward using the next map.
nextNode := next[currentNode]
// Add the next hop to the list of path edges.
pathEdges = append(pathEdges, nextNode)
// Advance current node.
currentNode = route.Vertex(nextNode.Node.PubKeyBytes)
}
// The route is invalid if it spans more than 20 hops. The current
// Sphinx (onion routing) implementation can only encode up to 20 hops
// as the entire packet is fixed size. If this route is more than 20
// hops, then it's invalid.
numEdges := len(pathEdges)
if numEdges > HopLimit {
return nil, newErr(ErrMaxHopsExceeded, "potential path has "+
"too many hops")
}
return pathEdges, nil
}
// findPaths implements a k-shortest paths algorithm to find all the reachable
// paths between the passed source and target. The algorithm will continue to
// traverse the graph until all possible candidate paths have been depleted.
// This function implements a modified version of Yen's. To find each path
// itself, we utilize our modified version of Dijkstra's found above. When
// examining possible spur and root paths, rather than removing edges or
// Vertexes from the graph, we instead utilize a Vertex+edge black-list that
// will be ignored by our modified Dijkstra's algorithm. With this approach, we
// make our inner path finding algorithm aware of our k-shortest paths
// algorithm, rather than attempting to use an unmodified path finding
// algorithm in a block box manner.
func findPaths(tx *bbolt.Tx, graph *channeldb.ChannelGraph,
source, target route.Vertex, amt lnwire.MilliSatoshi,
restrictions *RestrictParams, numPaths uint32,
bandwidthHints map[uint64]lnwire.MilliSatoshi) (
[][]*channeldb.ChannelEdgePolicy, error) {
// TODO(roasbeef): modifying ordering within heap to eliminate final
// sorting step?
var (
shortestPaths [][]*channeldb.ChannelEdgePolicy
candidatePaths pathHeap
)
// First we'll find a single shortest path from the source (our
// selfNode) to the target destination that's capable of carrying amt
// satoshis along the path before fees are calculated.
startingPath, err := findPath(
&graphParams{
tx: tx,
graph: graph,
bandwidthHints: bandwidthHints,
},
restrictions, source, target, amt,
)
if err != nil {
log.Errorf("Unable to find path: %v", err)
return nil, err
}
// Manually insert a "self" edge emanating from ourselves. This
// self-edge is required in order for the path finding algorithm to
// function properly.
firstPath := make([]*channeldb.ChannelEdgePolicy, 0, len(startingPath)+1)
firstPath = append(firstPath, &channeldb.ChannelEdgePolicy{
Node: &channeldb.LightningNode{PubKeyBytes: source},
})
firstPath = append(firstPath, startingPath...)
shortestPaths = append(shortestPaths, firstPath)
// While we still have candidate paths to explore we'll keep exploring
// the sub-graphs created to find the next k-th shortest path.
for k := uint32(1); k < numPaths; k++ {
prevShortest := shortestPaths[k-1]
// We'll examine each edge in the previous iteration's shortest
// path in order to find path deviations from each node in the
// path.
for i := 0; i < len(prevShortest)-1; i++ {
// These two maps will mark the edges and Vertexes
// we'll exclude from the next path finding attempt.
// These are required to ensure the paths are unique
// and loopless.
ignoredEdges := make(map[EdgeLocator]struct{})
ignoredVertexes := make(map[route.Vertex]struct{})
for e := range restrictions.IgnoredEdges {
ignoredEdges[e] = struct{}{}
}
for n := range restrictions.IgnoredNodes {
ignoredVertexes[n] = struct{}{}
}
// Our spur node is the i-th node in the prior shortest
// path, and our root path will be all nodes in the
// path leading up to our spurNode.
spurNode := prevShortest[i].Node
rootPath := prevShortest[:i+1]
// Before we kickoff our next path finding iteration,
// we'll find all the edges we need to ignore in this
// next round. This ensures that we create a new unique
// path.
for _, path := range shortestPaths {
// If our current rootPath is a prefix of this
// shortest path, then we'll remove the edge
// directly _after_ our spur node from the
// graph so we don't repeat paths.
if len(path) > i+1 &&
isSamePath(rootPath, path[:i+1]) {
locator := newEdgeLocator(path[i+1])
ignoredEdges[*locator] = struct{}{}
}
}
// Next we'll remove all entries in the root path that
// aren't the current spur node from the graph. This
// ensures we don't create a path with loops.
for _, hop := range rootPath {
node := hop.Node.PubKeyBytes
if node == spurNode.PubKeyBytes {
continue
}
ignoredVertexes[route.Vertex(node)] = struct{}{}
}
// With the edges that are part of our root path, and
// the Vertexes (other than the spur path) within the
// root path removed, we'll attempt to find another
// shortest path from the spur node to the destination.
//
// TODO: Fee limit passed to spur path finding isn't
// correct, because it doesn't take into account the
// fees already paid on the root path.
//
// TODO: Outgoing channel restriction isn't obeyed for
// spur paths.
spurRestrictions := &RestrictParams{
IgnoredEdges: ignoredEdges,
IgnoredNodes: ignoredVertexes,
FeeLimit: restrictions.FeeLimit,
}
spurPath, err := findPath(
&graphParams{
tx: tx,
graph: graph,
bandwidthHints: bandwidthHints,
},
spurRestrictions, spurNode.PubKeyBytes,
target, amt,
)
// If we weren't able to find a path, we'll continue to
// the next round.
if IsError(err, ErrNoPathFound) {
continue
} else if err != nil {
return nil, err
}
// Create the new combined path by concatenating the
// rootPath to the spurPath.
newPathLen := len(rootPath) + len(spurPath)
newPath := path{
hops: make([]*channeldb.ChannelEdgePolicy, 0, newPathLen),
dist: newPathLen,
}
newPath.hops = append(newPath.hops, rootPath...)
newPath.hops = append(newPath.hops, spurPath...)
// TODO(roasbeef): add and consult path finger print
// We'll now add this newPath to the heap of candidate
// shortest paths.
heap.Push(&candidatePaths, newPath)
}
// If our min-heap of candidate paths is empty, then we can
// exit early.
if candidatePaths.Len() == 0 {
break
}
// To conclude this latest iteration, we'll take the shortest
// path in our set of candidate paths and add it to our
// shortestPaths list as the *next* shortest path.
nextShortestPath := heap.Pop(&candidatePaths).(path).hops
shortestPaths = append(shortestPaths, nextShortestPath)
}
return shortestPaths, nil
}