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routing: rename findRoute to findPath, return path in forwards order

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This commit modifies the findRoute method by first calling it findPath,
but also making the following modifications.

First, two new black-listing maps are now passed in. These two maps
contain vertexes but also edges to ignore while performing path
finding. These maps will be used in order to ensure that we don’t
duplicate paths or back-track when executing our KSP algorithm.

Next, we now ensure that the path returned from the findPath function
is ordered properly in the direction of source to target. Such a change
is required for our KSP algorithm to function properly.
This commit is contained in:
Olaoluwa Osuntokun 2017-03-20 18:15:50 -07:00
parent fd18c2d036
commit 56d27f2d58
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GPG Key ID: 9CC5B105D03521A2
2 changed files with 116 additions and 64 deletions
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150
routing/pathfind.go
View File

@ -22,6 +22,68 @@ const (
infinity = math.MaxFloat64
)
// ChannelHop is an intermediate hop within the network with a greater
// multi-hop payment route. This struct contains the relevant routing policy of
// the particular edge, as well as the total capacity, and origin chain of the
// channel itself.
type ChannelHop struct {
// Capacity is the total capacity of the channel being traversed. This
// value is expressed for stability in satoshis.
Capacity btcutil.Amount
// Chain is a 32-byte has that denotes the base blockchain network of
// the channel. The 32-byte hash is the "genesis" block of the
// blockchain, or the very first block in the chain.
//
// TODO(roasbeef): store chain within edge info/policy in database.
Chain chainhash.Hash
*channeldb.ChannelEdgePolicy
}
// Hop represents the forwarding details at a particular position within the
// final route. This struct houses the values necessary to create the HTLC
// which will travel along this hop, and also encode the per-hop payload
// included within the Sphinx packet.
type Hop struct {
// Channel is the active payment channel edge that this hop will travel
// along.
Channel *ChannelHop
// TimeLockDelta is the delta that this hop will subtract from the HTLC
// before extending it to the next hop in the route.
TimeLockDelta uint16
// AmtToForward is the amount that this hop will forward to the next
// hop. This value is less than the value that the incoming HTLC
// carries as a fee will be subtracted by the hop.
AmtToForward btcutil.Amount
// Fee is the total fee that this hop will subtract from the incoming
// payment, this difference nets the hop fees for forwarding the
// payment.
Fee btcutil.Amount
}
// computeFee computes the fee to forward an HTLC of `amt` 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 btcutil.Amount, edge *ChannelHop) btcutil.Amount {
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 []*ChannelHop) bool {
for i := 0; i < len(path1); i++ {
if path1[i].ChannelID != path2[i].ChannelID {
return false
}
}
return true
}
// Route represents a path through the channel graph which runs over one or
// more channels in succession. This struct carries all the information
// required to craft the Sphinx onion packet, and send the payment along the
@ -54,56 +116,6 @@ type Route struct {
Hops []*Hop
}
// Hop represents the forwarding details at a particular position within the
// final route. This struct houses the values necessary to create the HTLC
// which will travel along this hop, and also encode the per-hop payload
// included within the Sphinx packet.
type Hop struct {
// Channel is the active payment channel edge that this hop will travel
// along.
Channel *ChannelHop
// TimeLockDelta is the delta that this hop will subtract from the HTLC
// before extending it to the next hop in the route.
TimeLockDelta uint16
// AmtToForward is the amount that this hop will forward to the next
// hop. This value is less than the value that the incoming HTLC
// carries as a fee will be subtracted by the hop.
AmtToForward btcutil.Amount
// Fee is the total fee that this hop will subtract from the incoming
// payment, this difference nets the hop fees for forwarding the
// payment.
Fee btcutil.Amount
}
// ChannelHop is an intermediate hop within the network with a greater
// multi-hop payment route. This struct contains the relevant routing policy of
// the particular edge, as well as the total capacity, and origin chain of the
// channel itself.
type ChannelHop struct {
// Capacity is the total capacity of the channel being traversed. This
// value is expressed for stability in satoshis.
Capacity btcutil.Amount
// Chain is a 32-byte has that denotes the base blockchain network of
// the channel. The 32-byte hash is the "genesis" block of the
// blockchain, or the very first block in the chain.
//
// TODO(roasbeef): store chain within edge info/policy in database.
Chain chainhash.Hash
*channeldb.ChannelEdgePolicy
}
// computeFee computes the fee to forward an HTLC of `amt` 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 btcutil.Amount, edge *ChannelHop) btcutil.Amount {
return edge.FeeBaseMSat + (amt*edge.FeeProportionalMillionths)/1000000
}
// 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
@ -204,17 +216,17 @@ func edgeWeight(e *channeldb.ChannelEdgePolicy) float64 {
return float64(1 + e.TimeLockDelta)
}
// findRoute attempts to find a path from the source node within the
// 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
// (backwards) from the target to the source.
func findRoute(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNode,
target *btcec.PublicKey, amt btcutil.Amount) ([]*ChannelHop, error) {
// from the target to the source.
func findPath(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNode,
target *btcec.PublicKey, ignoredNodes map[vertex]struct{},
ignoredEdges map[uint64]struct{}, amt btcutil.Amount) ([]*ChannelHop, error) {
// First we'll initialize an empty heap which'll help us to quickly
// locate the next edge we should visit next during our graph
@ -257,7 +269,8 @@ func findRoute(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNod
for nodeHeap.Len() != 0 {
// Fetch the node within the smallest distance from our source
// from the heap.
bestNode := heap.Pop(&nodeHeap).(nodeWithDist).node
partialPath := heap.Pop(&nodeHeap).(nodeWithDist)
bestNode := partialPath.node
// If we've reached our target (or we don't have any outgoing
// edges), then we're done here and can exit the graph
@ -273,6 +286,18 @@ func findRoute(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNod
err := bestNode.ForEachChannel(nil, func(edgeInfo *channeldb.ChannelEdgeInfo,
edge *channeldb.ChannelEdgePolicy) error {
v := newVertex(edge.Node.PubKey)
// If this vertex or edge has been black listed, then
// we'll skip exploring this edge during this
// iteration.
if _, ok := ignoredNodes[v]; ok {
return nil
}
if _, ok := ignoredEdges[edge.ChannelID]; ok {
return nil
}
// Compute the tentative distance to this new
// channel/edge which is the distance to our current
// pivot node plus the weight of this edge.
@ -284,7 +309,6 @@ func findRoute(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNod
// our "next hop" map with this edge. We'll also shave
// off irrelevant edges by adding the sufficient
// capacity of an edge to our relaxation condition.
v := newVertex(edge.Node.PubKey)
if tempDist < distance[v].dist &&
edgeInfo.Capacity >= amt {
@ -328,6 +352,8 @@ func findRoute(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNod
// backwards from this hop via the prev pointer for this hop
// within the prevHop map.
pathEdges = append(pathEdges, prev[prevNode].edge)
prev[prevNode].edge.Node.PubKey.Curve = nil
prevNode = newVertex(prev[prevNode].prevNode)
}
@ -335,10 +361,18 @@ func findRoute(graph *channeldb.ChannelGraph, sourceNode *channeldb.LightningNod
// 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.
if len(pathEdges) > HopLimit {
numEdges := len(pathEdges)
if numEdges > HopLimit {
return nil, ErrMaxHopsExceeded
}
// As our traversal of the prev map above walked backwards from the
// target to the source in the route, we need to reverse it before
// returning the final route.
for i := 0; i < numEdges/2; i++ {
pathEdges[i], pathEdges[numEdges-i-1] = pathEdges[numEdges-i-1], pathEdges[i]
}
return pathEdges, nil
}
}

30
routing/pathfind_test.go
View File

@ -293,6 +293,9 @@ func TestBasicGraphPathFinding(t *testing.T) {
t.Fatalf("unable to fetch source node: %v", err)
}
ignoredEdges := make(map[uint64]struct{})
ignoredVertexes := make(map[vertex]struct{})
// With the test graph loaded, we'll test some basic path finding using
// the pre-generated graph. Consult the testdata/basic_graph.json file
// to follow along with the assumptions we'll use to test the path
@ -300,7 +303,8 @@ func TestBasicGraphPathFinding(t *testing.T) {
const paymentAmt = btcutil.Amount(100)
target := aliases["sophon"]
path, err := findRoute(graph, sourceNode, target, paymentAmt)
path, err := findPath(graph, sourceNode, target, ignoredVertexes,
ignoredEdges, paymentAmt)
if err != nil {
t.Fatalf("unable to find path: %v", err)
}
@ -338,7 +342,8 @@ func TestBasicGraphPathFinding(t *testing.T) {
// exist two possible paths in the graph, but the shorter (1 hop) path
// should be selected.
target = aliases["luoji"]
path, err = findRoute(graph, sourceNode, target, paymentAmt)
path, err = findPath(graph, sourceNode, target, ignoredVertexes,
ignoredEdges, paymentAmt)
if err != nil {
t.Fatalf("unable to find route: %v", err)
}
@ -384,19 +389,25 @@ func TestNewRoutePathTooLong(t *testing.T) {
t.Fatalf("unable to fetch source node: %v", err)
}
ignoredEdges := make(map[uint64]struct{})
ignoredVertexes := make(map[vertex]struct{})
const paymentAmt = btcutil.Amount(100)
// We start by confirminig that routing a payment 20 hops away is possible.
// Alice should be able to find a valid route to ursula.
target := aliases["ursula"]
if _, err = findRoute(graph, sourceNode, target, paymentAmt); err != nil {
_, err = findPath(graph, sourceNode, target, ignoredVertexes,
ignoredEdges, paymentAmt)
if err != nil {
t.Fatalf("path should have been found")
}
// Vincent is 21 hops away from Alice, and thus no valid route should be
// presented to Alice.
target = aliases["vincent"]
path, err := findRoute(graph, sourceNode, target, paymentAmt)
path, err := findPath(graph, sourceNode, target, ignoredVertexes,
ignoredEdges, paymentAmt)
if err == nil {
t.Fatalf("should not have been able to find path, supposed to be "+
"greater than 20 hops, found route with %v hops",
@ -417,6 +428,9 @@ func TestPathNotAvailable(t *testing.T) {
t.Fatalf("unable to fetch source node: %v", err)
}
ignoredEdges := make(map[uint64]struct{})
ignoredVertexes := make(map[vertex]struct{})
// With the test graph loaded, we'll test that queries for target that
// are either unreachable within the graph, or unknown result in an
// error.
@ -430,7 +444,8 @@ func TestPathNotAvailable(t *testing.T) {
t.Fatalf("unable to parse pubkey: %v", err)
}
_, err = findRoute(graph, sourceNode, unknownNode, 100)
_, err = findPath(graph, sourceNode, unknownNode, ignoredVertexes,
ignoredEdges, 100)
if err != ErrNoPathFound {
t.Fatalf("path shouldn't have been found: %v", err)
}
@ -447,6 +462,8 @@ func TestPathInsufficientCapacity(t *testing.T) {
if err != nil {
t.Fatalf("unable to fetch source node: %v", err)
}
ignoredEdges := make(map[uint64]struct{})
ignoredVertexes := make(map[vertex]struct{})
// Next, test that attempting to find a path in which the current
// channel graph cannot support due to insufficient capacity triggers
@ -459,7 +476,8 @@ func TestPathInsufficientCapacity(t *testing.T) {
target := aliases["sophon"]
const payAmt = btcutil.SatoshiPerBitcoin
_, err = findRoute(graph, sourceNode, target, payAmt)
_, err = findPath(graph, sourceNode, target, ignoredVertexes,
ignoredEdges, payAmt)
if err != ErrNoPathFound {
t.Fatalf("graph shouldn't be able to support payment: %v", err)
}