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routing: use unified policy for build route

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This commit is contained in:
Joost Jager 2019-09-30 15:45:16 +02:00
parent a347237e7a
commit 729c3a6bd6
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GPG Key ID: A61B9D4C393C59C7
3 changed files with 85 additions and 217 deletions
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272
routing/router.go
View File

@ -2254,90 +2254,6 @@ func generateBandwidthHints(sourceNode *channeldb.LightningNode,
return bandwidthHints, nil
}
// runningAmounts keeps running amounts while the route is traversed.
type runningAmounts struct {
// amt is the intended amount to send via the route.
amt lnwire.MilliSatoshi
// max is the running maximum that the route can carry.
max lnwire.MilliSatoshi
}
// prependChannel returns a new set of running amounts that would result from
// prepending the given channel to the route. If canIncreaseAmt is set, the
// amount may be increased if it is too small to satisfy the channel's minimum
// htlc amount.
func (r *runningAmounts) prependChannel(policy *channeldb.ChannelEdgePolicy,
capacity btcutil.Amount, localChan bool, canIncreaseAmt bool) (
runningAmounts, error) {
// Determine max htlc value.
maxHtlc := lnwire.NewMSatFromSatoshis(capacity)
if policy.MessageFlags.HasMaxHtlc() {
maxHtlc = policy.MaxHTLC
}
amt := r.amt
// If we have a specific amount for which we are building the route,
// validate it against the channel constraints and return the new
// running amount.
if !canIncreaseAmt {
if amt < policy.MinHTLC || amt > maxHtlc {
return runningAmounts{}, fmt.Errorf("channel htlc "+
"constraints [%v - %v] violated with amt %v",
policy.MinHTLC, maxHtlc, amt)
}
// Update running amount by adding the fee for non-local
// channels.
if !localChan {
amt += policy.ComputeFee(amt)
}
return runningAmounts{
amt: amt,
}, nil
}
// Adapt the minimum amount to what this channel allows.
if policy.MinHTLC > r.amt {
amt = policy.MinHTLC
}
// Update the maximum amount too to be able to detect incompatible
// channels.
max := r.max
if maxHtlc < r.max {
max = maxHtlc
}
// If we get in the situation that the minimum amount exceeds the
// maximum amount (enforced further down stream), we have incompatible
// channel policies.
//
// There is possibility with pubkey addressing that we should have
// selected a different channel downstream, but we don't backtrack to
// try to fix that. It would complicate path finding while we expect
// this situation to be rare. The spec recommends to keep all policies
// towards a peer identical. If that is the case, there isn't a better
// channel that we should have selected.
if amt > max {
return runningAmounts{},
fmt.Errorf("incompatible channel policies: %v "+
"exceeds %v", amt, max)
}
// Add fees to the running amounts. Skip the source node fees as
// those do not need to be paid.
if !localChan {
amt += policy.ComputeFee(amt)
max += policy.ComputeFee(max)
}
return runningAmounts{amt: amt, max: max}, nil
}
// ErrNoChannel is returned when a route cannot be built because there are no
// channels that satisfy all requirements.
type ErrNoChannel struct {
@ -2374,24 +2290,21 @@ func (r *ChannelRouter) BuildRoute(amt *lnwire.MilliSatoshi,
return nil, err
}
// Allocate a list that will contain the selected channels for this
// Allocate a list that will contain the unified policies for this
// route.
edges := make([]*channeldb.ChannelEdgePolicy, len(hops))
edges := make([]*unifiedPolicy, len(hops))
// Keep a running amount and the maximum for this route.
amts := runningAmounts{
max: lnwire.MilliSatoshi(^uint64(0)),
}
var runningAmt lnwire.MilliSatoshi
if useMinAmt {
// For minimum amount routes, aim to deliver at least 1 msat to
// the destination. There are nodes in the wild that have a
// min_htlc channel policy of zero, which could lead to a zero
// amount payment being made.
amts.amt = 1
runningAmt = 1
} else {
// If an amount is specified, we need to build a route that
// delivers exactly this amount to the final destination.
amts.amt = *amt
runningAmt = *amt
}
// Traverse hops backwards to accumulate fees in the running amounts.
@ -2408,142 +2321,85 @@ func (r *ChannelRouter) BuildRoute(amt *lnwire.MilliSatoshi,
localChan := i == 0
// Iterate over candidate channels to select the channel
// to use for the final route.
var (
bestEdge *channeldb.ChannelEdgePolicy
bestAmts *runningAmounts
bestBandwidth lnwire.MilliSatoshi
)
// Build unified policies for this hop based on the channels
// known in the graph.
u := newUnifiedPolicies(source, toNode, outgoingChan)
cb := func(tx *bbolt.Tx,
edgeInfo *channeldb.ChannelEdgeInfo,
_, inEdge *channeldb.ChannelEdgePolicy) error {
chanID := edgeInfo.ChannelID
// Apply outgoing channel restriction is active.
if localChan && outgoingChan != nil &&
chanID != *outgoingChan {
return nil
}
// No unknown policy channels.
if inEdge == nil {
return nil
}
// 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.
chanFromNode, err := edgeInfo.FetchOtherNode(
tx, toNode[:],
)
if err != nil {
return err
}
// Continue searching if this channel doesn't
// connect with the previous hop.
if chanFromNode.PubKeyBytes != fromNode {
return nil
}
// Validate whether this channel's policy is satisfied
// and obtain the new running amounts if this channel
// was to be selected.
newAmts, err := amts.prependChannel(
inEdge, edgeInfo.Capacity, localChan,
useMinAmt,
)
if err != nil {
log.Tracef("Skipping chan %v: %v",
inEdge.ChannelID, err)
return nil
}
// If we already have a best edge, check whether this
// edge is better.
bandwidth := bandwidthHints[chanID]
if bestEdge != nil {
if localChan {
// For local channels, better is defined
// as having more bandwidth. We try to
// maximize the chance that the returned
// route succeeds.
if bandwidth < bestBandwidth {
return nil
}
} else {
// For other channels, better is defined
// as lower fees for the amount to send.
// Normally all channels between two
// nodes should have the same policy,
// but in case not we minimize our cost
// here. Regular path finding would do
// the same.
if newAmts.amt > bestAmts.amt {
return nil
}
}
}
// If we get here, the current edge is better. Replace
// the best.
bestEdge = inEdge
bestAmts = &newAmts
bestBandwidth = bandwidth
return nil
}
err := r.cfg.Graph.ForEachNodeChannel(nil, toNode[:], cb)
err := u.addGraphPolicies(r.cfg.Graph, nil)
if err != nil {
return nil, err
}
// There is no matching channel. Stop building the route here.
if bestEdge == nil {
// Exit if there are no channels.
unifiedPolicy, ok := u.policies[fromNode]
if !ok {
return nil, ErrNoChannel{
fromNode: fromNode,
position: i,
}
}
log.Tracef("Select channel %v at position %v", bestEdge.ChannelID, i)
// If using min amt, increase amt if needed.
if useMinAmt {
min := unifiedPolicy.minAmt()
if min > runningAmt {
runningAmt = min
}
}
edges[i] = bestEdge
amts = *bestAmts
// Get a forwarding policy for the specific amount that we want
// to forward.
policy := unifiedPolicy.getPolicy(runningAmt, bandwidthHints)
if policy == nil {
return nil, ErrNoChannel{
fromNode: fromNode,
position: i,
}
}
// Add fee for this hop.
if !localChan {
runningAmt += policy.ComputeFee(runningAmt)
}
log.Tracef("Select channel %v at position %v", policy.ChannelID, i)
edges[i] = unifiedPolicy
}
// Now that we arrived at the start of the route and found out the route
// total amount, we make a forward pass. Because the amount may have
// been increased in the backward pass, fees need to be recalculated and
// amount ranges re-checked.
var pathEdges []*channeldb.ChannelEdgePolicy
receiverAmt := runningAmt
for i, edge := range edges {
policy := edge.getPolicy(receiverAmt, bandwidthHints)
if policy == nil {
return nil, ErrNoChannel{
fromNode: hops[i-1],
position: i,
}
}
if i > 0 {
// Decrease the amount to send while going forward.
receiverAmt -= policy.ComputeFeeFromIncoming(
receiverAmt,
)
}
pathEdges = append(pathEdges, policy)
}
// Build and return the final route.
_, height, err := r.cfg.Chain.GetBestBlock()
if err != nil {
return nil, err
}
var receiverAmt lnwire.MilliSatoshi
if useMinAmt {
// We've calculated the minimum amount for the htlc that the
// source node hands out. The newRoute call below expects the
// amount that must reach the receiver after subtraction of fees
// along the way. Iterate over all edges to calculate the
// receiver amount.
receiverAmt = amts.amt
for _, edge := range edges[1:] {
receiverAmt -= edge.ComputeFeeFromIncoming(receiverAmt)
}
} else {
// Deliver the specified amount to the receiver.
receiverAmt = *amt
}
// Build and return the final route.
return newRoute(
receiverAmt, source, edges, uint32(height),
receiverAmt, source, pathEdges, uint32(height),
uint16(finalCltvDelta), nil,
)
}

18
routing/router_test.go
View File

@ -3434,10 +3434,10 @@ func TestBuildRoute(t *testing.T) {
}
// Check that we get the expected route back. The total amount should be
// the amount to deliver to hop c (100 sats) plus the fee for hop b (5
// sats).
checkHops(rt, []uint64{1, 2})
if rt.TotalAmount != 105000 {
// the amount to deliver to hop c (100 sats) plus the max fee for the
// connection b->c (6 sats).
checkHops(rt, []uint64{1, 7})
if rt.TotalAmount != 106000 {
t.Fatalf("unexpected total amount %v", rt.TotalAmount)
}
@ -3450,11 +3450,11 @@ func TestBuildRoute(t *testing.T) {
}
// Check that we get the expected route back. The minimum that we can
// send from b to c is 20 sats. Hop b charges 1 sat for the forwarding.
// The channel between hop a and b can carry amounts in the range [5,
// 100], so 21 sats is the minimum amount for this route.
checkHops(rt, []uint64{1, 2})
if rt.TotalAmount != 21000 {
// send from b to c is 20 sats. Hop b charges 1200 msat for the
// forwarding. The channel between hop a and b can carry amounts in the
// range [5, 100], so 21200 msats is the minimum amount for this route.
checkHops(rt, []uint64{1, 7})
if rt.TotalAmount != 21200 {
t.Fatalf("unexpected total amount %v", rt.TotalAmount)
}

12
routing/unified_policies.go
View File

@ -267,3 +267,15 @@ func (u *unifiedPolicy) getPolicyNetwork(
return &modifiedPolicy
}
// minAmt returns the minimum amount that can be forwarded on this connection.
func (u *unifiedPolicy) minAmt() lnwire.MilliSatoshi {
min := lnwire.MaxMilliSatoshi
for _, edge := range u.edges {
if edge.policy.MinHTLC < min {
min = edge.policy.MinHTLC
}
}
return min
}