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unified_edges.go
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unified_edges.go
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package routing
import (
"math"
"github.com/btcsuite/btcd/btcutil"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/channeldb/models"
"github.com/lightningnetwork/lnd/lntypes"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/routing/route"
)
// nodeEdgeUnifier holds all edge unifiers for connections towards a node.
type nodeEdgeUnifier struct {
// edgeUnifiers contains an edge unifier for every from node.
edgeUnifiers map[route.Vertex]*edgeUnifier
// sourceNode is the sender of a payment. The rules to pick the final
// policy are different for local channels.
sourceNode route.Vertex
// toNode is the node for which the edge unifiers are instantiated.
toNode route.Vertex
// useInboundFees indicates whether to take inbound fees into account.
useInboundFees bool
// outChanRestr is an optional outgoing channel restriction for the
// local channel to use.
outChanRestr map[uint64]struct{}
}
// newNodeEdgeUnifier instantiates a new nodeEdgeUnifier object. Channel
// policies can be added to this object.
func newNodeEdgeUnifier(sourceNode, toNode route.Vertex, useInboundFees bool,
outChanRestr map[uint64]struct{}) *nodeEdgeUnifier {
return &nodeEdgeUnifier{
edgeUnifiers: make(map[route.Vertex]*edgeUnifier),
toNode: toNode,
useInboundFees: useInboundFees,
sourceNode: sourceNode,
outChanRestr: outChanRestr,
}
}
// addPolicy adds a single channel policy. Capacity may be zero if unknown
// (light clients). We expect a non-nil payload size function and will request a
// graceful shutdown if it is not provided as this indicates that edges are
// incorrectly specified.
func (u *nodeEdgeUnifier) addPolicy(fromNode route.Vertex,
edge *models.CachedEdgePolicy, inboundFee models.InboundFee,
capacity btcutil.Amount, hopPayloadSizeFn PayloadSizeFunc) {
localChan := fromNode == u.sourceNode
// Skip channels if there is an outgoing channel restriction.
if localChan && u.outChanRestr != nil {
if _, ok := u.outChanRestr[edge.ChannelID]; !ok {
return
}
}
// Update the edgeUnifiers map.
unifier, ok := u.edgeUnifiers[fromNode]
if !ok {
unifier = &edgeUnifier{
localChan: localChan,
}
u.edgeUnifiers[fromNode] = unifier
}
// In case no payload size function was provided a graceful shutdown
// is requested, because this function is not used as intended.
if hopPayloadSizeFn == nil {
log.Criticalf("No payloadsize function was provided for the "+
"edge (chanid=%v) when adding it to the edge unifier "+
"of node: %v", edge.ChannelID, fromNode)
return
}
// Zero inbound fee for exit hops.
if !u.useInboundFees {
inboundFee = models.InboundFee{}
}
unifier.edges = append(unifier.edges, &unifiedEdge{
policy: edge,
capacity: capacity,
hopPayloadSizeFn: hopPayloadSizeFn,
inboundFees: inboundFee,
})
}
// addGraphPolicies adds all policies that are known for the toNode in the
// graph.
func (u *nodeEdgeUnifier) addGraphPolicies(g routingGraph) error {
cb := func(channel *channeldb.DirectedChannel) 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 channel.InPolicy == nil {
return nil
}
// Add this policy to the corresponding edgeUnifier. We default
// to the clear hop payload size function because
// `addGraphPolicies` is only used for cleartext intermediate
// hops in a route.
inboundFee := models.NewInboundFeeFromWire(
channel.InboundFee,
)
u.addPolicy(
channel.OtherNode, channel.InPolicy, inboundFee,
channel.Capacity, defaultHopPayloadSize,
)
return nil
}
// Iterate over all channels of the to node.
return g.forEachNodeChannel(u.toNode, cb)
}
// unifiedEdge is the individual channel data that is kept inside an edgeUnifier
// object.
type unifiedEdge struct {
policy *models.CachedEdgePolicy
capacity btcutil.Amount
inboundFees models.InboundFee
// hopPayloadSize supplies an edge with the ability to calculate the
// exact payload size if this edge would be included in a route. This
// is needed because hops of a blinded path differ in their payload
// structure compared to cleartext hops.
hopPayloadSizeFn PayloadSizeFunc
}
// amtInRange checks whether an amount falls within the valid range for a
// channel.
func (u *unifiedEdge) amtInRange(amt lnwire.MilliSatoshi) bool {
// If the capacity is available (non-light clients), skip channels that
// are too small.
if u.capacity > 0 &&
amt > lnwire.NewMSatFromSatoshis(u.capacity) {
log.Tracef("Not enough capacity: amt=%v, capacity=%v",
amt, u.capacity)
return false
}
// Skip channels for which this htlc is too large.
if u.policy.MessageFlags.HasMaxHtlc() &&
amt > u.policy.MaxHTLC {
log.Tracef("Exceeds policy's MaxHTLC: amt=%v, MaxHTLC=%v",
amt, u.policy.MaxHTLC)
return false
}
// Skip channels for which this htlc is too small.
if amt < u.policy.MinHTLC {
log.Tracef("below policy's MinHTLC: amt=%v, MinHTLC=%v",
amt, u.policy.MinHTLC)
return false
}
return true
}
// edgeUnifier is an object that covers all channels between a pair of nodes.
type edgeUnifier struct {
edges []*unifiedEdge
localChan bool
}
// getEdge returns the optimal unified edge to use for this connection given a
// specific amount to send. It differentiates between local and network
// channels.
func (u *edgeUnifier) getEdge(netAmtReceived lnwire.MilliSatoshi,
bandwidthHints bandwidthHints,
nextOutFee lnwire.MilliSatoshi) *unifiedEdge {
if u.localChan {
return u.getEdgeLocal(
netAmtReceived, bandwidthHints, nextOutFee,
)
}
return u.getEdgeNetwork(netAmtReceived, nextOutFee)
}
// calcCappedInboundFee calculates the inbound fee for a channel, taking into
// account the total node fee for the "to" node.
func calcCappedInboundFee(edge *unifiedEdge, amt lnwire.MilliSatoshi,
nextOutFee lnwire.MilliSatoshi) int64 {
// Calculate the inbound fee charged for the amount that passes over the
// channel.
inboundFee := edge.inboundFees.CalcFee(amt)
// Take into account that the total node fee cannot be negative.
if inboundFee < -int64(nextOutFee) {
inboundFee = -int64(nextOutFee)
}
return inboundFee
}
// getEdgeLocal returns the optimal unified edge to use for this local
// connection given a specific amount to send.
func (u *edgeUnifier) getEdgeLocal(netAmtReceived lnwire.MilliSatoshi,
bandwidthHints bandwidthHints,
nextOutFee lnwire.MilliSatoshi) *unifiedEdge {
var (
bestEdge *unifiedEdge
maxBandwidth lnwire.MilliSatoshi
)
for _, edge := range u.edges {
// Calculate the inbound fee charged at the receiving node.
inboundFee := calcCappedInboundFee(
edge, netAmtReceived, nextOutFee,
)
// Add inbound fee to get to the amount that is sent over the
// local channel.
amt := netAmtReceived + lnwire.MilliSatoshi(inboundFee)
// Check valid amount range for the channel.
if !edge.amtInRange(amt) {
log.Debugf("Amount %v not in range for edge %v",
netAmtReceived, edge.policy.ChannelID)
continue
}
// For local channels, there is no fee to pay or an extra time
// lock. We only consider the currently available bandwidth for
// channel selection. The disabled flag is ignored for local
// channels.
// Retrieve bandwidth for this local channel. If not
// available, assume this channel has enough bandwidth.
//
// TODO(joostjager): Possibly change to skipping this
// channel. The bandwidth hint is expected to be
// available.
bandwidth, ok := bandwidthHints.availableChanBandwidth(
edge.policy.ChannelID, amt,
)
if !ok {
log.Debugf("Cannot get bandwidth for edge %v, use max "+
"instead", edge.policy.ChannelID)
bandwidth = lnwire.MaxMilliSatoshi
}
// TODO(yy): if the above `!ok` is chosen, we'd have
// `bandwidth` to be the max value, which will end up having
// the `maxBandwidth` to be have the largest value and this
// edge will be the chosen one. This is wrong in two ways,
// 1. we need to understand why `availableChanBandwidth` cannot
// find bandwidth for this edge as something is wrong with this
// channel, and,
// 2. this edge is likely NOT the local channel with the
// highest available bandwidth.
//
// Skip channels that can't carry the payment.
if amt > bandwidth {
log.Debugf("Skipped edge %v: not enough bandwidth, "+
"bandwidth=%v, amt=%v", edge.policy.ChannelID,
bandwidth, amt)
continue
}
// We pick the local channel with the highest available
// bandwidth, to maximize the success probability. It
// can be that the channel state changes between
// querying the bandwidth hints and sending out the
// htlc.
if bandwidth < maxBandwidth {
log.Debugf("Skipped edge %v: not max bandwidth, "+
"bandwidth=%v, maxBandwidth=%v",
bandwidth, maxBandwidth)
continue
}
maxBandwidth = bandwidth
// Update best edge.
bestEdge = &unifiedEdge{
policy: edge.policy,
capacity: edge.capacity,
hopPayloadSizeFn: edge.hopPayloadSizeFn,
inboundFees: edge.inboundFees,
}
}
return bestEdge
}
// getEdgeNetwork returns the optimal unified edge to use for this connection
// given a specific amount to send. The goal is to return a unified edge with a
// policy that maximizes the probability of a successful forward in a non-strict
// forwarding context.
func (u *edgeUnifier) getEdgeNetwork(netAmtReceived lnwire.MilliSatoshi,
nextOutFee lnwire.MilliSatoshi) *unifiedEdge {
var (
bestPolicy *unifiedEdge
maxFee int64 = math.MinInt64
maxTimelock uint16
maxCapMsat lnwire.MilliSatoshi
hopPayloadSizeFn PayloadSizeFunc
)
for _, edge := range u.edges {
// Calculate the inbound fee charged at the receiving node.
inboundFee := calcCappedInboundFee(
edge, netAmtReceived, nextOutFee,
)
// Add inbound fee to get to the amount that is sent over the
// channel.
amt := netAmtReceived + lnwire.MilliSatoshi(inboundFee)
// Check valid amount range for the channel.
if !edge.amtInRange(amt) {
log.Debugf("Amount %v not in range for edge %v",
amt, edge.policy.ChannelID)
continue
}
// For network channels, skip the disabled ones.
edgeFlags := edge.policy.ChannelFlags
isDisabled := edgeFlags&lnwire.ChanUpdateDisabled != 0
if isDisabled {
log.Debugf("Skipped edge %v due to it being disabled",
edge.policy.ChannelID)
continue
}
// Track the maximal capacity for usable channels. If we don't
// know the capacity, we fall back to MaxHTLC.
capMsat := lnwire.NewMSatFromSatoshis(edge.capacity)
if capMsat == 0 && edge.policy.MessageFlags.HasMaxHtlc() {
log.Tracef("No capacity available for channel %v, "+
"using MaxHtlcMsat (%v) as a fallback.",
edge.policy.ChannelID, edge.policy.MaxHTLC)
capMsat = edge.policy.MaxHTLC
}
maxCapMsat = lntypes.Max(capMsat, maxCapMsat)
// Track the maximum time lock of all channels that are
// candidate for non-strict forwarding at the routing node.
maxTimelock = lntypes.Max(
maxTimelock, edge.policy.TimeLockDelta,
)
outboundFee := int64(edge.policy.ComputeFee(amt))
fee := outboundFee + inboundFee
// Use the policy that results in the highest fee for this
// specific amount.
if fee < maxFee {
log.Debugf("Skipped edge %v due to it produces less "+
"fee: fee=%v, maxFee=%v",
edge.policy.ChannelID, fee, maxFee)
continue
}
maxFee = fee
bestPolicy = &unifiedEdge{
policy: edge.policy,
inboundFees: edge.inboundFees,
}
// The payload size function for edges to a connected peer is
// always the same hence there is not need to find the maximum.
// This also counts for blinded edges where we only have one
// edge to a blinded peer.
hopPayloadSizeFn = edge.hopPayloadSizeFn
}
// Return early if no channel matches.
if bestPolicy == nil {
return nil
}
// We have already picked the highest fee that could be required for
// non-strict forwarding. To also cover the case where a lower fee
// channel requires a longer time lock, we modify the policy by setting
// the maximum encountered time lock. Note that this results in a
// synthetic policy that is not actually present on the routing node.
//
// The reason we do this, is that we try to maximize the chance that we
// get forwarded. Because we penalize pair-wise, there won't be a second
// chance for this node pair. But this is all only needed for nodes that
// have distinct policies for channels to the same peer.
policyCopy := *bestPolicy.policy
modifiedEdge := unifiedEdge{
policy: &policyCopy,
inboundFees: bestPolicy.inboundFees,
}
modifiedEdge.policy.TimeLockDelta = maxTimelock
modifiedEdge.capacity = maxCapMsat.ToSatoshis()
modifiedEdge.hopPayloadSizeFn = hopPayloadSizeFn
return &modifiedEdge
}
// minAmt returns the minimum amount that can be forwarded on this connection.
func (u *edgeUnifier) minAmt() lnwire.MilliSatoshi {
min := lnwire.MaxMilliSatoshi
for _, edge := range u.edges {
min = lntypes.Min(min, edge.policy.MinHTLC)
}
return min
}