Merge pull request #8908 from lightningnetwork/traffic-shaper-htlc-amount-fix

routing: don't assume HTLC amount for custom channel

htlcswitch/interceptable_switch.go

@@ -658,6 +658,7 @@ func (f *interceptedForward) ResumeModified(
 	switch htlc := f.packet.htlc.(type) {
 	case *lnwire.UpdateAddHTLC:
 		outgoingAmountMsat.WhenSome(func(amount lnwire.MilliSatoshi) {
+			f.packet.amount = amount
 			htlc.Amount = amount
 		})
 

itest/lnd_forward_interceptor_test.go

@@ -407,7 +407,7 @@ func testForwardInterceptorModifiedHtlc(ht *lntest.HarnessTest) {
 	customRecords[crKey] = crValue
 
 	action := routerrpc.ResolveHoldForwardAction_RESUME_MODIFIED
-	newOutgoingAmountMsat := packet.OutgoingAmountMsat + 4000
+	newOutgoingAmountMsat := packet.OutgoingAmountMsat
 
 	err := bobInterceptor.Send(&routerrpc.ForwardHtlcInterceptResponse{
 		IncomingCircuitKey:            packet.IncomingCircuitKey,
@@ -539,7 +539,7 @@ func testForwardInterceptorWireRecords(ht *lntest.HarnessTest) {
 	require.Equal(ht, []byte("test"), val)
 
 	action := routerrpc.ResolveHoldForwardAction_RESUME_MODIFIED
-	newOutgoingAmountMsat := packet.OutgoingAmountMsat + 800
+	newOutgoingAmountMsat := packet.OutgoingAmountMsat
 
 	err := bobInterceptor.Send(&routerrpc.ForwardHtlcInterceptResponse{
 		IncomingCircuitKey: packet.IncomingCircuitKey,

routing/bandwidth.go

@@ -138,6 +138,13 @@ func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID,
 
 		auxBandwidth           lnwire.MilliSatoshi
 		auxBandwidthDetermined bool
+
+		// htlcAmount is the amount we're going to use to check if we
+		// can add another HTLC to the channel. If the external traffic
+		// shaper is handling the channel, we'll use 0 to just sanity
+		// check the number of HTLCs on the channel, since we don't know
+		// the actual HTLC amount that will be sent.
+		htlcAmount = amount
 	)
 	err = fn.MapOptionZ(b.trafficShaper, func(ts TlvTrafficShaper) error {
 		fundingBlob := link.FundingCustomBlob()
@@ -171,6 +178,15 @@ func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID,
 
 		auxBandwidthDetermined = true
 
+		// We don't know the actual HTLC amount that will be sent using
+		// the custom channel. But we'll still want to make sure we can
+		// add another HTLC, using the MayAddOutgoingHtlc method below.
+		// Passing 0 into that method will use the minimum HTLC value
+		// for the channel, which is okay to just check we don't exceed
+		// the max number of HTLCs on the channel. A proper balance
+		// check is done elsewhere.
+		htlcAmount = 0
+
 		return nil
 	})
 	if err != nil {
@@ -180,11 +196,11 @@ func (b *bandwidthManager) getBandwidth(cid lnwire.ShortChannelID,
 		return 0
 	}
 
-	// If our link isn't currently in a state where it can add
-	// another outgoing htlc, treat the link as unusable.
-	if err := link.MayAddOutgoingHtlc(amount); err != nil {
+	// If our link isn't currently in a state where it can add another
+	// outgoing htlc, treat the link as unusable.
+	if err := link.MayAddOutgoingHtlc(htlcAmount); err != nil {
 		log.Warnf("ShortChannelID=%v: cannot add outgoing "+
-			"htlc: %v", cid, err)
+			"htlc with amount %v: %v", cid, htlcAmount, err)
 		return 0
 	}
 

routing/pathfind.go

@@ -1007,18 +1007,22 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 				continue
 			}
 
-			firstHopTLVs := lnwire.CustomRecords(
-				r.FirstHopCustomRecords,
-			)
-			firstHopData, err := firstHopTLVs.Serialize()
-			if err != nil {
-				return nil, 0, err
+			var firstHopBlob fn.Option[tlv.Blob]
+			if r.FirstHopCustomRecords != nil {
+				firstHopTLVs := lnwire.CustomRecords(
+					r.FirstHopCustomRecords,
+				)
+				firstHopData, err := firstHopTLVs.Serialize()
+				if err != nil {
+					return nil, 0, err
+				}
+
+				firstHopBlob = fn.Some(firstHopData)
 			}
 
 			edge := edgeUnifier.getEdge(
 				netAmountReceived, g.bandwidthHints,
-				partialPath.outboundFee,
-				fn.Some[tlv.Blob](firstHopData),
+				partialPath.outboundFee, firstHopBlob,
 			)
 
 			if edge == nil {

routing/unified_edges.go

@@ -234,7 +234,7 @@ func (u *edgeUnifier) getEdgeLocal(netAmtReceived lnwire.MilliSatoshi,
 		amt := netAmtReceived + lnwire.MilliSatoshi(inboundFee)
 
 		// Check valid amount range for the channel.
-		if !edge.amtInRange(amt) {
+		if htlcBlob.IsNone() && !edge.amtInRange(amt) {
 			log.Debugf("Amount %v not in range for edge %v",
 				netAmtReceived, edge.policy.ChannelID)