routing: inbound fees support for BuildRoute

channeldb/graph_test.go

@@ -3688,7 +3688,7 @@ func TestLightningNodeSigVerification(t *testing.T) {
 	}
 }
 
-// TestComputeFee tests fee calculation based on both in- and outgoing amt.
+// TestComputeFee tests fee calculation based on the outgoing amt.
 func TestComputeFee(t *testing.T) {
 	var (
 		policy = models.ChannelEdgePolicy{
@@ -3703,11 +3703,6 @@ func TestComputeFee(t *testing.T) {
 	if fee != expectedFee {
 		t.Fatalf("expected fee %v, got %v", expectedFee, fee)
 	}
-
-	fwdFee := policy.ComputeFeeFromIncoming(outgoingAmt + fee)
-	if fwdFee != expectedFee {
-		t.Fatalf("expected fee %v, but got %v", fee, fwdFee)
-	}
 }
 
 // TestBatchedAddChannelEdge asserts that BatchedAddChannelEdge properly

channeldb/models/cached_edge_policy.go

@@ -71,17 +71,6 @@ func (c *CachedEdgePolicy) ComputeFee(
 	return c.FeeBaseMSat + (amt*c.FeeProportionalMillionths)/feeRateParts
 }
 
-// ComputeFeeFromIncoming computes the fee to forward an HTLC given the incoming
-// amount.
-func (c *CachedEdgePolicy) ComputeFeeFromIncoming(
-	incomingAmt lnwire.MilliSatoshi) lnwire.MilliSatoshi {
-
-	return incomingAmt - divideCeil(
-		feeRateParts*(incomingAmt-c.FeeBaseMSat),
-		feeRateParts+c.FeeProportionalMillionths,
-	)
-}
-
 // NewCachedPolicy turns a full policy into a minimal one that can be cached.
 func NewCachedPolicy(policy *ChannelEdgePolicy) *CachedEdgePolicy {
 	return &CachedEdgePolicy{

channeldb/models/channel_edge_policy.go

@@ -113,19 +113,3 @@ func (c *ChannelEdgePolicy) ComputeFee(
 
 	return c.FeeBaseMSat + (amt*c.FeeProportionalMillionths)/feeRateParts
 }
-
-// divideCeil divides dividend by factor and rounds the result up.
-func divideCeil(dividend, factor lnwire.MilliSatoshi) lnwire.MilliSatoshi {
-	return (dividend + factor - 1) / factor
-}
-
-// ComputeFeeFromIncoming computes the fee to forward an HTLC given the incoming
-// amount.
-func (c *ChannelEdgePolicy) ComputeFeeFromIncoming(
-	incomingAmt lnwire.MilliSatoshi) lnwire.MilliSatoshi {
-
-	return incomingAmt - divideCeil(
-		feeRateParts*(incomingAmt-c.FeeBaseMSat),
-		feeRateParts+c.FeeProportionalMillionths,
-	)
-}

docs/release-notes/release-notes-0.18.3.md

@@ -84,6 +84,9 @@
 * [`ChanInfoRequest`](https://github.com/lightningnetwork/lnd/pull/8813)
   adds support for channel points.
 
+* [BuildRoute](https://github.com/lightningnetwork/lnd/pull/8886) now supports
+  inbound fees.
+
 ## lncli Updates
 
 * [`importmc`](https://github.com/lightningnetwork/lnd/pull/8779) now accepts

lnrpc/routerrpc/router_server.go

@@ -15,6 +15,7 @@ import (
 	"github.com/btcsuite/btcd/wire"
 	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -1400,6 +1401,10 @@ func (s *Server) trackPaymentStream(context context.Context,
 func (s *Server) BuildRoute(_ context.Context,
 	req *BuildRouteRequest) (*BuildRouteResponse, error) {
 
+	if len(req.HopPubkeys) == 0 {
+		return nil, errors.New("no hops specified")
+	}
+
 	// Unmarshall hop list.
 	hops := make([]route.Vertex, len(req.HopPubkeys))
 	for i, pubkeyBytes := range req.HopPubkeys {
@@ -1411,10 +1416,10 @@ func (s *Server) BuildRoute(_ context.Context,
 	}
 
 	// Prepare BuildRoute call parameters from rpc request.
-	var amt *lnwire.MilliSatoshi
+	var amt fn.Option[lnwire.MilliSatoshi]
 	if req.AmtMsat != 0 {
 		rpcAmt := lnwire.MilliSatoshi(req.AmtMsat)
-		amt = &rpcAmt
+		amt = fn.Some(rpcAmt)
 	}
 
 	var outgoingChan *uint64