routing+lnrpc: add inbound fee policy update

Author: joostjager

cmd/lncli/commands.go

@@ -2091,6 +2091,31 @@ var updateChannelPolicyCommand = cli.Command{
 				"0.000001 (millionths). Can not be set at " +
 				"the same time as fee_rate",
 		},
+		cli.Int64Flag{
+			Name: "inbound_base_fee_msat",
+			Usage: "the base inbound fee in milli-satoshis that " +
+				"will be charged for each forwarded HTLC, " +
+				"regardless of payment size. Its value must " +
+				"be zero or negative - it is a discount " +
+				"for using a particular incoming channel. " +
+				"Note that forwards will be rejected if the " +
+				"discount exceeds the outbound fee " +
+				"(forward at a loss), and lead to " +
+				"penalization by the sender",
+		},
+		cli.Int64Flag{
+			Name: "inbound_fee_rate_ppm",
+			Usage: "the inbound fee rate that will be charged " +
+				"proportionally based on the value of each " +
+				"forwarded HTLC and the outbound fee. Fee " +
+				"rate is expressed in parts per million and " +
+				"must be zero or negative - it is a discount " +
+				"for using a particular incoming channel." +
+				"Note that forwards will be rejected if the " +
+				"discount exceeds the outbound fee " +
+				"(forward at a loss), and lead to " +
+				"penalization by the sender",
+		},
 		cli.Uint64Flag{
 			Name: "time_lock_delta",
 			Usage: "the CLTV delta that will be applied to all " +
@@ -2242,10 +2267,26 @@ func updateChannelPolicy(ctx *cli.Context) error {
 		}
 	}
 
+	inboundBaseFeeMsat := ctx.Int64("inbound_base_fee_msat")
+	if inboundBaseFeeMsat < math.MinInt32 ||
+		inboundBaseFeeMsat > 0 {
+
+		return errors.New("inbound_base_fee_msat out of range")
+	}
+
+	inboundFeeRatePpm := ctx.Int64("inbound_fee_rate_ppm")
+	if inboundFeeRatePpm < math.MinInt32 ||
+		inboundFeeRatePpm > 0 {
+
+		return errors.New("inbound_fee_rate_ppm out of range")
+	}
+
 	req := &lnrpc.PolicyUpdateRequest{
-		BaseFeeMsat:   baseFee,
-		TimeLockDelta: uint32(timeLockDelta),
-		MaxHtlcMsat:   ctx.Uint64("max_htlc_msat"),
+		BaseFeeMsat:        baseFee,
+		TimeLockDelta:      uint32(timeLockDelta),
+		MaxHtlcMsat:        ctx.Uint64("max_htlc_msat"),
+		InboundBaseFeeMsat: int32(inboundBaseFeeMsat),
+		InboundFeeRatePpm:  int32(inboundFeeRatePpm),
 	}
 
 	if ctx.IsSet("min_htlc_msat") {

lnrpc/lightning.pb.go

@@ -4274,7 +4274,15 @@ message ChannelFeeReport {
     // The effective fee rate in milli-satoshis. Computed by dividing the
     // fee_per_mil value by 1 million.
     double fee_rate = 4;
+
+    // The base fee charged regardless of the number of milli-satoshis sent.
+    int32 inbound_base_fee_msat = 6;
+
+    // The amount charged per milli-satoshis transferred expressed in
+    // millionths of a satoshi.
+    int32 inbound_fee_per_mil = 7;
 }
+
 message FeeReportResponse {
     // An array of channel fee reports which describes the current fee schedule
     // for each channel.
@@ -4325,7 +4333,11 @@ message PolicyUpdateRequest {
 
     // If true, min_htlc_msat is applied.
     bool min_htlc_msat_specified = 8;
+
+    int32 inbound_base_fee_msat = 10;
+    int32 inbound_fee_rate_ppm = 11;
 }
+
 enum UpdateFailure {
     UPDATE_FAILURE_UNKNOWN = 0;
     UPDATE_FAILURE_PENDING = 1;

lnrpc/lightning.proto

@@ -4194,6 +4194,16 @@
           "type": "number",
           "format": "double",
           "description": "The effective fee rate in milli-satoshis. Computed by dividing the\nfee_per_mil value by 1 million."
+        },
+        "inbound_base_fee_msat": {
+          "type": "integer",
+          "format": "int32",
+          "description": "The base fee charged regardless of the number of milli-satoshis sent."
+        },
+        "inbound_fee_per_mil": {
+          "type": "integer",
+          "format": "int32",
+          "description": "The amount charged per milli-satoshis transferred expressed in\nmillionths of a satoshi."
         }
       }
     },
@@ -6469,6 +6479,14 @@
         "min_htlc_msat_specified": {
           "type": "boolean",
           "description": "If true, min_htlc_msat is applied."
+        },
+        "inbound_base_fee_msat": {
+          "type": "integer",
+          "format": "int32"
+        },
+        "inbound_fee_rate_ppm": {
+          "type": "integer",
+          "format": "int32"
         }
       }
     },

lnrpc/lightning.swagger.json

@@ -112,6 +112,7 @@ func (r *Manager) UpdatePolicy(newSchema routing.ChannelPolicy,
 			TimeLockDelta: uint32(edge.TimeLockDelta),
 			MinHTLCOut:    edge.MinHTLC,
 			MaxHTLC:       edge.MaxHTLC,
+			InboundFee:    newSchema.InboundFee,
 		}
 
 		return nil
@@ -180,6 +181,12 @@ func (r *Manager) updateEdge(tx kvdb.RTx, chanPoint wire.OutPoint,
 	edge.FeeProportionalMillionths = lnwire.MilliSatoshi(
 		newSchema.FeeRate,
 	)
+
+	inboundFee := newSchema.InboundFee.ToWire()
+	if err := edge.ExtraOpaqueData.PackRecords(&inboundFee); err != nil {
+		return err
+	}
+
 	edge.TimeLockDelta = uint16(newSchema.TimeLockDelta)
 
 	// Retrieve negotiated channel htlc amt limits.

routing/localchans/manager.go

@@ -287,6 +287,10 @@ type FeeSchema struct {
 	// the effective fee rate charged per mSAT will be: (amount *
 	// FeeRate/1,000,000).
 	FeeRate uint32
+
+	// InboundFee is the inbound fee schedule that applies to forwards
+	// coming in through a channel to which this FeeSchema pertains.
+	InboundFee models.InboundFee
 }
 
 // ChannelPolicy holds the parameters that determine the policy we enforce

routing/router.go

@@ -6811,6 +6811,15 @@ func (r *rpcServer) FeeReport(ctx context.Context,
 				edgePolicy.FeeProportionalMillionths
 			feeRate := float64(feeRateFixedPoint) / feeBase
 
+			// Decode inbound fee from extra data.
+			var inboundFee lnwire.Fee
+			_, err := edgePolicy.ExtraOpaqueData.ExtractRecords(
+				&inboundFee,
+			)
+			if err != nil {
+				return err
+			}
+
 			// TODO(roasbeef): also add stats for revenue for each
 			// channel
 			feeReports = append(feeReports, &lnrpc.ChannelFeeReport{
@@ -6819,6 +6828,9 @@ func (r *rpcServer) FeeReport(ctx context.Context,
 				BaseFeeMsat:  int64(edgePolicy.FeeBaseMSat),
 				FeePerMil:    int64(feeRateFixedPoint),
 				FeeRate:      feeRate,
+
+				InboundBaseFeeMsat: inboundFee.BaseFee,
+				InboundFeePerMil:   inboundFee.FeeRate,
 			})
 
 			return nil
@@ -7005,6 +7017,10 @@ func (r *rpcServer) UpdateChannelPolicy(ctx context.Context,
 	feeSchema := routing.FeeSchema{
 		BaseFee: baseFeeMsat,
 		FeeRate: feeRateFixed,
+		InboundFee: models.InboundFee{
+			Base: req.InboundBaseFeeMsat,
+			Rate: req.InboundFeeRatePpm,
+		},
 	}
 
 	maxHtlc := lnwire.MilliSatoshi(req.MaxHtlcMsat)