walletrpc: add sat_per_kw fee rate option

To allow more precise fee rates, we add a sat_per_kw option to the fee
oneof in the gRPC definition.

lnrpc/walletrpc/walletkit.pb.go

@@ -3645,6 +3645,7 @@ type FundPsbtRequest struct {
 	//
 	//	*FundPsbtRequest_TargetConf
 	//	*FundPsbtRequest_SatPerVbyte
+	//	*FundPsbtRequest_SatPerKw
 	Fees isFundPsbtRequest_Fees `protobuf_oneof:"fees"`
 	// The name of the account to fund the PSBT with. If empty, the default wallet
 	// account is used.
@@ -3744,6 +3745,13 @@ func (x *FundPsbtRequest) GetSatPerVbyte() uint64 {
 	return 0
 }
 
+func (x *FundPsbtRequest) GetSatPerKw() uint64 {
+	if x, ok := x.GetFees().(*FundPsbtRequest_SatPerKw); ok {
+		return x.SatPerKw
+	}
+	return 0
+}
+
 func (x *FundPsbtRequest) GetAccount() string {
 	if x != nil {
 		return x.Account
@@ -3841,10 +3849,18 @@ type FundPsbtRequest_SatPerVbyte struct {
 	SatPerVbyte uint64 `protobuf:"varint,4,opt,name=sat_per_vbyte,json=satPerVbyte,proto3,oneof"`
 }
 
+type FundPsbtRequest_SatPerKw struct {
+	// The fee rate, expressed in sat/kWU, that should be used to spend the
+	// input with.
+	SatPerKw uint64 `protobuf:"varint,11,opt,name=sat_per_kw,json=satPerKw,proto3,oneof"`
+}
+
 func (*FundPsbtRequest_TargetConf) isFundPsbtRequest_Fees() {}
 
 func (*FundPsbtRequest_SatPerVbyte) isFundPsbtRequest_Fees() {}
 
+func (*FundPsbtRequest_SatPerKw) isFundPsbtRequest_Fees() {}
+
 type FundPsbtResponse struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -4905,7 +4921,7 @@ var file_walletrpc_walletkit_proto_rawDesc = []byte{
 	0x65, 0x6c, 0x12, 0x1c, 0x0a, 0x09, 0x6f, 0x76, 0x65, 0x72, 0x77, 0x72, 0x69, 0x74, 0x65, 0x18,
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@@ -4919,7 +4935,9 @@ var file_walletrpc_walletkit_proto_rawDesc = []byte{
 	0x20, 0x01, 0x28, 0x0d, 0x48, 0x01, 0x52, 0x0a, 0x74, 0x61, 0x72, 0x67, 0x65, 0x74, 0x43, 0x6f,
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@@ -6200,6 +6218,7 @@ func file_walletrpc_walletkit_proto_init() {
 		(*FundPsbtRequest_CoinSelect)(nil),
 		(*FundPsbtRequest_TargetConf)(nil),
 		(*FundPsbtRequest_SatPerVbyte)(nil),
+		(*FundPsbtRequest_SatPerKw)(nil),
 	}
 	file_walletrpc_walletkit_proto_msgTypes[53].OneofWrappers = []interface{}{
 		(*PsbtCoinSelect_ExistingOutputIndex)(nil),

lnrpc/walletrpc/walletkit.proto

@@ -1388,6 +1388,12 @@ message FundPsbtRequest {
         input with.
         */
         uint64 sat_per_vbyte = 4;
+
+        /*
+        The fee rate, expressed in sat/kWU, that should be used to spend the
+        input with.
+        */
+        uint64 sat_per_kw = 11;
     }
 
     /*

lnrpc/walletrpc/walletkit.swagger.json

@@ -1564,6 +1564,11 @@
           "format": "uint64",
           "description": "The fee rate, expressed in sat/vbyte, that should be used to spend the\ninput with."
         },
+        "sat_per_kw": {
+          "type": "string",
+          "format": "uint64",
+          "description": "The fee rate, expressed in sat/kWU, that should be used to spend the\ninput with."
+        },
         "account": {
           "type": "string",
           "description": "The name of the account to fund the PSBT with. If empty, the default wallet\naccount is used."

lnrpc/walletrpc/walletkit_server.go

@@ -1511,9 +1511,13 @@ func (w *WalletKit) FundPsbt(_ context.Context,
 			req.GetSatPerVbyte() * 1000,
 		).FeePerKWeight()
 
+	case req.GetSatPerKw() != 0:
+		feeSatPerKW = chainfee.SatPerKWeight(req.GetSatPerKw())
+
 	default:
 		return nil, fmt.Errorf("fee definition missing, need to " +
-			"specify either target_conf or sat_per_vbyte")
+			"specify either target_conf, sat_per_vbyte or " +
+			"sat_per_kw")
 	}
 
 	// Then, we'll extract the minimum number of confirmations that each