lnrpc: move CalculateFeeRate from rpcserver.go to rpc_utils.go

This refactor aims to house the CalculateFeeRate function in a more
"shareable" location. It used to be a non-exported function inside
of rpcserver.go. However, other routines, such as FundPsbt inside
of walletkit_server.go, could also rely on the same fee calculation
functionality. So we move the function to rpc_utils.go and export it,
and we will reuse it in the FundPsbt workflow in a future PR.

lnrpc/rpc_utils.go

@@ -3,10 +3,13 @@ package lnrpc
 import (
 	"encoding/hex"
 	"errors"
+	"fmt"
 	"sort"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+	"github.com/lightningnetwork/lnd/sweep"
 	"google.golang.org/protobuf/encoding/protojson"
 )
 
@@ -193,3 +196,41 @@ func GetChanPointFundingTxid(chanPoint *ChannelPoint) (*chainhash.Hash, error) {
 
 	return chainhash.NewHash(txid)
 }
+
+// CalculateFeeRate uses either satPerByte or satPerVByte, but not both, from a
+// request to calculate the fee rate. It provides compatibility for the
+// deprecated field, satPerByte. Once the field is safe to be removed, the
+// check can then be deleted.
+func CalculateFeeRate(satPerByte, satPerVByte uint64, targetConf uint32,
+	estimator chainfee.Estimator) (chainfee.SatPerKWeight, error) {
+
+	var feeRate chainfee.SatPerKWeight
+
+	// We only allow using either the deprecated field or the new field.
+	if satPerByte != 0 && satPerVByte != 0 {
+		return feeRate, fmt.Errorf("either SatPerByte or " +
+			"SatPerVByte should be set, but not both")
+	}
+
+	// Default to satPerVByte, and overwrite it if satPerByte is set.
+	satPerKw := chainfee.SatPerKVByte(satPerVByte * 1000).FeePerKWeight()
+	if satPerByte != 0 {
+		satPerKw = chainfee.SatPerKVByte(
+			satPerByte * 1000,
+		).FeePerKWeight()
+	}
+
+	// Based on the passed fee related parameters, we'll determine an
+	// appropriate fee rate for this transaction.
+	feeRate, err := sweep.DetermineFeePerKw(
+		estimator, sweep.FeePreference{
+			ConfTarget: targetConf,
+			FeeRate:    satPerKw,
+		},
+	)
+	if err != nil {
+		return feeRate, err
+	}
+
+	return feeRate, nil
+}

rpcserver.go

@@ -222,44 +222,6 @@ func stringInSlice(a string, slice []string) bool {
 	return false
 }
 
-// calculateFeeRate uses either satPerByte or satPerVByte, but not both, from a
-// request to calculate the fee rate. It provides compatibility for the
-// deprecated field, satPerByte. Once the field is safe to be removed, the
-// check can then be deleted.
-func calculateFeeRate(satPerByte, satPerVByte uint64, targetConf uint32,
-	estimator chainfee.Estimator) (chainfee.SatPerKWeight, error) {
-
-	var feeRate chainfee.SatPerKWeight
-
-	// We only allow using either the deprecated field or the new field.
-	if satPerByte != 0 && satPerVByte != 0 {
-		return feeRate, fmt.Errorf("either SatPerByte or " +
-			"SatPerVByte should be set, but not both")
-	}
-
-	// Default to satPerVByte, and overwrite it if satPerByte is set.
-	satPerKw := chainfee.SatPerKVByte(satPerVByte * 1000).FeePerKWeight()
-	if satPerByte != 0 {
-		satPerKw = chainfee.SatPerKVByte(
-			satPerByte * 1000,
-		).FeePerKWeight()
-	}
-
-	// Based on the passed fee related parameters, we'll determine an
-	// appropriate fee rate for this transaction.
-	feeRate, err := sweep.DetermineFeePerKw(
-		estimator, sweep.FeePreference{
-			ConfTarget: targetConf,
-			FeeRate:    satPerKw,
-		},
-	)
-	if err != nil {
-		return feeRate, err
-	}
-
-	return feeRate, nil
-}
-
 // GetAllPermissions returns all the permissions required to interact with lnd.
 func GetAllPermissions() []bakery.Op {
 	allPerms := make([]bakery.Op, 0)
@@ -1239,7 +1201,7 @@ func (r *rpcServer) SendCoins(ctx context.Context,
 	in *lnrpc.SendCoinsRequest) (*lnrpc.SendCoinsResponse, error) {
 
 	// Calculate an appropriate fee rate for this transaction.
-	feePerKw, err := calculateFeeRate(
+	feePerKw, err := lnrpc.CalculateFeeRate(
 		uint64(in.SatPerByte), in.SatPerVbyte, // nolint:staticcheck
 		uint32(in.TargetConf), r.server.cc.FeeEstimator,
 	)
@@ -1452,7 +1414,7 @@ func (r *rpcServer) SendMany(ctx context.Context,
 	in *lnrpc.SendManyRequest) (*lnrpc.SendManyResponse, error) {
 
 	// Calculate an appropriate fee rate for this transaction.
-	feePerKw, err := calculateFeeRate(
+	feePerKw, err := lnrpc.CalculateFeeRate(
 		uint64(in.SatPerByte), in.SatPerVbyte, // nolint:staticcheck
 		uint32(in.TargetConf), r.server.cc.FeeEstimator,
 	)
@@ -2093,7 +2055,7 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 	}
 
 	// Calculate an appropriate fee rate for this transaction.
-	feeRate, err := calculateFeeRate(
+	feeRate, err := lnrpc.CalculateFeeRate(
 		uint64(in.SatPerByte), in.SatPerVbyte, // nolint:staticcheck
 		uint32(in.TargetConf), r.server.cc.FeeEstimator,
 	)
@@ -2574,7 +2536,7 @@ func (r *rpcServer) CloseChannel(in *lnrpc.CloseChannelRequest,
 		// Based on the passed fee related parameters, we'll determine
 		// an appropriate fee rate for the cooperative closure
 		// transaction.
-		feeRate, err := calculateFeeRate(
+		feeRate, err := lnrpc.CalculateFeeRate(
 			uint64(in.SatPerByte), in.SatPerVbyte, // nolint:staticcheck
 			uint32(in.TargetConf), r.server.cc.FeeEstimator,
 		)