btcclient+btcjson: add type alias for BTC/kvB

Added type alias BTC/kvB to explicitly indicate that
it represents the fee in BTC for a transaction size of 1 kB.
Because bitcoind uses its own fee rate type
(BTC/kvB instead of sat/kWU we use in lnd),
define the type in btcjson package,
as it's the only place where we actually use BTC/kvB.

btcjson/chainsvrcmds.go

@@ -16,6 +16,10 @@ import (
 	"github.com/btcsuite/btcd/wire"
 )
 
+// BTCPerkvB is the units used to represent Bitcoin transaction fees.
+// This unit represents the fee in BTC for a transaction size of 1 kB.
+type BTCPerkvB = float64
+
 // AddNodeSubCmd defines the type used in the addnode JSON-RPC command for the
 // sub command field.
 type AddNodeSubCmd string
@@ -142,7 +146,7 @@ type FundRawTransactionOpts struct {
 	ChangeType             *ChangeType           `json:"change_type,omitempty"`
 	IncludeWatching        *bool                 `json:"includeWatching,omitempty"`
 	LockUnspents           *bool                 `json:"lockUnspents,omitempty"`
-	FeeRate                *float64              `json:"feeRate,omitempty"` // BTC/kB
+	FeeRate                *BTCPerkvB            `json:"feeRate,omitempty"` // BTC/kB
 	SubtractFeeFromOutputs []int                 `json:"subtractFeeFromOutputs,omitempty"`
 	Replaceable            *bool                 `json:"replaceable,omitempty"`
 	ConfTarget             *int                  `json:"conf_target,omitempty"`
@@ -822,7 +826,7 @@ func NewSearchRawTransactionsCmd(address string, verbose, skip, count *int, vinE
 }
 
 // AllowHighFeesOrMaxFeeRate defines a type that can either be the legacy
-// allowhighfees boolean field or the new maxfeerate int field.
+// allowhighfees boolean field or the new maxfeerate float64 field.
 type AllowHighFeesOrMaxFeeRate struct {
 	Value interface{}
 }
@@ -896,7 +900,7 @@ func NewSendRawTransactionCmd(hexTx string, allowHighFees *bool) *SendRawTransac
 // maxFeeRate is the maximum fee rate for the transaction in BTC/kvB.
 //
 // A 0 maxFeeRate indicates that a maximum fee rate won't be enforced.
-func NewBitcoindSendRawTransactionCmd(hexTx string, maxFeeRate float64) *SendRawTransactionCmd {
+func NewBitcoindSendRawTransactionCmd(hexTx string, maxFeeRate BTCPerkvB) *SendRawTransactionCmd {
 	return &SendRawTransactionCmd{
 		HexTx: hexTx,
 		FeeSetting: &AllowHighFeesOrMaxFeeRate{
@@ -1051,13 +1055,13 @@ type TestMempoolAcceptCmd struct {
 
 	// Reject transactions whose fee rate is higher than the specified
 	// value, expressed in BTC/kvB, optional, default="0.10".
-	MaxFeeRate float64 `json:"omitempty"`
+	MaxFeeRate BTCPerkvB `json:"omitempty"`
 }
 
 // NewTestMempoolAcceptCmd returns a new instance which can be used to issue a
 // testmempoolaccept JSON-RPC command.
 func NewTestMempoolAcceptCmd(rawTxns []string,
-	maxFeeRate float64) *TestMempoolAcceptCmd {
+	maxFeeRate BTCPerkvB) *TestMempoolAcceptCmd {
 
 	return &TestMempoolAcceptCmd{
 		RawTxns:    rawTxns,

rpcclient/rawtransactions.go

@@ -19,7 +19,7 @@ import (
 const (
 	// defaultMaxFeeRate is the default maximum fee rate in BTC/kvB enforced
 	// by bitcoind v0.19.0 or after for transaction broadcast.
-	defaultMaxFeeRate float64 = 0.1
+	defaultMaxFeeRate btcjson.BTCPerkvB = 0.1
 )
 
 // SigHashType enumerates the available signature hashing types that the
@@ -365,7 +365,7 @@ func (c *Client) SendRawTransactionAsync(tx *wire.MsgTx, allowHighFees bool) Fut
 	if version.SupportUnifiedSoftForks() {
 		// Using a 0 MaxFeeRate is interpreted as a maximum fee rate not
 		// being enforced by bitcoind.
-		var maxFeeRate float64
+		var maxFeeRate btcjson.BTCPerkvB
 		if !allowHighFees {
 			maxFeeRate = defaultMaxFeeRate
 		}
@@ -915,7 +915,7 @@ func (r FutureTestMempoolAcceptResult) Receive() (
 //
 // See TestMempoolAccept for the blocking version and more details.
 func (c *Client) TestMempoolAcceptAsync(txns []*wire.MsgTx,
-	maxFeeRate float64) FutureTestMempoolAcceptResult {
+	maxFeeRate btcjson.BTCPerkvB) FutureTestMempoolAcceptResult {
 
 	// Due to differences in the testmempoolaccept API for different
 	// backends, we'll need to inspect our version and construct the
@@ -1010,7 +1010,7 @@ func (c *Client) TestMempoolAcceptAsync(txns []*wire.MsgTx,
 //
 // The maximum number of transactions allowed is 25.
 func (c *Client) TestMempoolAccept(txns []*wire.MsgTx,
-	maxFeeRate float64) ([]*btcjson.TestMempoolAcceptResult, error) {
+	maxFeeRate btcjson.BTCPerkvB) ([]*btcjson.TestMempoolAcceptResult, error) {
 
 	return c.TestMempoolAcceptAsync(txns, maxFeeRate).Receive()
 }