btcjson+rpcclient: support new bitcoind sendrawtransaction request

btcjson/chainsvrcmds.go

@@ -638,6 +638,7 @@ func NewSearchRawTransactionsCmd(address string, verbose, skip, count *int, vinE
 type SendRawTransactionCmd struct {
 	HexTx         string
 	AllowHighFees *bool `jsonrpcdefault:"false"`
+	MaxFeeRate    *int32
 }
 
 // NewSendRawTransactionCmd returns a new instance which can be used to issue a
@@ -652,6 +653,17 @@ func NewSendRawTransactionCmd(hexTx string, allowHighFees *bool) *SendRawTransac
 	}
 }
 
+// NewSendRawTransactionCmd returns a new instance which can be used to issue a
+// sendrawtransaction JSON-RPC command to a bitcoind node.
+//
+// A 0 maxFeeRate indicates that a maximum fee rate won't be enforced.
+func NewBitcoindSendRawTransactionCmd(hexTx string, maxFeeRate int32) *SendRawTransactionCmd {
+	return &SendRawTransactionCmd{
+		HexTx:      hexTx,
+		MaxFeeRate: &maxFeeRate,
+	}
+}
+
 // SetGenerateCmd defines the setgenerate JSON-RPC command.
 type SetGenerateCmd struct {
 	Generate     bool

rpcclient/rawtransactions.go

@@ -15,6 +15,12 @@ import (
 	"github.com/btcsuite/btcutil"
 )
 
+const (
+	// defaultMaxFeeRate is the default maximum fee rate in sat/KB enforced
+	// by bitcoind v0.19.0 or after for transaction broadcast.
+	defaultMaxFeeRate = btcutil.SatoshiPerBitcoin / 10
+)
+
 // SigHashType enumerates the available signature hashing types that the
 // SignRawTransaction function accepts.
 type SigHashType string
@@ -296,7 +302,31 @@ func (c *Client) SendRawTransactionAsync(tx *wire.MsgTx, allowHighFees bool) Fut
 		txHex = hex.EncodeToString(buf.Bytes())
 	}
 
-	cmd := btcjson.NewSendRawTransactionCmd(txHex, &allowHighFees)
+	// Due to differences in the sendrawtransaction API for different
+	// backends, we'll need to inspect our version and construct the
+	// appropriate request.
+	version, err := c.BackendVersion()
+	if err != nil {
+		return newFutureError(err)
+	}
+
+	var cmd *btcjson.SendRawTransactionCmd
+	switch version {
+	// Starting from bitcoind v0.19.0, the MaxFeeRate field should be used.
+	case BitcoindPost19:
+		// Using a 0 MaxFeeRate is interpreted as a maximum fee rate not
+		// being enforced by bitcoind.
+		var maxFeeRate int32
+		if !allowHighFees {
+			maxFeeRate = defaultMaxFeeRate
+		}
+		cmd = btcjson.NewBitcoindSendRawTransactionCmd(txHex, maxFeeRate)
+
+	// Otherwise, use the AllowHighFees field.
+	default:
+		cmd = btcjson.NewSendRawTransactionCmd(txHex, &allowHighFees)
+	}
+
 	return c.sendCmd(cmd)
 }
 

rpcserverhelp.go

@@ -552,6 +552,7 @@ var helpDescsEnUS = map[string]string{
 	"sendrawtransaction--synopsis":     "Submits the serialized, hex-encoded transaction to the local peer and relays it to the network.",
 	"sendrawtransaction-hextx":         "Serialized, hex-encoded signed transaction",
 	"sendrawtransaction-allowhighfees": "Whether or not to allow insanely high fees (btcd does not yet implement this parameter, so it has no effect)",
+	"sendrawtransaction-maxfeerate":    "Used by bitcoind on or after v0.19.0",
 	"sendrawtransaction--result0":      "The hash of the transaction",
 
 	// SetGenerateCmd help.