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rules.go
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rules.go
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// Copyright (c) 2016 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
// Package txrules provides transaction rules that should be followed by
// transaction authors for wide mempool acceptance and quick mining.
package txrules
import (
"errors"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
)
// DefaultRelayFeePerKb is the default minimum relay fee policy for a mempool.
const DefaultRelayFeePerKb btcutil.Amount = 1e3
// GetDustThreshold is used to define the amount below which output will be
// determined as dust. Threshold is determined as 3 times the relay fee.
func GetDustThreshold(scriptSize int, relayFeePerKb btcutil.Amount) btcutil.Amount {
// Calculate the total (estimated) cost to the network. This is
// calculated using the serialize size of the output plus the serial
// size of a transaction input which redeems it. The output is assumed
// to be compressed P2PKH as this is the most common script type. Use
// the average size of a compressed P2PKH redeem input (148) rather than
// the largest possible (txsizes.RedeemP2PKHInputSize).
totalSize := 8 + wire.VarIntSerializeSize(uint64(scriptSize)) +
scriptSize + 148
byteFee := relayFeePerKb / 1000
relayFee := btcutil.Amount(totalSize) * byteFee
return 3 * relayFee
}
// IsDustAmount determines whether a transaction output value and script length would
// cause the output to be considered dust. Transactions with dust outputs are
// not standard and are rejected by mempools with default policies.
func IsDustAmount(amount btcutil.Amount, scriptSize int, relayFeePerKb btcutil.Amount) bool {
return amount < GetDustThreshold(scriptSize, relayFeePerKb)
}
// IsDustOutput determines whether a transaction output is considered dust.
// Transactions with dust outputs are not standard and are rejected by mempools
// with default policies.
func IsDustOutput(output *wire.TxOut, relayFeePerKb btcutil.Amount) bool {
// Unspendable outputs which solely carry data are not checked for dust.
if txscript.GetScriptClass(output.PkScript) == txscript.NullDataTy {
return false
}
// All other unspendable outputs are considered dust.
if txscript.IsUnspendable(output.PkScript) {
return true
}
return IsDustAmount(btcutil.Amount(output.Value), len(output.PkScript),
relayFeePerKb)
}
// Transaction rule violations
var (
ErrAmountNegative = errors.New("transaction output amount is negative")
ErrAmountExceedsMax = errors.New("transaction output amount exceeds maximum value")
ErrOutputIsDust = errors.New("transaction output is dust")
)
// CheckOutput performs simple consensus and policy tests on a transaction
// output.
func CheckOutput(output *wire.TxOut, relayFeePerKb btcutil.Amount) error {
if output.Value < 0 {
return ErrAmountNegative
}
if output.Value > btcutil.MaxSatoshi {
return ErrAmountExceedsMax
}
if IsDustOutput(output, relayFeePerKb) {
return ErrOutputIsDust
}
return nil
}
// FeeForSerializeSize calculates the required fee for a transaction of some
// arbitrary size given a mempool's relay fee policy.
func FeeForSerializeSize(relayFeePerKb btcutil.Amount, txSerializeSize int) btcutil.Amount {
fee := relayFeePerKb * btcutil.Amount(txSerializeSize) / 1000
if fee == 0 && relayFeePerKb > 0 {
fee = relayFeePerKb
}
if fee < 0 || fee > btcutil.MaxSatoshi {
fee = btcutil.MaxSatoshi
}
return fee
}