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rules.go
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rules.go
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// Copyright (c) 2016 The btcsuite developers
// Copyright (c) 2016 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package txrules
import (
"errors"
"github.com/decred/dcrd/dcrutil"
"github.com/decred/dcrd/txscript"
"github.com/decred/dcrd/wire"
h "github.com/decred/dcrwallet/internal/helpers"
)
// DefaultRelayFeePerKb is the default minimum relay fee policy for a mempool.
const DefaultRelayFeePerKb dcrutil.Amount = 1e5
// 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 dcrutil.Amount, scriptSize int, relayFeePerKb dcrutil.Amount) bool {
// 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 (165) rather than
// the largest possible (txsizes.RedeemP2PKHInputSize).
totalSize := 8 + 2 + wire.VarIntSerializeSize(uint64(scriptSize)) +
scriptSize + 165
// Dust is defined as an output value where the total cost to the network
// (output size + input size) is greater than 1/3 of the relay fee.
return int64(amount)*1000/(3*int64(totalSize)) < int64(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 dcrutil.Amount) bool {
// Unspendable outputs which solely carry data are not checked for dust.
if txscript.GetScriptClass(output.Version, output.PkScript) == txscript.NullDataTy {
return false
}
// All other unspendable outputs are considered dust.
if txscript.IsUnspendable(output.Value, output.PkScript) {
return true
}
return IsDustAmount(dcrutil.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 dcrutil.Amount) error {
if output.Value < 0 {
return ErrAmountNegative
}
if output.Value > dcrutil.MaxAmount {
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 dcrutil.Amount, txSerializeSize int) dcrutil.Amount {
fee := relayFeePerKb * dcrutil.Amount(txSerializeSize) / 1000
if fee == 0 && relayFeePerKb > 0 {
fee = relayFeePerKb
}
if fee < 0 || fee > dcrutil.MaxAmount {
fee = dcrutil.MaxAmount
}
return fee
}
// PaysHighFees checks whether the signed transaction pays insanely high fees.
// Transactons are defined to have a high fee if they have pay a fee rate that
// is 1000 time higher than the default fee.
func PaysHighFees(totalInput dcrutil.Amount, tx *wire.MsgTx) bool {
fee := totalInput - h.SumOutputValues(tx.TxOut)
if fee <= 0 {
// Impossible to determine
return false
}
maxFee := FeeForSerializeSize(1000*DefaultRelayFeePerKb, tx.SerializeSize())
return fee > maxFee
}