f084802fec
This began as a change to improve the fee calculation code and evolved into a much larger refactor which improves the readability and modularity of all of the transaction creation code. Transaction fee calculations have been switched from full increments of the relay fee to a proportion based on the transaction size. This means that for a relay fee of 1e3 satoshis/kB, a 500 byte transaction is only required to pay a 5e2 satoshi fee and a 1500 byte transaction only need pay a 1.5e3 fee. The previous code would end up estimating these fees to be 1e3 and 2e3 respectively. Because the previous code would add more fee than needed in almost every case, the transaction size estimations were optimistic (best/smallest case) and signing was done in a loop where the fee was incremented by the relay fee again each time the actual size of the signed transaction rendered the fee too low. This has switched to using worst case transaction size estimates rather than best case, and signing is only performed once. Transaction input signature creation has switched from using txscript.SignatureScript to txscript.SignTxOutput. The new API is able to redeem outputs other than just P2PKH, so the previous restrictions about P2SH outputs being unspendable (except through the signrawtransaction RPC) no longer hold. Several new public packages have been added: wallet/txauthor - transaction authoring and signing wallet/txfees - fee estimations and change output inclusion wallet/txrules - simple consensus and mempool policy rule checks Along with some internal packages: wallet/internal/txsizes - transaction size estimation internal/helpers - context free convenience functions The txsizes package is internal as the estimations it provides are specific for the algorithms used by these new packages.
74 lines
2.4 KiB
Go
74 lines
2.4 KiB
Go
// Copyright (c) 2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package txsizes
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import (
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"github.com/btcsuite/btcd/wire"
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h "github.com/btcsuite/btcwallet/internal/helpers"
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)
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// Worst case script and input/output size estimates.
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const (
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// RedeemP2PKHSigScriptSize is the worst case (largest) serialize size
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// of a transaction input script that redeems a compressed P2PKH output.
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// It is calculated as:
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//
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// - OP_DATA_73
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// - 72 bytes DER signature + 1 byte sighash
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// - OP_DATA_33
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// - 33 bytes serialized compressed pubkey
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RedeemP2PKHSigScriptSize = 1 + 73 + 1 + 33
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// P2PKHPkScriptSize is the size of a transaction output script that
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// pays to a compressed pubkey hash. It is calculated as:
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//
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// - OP_DUP
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// - OP_HASH160
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// - OP_DATA_20
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// - 20 bytes pubkey hash
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// - OP_EQUALVERIFY
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// - OP_CHECKSIG
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P2PKHPkScriptSize = 1 + 1 + 1 + 20 + 1 + 1
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// RedeemP2PKHInputSize is the worst case (largest) serialize size of a
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// transaction input redeeming a compressed P2PKH output. It is
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// calculated as:
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//
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// - 32 bytes previous tx
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// - 4 bytes output index
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// - 1 byte compact int encoding value 107
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// - 107 bytes signature script
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// - 4 bytes sequence
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RedeemP2PKHInputSize = 32 + 4 + 1 + RedeemP2PKHSigScriptSize + 4
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// P2PKHOutputSize is the serialize size of a transaction output with a
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// P2PKH output script. It is calculated as:
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//
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// - 8 bytes output value
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// - 1 byte compact int encoding value 25
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// - 25 bytes P2PKH output script
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P2PKHOutputSize = 8 + 1 + P2PKHPkScriptSize
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)
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// EstimateSerializeSize returns a worst case serialize size estimate for a
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// signed transaction that spends inputCount number of compressed P2PKH outputs
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// and contains each transaction output from txOuts. The estimated size is
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// incremented for an additional P2PKH change output if addChangeOutput is true.
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func EstimateSerializeSize(inputCount int, txOuts []*wire.TxOut, addChangeOutput bool) int {
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changeSize := 0
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outputCount := len(txOuts)
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if addChangeOutput {
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changeSize = P2PKHOutputSize
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outputCount++
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}
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// 8 additional bytes are for version and locktime
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return 8 + wire.VarIntSerializeSize(uint64(inputCount)) +
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wire.VarIntSerializeSize(uint64(outputCount)) +
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inputCount*RedeemP2PKHInputSize +
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h.SumOutputSerializeSizes(txOuts) +
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changeSize
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}
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