77 lines
2.4 KiB
Go
77 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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// TODO(roasbeef): add estimates for nested p2wkh and p2pkh
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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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