3cb2c46b02
We can now get rid of our incorrect dust calculation which did not give exact values for segwit outputs as it was based on spending a P2PKH output instead.
375 lines
13 KiB
Go
375 lines
13 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 txauthor provides transaction creation code for wallets.
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package txauthor
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import (
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"errors"
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"github.com/btcsuite/btcd/chaincfg"
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"github.com/btcsuite/btcd/txscript"
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"github.com/btcsuite/btcd/wire"
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"github.com/btcsuite/btcutil"
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"github.com/btcsuite/btcwallet/wallet/txrules"
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"github.com/btcsuite/btcwallet/wallet/txsizes"
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)
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// SumOutputValues sums up the list of TxOuts and returns an Amount.
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func SumOutputValues(outputs []*wire.TxOut) (totalOutput btcutil.Amount) {
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for _, txOut := range outputs {
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totalOutput += btcutil.Amount(txOut.Value)
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}
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return totalOutput
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}
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// InputSource provides transaction inputs referencing spendable outputs to
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// construct a transaction outputting some target amount. If the target amount
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// can not be satisified, this can be signaled by returning a total amount less
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// than the target or by returning a more detailed error implementing
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// InputSourceError.
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type InputSource func(target btcutil.Amount) (total btcutil.Amount, inputs []*wire.TxIn,
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inputValues []btcutil.Amount, scripts [][]byte, err error)
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// InputSourceError describes the failure to provide enough input value from
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// unspent transaction outputs to meet a target amount. A typed error is used
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// so input sources can provide their own implementations describing the reason
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// for the error, for example, due to spendable policies or locked coins rather
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// than the wallet not having enough available input value.
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type InputSourceError interface {
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error
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InputSourceError()
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}
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// Default implementation of InputSourceError.
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type insufficientFundsError struct{}
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func (insufficientFundsError) InputSourceError() {}
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func (insufficientFundsError) Error() string {
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return "insufficient funds available to construct transaction"
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}
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// AuthoredTx holds the state of a newly-created transaction and the change
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// output (if one was added).
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type AuthoredTx struct {
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Tx *wire.MsgTx
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PrevScripts [][]byte
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PrevInputValues []btcutil.Amount
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TotalInput btcutil.Amount
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ChangeIndex int // negative if no change
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}
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// ChangeSource provides change output scripts for transaction creation.
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type ChangeSource struct {
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// NewScript is a closure that produces unique change output scripts per
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// invocation.
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NewScript func() ([]byte, error)
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// ScriptSize is the size in bytes of scripts produced by `NewScript`.
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ScriptSize int
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}
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// NewUnsignedTransaction creates an unsigned transaction paying to one or more
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// non-change outputs. An appropriate transaction fee is included based on the
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// transaction size.
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//
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// Transaction inputs are chosen from repeated calls to fetchInputs with
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// increasing targets amounts.
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//
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// If any remaining output value can be returned to the wallet via a change
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// output without violating mempool dust rules, a P2WPKH change output is
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// appended to the transaction outputs. Since the change output may not be
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// necessary, fetchChange is called zero or one times to generate this script.
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// This function must return a P2WPKH script or smaller, otherwise fee estimation
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// will be incorrect.
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//
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// If successful, the transaction, total input value spent, and all previous
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// output scripts are returned. If the input source was unable to provide
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// enough input value to pay for every output any any necessary fees, an
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// InputSourceError is returned.
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//
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// BUGS: Fee estimation may be off when redeeming non-compressed P2PKH outputs.
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func NewUnsignedTransaction(outputs []*wire.TxOut, feeRatePerKb btcutil.Amount,
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fetchInputs InputSource, changeSource *ChangeSource) (*AuthoredTx, error) {
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targetAmount := SumOutputValues(outputs)
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estimatedSize := txsizes.EstimateVirtualSize(
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0, 1, 0, outputs, changeSource.ScriptSize,
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)
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targetFee := txrules.FeeForSerializeSize(feeRatePerKb, estimatedSize)
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for {
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inputAmount, inputs, inputValues, scripts, err := fetchInputs(targetAmount + targetFee)
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if err != nil {
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return nil, err
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}
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if inputAmount < targetAmount+targetFee {
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return nil, insufficientFundsError{}
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}
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// We count the types of inputs, which we'll use to estimate
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// the vsize of the transaction.
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var nested, p2wpkh, p2pkh int
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for _, pkScript := range scripts {
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switch {
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// If this is a p2sh output, we assume this is a
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// nested P2WKH.
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case txscript.IsPayToScriptHash(pkScript):
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nested++
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case txscript.IsPayToWitnessPubKeyHash(pkScript):
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p2wpkh++
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default:
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p2pkh++
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}
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}
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maxSignedSize := txsizes.EstimateVirtualSize(
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p2pkh, p2wpkh, nested, outputs, changeSource.ScriptSize,
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)
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maxRequiredFee := txrules.FeeForSerializeSize(feeRatePerKb, maxSignedSize)
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remainingAmount := inputAmount - targetAmount
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if remainingAmount < maxRequiredFee {
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targetFee = maxRequiredFee
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continue
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}
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unsignedTransaction := &wire.MsgTx{
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Version: wire.TxVersion,
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TxIn: inputs,
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TxOut: outputs,
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LockTime: 0,
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}
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changeIndex := -1
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changeAmount := inputAmount - targetAmount - maxRequiredFee
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changeScript, err := changeSource.NewScript()
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if err != nil {
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return nil, err
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}
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change := wire.NewTxOut(int64(changeAmount), changeScript)
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if changeAmount != 0 && !txrules.IsDustOutput(change,
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txrules.DefaultRelayFeePerKb) {
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l := len(outputs)
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unsignedTransaction.TxOut = append(outputs[:l:l], change)
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changeIndex = l
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}
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return &AuthoredTx{
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Tx: unsignedTransaction,
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PrevScripts: scripts,
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PrevInputValues: inputValues,
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TotalInput: inputAmount,
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ChangeIndex: changeIndex,
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}, nil
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}
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}
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// RandomizeOutputPosition randomizes the position of a transaction's output by
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// swapping it with a random output. The new index is returned. This should be
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// done before signing.
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func RandomizeOutputPosition(outputs []*wire.TxOut, index int) int {
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r := cprng.Int31n(int32(len(outputs)))
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outputs[r], outputs[index] = outputs[index], outputs[r]
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return int(r)
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}
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// RandomizeChangePosition randomizes the position of an authored transaction's
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// change output. This should be done before signing.
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func (tx *AuthoredTx) RandomizeChangePosition() {
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tx.ChangeIndex = RandomizeOutputPosition(tx.Tx.TxOut, tx.ChangeIndex)
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}
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// SecretsSource provides private keys and redeem scripts necessary for
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// constructing transaction input signatures. Secrets are looked up by the
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// corresponding Address for the previous output script. Addresses for lookup
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// are created using the source's blockchain parameters and means a single
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// SecretsSource can only manage secrets for a single chain.
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//
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// TODO: Rewrite this interface to look up private keys and redeem scripts for
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// pubkeys, pubkey hashes, script hashes, etc. as separate interface methods.
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// This would remove the ChainParams requirement of the interface and could
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// avoid unnecessary conversions from previous output scripts to Addresses.
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// This can not be done without modifications to the txscript package.
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type SecretsSource interface {
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txscript.KeyDB
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txscript.ScriptDB
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ChainParams() *chaincfg.Params
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}
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// AddAllInputScripts modifies transaction a transaction by adding inputs
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// scripts for each input. Previous output scripts being redeemed by each input
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// are passed in prevPkScripts and the slice length must match the number of
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// inputs. Private keys and redeem scripts are looked up using a SecretsSource
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// based on the previous output script.
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func AddAllInputScripts(tx *wire.MsgTx, prevPkScripts [][]byte, inputValues []btcutil.Amount,
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secrets SecretsSource) error {
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inputs := tx.TxIn
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hashCache := txscript.NewTxSigHashes(tx)
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chainParams := secrets.ChainParams()
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if len(inputs) != len(prevPkScripts) {
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return errors.New("tx.TxIn and prevPkScripts slices must " +
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"have equal length")
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}
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for i := range inputs {
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pkScript := prevPkScripts[i]
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switch {
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// If this is a p2sh output, who's script hash pre-image is a
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// witness program, then we'll need to use a modified signing
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// function which generates both the sigScript, and the witness
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// script.
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case txscript.IsPayToScriptHash(pkScript):
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err := spendNestedWitnessPubKeyHash(inputs[i], pkScript,
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int64(inputValues[i]), chainParams, secrets,
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tx, hashCache, i)
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if err != nil {
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return err
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}
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case txscript.IsPayToWitnessPubKeyHash(pkScript):
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err := spendWitnessKeyHash(inputs[i], pkScript,
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int64(inputValues[i]), chainParams, secrets,
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tx, hashCache, i)
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if err != nil {
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return err
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}
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default:
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sigScript := inputs[i].SignatureScript
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script, err := txscript.SignTxOutput(chainParams, tx, i,
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pkScript, txscript.SigHashAll, secrets, secrets,
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sigScript)
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if err != nil {
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return err
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}
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inputs[i].SignatureScript = script
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}
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}
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return nil
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}
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// spendWitnessKeyHash generates, and sets a valid witness for spending the
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// passed pkScript with the specified input amount. The input amount *must*
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// correspond to the output value of the previous pkScript, or else verification
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// will fail since the new sighash digest algorithm defined in BIP0143 includes
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// the input value in the sighash.
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func spendWitnessKeyHash(txIn *wire.TxIn, pkScript []byte,
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inputValue int64, chainParams *chaincfg.Params, secrets SecretsSource,
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tx *wire.MsgTx, hashCache *txscript.TxSigHashes, idx int) error {
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// First obtain the key pair associated with this p2wkh address.
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_, addrs, _, err := txscript.ExtractPkScriptAddrs(pkScript,
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chainParams)
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if err != nil {
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return err
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}
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privKey, compressed, err := secrets.GetKey(addrs[0])
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if err != nil {
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return err
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}
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pubKey := privKey.PubKey()
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// Once we have the key pair, generate a p2wkh address type, respecting
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// the compression type of the generated key.
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var pubKeyHash []byte
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if compressed {
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pubKeyHash = btcutil.Hash160(pubKey.SerializeCompressed())
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} else {
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pubKeyHash = btcutil.Hash160(pubKey.SerializeUncompressed())
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}
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p2wkhAddr, err := btcutil.NewAddressWitnessPubKeyHash(pubKeyHash, chainParams)
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if err != nil {
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return err
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}
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// With the concrete address type, we can now generate the
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// corresponding witness program to be used to generate a valid witness
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// which will allow us to spend this output.
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witnessProgram, err := txscript.PayToAddrScript(p2wkhAddr)
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if err != nil {
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return err
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}
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witnessScript, err := txscript.WitnessSignature(tx, hashCache, idx,
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inputValue, witnessProgram, txscript.SigHashAll, privKey, true)
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if err != nil {
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return err
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}
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txIn.Witness = witnessScript
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return nil
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}
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// spendNestedWitnessPubKey generates both a sigScript, and valid witness for
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// spending the passed pkScript with the specified input amount. The generated
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// sigScript is the version 0 p2wkh witness program corresponding to the queried
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// key. The witness stack is identical to that of one which spends a regular
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// p2wkh output. The input amount *must* correspond to the output value of the
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// previous pkScript, or else verification will fail since the new sighash
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// digest algorithm defined in BIP0143 includes the input value in the sighash.
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func spendNestedWitnessPubKeyHash(txIn *wire.TxIn, pkScript []byte,
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inputValue int64, chainParams *chaincfg.Params, secrets SecretsSource,
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tx *wire.MsgTx, hashCache *txscript.TxSigHashes, idx int) error {
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// First we need to obtain the key pair related to this p2sh output.
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_, addrs, _, err := txscript.ExtractPkScriptAddrs(pkScript,
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chainParams)
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if err != nil {
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return err
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}
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privKey, compressed, err := secrets.GetKey(addrs[0])
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if err != nil {
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return err
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}
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pubKey := privKey.PubKey()
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var pubKeyHash []byte
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if compressed {
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pubKeyHash = btcutil.Hash160(pubKey.SerializeCompressed())
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} else {
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pubKeyHash = btcutil.Hash160(pubKey.SerializeUncompressed())
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}
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// Next, we'll generate a valid sigScript that'll allow us to spend
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// the p2sh output. The sigScript will contain only a single push of
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// the p2wkh witness program corresponding to the matching public key
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// of this address.
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p2wkhAddr, err := btcutil.NewAddressWitnessPubKeyHash(pubKeyHash, chainParams)
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if err != nil {
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return err
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}
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witnessProgram, err := txscript.PayToAddrScript(p2wkhAddr)
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if err != nil {
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return err
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}
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bldr := txscript.NewScriptBuilder()
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bldr.AddData(witnessProgram)
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sigScript, err := bldr.Script()
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if err != nil {
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return err
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}
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txIn.SignatureScript = sigScript
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// With the sigScript in place, we'll next generate the proper witness
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// that'll allow us to spend the p2wkh output.
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witnessScript, err := txscript.WitnessSignature(tx, hashCache, idx,
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inputValue, witnessProgram, txscript.SigHashAll, privKey, compressed)
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if err != nil {
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return err
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}
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txIn.Witness = witnessScript
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return nil
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}
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// AddAllInputScripts modifies an authored transaction by adding inputs scripts
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// for each input of an authored transaction. Private keys and redeem scripts
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// are looked up using a SecretsSource based on the previous output script.
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func (tx *AuthoredTx) AddAllInputScripts(secrets SecretsSource) error {
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return AddAllInputScripts(tx.Tx, tx.PrevScripts, tx.PrevInputValues, secrets)
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}
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