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author.go
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author.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 txauthor provides transaction creation code for wallets.
package txauthor
import (
"errors"
"github.com/dcrlabs/bchwallet/wallet/txrules"
"github.com/gcash/bchd/chaincfg"
"github.com/gcash/bchd/txscript"
"github.com/gcash/bchd/wire"
"github.com/gcash/bchutil"
h "github.com/dcrlabs/bchwallet/internal/helpers"
"github.com/dcrlabs/bchwallet/wallet/txsizes"
)
// InputSource provides transaction inputs referencing spendable outputs to
// construct a transaction outputting some target amount. If the target amount
// can not be satisified, this can be signaled by returning a total amount less
// than the target or by returning a more detailed error implementing
// InputSourceError.
type InputSource func(target bchutil.Amount) (total bchutil.Amount, inputs []*wire.TxIn,
inputValues []bchutil.Amount, scripts [][]byte, err error)
// InputSourceError describes the failure to provide enough input value from
// unspent transaction outputs to meet a target amount. A typed error is used
// so input sources can provide their own implementations describing the reason
// for the error, for example, due to spendable policies or locked coins rather
// than the wallet not having enough available input value.
type InputSourceError interface {
error
InputSourceError()
}
// Default implementation of InputSourceError.
type insufficientFundsError struct{}
func (insufficientFundsError) InputSourceError() {}
func (insufficientFundsError) Error() string {
return "insufficient funds available to construct transaction"
}
// AuthoredTx holds the state of a newly-created transaction and the change
// output (if one was added).
type AuthoredTx struct {
Tx *wire.MsgTx
PrevScripts [][]byte
PrevInputValues []bchutil.Amount
TotalInput bchutil.Amount
ChangeIndex int // negative if no change
}
// ChangeSource provides P2PKH change output scripts for transaction creation.
type ChangeSource func() ([]byte, error)
// NewUnsignedTransaction creates an unsigned transaction paying to one or more
// non-change outputs. An appropriate transaction fee is included based on the
// transaction size.
//
// Transaction inputs are chosen from repeated calls to fetchInputs with
// increasing targets amounts.
//
// If any remaining output value can be returned to the wallet via a change
// output without violating mempool dust rules, a P2WPKH change output is
// appended to the transaction outputs. Since the change output may not be
// necessary, fetchChange is called zero or one times to generate this script.
// This function must return a P2WPKH script or smaller, otherwise fee estimation
// will be incorrect.
//
// If successful, the transaction, total input value spent, and all previous
// output scripts are returned. If the input source was unable to provide
// enough input value to pay for every output any any necessary fees, an
// InputSourceError is returned.
//
// BUGS: Fee estimation may be off when redeeming non-compressed P2PKH outputs.
func NewUnsignedTransaction(outputs []*wire.TxOut, relayFeePerKb bchutil.Amount,
fetchInputs InputSource, fetchChange ChangeSource) (*AuthoredTx, error) {
targetAmount := h.SumOutputValues(outputs)
estimatedSize := txsizes.EstimateSerializeSize(0, outputs, true)
targetFee := txrules.FeeForSerializeSize(relayFeePerKb, estimatedSize)
for {
inputAmount, inputs, inputValues, scripts, err := fetchInputs(targetAmount + targetFee)
if err != nil {
return nil, err
}
if inputAmount < targetAmount+targetFee {
return nil, insufficientFundsError{}
}
maxSignedSize := txsizes.EstimateSerializeSize(len(inputs), outputs, true)
maxRequiredFee := txrules.FeeForSerializeSize(relayFeePerKb, maxSignedSize)
remainingAmount := inputAmount - targetAmount
if remainingAmount < maxRequiredFee {
targetFee = maxRequiredFee
continue
}
unsignedTransaction := &wire.MsgTx{
Version: wire.TxVersion,
TxIn: inputs,
TxOut: outputs,
LockTime: 0,
}
changeIndex := -1
changeAmount := inputAmount - targetAmount - maxRequiredFee
if changeAmount != 0 && !txrules.IsDustAmount(changeAmount,
txsizes.P2PKHPkScriptSize, relayFeePerKb) {
changeScript, err := fetchChange()
if err != nil {
return nil, err
}
if len(changeScript) > txsizes.P2PKHPkScriptSize {
return nil, errors.New("fee estimation requires change " +
"scripts no larger than P2PKH output scripts")
}
change := wire.NewTxOut(int64(changeAmount), changeScript)
l := len(outputs)
unsignedTransaction.TxOut = append(outputs[:l:l], change)
changeIndex = l
}
return &AuthoredTx{
Tx: unsignedTransaction,
PrevScripts: scripts,
PrevInputValues: inputValues,
TotalInput: inputAmount,
ChangeIndex: changeIndex,
}, nil
}
}
// RandomizeOutputPosition randomizes the position of a transaction's output by
// swapping it with a random output. The new index is returned. This should be
// done before signing.
func RandomizeOutputPosition(outputs []*wire.TxOut, index int) int {
r := cprng.Int31n(int32(len(outputs)))
outputs[r], outputs[index] = outputs[index], outputs[r]
return int(r)
}
// RandomizeChangePosition randomizes the position of an authored transaction's
// change output. This should be done before signing.
func (tx *AuthoredTx) RandomizeChangePosition() {
tx.ChangeIndex = RandomizeOutputPosition(tx.Tx.TxOut, tx.ChangeIndex)
}
// SecretsSource provides private keys and redeem scripts necessary for
// constructing transaction input signatures. Secrets are looked up by the
// corresponding Address for the previous output script. Addresses for lookup
// are created using the source's blockchain parameters and means a single
// SecretsSource can only manage secrets for a single chain.
//
// TODO: Rewrite this interface to look up private keys and redeem scripts for
// pubkeys, pubkey hashes, script hashes, etc. as separate interface methods.
// This would remove the ChainParams requirement of the interface and could
// avoid unnecessary conversions from previous output scripts to Addresses.
// This can not be done without modifications to the txscript package.
type SecretsSource interface {
txscript.KeyDB
txscript.ScriptDB
ChainParams() *chaincfg.Params
}
// AddAllInputScripts modifies a transaction by adding inputs scripts for each input.
// Previous output scripts being redeemed by each input are passed in prevPkScripts
// and the slice length must match the number of inputs. Private keys and redeem
// scripts are looked up using a SecretsSource based on the previous output script.
func AddAllInputScripts(tx *wire.MsgTx, prevPkScripts [][]byte, inputValues []bchutil.Amount,
secrets SecretsSource) error {
inputs := tx.TxIn
chainParams := secrets.ChainParams()
if len(inputs) != len(prevPkScripts) {
return errors.New("tx.TxIn and prevPkScripts slices must " +
"have equal length")
}
for i := range inputs {
pkScript := prevPkScripts[i]
// tx, idx, amt, subscript, hashtype, pk, compress
// First obtain the key pair associated with this p2wkh address.
_, addrs, _, err := txscript.ExtractPkScriptAddrs(pkScript,
chainParams)
if err != nil {
return err
}
privKey, compressed, err := secrets.GetKey(addrs[0])
if err != nil {
return err
}
script, err := txscript.SignatureScript(tx, i, int64(inputValues[i].ToUnit(bchutil.AmountSatoshi)),
pkScript, txscript.SigHashAll, privKey, compressed)
if err != nil {
return err
}
inputs[i].SignatureScript = script
}
return nil
}
// AddAllInputScripts modifies an authored transaction by adding inputs scripts
// for each input of an authored transaction. Private keys and redeem scripts
// are looked up using a SecretsSource based on the previous output script.
func (tx *AuthoredTx) AddAllInputScripts(secrets SecretsSource) error {
return AddAllInputScripts(tx.Tx, tx.PrevScripts, tx.PrevInputValues, secrets)
}