// 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 P2PKH 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 P2PKH 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 btcutil.Amount,
fetchInputs InputSource, fetchChange ChangeSource) (*AuthoredTx, error) {
targetAmount := h.SumOutputValues(outputs)
estimatedSize := txsizes.EstimateSerializeSize(1, outputs, true)
targetFee := txrules.FeeForSerializeSize(relayFeePerKb, estimatedSize)
for {
inputAmount, inputs, 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,
TotalInput: inputAmount,
ChangeIndex: changeIndex,
}, nil
}
}
func TestNewUnsignedTransaction(t *testing.T) {
tests := []struct {
UnspentOutputs []*wire.TxOut
Outputs []*wire.TxOut
RelayFee btcutil.Amount
ChangeAmount btcutil.Amount
InputSourceError bool
InputCount int
}{
0: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e8),
RelayFee: 1e3,
InputSourceError: true,
},
1: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e6),
RelayFee: 1e3,
ChangeAmount: 1e8 - 1e6 - txrules.FeeForSerializeSize(1e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(1e6), true)),
InputCount: 1,
},
2: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e6),
RelayFee: 1e4,
ChangeAmount: 1e8 - 1e6 - txrules.FeeForSerializeSize(1e4,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(1e6), true)),
InputCount: 1,
},
3: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e6, 1e6, 1e6),
RelayFee: 1e4,
ChangeAmount: 1e8 - 3e6 - txrules.FeeForSerializeSize(1e4,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(1e6, 1e6, 1e6), true)),
InputCount: 1,
},
4: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e6, 1e6, 1e6),
RelayFee: 2.55e3,
ChangeAmount: 1e8 - 3e6 - txrules.FeeForSerializeSize(2.55e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(1e6, 1e6, 1e6), true)),
InputCount: 1,
},
// Test dust thresholds (546 for a 1e3 relay fee).
5: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e8 - 545 - txrules.FeeForSerializeSize(1e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(0), true))),
RelayFee: 1e3,
ChangeAmount: 0,
InputCount: 1,
},
6: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e8 - 546 - txrules.FeeForSerializeSize(1e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(0), true))),
RelayFee: 1e3,
ChangeAmount: 546,
InputCount: 1,
},
// Test dust thresholds (1392.3 for a 2.55e3 relay fee).
7: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e8 - 1392 - txrules.FeeForSerializeSize(2.55e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(0), true))),
RelayFee: 2.55e3,
ChangeAmount: 0,
InputCount: 1,
},
8: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e8 - 1393 - txrules.FeeForSerializeSize(2.55e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(0), true))),
RelayFee: 2.55e3,
ChangeAmount: 1393,
InputCount: 1,
},
// Test two unspent outputs available but only one needed
// (tested fee only includes one input rather than using a
// serialize size for each).
9: {
UnspentOutputs: p2pkhOutputs(1e8, 1e8),
Outputs: p2pkhOutputs(1e8 - 546 - txrules.FeeForSerializeSize(1e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(0), true))),
RelayFee: 1e3,
ChangeAmount: 546,
InputCount: 1,
},
// Test that second output is not included to make the change
// output not dust and be included in the transaction.
//
// It's debatable whether or not this is a good idea, but it's
// how the function was written, so test it anyways.
10: {
UnspentOutputs: p2pkhOutputs(1e8, 1e8),
Outputs: p2pkhOutputs(1e8 - 545 - txrules.FeeForSerializeSize(1e3,
txsizes.EstimateSerializeSize(1, p2pkhOutputs(0), true))),
RelayFee: 1e3,
ChangeAmount: 0,
InputCount: 1,
},
// Test two unspent outputs available where both are needed.
11: {
UnspentOutputs: p2pkhOutputs(1e8, 1e8),
Outputs: p2pkhOutputs(1e8),
RelayFee: 1e3,
ChangeAmount: 1e8 - txrules.FeeForSerializeSize(1e3,
txsizes.EstimateSerializeSize(2, p2pkhOutputs(1e8), true)),
InputCount: 2,
},
// Test that zero change outputs are not included
// (ChangeAmount=0 means don't include any change output).
12: {
UnspentOutputs: p2pkhOutputs(1e8),
Outputs: p2pkhOutputs(1e8),
RelayFee: 0,
ChangeAmount: 0,
InputCount: 1,
},
}
changeSource := func() ([]byte, error) {
// Only length matters for these tests.
return make([]byte, txsizes.P2PKHPkScriptSize), nil
}
for i, test := range tests {
inputSource := makeInputSource(test.UnspentOutputs)
tx, err := NewUnsignedTransaction(test.Outputs, test.RelayFee, inputSource, changeSource)
switch e := err.(type) {
case nil:
case InputSourceError:
if !test.InputSourceError {
t.Errorf("Test %d: Returned InputSourceError but expected "+
"change output with amount %v", i, test.ChangeAmount)
}
continue
default:
t.Errorf("Test %d: Unexpected error: %v", i, e)
continue
}
if tx.ChangeIndex < 0 {
if test.ChangeAmount != 0 {
t.Errorf("Test %d: No change output added but expected output with amount %v",
i, test.ChangeAmount)
continue
}
} else {
changeAmount := btcutil.Amount(tx.Tx.TxOut[tx.ChangeIndex].Value)
if test.ChangeAmount == 0 {
t.Errorf("Test %d: Included change output with value %v but expected no change",
i, changeAmount)
continue
}
if changeAmount != test.ChangeAmount {
t.Errorf("Test %d: Got change amount %v, Expected %v",
i, changeAmount, test.ChangeAmount)
continue
}
}
if len(tx.Tx.TxIn) != test.InputCount {
t.Errorf("Test %d: Used %d outputs from input source, Expected %d",
i, len(tx.Tx.TxIn), test.InputCount)
}
}
}