Example #1
0
// 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.
// TODO(roasbeef): fix fee estimation for witness 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, 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
	}
}
Example #2
0
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)
		}
	}
}