13586005509

Committed 28 Feb 2025 10:14AM UTC coverage: 68.629% (+9.9%) from 58.77%

Build # 13586005509

Build Type

Pull #9521

github

Committed by

web-flow

Commit Message

Merge 37d3a70a5 into 8532955b3

Pull Request Pull Request #9521: unit: remove GOACC, use Go 1.20 native coverage functionality

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92.74

/lnwallet/chanfunding/coin_select.go

package chanfunding

import (
        "errors"
        "fmt"

        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcwallet/wallet"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/lnwallet/chainfee"
)

// ErrInsufficientFunds is a type matching the error interface which is
// returned when coin selection for a new funding transaction fails due to
// having an insufficient amount of confirmed funds.
type ErrInsufficientFunds struct {
        amountAvailable btcutil.Amount
        amountSelected  btcutil.Amount
}

// Error returns a human-readable string describing the error.
func (e *ErrInsufficientFunds) Error() string {
        return fmt.Sprintf("not enough witness outputs to create funding "+
                "transaction, need %v only have %v available",
                e.amountAvailable, e.amountSelected)
}

// errUnsupportedInput is a type matching the error interface, which is returned
// when trying to calculate the fee of a transaction that references an
// unsupported script in the outpoint of a transaction input.
type errUnsupportedInput struct {
        PkScript []byte
}

// Error returns a human-readable string describing the error.
func (e *errUnsupportedInput) Error() string {
        return fmt.Sprintf("unsupported address type: %x", e.PkScript)
}

// ChangeAddressType is an enum-like type that describes the type of change
// address that should be generated for a transaction.
type ChangeAddressType uint8

const (
        // P2WKHChangeAddress indicates that the change output should be a
        // P2WKH output.
        P2WKHChangeAddress ChangeAddressType = 0

        // P2TRChangeAddress indicates that the change output should be a
        // P2TR output.
        P2TRChangeAddress ChangeAddressType = 1

        // ExistingChangeAddress indicates that the coin selection algorithm
        // should assume an existing output will be used for any change, meaning
        // that the change amount calculated will be added to an existing output
        // and no weight for a new change output should be assumed. The caller
        // must assert that the output value of the selected existing output
        // already is above dust when using this change address type.
        ExistingChangeAddress ChangeAddressType = 2

        // DefaultMaxFeeRatio is the default fee to total amount of outputs
        // ratio that is used to sanity check the fees of a transaction.
        DefaultMaxFeeRatio float64 = 0.2
)

// selectInputs selects a slice of inputs necessary to meet the specified
// selection amount. If input selection is unable to succeed due to insufficient
// funds, a non-nil error is returned. Additionally, the total amount of the
// selected coins are returned in order for the caller to properly handle
// change+fees.
func selectInputs(amt btcutil.Amount, coins []wallet.Coin,
        strategy wallet.CoinSelectionStrategy,
        feeRate chainfee.SatPerKWeight) (btcutil.Amount, []wallet.Coin, error) {

        // All coin selection code in the btcwallet library requires sat/KB.
        feeSatPerKB := btcutil.Amount(feeRate.FeePerKVByte())

        arrangedCoins, err := strategy.ArrangeCoins(coins, feeSatPerKB)
        if err != nil {
                return 0, nil, err
        }

        satSelected := btcutil.Amount(0)
        for i, coin := range arrangedCoins {
                satSelected += btcutil.Amount(coin.Value)
                if satSelected >= amt {
                        return satSelected, arrangedCoins[:i+1], nil
                }
        }

        return 0, nil, &ErrInsufficientFunds{amt, satSelected}
}

// calculateFees returns for the specified utxos and fee rate two fee
// estimates, one calculated using a change output and one without. The weight
// added to the estimator from a change output is for a P2WKH output.
func calculateFees(utxos []wallet.Coin, feeRate chainfee.SatPerKWeight,
        existingWeight input.TxWeightEstimator,
        changeType ChangeAddressType) (btcutil.Amount, btcutil.Amount, error) {

        weightEstimate := existingWeight
        for _, utxo := range utxos {
                switch {
                case txscript.IsPayToWitnessPubKeyHash(utxo.PkScript):
                        weightEstimate.AddP2WKHInput()

                case txscript.IsPayToScriptHash(utxo.PkScript):
                        weightEstimate.AddNestedP2WKHInput()

                case txscript.IsPayToTaproot(utxo.PkScript):
                        weightEstimate.AddTaprootKeySpendInput(
                                txscript.SigHashDefault,
                        )

                default:
                        return 0, 0, &errUnsupportedInput{utxo.PkScript}
                }
        }

        // Estimate the fee required for a transaction without a change
        // output.
        totalWeight := weightEstimate.Weight()
        requiredFeeNoChange := feeRate.FeeForWeight(totalWeight)

        // Estimate the fee required for a transaction with a change output.
        switch changeType {
        case P2WKHChangeAddress:
                weightEstimate.AddP2WKHOutput()

        case P2TRChangeAddress:
                weightEstimate.AddP2TROutput()

        case ExistingChangeAddress:
                // Don't add an extra output.

        default:
                return 0, 0, fmt.Errorf("unknown change address type: %v",
                        changeType)
        }

        // Now that we have added the change output, redo the fee
        // estimate.
        totalWeight = weightEstimate.Weight()
        requiredFeeWithChange := feeRate.FeeForWeight(totalWeight)

        return requiredFeeNoChange, requiredFeeWithChange, nil
}

// sanityCheckFee checks if the specified fee amounts to what the provided ratio
// allows.
func sanityCheckFee(totalOut, fee btcutil.Amount, maxFeeRatio float64) error {
        // Sanity check the maxFeeRatio itself.
        if maxFeeRatio <= 0.00 || maxFeeRatio > 1.00 {
                return fmt.Errorf("maxFeeRatio must be between 0.00 and 1.00 "+
                        "got %.2f", maxFeeRatio)
        }

        maxFee := btcutil.Amount(float64(totalOut) * maxFeeRatio)

        // Check that the fees do not exceed the max allowed value.
        if fee > maxFee {
                return fmt.Errorf("fee %v exceeds max fee (%v) on total "+
                        "output value %v with max fee ratio of %.2f", fee,
                        maxFee, totalOut, maxFeeRatio)
        }

        // All checks passed, we return nil to signal that the fees are valid.
        return nil
}

// CoinSelect attempts to select a sufficient amount of coins, including a
// change output to fund amt satoshis, adhering to the specified fee rate. The
// specified fee rate should be expressed in sat/kw for coin selection to
// function properly.
func CoinSelect(feeRate chainfee.SatPerKWeight, amt, dustLimit btcutil.Amount,
        coins []wallet.Coin, strategy wallet.CoinSelectionStrategy,
        existingWeight input.TxWeightEstimator,
        changeType ChangeAddressType, maxFeeRatio float64) ([]wallet.Coin,
        btcutil.Amount, error) {

        amtNeeded := amt
        for {
                // First perform an initial round of coin selection to estimate
                // the required fee.
                totalSat, selectedUtxos, err := selectInputs(
                        amtNeeded, coins, strategy, feeRate,
                )
                if err != nil {
                        return nil, 0, err
                }

                // Obtain fee estimates both with and without using a change
                // output.
                requiredFeeNoChange, requiredFeeWithChange, err := calculateFees(
                        selectedUtxos, feeRate, existingWeight, changeType,
                )
                if err != nil {
                        return nil, 0, err
                }

                changeAmount, newAmtNeeded, err := CalculateChangeAmount(
                        totalSat, amt, requiredFeeNoChange,
                        requiredFeeWithChange, dustLimit, changeType,
                        maxFeeRatio,
                )
                if err != nil {
                        return nil, 0, err
                }

                // Need another round, the selected coins aren't enough to pay
                // for the fees.
                if newAmtNeeded != 0 {
                        amtNeeded = newAmtNeeded

                        continue
                }

                // Coin selection was successful.
                return selectedUtxos, changeAmount, nil
        }
}

// CalculateChangeAmount calculates the change amount being left over when the
// given total amount of sats is provided as inputs for the required output
// amount. The calculation takes into account that we might not want to add a
// change output if the change amount is below the dust limit. The first amount
// returned is the change amount. If that is non-zero, change is left over and
// should be dealt with. The second amount, if non-zero, indicates that the
// total input amount was just not enough to pay for the required amount and
// fees and that more coins need to be selected.
func CalculateChangeAmount(totalInputAmt, requiredAmt, requiredFeeNoChange,
        requiredFeeWithChange, dustLimit btcutil.Amount,
        changeType ChangeAddressType, maxFeeRatio float64) (btcutil.Amount,
        btcutil.Amount, error) {

        // This is just a sanity check to make sure the function is used
        // correctly.
        if changeType == ExistingChangeAddress &&
                requiredFeeNoChange != requiredFeeWithChange {

                return 0, 0, fmt.Errorf("when using existing change address, " +
                        "the fees for with or without change must be the same")
        }

        // The difference between the selected amount and the amount
        // requested will be used to pay fees, and generate a change
        // output with the remaining.
        overShootAmt := totalInputAmt - requiredAmt

        var changeAmt btcutil.Amount

        switch {
        // If the excess amount isn't enough to pay for fees based on
        // fee rate and estimated size without using a change output,
        // then increase the requested coin amount by the estimate
        // required fee without using change, performing another round
        // of coin selection.
        case overShootAmt < requiredFeeNoChange:
                return 0, requiredAmt + requiredFeeNoChange, nil

        // If sufficient funds were selected to cover the fee required
        // to include a change output, the remainder will be our change
        // amount.
        case overShootAmt > requiredFeeWithChange:
                changeAmt = overShootAmt - requiredFeeWithChange

        // Otherwise we have selected enough to pay for a tx without a
        // change output.
        default:
                changeAmt = 0
        }

        // In case we would end up with a dust output if we created a
        // change output, we instead just let the dust amount go to
        // fees. Unless we want the change to go to an existing output,
        // in that case we can increase that output value by any amount.
        if changeAmt < dustLimit && changeType != ExistingChangeAddress {
                changeAmt = 0
        }

        // Sanity check the resulting output values to make sure we
        // don't burn a great part to fees.
        totalOut := requiredAmt + changeAmt

        err := sanityCheckFee(totalOut, totalInputAmt-totalOut, maxFeeRatio)
        if err != nil {
                return 0, 0, err
        }

        return changeAmt, 0, nil
}

// CoinSelectSubtractFees attempts to select coins such that we'll spend up to
// amt in total after fees, adhering to the specified fee rate. The selected
// coins, the final output and change values are returned.
func CoinSelectSubtractFees(feeRate chainfee.SatPerKWeight, amt,
        dustLimit btcutil.Amount, coins []wallet.Coin,
        strategy wallet.CoinSelectionStrategy,
        existingWeight input.TxWeightEstimator, changeType ChangeAddressType,
        maxFeeRatio float64) ([]wallet.Coin, btcutil.Amount, btcutil.Amount,
        error) {

        // First perform an initial round of coin selection to estimate
        // the required fee.
        totalSat, selectedUtxos, err := selectInputs(
                amt, coins, strategy, feeRate,
        )
        if err != nil {
                return nil, 0, 0, err
        }

        // Obtain fee estimates both with and without using a change
        // output.
        requiredFeeNoChange, requiredFeeWithChange, err := calculateFees(
                selectedUtxos, feeRate, existingWeight, changeType,
        )
        if err != nil {
                return nil, 0, 0, err
        }

        // For a transaction without a change output, we'll let everything go
        // to our multi-sig output after subtracting fees.
        outputAmt := totalSat - requiredFeeNoChange
        changeAmt := btcutil.Amount(0)

        // If the output is too small after subtracting the fee, the coin
        // selection cannot be performed with an amount this small.
        if outputAmt < dustLimit {
                return nil, 0, 0, fmt.Errorf("output amount(%v) after "+
                        "subtracting fees(%v) below dust limit(%v)", outputAmt,
                        requiredFeeNoChange, dustLimit)
        }

        // For a transaction with a change output, everything we don't spend
        // will go to change.
        newOutput := amt - requiredFeeWithChange
        newChange := totalSat - amt

        // If adding a change output leads to both outputs being above
        // the dust limit, we'll add the change output. Otherwise we'll
        // go with the no change tx we originally found.
        if newChange >= dustLimit && newOutput >= dustLimit {
                outputAmt = newOutput
                changeAmt = newChange
        }

        // Sanity check the resulting output values to make sure we
        // don't burn a great part to fees.
        totalOut := outputAmt + changeAmt
        err = sanityCheckFee(totalOut, totalSat-totalOut, maxFeeRatio)
        if err != nil {
                return nil, 0, 0, err
        }

        return selectedUtxos, outputAmt, changeAmt, nil
}

// CoinSelectUpToAmount attempts to select coins such that we'll select up to
// maxAmount exclusive of fees and optional reserve if sufficient funds are
// available. If insufficient funds are available this method selects all
// available coins.
func CoinSelectUpToAmount(feeRate chainfee.SatPerKWeight, minAmount, maxAmount,
        reserved, dustLimit btcutil.Amount, coins []wallet.Coin,
        strategy wallet.CoinSelectionStrategy,
        existingWeight input.TxWeightEstimator,
        changeType ChangeAddressType, maxFeeRatio float64) ([]wallet.Coin,
        btcutil.Amount, btcutil.Amount, error) {

        var (
                // selectSubtractFee is tracking if our coin selection was
                // unsuccessful and whether we have to start a new round of
                // selecting coins considering fees.
                selectSubtractFee = false
                outputAmount      = maxAmount
        )

        // Get total balance from coins which we need for reserve considerations
        // and fee sanity checks.
        var totalBalance btcutil.Amount
        for _, coin := range coins {
                totalBalance += btcutil.Amount(coin.Value)
        }

        // First we try to select coins to create an output of the specified
        // maxAmount with or without a change output that covers the miner fee.
        selected, changeAmt, err := CoinSelect(
                feeRate, maxAmount, dustLimit, coins, strategy, existingWeight,
                changeType, maxFeeRatio,
        )

        var errInsufficientFunds *ErrInsufficientFunds
        switch {
        case err == nil:
                // If the coin selection succeeds we check if our total balance
                // covers the selected set of coins including fees plus an
                // optional anchor reserve.

                // First we sum up the value of all selected coins.
                var sumSelected btcutil.Amount
                for _, coin := range selected {
                        sumSelected += btcutil.Amount(coin.Value)
                }

                // We then subtract the change amount from the value of all
                // selected coins to obtain the actual amount that is selected.
                sumSelected -= changeAmt

                // Next we check if our total balance can cover for the selected
                // output plus the optional anchor reserve.
                if totalBalance-sumSelected < reserved {
                        // If our local balance is insufficient to cover for the
                        // reserve we try to select an output amount that uses
                        // our total balance minus reserve and fees.
                        selectSubtractFee = true
                }

        case errors.As(err, &errInsufficientFunds):
                // If the initial coin selection fails due to insufficient funds
                // we select our total available balance minus fees.
                selectSubtractFee = true

        default:
                return nil, 0, 0, err
        }

        // If we determined that our local balance is insufficient we check
        // our total balance minus fees and optional reserve.
        if selectSubtractFee {
                selected, outputAmount, changeAmt, err = CoinSelectSubtractFees(
                        feeRate, totalBalance-reserved, dustLimit, coins,
                        strategy, existingWeight, changeType, maxFeeRatio,
                )
                if err != nil {
                        return nil, 0, 0, err
                }
        }

        // Sanity check the resulting output values to make sure we don't burn a
        // great part to fees.
        totalOut := outputAmount + changeAmt
        sum := func(coins []wallet.Coin) btcutil.Amount {
                var sum btcutil.Amount
                for _, coin := range coins {
                        sum += btcutil.Amount(coin.Value)
                }

                return sum
        }
        err = sanityCheckFee(totalOut, sum(selected)-totalOut, maxFeeRatio)
        if err != nil {
                return nil, 0, 0, err
        }

        // In case the selected amount is lower than minimum funding amount we
        // must return an error. The minimum funding amount is determined
        // upstream and denotes either the minimum viable channel size or an
        // amount sufficient to cover for the initial remote balance.
        if outputAmount < minAmount {
                return nil, 0, 0, fmt.Errorf("available funds(%v) below the "+
                        "minimum amount(%v)", outputAmount, minAmount)
        }

        return selected, outputAmount, changeAmt, nil
}

1	package chanfunding
2
3	import (
4	"errors"
5	"fmt"
6
7	"github.com/btcsuite/btcd/btcutil"
8	"github.com/btcsuite/btcd/txscript"
9	"github.com/btcsuite/btcwallet/wallet"
10	"github.com/lightningnetwork/lnd/input"
11	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
12	)
13
14	// ErrInsufficientFunds is a type matching the error interface which is
15	// returned when coin selection for a new funding transaction fails due to
16	// having an insufficient amount of confirmed funds.
17	type ErrInsufficientFunds struct {
18	amountAvailable btcutil.Amount
19	amountSelected btcutil.Amount
20	}
21
22	// Error returns a human-readable string describing the error.
23	func (e *ErrInsufficientFunds) Error() string {	3✔
24	return fmt.Sprintf("not enough witness outputs to create funding "+	3✔
25	"transaction, need %v only have %v available",	3✔
26	e.amountAvailable, e.amountSelected)	3✔
27	}	3✔
28
29	// errUnsupportedInput is a type matching the error interface, which is returned
30	// when trying to calculate the fee of a transaction that references an
31	// unsupported script in the outpoint of a transaction input.
32	type errUnsupportedInput struct {
33	PkScript []byte
34	}
35
36	// Error returns a human-readable string describing the error.
37	func (e *errUnsupportedInput) Error() string {	×
38	return fmt.Sprintf("unsupported address type: %x", e.PkScript)	×
39	}	×
40
41	// ChangeAddressType is an enum-like type that describes the type of change
42	// address that should be generated for a transaction.
43	type ChangeAddressType uint8
44
45	const (
46	// P2WKHChangeAddress indicates that the change output should be a
47	// P2WKH output.
48	P2WKHChangeAddress ChangeAddressType = 0
49
50	// P2TRChangeAddress indicates that the change output should be a
51	// P2TR output.
52	P2TRChangeAddress ChangeAddressType = 1
53
54	// ExistingChangeAddress indicates that the coin selection algorithm
55	// should assume an existing output will be used for any change, meaning
56	// that the change amount calculated will be added to an existing output
57	// and no weight for a new change output should be assumed. The caller
58	// must assert that the output value of the selected existing output
59	// already is above dust when using this change address type.
60	ExistingChangeAddress ChangeAddressType = 2
61
62	// DefaultMaxFeeRatio is the default fee to total amount of outputs
63	// ratio that is used to sanity check the fees of a transaction.
64	DefaultMaxFeeRatio float64 = 0.2
65	)
66
67	// selectInputs selects a slice of inputs necessary to meet the specified
68	// selection amount. If input selection is unable to succeed due to insufficient
69	// funds, a non-nil error is returned. Additionally, the total amount of the
70	// selected coins are returned in order for the caller to properly handle
71	// change+fees.
72	func selectInputs(amt btcutil.Amount, coins []wallet.Coin,
73	strategy wallet.CoinSelectionStrategy,
74	feeRate chainfee.SatPerKWeight) (btcutil.Amount, []wallet.Coin, error) {	146✔
75		146✔
76	// All coin selection code in the btcwallet library requires sat/KB.	146✔
77	feeSatPerKB := btcutil.Amount(feeRate.FeePerKVByte())	146✔
78		146✔
79	arrangedCoins, err := strategy.ArrangeCoins(coins, feeSatPerKB)	146✔
80	if err != nil {	146✔
81	return 0, nil, err	×
82	}	×
83
84	satSelected := btcutil.Amount(0)	146✔
85	for i, coin := range arrangedCoins {	475✔
86	satSelected += btcutil.Amount(coin.Value)	329✔
87	if satSelected >= amt {	460✔
88	return satSelected, arrangedCoins[:i+1], nil	131✔
89	}	131✔
90	}
91
92	return 0, nil, &ErrInsufficientFunds{amt, satSelected}	18✔
93	}
94
95	// calculateFees returns for the specified utxos and fee rate two fee
96	// estimates, one calculated using a change output and one without. The weight
97	// added to the estimator from a change output is for a P2WKH output.
98	func calculateFees(utxos []wallet.Coin, feeRate chainfee.SatPerKWeight,
99	existingWeight input.TxWeightEstimator,
100	changeType ChangeAddressType) (btcutil.Amount, btcutil.Amount, error) {	134✔
101		134✔
102	weightEstimate := existingWeight	134✔
103	for _, utxo := range utxos {	388✔
104	switch {	254✔
105	case txscript.IsPayToWitnessPubKeyHash(utxo.PkScript):	230✔
106	weightEstimate.AddP2WKHInput()	230✔
107
108	case txscript.IsPayToScriptHash(utxo.PkScript):	4✔
109	weightEstimate.AddNestedP2WKHInput()	4✔
110
111	case txscript.IsPayToTaproot(utxo.PkScript):	25✔
112	weightEstimate.AddTaprootKeySpendInput(	25✔
113	txscript.SigHashDefault,	25✔
114	)	25✔
115
116	default:	1✔
117	return 0, 0, &errUnsupportedInput{utxo.PkScript}	1✔
118	}
119	}
120
121	// Estimate the fee required for a transaction without a change
122	// output.
123	totalWeight := weightEstimate.Weight()	133✔
124	requiredFeeNoChange := feeRate.FeeForWeight(totalWeight)	133✔
125		133✔
126	// Estimate the fee required for a transaction with a change output.	133✔
127	switch changeType {	133✔
128	case P2WKHChangeAddress:	×
129	weightEstimate.AddP2WKHOutput()	×
130
131	case P2TRChangeAddress:	132✔
132	weightEstimate.AddP2TROutput()	132✔
133
134	case ExistingChangeAddress:	4✔
135	// Don't add an extra output.
136
137	default:	×
138	return 0, 0, fmt.Errorf("unknown change address type: %v",	×
139	changeType)	×
140	}
141
142	// Now that we have added the change output, redo the fee
143	// estimate.
144	totalWeight = weightEstimate.Weight()	133✔
145	requiredFeeWithChange := feeRate.FeeForWeight(totalWeight)	133✔
146		133✔
147	return requiredFeeNoChange, requiredFeeWithChange, nil	133✔
148	}
149
150	// sanityCheckFee checks if the specified fee amounts to what the provided ratio
151	// allows.
152	func sanityCheckFee(totalOut, fee btcutil.Amount, maxFeeRatio float64) error {	121✔
153	// Sanity check the maxFeeRatio itself.	121✔
154	if maxFeeRatio <= 0.00 \|\| maxFeeRatio > 1.00 {	122✔
155	return fmt.Errorf("maxFeeRatio must be between 0.00 and 1.00 "+	1✔
156	"got %.2f", maxFeeRatio)	1✔
157	}	1✔
158
159	maxFee := btcutil.Amount(float64(totalOut) * maxFeeRatio)	120✔
160		120✔
161	// Check that the fees do not exceed the max allowed value.	120✔
162	if fee > maxFee {	124✔
163	return fmt.Errorf("fee %v exceeds max fee (%v) on total "+	4✔
164	"output value %v with max fee ratio of %.2f", fee,	4✔
165	maxFee, totalOut, maxFeeRatio)	4✔
166	}	4✔
167
168	// All checks passed, we return nil to signal that the fees are valid.
169	return nil	116✔
170	}
171
172	// CoinSelect attempts to select a sufficient amount of coins, including a
173	// change output to fund amt satoshis, adhering to the specified fee rate. The
174	// specified fee rate should be expressed in sat/kw for coin selection to
175	// function properly.
176	func CoinSelect(feeRate chainfee.SatPerKWeight, amt, dustLimit btcutil.Amount,
177	coins []wallet.Coin, strategy wallet.CoinSelectionStrategy,
178	existingWeight input.TxWeightEstimator,
179	changeType ChangeAddressType, maxFeeRatio float64) ([]wallet.Coin,
180	btcutil.Amount, error) {	104✔
181		104✔
182	amtNeeded := amt	104✔
183	for {	234✔
184	// First perform an initial round of coin selection to estimate	130✔
185	// the required fee.	130✔
186	totalSat, selectedUtxos, err := selectInputs(	130✔
187	amtNeeded, coins, strategy, feeRate,	130✔
188	)	130✔
189	if err != nil {	148✔
190	return nil, 0, err	18✔
191	}	18✔
192
193	// Obtain fee estimates both with and without using a change
194	// output.
195	requiredFeeNoChange, requiredFeeWithChange, err := calculateFees(	115✔
196	selectedUtxos, feeRate, existingWeight, changeType,	115✔
197	)	115✔
198	if err != nil {	115✔
199	return nil, 0, err	×
200	}	×
201
202	changeAmount, newAmtNeeded, err := CalculateChangeAmount(	115✔
203	totalSat, amt, requiredFeeNoChange,	115✔
204	requiredFeeWithChange, dustLimit, changeType,	115✔
205	maxFeeRatio,	115✔
206	)	115✔
207	if err != nil {	117✔
208	return nil, 0, err	2✔
209	}	2✔
210
211	// Need another round, the selected coins aren't enough to pay
212	// for the fees.
213	if newAmtNeeded != 0 {	139✔
214	amtNeeded = newAmtNeeded	26✔
215		26✔
216	continue	26✔
217	}
218
219	// Coin selection was successful.
220	return selectedUtxos, changeAmount, nil	87✔
221	}
222	}
223
224	// CalculateChangeAmount calculates the change amount being left over when the
225	// given total amount of sats is provided as inputs for the required output
226	// amount. The calculation takes into account that we might not want to add a
227	// change output if the change amount is below the dust limit. The first amount
228	// returned is the change amount. If that is non-zero, change is left over and
229	// should be dealt with. The second amount, if non-zero, indicates that the
230	// total input amount was just not enough to pay for the required amount and
231	// fees and that more coins need to be selected.
232	func CalculateChangeAmount(totalInputAmt, requiredAmt, requiredFeeNoChange,
233	requiredFeeWithChange, dustLimit btcutil.Amount,
234	changeType ChangeAddressType, maxFeeRatio float64) (btcutil.Amount,
235	btcutil.Amount, error) {	123✔
236		123✔
237	// This is just a sanity check to make sure the function is used	123✔
238	// correctly.	123✔
239	if changeType == ExistingChangeAddress &&	123✔
240	requiredFeeNoChange != requiredFeeWithChange {	124✔
241		1✔
242	return 0, 0, fmt.Errorf("when using existing change address, " +	1✔
243	"the fees for with or without change must be the same")	1✔
244	}	1✔
245
246	// The difference between the selected amount and the amount
247	// requested will be used to pay fees, and generate a change
248	// output with the remaining.
249	overShootAmt := totalInputAmt - requiredAmt	122✔
250		122✔
251	var changeAmt btcutil.Amount	122✔
252		122✔
253	switch {	122✔
254	// If the excess amount isn't enough to pay for fees based on
255	// fee rate and estimated size without using a change output,
256	// then increase the requested coin amount by the estimate
257	// required fee without using change, performing another round
258	// of coin selection.
259	case overShootAmt < requiredFeeNoChange:	27✔
260	return 0, requiredAmt + requiredFeeNoChange, nil	27✔
261
262	// If sufficient funds were selected to cover the fee required
263	// to include a change output, the remainder will be our change
264	// amount.
265	case overShootAmt > requiredFeeWithChange:	92✔
266	changeAmt = overShootAmt - requiredFeeWithChange	92✔
267
268	// Otherwise we have selected enough to pay for a tx without a
269	// change output.
270	default:	6✔
271	changeAmt = 0	6✔
272	}
273
274	// In case we would end up with a dust output if we created a
275	// change output, we instead just let the dust amount go to
276	// fees. Unless we want the change to go to an existing output,
277	// in that case we can increase that output value by any amount.
278	if changeAmt < dustLimit && changeType != ExistingChangeAddress {	102✔
279	changeAmt = 0	7✔
280	}	7✔
281
282	// Sanity check the resulting output values to make sure we
283	// don't burn a great part to fees.
284	totalOut := requiredAmt + changeAmt	95✔
285		95✔
286	err := sanityCheckFee(totalOut, totalInputAmt-totalOut, maxFeeRatio)	95✔
287	if err != nil {	99✔
288	return 0, 0, err	4✔
289	}	4✔
290
291	return changeAmt, 0, nil	91✔
292	}
293
294	// CoinSelectSubtractFees attempts to select coins such that we'll spend up to
295	// amt in total after fees, adhering to the specified fee rate. The selected
296	// coins, the final output and change values are returned.
297	func CoinSelectSubtractFees(feeRate chainfee.SatPerKWeight, amt,
298	dustLimit btcutil.Amount, coins []wallet.Coin,
299	strategy wallet.CoinSelectionStrategy,
300	existingWeight input.TxWeightEstimator, changeType ChangeAddressType,
301	maxFeeRatio float64) ([]wallet.Coin, btcutil.Amount, btcutil.Amount,
302	error) {	19✔
303		19✔
304	// First perform an initial round of coin selection to estimate	19✔
305	// the required fee.	19✔
306	totalSat, selectedUtxos, err := selectInputs(	19✔
307	amt, coins, strategy, feeRate,	19✔
308	)	19✔
309	if err != nil {	19✔
310	return nil, 0, 0, err	×
311	}	×
312
313	// Obtain fee estimates both with and without using a change
314	// output.
315	requiredFeeNoChange, requiredFeeWithChange, err := calculateFees(	19✔
316	selectedUtxos, feeRate, existingWeight, changeType,	19✔
317	)	19✔
318	if err != nil {	19✔
319	return nil, 0, 0, err	×
320	}	×
321
322	// For a transaction without a change output, we'll let everything go
323	// to our multi-sig output after subtracting fees.
324	outputAmt := totalSat - requiredFeeNoChange	19✔
325	changeAmt := btcutil.Amount(0)	19✔
326		19✔
327	// If the output is too small after subtracting the fee, the coin	19✔
328	// selection cannot be performed with an amount this small.	19✔
329	if outputAmt < dustLimit {	24✔
330	return nil, 0, 0, fmt.Errorf("output amount(%v) after "+	5✔
331	"subtracting fees(%v) below dust limit(%v)", outputAmt,	5✔
332	requiredFeeNoChange, dustLimit)	5✔
333	}	5✔
334
335	// For a transaction with a change output, everything we don't spend
336	// will go to change.
337	newOutput := amt - requiredFeeWithChange	17✔
338	newChange := totalSat - amt	17✔
339		17✔
340	// If adding a change output leads to both outputs being above	17✔
341	// the dust limit, we'll add the change output. Otherwise we'll	17✔
342	// go with the no change tx we originally found.	17✔
343	if newChange >= dustLimit && newOutput >= dustLimit {	23✔
344	outputAmt = newOutput	6✔
345	changeAmt = newChange	6✔
346	}	6✔
347
348	// Sanity check the resulting output values to make sure we
349	// don't burn a great part to fees.
350	totalOut := outputAmt + changeAmt	17✔
351	err = sanityCheckFee(totalOut, totalSat-totalOut, maxFeeRatio)	17✔
352	if err != nil {	18✔
353	return nil, 0, 0, err	1✔
354	}	1✔
355
356	return selectedUtxos, outputAmt, changeAmt, nil	16✔
357	}
358
359	// CoinSelectUpToAmount attempts to select coins such that we'll select up to
360	// maxAmount exclusive of fees and optional reserve if sufficient funds are
361	// available. If insufficient funds are available this method selects all
362	// available coins.
363	func CoinSelectUpToAmount(feeRate chainfee.SatPerKWeight, minAmount, maxAmount,
364	reserved, dustLimit btcutil.Amount, coins []wallet.Coin,
365	strategy wallet.CoinSelectionStrategy,
366	existingWeight input.TxWeightEstimator,
367	changeType ChangeAddressType, maxFeeRatio float64) ([]wallet.Coin,
368	btcutil.Amount, btcutil.Amount, error) {	17✔
369		17✔
370	var (	17✔
371	// selectSubtractFee is tracking if our coin selection was	17✔
372	// unsuccessful and whether we have to start a new round of	17✔
373	// selecting coins considering fees.	17✔
374	selectSubtractFee = false	17✔
375	outputAmount = maxAmount	17✔
376	)	17✔
377		17✔
378	// Get total balance from coins which we need for reserve considerations	17✔
379	// and fee sanity checks.	17✔
380	var totalBalance btcutil.Amount	17✔
381	for _, coin := range coins {	36✔
382	totalBalance += btcutil.Amount(coin.Value)	19✔
383	}	19✔
384
385	// First we try to select coins to create an output of the specified
386	// maxAmount with or without a change output that covers the miner fee.
387	selected, changeAmt, err := CoinSelect(	17✔
388	feeRate, maxAmount, dustLimit, coins, strategy, existingWeight,	17✔
389	changeType, maxFeeRatio,	17✔
390	)	17✔
391		17✔
392	var errInsufficientFunds *ErrInsufficientFunds	17✔
393	switch {	17✔
394	case err == nil:	10✔
395	// If the coin selection succeeds we check if our total balance	10✔
396	// covers the selected set of coins including fees plus an	10✔
397	// optional anchor reserve.	10✔
398		10✔
399	// First we sum up the value of all selected coins.	10✔
400	var sumSelected btcutil.Amount	10✔
401	for _, coin := range selected {	21✔
402	sumSelected += btcutil.Amount(coin.Value)	11✔
403	}	11✔
404
405	// We then subtract the change amount from the value of all
406	// selected coins to obtain the actual amount that is selected.
407	sumSelected -= changeAmt	10✔
408		10✔
409	// Next we check if our total balance can cover for the selected	10✔
410	// output plus the optional anchor reserve.	10✔
411	if totalBalance-sumSelected < reserved {	11✔
412	// If our local balance is insufficient to cover for the	1✔
413	// reserve we try to select an output amount that uses	1✔
414	// our total balance minus reserve and fees.	1✔
415	selectSubtractFee = true	1✔
416	}	1✔
417
418	case errors.As(err, &errInsufficientFunds):	9✔
419	// If the initial coin selection fails due to insufficient funds	9✔
420	// we select our total available balance minus fees.	9✔
421	selectSubtractFee = true	9✔
422
423	default:	1✔
424	return nil, 0, 0, err	1✔
425	}
426
427	// If we determined that our local balance is insufficient we check
428	// our total balance minus fees and optional reserve.
429	if selectSubtractFee {	26✔
430	selected, outputAmount, changeAmt, err = CoinSelectSubtractFees(	10✔
431	feeRate, totalBalance-reserved, dustLimit, coins,	10✔
432	strategy, existingWeight, changeType, maxFeeRatio,	10✔
433	)	10✔
434	if err != nil {	14✔
435	return nil, 0, 0, err	4✔
436	}	4✔
437	}
438
439	// Sanity check the resulting output values to make sure we don't burn a
440	// great part to fees.
441	totalOut := outputAmount + changeAmt	15✔
442	sum := func(coins []wallet.Coin) btcutil.Amount {	30✔
443	var sum btcutil.Amount	15✔
444	for _, coin := range coins {	32✔
445	sum += btcutil.Amount(coin.Value)	17✔
446	}	17✔
447
448	return sum	15✔
449	}
450	err = sanityCheckFee(totalOut, sum(selected)-totalOut, maxFeeRatio)	15✔
451	if err != nil {	15✔
452	return nil, 0, 0, err	×
453	}	×
454
455	// In case the selected amount is lower than minimum funding amount we
456	// must return an error. The minimum funding amount is determined
457	// upstream and denotes either the minimum viable channel size or an
458	// amount sufficient to cover for the initial remote balance.
459	if outputAmount < minAmount {	18✔
460	return nil, 0, 0, fmt.Errorf("available funds(%v) below the "+	3✔
461	"minimum amount(%v)", outputAmount, minAmount)	3✔
462	}	3✔
463
464	return selected, outputAmount, changeAmt, nil	15✔
465	}

lightningnetwork / lnd / 13586005509

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