9915780197

Committed 13 Jul 2024 12:30AM UTC coverage: 49.268% (-9.1%) from 58.413%

Build # 9915780197

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Merge pull request #8653 from ProofOfKeags/fn-prim

DynComms [0/n]: `fn` package additions

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/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
)

// 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 over 20% of the total
// output amount and raises an error.
func sanityCheckFee(totalOut, fee btcutil.Amount) error {
        // Fail if more than 20% goes to fees.
        // TODO(halseth): smarter fee limit. Make configurable or dynamic wrt
        // total funding size?
        if fee > totalOut/5 {
                return fmt.Errorf("fee %v on total output value %v", fee,
                        totalOut)
        }
        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) ([]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,
                )
                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) (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)
        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) ([]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)
        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) ([]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,
        )

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

lightningnetwork / lnd / 9915780197

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