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Fix intermittent "fee cannot be less than vSize" errors and Firo EX address sends #1426

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Fix intermittent "fee cannot be less than vSize" errors and Firo EX address sends #1426

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c8c871f
Fix intermittent fee-less-than-vSize failures in fee estimation
claude Aug 6, 2026
741bd24
Fix sends to Firo EX addresses via optimal coin selection
claude Aug 6, 2026
f1010bc
Merge branch 'staging' into claude/fee-vsize-consistency
reubenyap Aug 6, 2026
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2 changes: 2 additions & 0 deletions lib/utilities/extensions/impl/big_int.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@
import 'dart:typed_data';

extension BigIntExtensions on BigInt {
BigInt atLeast(BigInt minimum) => this < minimum ? minimum : this;

String get toHex {
if (this < BigInt.zero) {
throw Exception("BigInt value is negative");
Expand Down
166 changes: 78 additions & 88 deletions lib/wallets/wallet/wallet_mixin_interfaces/electrumx_interface.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -404,8 +404,10 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
),
);
return txnData.copyWith(
// No change output, so the whole difference is the fee (which can
// exceed [feeForOneOutput]).
fee: Amount(
rawValue: feeForOneOutput,
rawValue: difference,
fractionDigits: cryptoCurrency.fractionDigits,
),
usedUTXOs: inputsWithKeys,
Expand Down Expand Up @@ -470,24 +472,30 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
),
);

// make sure minimum fee is accurate if that is being used
if (BigInt.from(txnData.vSize!) - feeBeingPaid == BigInt.one) {
final changeOutputSize = difference - BigInt.from(txnData.vSize!);
feeBeingPaid = difference - changeOutputSize;
recipientsAmtArray.removeLast();
recipientsAmtArray.add(changeOutputSize);
// The fee was estimated from a differently signed build and
// re-signing can change vSize, so it may no longer cover the final
// signed size. Take any shortfall from change.
while (feeBeingPaid < BigInt.from(txnData.vSize!)) {
final vSize = BigInt.from(txnData.vSize!);
final adjustedChangeSize = difference - vSize;
if (adjustedChangeSize <= cryptoCurrency.dustLimit.raw) {
// Drop the change output entirely.
recipientsArray.removeLast();
recipientsAmtArray.removeLast();
Logging.instance.d(
'Adjusted change would be dust, reverting to 1 output in tx',
);
return await singleOutputTxn();
}
feeBeingPaid = vSize;
recipientsAmtArray.last = adjustedChangeSize;

Logging.instance.d('Adjusted Input size: $satoshisBeingUsed');
Logging.instance.d(
'Adjusted Recipient output size: $satoshiAmountToSend',
);
Logging.instance.d(
'Adjusted Change Output Size: $changeOutputSize',
'Adjusted Change Output Size: $adjustedChangeSize',
);
Logging.instance.d(
'Adjusted Difference (fee being paid): $feeBeingPaid sats',
);
Logging.instance.d('Adjusted Estimated fee: $feeForTwoOutputs');

txnData = await buildTransaction(
inputsWithKeys: inputsWithKeys,
Expand Down Expand Up @@ -570,45 +578,8 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
}

late TxData data;
if (txData.type == TxType.mwebPegIn) {
while (true) {
final satoshiAmountToSend = satoshisBeingUsed - feeForOneOutput;
if (satoshiAmountToSend.isNegative) {
throw Exception(
"Estimated fee ($feeForOneOutput sats) is greater than balance!",
);
}

data = await buildTransaction(
txData: txData.copyWith(
recipients: await helperRecipientsConvert(
[recipientAddress],
[satoshiAmountToSend],
),
),
inputsWithKeys: inputsWithKeys,
);

if (overrideFeeAmount != null) {
break;
}

// Signing can change vSize, so calculate the fee from the final tx.
final vSize = BigInt.from(data.vSize!);
final feeForFinalVSize = BigInt.from(
satsPerVByte != null
? satsPerVByte * data.vSize!
: estimateTxFee(vSize: data.vSize!, feeRatePerKB: feeRatePerKB),
);
final requiredFee = feeForFinalVSize > vSize ? feeForFinalVSize : vSize;
if (feeForOneOutput >= requiredFee) {
break;
}
feeForOneOutput = requiredFee;
}
} else {
while (true) {
final satoshiAmountToSend = satoshisBeingUsed - feeForOneOutput;

if (satoshiAmountToSend.isNegative) {
throw Exception(
"Estimated fee ($feeForOneOutput sats) is greater than balance!",
Expand All @@ -624,6 +595,27 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
),
inputsWithKeys: inputsWithKeys,
);

// Stop when the fee is not authoritative: overridden by the caller, or
// MWEB (except peg ins) whose fee is recalculated by the caller later.
if (overrideFeeAmount != null ||
txData.type == TxType.mweb ||
txData.type == TxType.mwebPegOut) {
break;
}

// Signing can change vSize, so calculate the fee from the final tx.
final vSize = BigInt.from(data.vSize!);
final feeForFinalVSize = BigInt.from(
satsPerVByte != null
? satsPerVByte * data.vSize!
: estimateTxFee(vSize: data.vSize!, feeRatePerKB: feeRatePerKB),
);
final requiredFee = feeForFinalVSize.atLeast(vSize);
if (feeForOneOutput >= requiredFee) {
break;
}
feeForOneOutput = requiredFee;
}

return data.copyWith(
Expand All @@ -635,6 +627,26 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
);
}

/// Parses [address], falling back to Firo EX (exchange) address parsing
/// which plain [coinlib.Address.fromString] does not support.
coinlib.Address _addressFromString(String address) {
final normalized = normalizeAddress(address);
try {
return coinlib.Address.fromString(
normalized,
cryptoCurrency.networkParams,
);
} catch (_) {
if (this is FiroWallet) {
return EXP2PKHAddress.fromString(
normalized,
(cryptoCurrency as Firo).exAddressVersion,
);
}
rethrow;
}
}

coinlib.Input standardInputToCoinlibInput(
StandardInput input, {
int sequence = 0xffffffff,
Expand Down Expand Up @@ -728,13 +740,9 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
candidateBaseInputs[i] = baseInput;
}

final coinlib.Address clRecipientAddress = coinlib.Address.fromString(
normalizeAddress(recipientAddress),
cryptoCurrency.networkParams,
);
final coinlib.Output recipientOutput = coinlib.Output.fromAddress(
satoshiAmountToSend,
clRecipientAddress,
_addressFromString(recipientAddress),
);

final coinlib.Address clChangeAddress = coinlib.Address.fromString(
Expand Down Expand Up @@ -1010,23 +1018,7 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>

// Add transaction output
for (var i = 0; i < txData.recipients!.length; i++) {
late final coinlib.Address address;

try {
address = coinlib.Address.fromString(
normalizeAddress(txData.recipients![i].address),
cryptoCurrency.networkParams,
);
} catch (_) {
if (this is FiroWallet) {
address = EXP2PKHAddress.fromString(
normalizeAddress(txData.recipients![i].address),
(cryptoCurrency as Firo).exAddressVersion,
);
} else {
rethrow;
}
}
final address = _addressFromString(txData.recipients![i].address);
final coinlib.Output output;
if (address is coinlib.MwebAddress) {
isMweb = true;
Expand Down Expand Up @@ -1655,26 +1647,24 @@ mixin ElectrumXInterface<T extends ElectrumXCurrencyInterface>
try {
const int f = 1, m = 5, s = 20;

final fast = await electrumXClient.estimateFee(blocks: f);
final medium = await electrumXClient.estimateFee(blocks: m);
final slow = await electrumXClient.estimateFee(blocks: s);
// Clamp server responses below the coin's default rate, consistent
// with the -1 fallback in [ElectrumXClient.estimateFee], so a broken
// estimate cannot force the fee-vs-vSize failure in prepareSend.
Future<BigInt> rate(int blocks) async {
final raw = Amount.fromDecimal(
await electrumXClient.estimateFee(blocks: blocks),
fractionDigits: info.coin.fractionDigits,
).raw;
return raw.atLeast(cryptoCurrency.defaultFeeRate);
}

final feeObject = FeeObject(
numberOfBlocksFast: f,
numberOfBlocksAverage: m,
numberOfBlocksSlow: s,
fast: Amount.fromDecimal(
fast,
fractionDigits: info.coin.fractionDigits,
).raw,
medium: Amount.fromDecimal(
medium,
fractionDigits: info.coin.fractionDigits,
).raw,
slow: Amount.fromDecimal(
slow,
fractionDigits: info.coin.fractionDigits,
).raw,
fast: await rate(f),
medium: await rate(m),
slow: await rate(s),
);

Logging.instance.d("fetched fees: $feeObject");
Expand Down
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