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fix(wallet): keep transactions under the standard 100 KvB relay limit

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Sending a large amount from a wallet with many small UTXOs could
produce a transaction over the standard relay size limit, surfaced
only as a cryptic "Invalid transaction: Transaction's size is too
high" from builder.Verify() after everything else had already
succeeded — with no way for the user to recover other than manually
picking fewer coins.

Build() now orders spendable UTXOs largest-first and binary-searches
the smallest prefix of them that produces a valid transaction, so it
naturally prefers big coins over dust and avoids the limit whenever a
smaller input set can cover the amount. NBitcoin's own coin selector
already refuses to assemble a combination over the size cap and
reports it via NotEnoughFundsException with a distinctive message
rather than ever handing back an oversized transaction, so that case
is now recognized and translated into a clear, actionable error
instead of being read as "insufficient funds".
This commit is contained in:
Davide Grilli
2026-07-17 19:44:36 +02:00
parent 3460e53b4f
commit 1a4fefadc3
2 changed files with 172 additions and 7 deletions
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src/Core/Wallet/TransactionFactory.cs
+111 -7
View File
@@ -29,6 +29,8 @@ public sealed class BuiltTransaction
/// </summary>
public sealed class TransactionFactory(IWalletAccount account)
{
private const int MaxStandardTransactionVirtualSize = 100_000;
private Network Network => PalladiumNetworks.For(account.Profile.Kind);
/// <summary>
@@ -68,9 +70,9 @@ public sealed class TransactionFactory(IWalletAccount account)
u.Confirmations(tipHeight) < u.RequiredConfirmations(profile)).ToList();
if (immature.Count > 0)
{
var best = immature.Max(u => u.Confirmations(tipHeight));
var bestImmatureConf = immature.Max(u => u.Confirmations(tipHeight));
var threshold = profile.CoinbaseMaturity + 1;
reasons.Append($"{immature.Count} coinbase output(s) not yet mature ({best}/{threshold} confirmations). ");
reasons.Append($"{immature.Count} coinbase output(s) not yet mature ({bestImmatureConf}/{threshold} confirmations). ");
}
var underConf = utxos.Where(u =>
@@ -78,8 +80,8 @@ public sealed class TransactionFactory(IWalletAccount account)
u.Confirmations(tipHeight) < u.RequiredConfirmations(profile)).ToList();
if (underConf.Count > 0)
{
var best = underConf.Max(u => u.Confirmations(tipHeight));
reasons.Append($"{underConf.Count} output(s) need {profile.MinConfirmations} confirmations ({best} so far). ");
var bestUnderConf = underConf.Max(u => u.Confirmations(tipHeight));
reasons.Append($"{underConf.Count} output(s) need {profile.MinConfirmations} confirmations ({bestUnderConf} so far). ");
}
var unverified = utxos.Where(u =>
@@ -94,11 +96,80 @@ public sealed class TransactionFactory(IWalletAccount account)
: "No spendable UTXOs selected.");
}
var coins = spendable.Select(u => new Coin(
var ordered = spendable
.OrderByDescending(u => u.ValueSats)
.ThenBy(u => u.Height)
.ThenBy(u => u.Txid, StringComparer.Ordinal)
.ThenBy(u => u.Vout)
.ToList();
var feeRate = new FeeRate(Money.Satoshis(feeRateSatPerVByte * 1000m), 1000);
if (sendAll)
{
try
{
return BuildWithSelectedUtxos(
ordered, transactions, destination, amountSats, feeRate, changeIndex, sendAll: true, totalSpendableCount: ordered.Count);
}
catch (TransactionTooLargeException ex)
{
throw new WalletSpendException(ex.Message);
}
}
NotEnoughFundsException? lastInsufficientFunds = null;
TransactionTooLargeException? tooLarge = null;
BuiltTransaction? best = null;
var low = 1;
var high = ordered.Count;
while (low <= high)
{
var count = low + ((high - low) / 2);
try
{
best = BuildWithSelectedUtxos(
ordered.Take(count).ToList(), transactions, destination, amountSats, feeRate, changeIndex,
sendAll: false, totalSpendableCount: ordered.Count);
high = count - 1;
}
catch (NotEnoughFundsException ex)
{
lastInsufficientFunds = ex;
low = count + 1;
}
catch (TransactionTooLargeException ex)
{
tooLarge = ex;
high = count - 1;
}
}
if (best is not null)
return best;
if (tooLarge is not null)
throw new WalletSpendException(tooLarge.Message);
throw new WalletSpendException(lastInsufficientFunds is null
? "Insufficient funds."
: $"Insufficient funds: {lastInsufficientFunds.Message}");
}
private BuiltTransaction BuildWithSelectedUtxos(
IReadOnlyList<CachedUtxo> selectedUtxos,
IReadOnlyDictionary<string, Transaction> transactions,
BitcoinAddress destination,
long amountSats,
FeeRate feeRate,
int changeIndex,
bool sendAll,
int totalSpendableCount)
{
var coins = selectedUtxos.Select(u => new Coin(
new OutPoint(uint256.Parse(u.Txid), (uint)u.Vout),
transactions[u.Txid].Outputs[u.Vout])).ToList();
var feeRate = new FeeRate(Money.Satoshis(feeRateSatPerVByte * 1000m), 1000);
var builder = Network.CreateTransactionBuilder();
builder.SetVersion(2);
// RBF sequence to allow fee bumping (§6.6).
@@ -114,7 +185,7 @@ public sealed class TransactionFactory(IWalletAccount account)
if (!account.IsWatchOnly)
{
builder.AddKeys(spendable
builder.AddKeys(selectedUtxos
.Select(u => account.GetPrivateKey(u.IsChange, u.AddressIndex))
.OfType<Key>()
.ToArray());
@@ -125,11 +196,27 @@ public sealed class TransactionFactory(IWalletAccount account)
{
tx = builder.BuildTransaction(sign: !account.IsWatchOnly);
}
catch (NotEnoughFundsException ex) when (ex.Message.Contains("size would be too high", StringComparison.OrdinalIgnoreCase))
{
// NBitcoin's coin selector refuses to assemble a combination over the standard size
// cap itself and reports it through NotEnoughFundsException rather than ever handing
// back an oversized transaction — the GetVirtualSize() check below is unreachable for
// this case and exists only as a defense-in-depth net for other NBitcoin versions.
throw new TransactionTooLargeException(
BuildTooLargeMessage(selectedUtxos.Count, totalSpendableCount, sendAll));
}
catch (NotEnoughFundsException) when (!sendAll)
{
throw;
}
catch (NotEnoughFundsException ex)
{
throw new WalletSpendException($"Insufficient funds: {ex.Message}");
}
if (tx.GetVirtualSize() > MaxStandardTransactionVirtualSize)
throw new TransactionTooLargeException(BuildTooLargeMessage(selectedUtxos.Count, totalSpendableCount, sendAll, tx.GetVirtualSize()));
if (!account.IsWatchOnly)
{
if (!builder.Verify(tx, out TransactionPolicyError[] errors))
@@ -147,6 +234,21 @@ public sealed class TransactionFactory(IWalletAccount account)
};
}
private static string BuildTooLargeMessage(
int selectedInputCount,
int totalSpendableCount,
bool sendAll,
int? actualVirtualSize = null)
{
var prefix = sendAll
? "Send-all cannot fit in one standard transaction"
: "Transaction cannot fit in one standard transaction";
var size = actualVirtualSize is { } vsize ? $"{vsize} vB exceeds" : "Estimated size exceeds";
return $"{prefix}: {size} the {MaxStandardTransactionVirtualSize} vB standard relay limit " +
$"with {selectedInputCount}/{totalSpendableCount} spendable input(s). Send a smaller amount or consolidate in multiple smaller transactions.";
}
private static Money GetFee(Transaction tx, IReadOnlyList<Coin> coins)
{
var spentOutpoints = tx.Inputs.Select(i => i.PrevOut).ToHashSet();
@@ -154,6 +256,8 @@ public sealed class TransactionFactory(IWalletAccount account)
.Sum(c => (Money)c.Amount);
return inputSum - tx.Outputs.Sum(o => o.Value);
}
private sealed class TransactionTooLargeException(string message) : Exception(message);
}
/// <summary>Error during transaction construction/signing (funds, policy, parameters).</summary>