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Do not remove outputs in payjoin tx

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nicolas.dorier 2020-04-07 15:10:19 +09:00
parent 9fc451c9ca
commit ba2184e21a
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GPG key ID: 6618763EF09186FE
4 changed files with 11 additions and 52 deletions
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1
BTCPayServer.Tests/BTCPayServerTester.cs
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@ -18,7 +18,6 @@ using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Routing;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using NBitcoin;
using NBXplorer;

11
BTCPayServer.Tests/PayJoinTests.cs
View file

@ -290,12 +290,15 @@ namespace BTCPayServer.Tests
// Same as above. Except the sender send one satoshi less, so the change
// output get below dust and should be removed completely.
// output would get below dust and would be removed completely.
// So we remove as much fee as we can, and still accept the transaction because it is above minrelay fee
vector = (SpentCoin: Money.Satoshis(1089), InvoiceAmount: Money.Satoshis(500), Paid: Money.Satoshis(510), Fee: Money.Satoshis(200), ExpectLocked: true, ExpectedError: null as string);
proposedPSBT = await RunVector();
var output = Assert.Single(proposedPSBT.Outputs);
// With the output removed, the user should have largely pay all the needed fee
Assert.Equal(Money.Satoshis(510) + receiverCoin.Amount, output.Value);
Assert.Equal(2, proposedPSBT.Outputs.Count);
// We should have our payment
Assert.Contains(proposedPSBT.Outputs, output => output.Value == Money.Satoshis(500) + receiverCoin.Amount);
// Plus our other change output with value just at dust level
Assert.Contains(proposedPSBT.Outputs, output => output.Value == Money.Satoshis(294));
proposedPSBT = await senderUser.Sign(proposedPSBT);
proposedPSBT = proposedPSBT.Finalize();
explorerClient = tester.PayTester.GetService<ExplorerClientProvider>().GetExplorerClient(proposedPSBT.Network.NetworkSet.CryptoCode);

43
BTCPayServer/Payments/PayJoin/PayJoinEndpointController.cs
View file

@ -283,10 +283,6 @@ namespace BTCPayServer.Payments.PayJoin
Money ourFeeContribution = Money.Zero;
// We need to adjust the fee to keep a constant fee rate
var originalNewTx = newTx.Clone();
bool isSecondPass = false;
recalculateFee:
ourOutput = newTx.Outputs[ourOutputIndex];
var txBuilder = network.NBitcoinNetwork.CreateTransactionBuilder();
txBuilder.AddCoins(psbt.Inputs.Select(i => i.GetCoin()));
txBuilder.AddCoins(selectedUTXOs.Select(o => o.Value.AsCoin()));
@ -316,49 +312,14 @@ namespace BTCPayServer.Payments.PayJoin
if (i != ourOutputIndex)
{
var outputContribution = Money.Min(additionalFee, newTx.Outputs[i].Value);
outputContribution = Money.Min(outputContribution,
newTx.Outputs[i].Value - newTx.Outputs[i].GetDustThreshold(minRelayTxFee));
newTx.Outputs[i].Value -= outputContribution;
additionalFee -= outputContribution;
}
}
}
List<int> dustIndices = new List<int>();
for (int i = 0; i < newTx.Outputs.Count; i++)
{
if (newTx.Outputs[i].IsDust(minRelayTxFee))
{
dustIndices.Insert(0, i);
}
}
if (dustIndices.Count > 0)
{
if (isSecondPass)
{
// This should not happen
await UnlockUTXOs();
await BroadcastNow();
return StatusCode(500,
CreatePayjoinError(500, "unavailable",
$"This service is unavailable for now (isSecondPass)"));
}
foreach (var dustIndex in dustIndices)
{
newTx.Outputs.RemoveAt(dustIndex);
}
ourOutputIndex = newTx.Outputs.IndexOf(ourOutput);
newTx = originalNewTx.Clone();
foreach (var dustIndex in dustIndices)
{
newTx.Outputs.RemoveAt(dustIndex);
}
ourFeeContribution = Money.Zero;
isSecondPass = true;
goto recalculateFee;
}
if (additionalFee > Money.Zero)
{
// We could not pay fully the additional fee, however, as long as

8
BTCPayServer/Services/PayjoinClient.cs
View file

@ -170,7 +170,7 @@ namespace BTCPayServer.Services
var additionalFee = newPSBT.GetFee() - originalFee;
if (overPaying > additionalFee)
throw new PayjoinSenderException("The payjoin receiver is sending more money to himself");
if (overPaying > 2 * originalFee)
if (overPaying > originalFee)
throw new PayjoinSenderException("The payjoin receiver is making us pay more than twice the original fee");
// Let's check the difference is only for the fee and that feerate
@ -178,11 +178,7 @@ namespace BTCPayServer.Services
var expectedFee = originalFeeRate.GetFee(newVirtualSize);
// Signing precisely is hard science, give some breathing room for error.
expectedFee += originalFeeRate.GetFee(newPSBT.Inputs.Count * 2);
// If the payjoin is removing some dust, we may pay a bit more as a whole output has been removed
var removedOutputs = Math.Max(0, originalTx.Outputs.Count - newPSBT.Outputs.Count);
expectedFee += removedOutputs * Money.Satoshis(294);
if (overPaying > expectedFee)
if (overPaying > (expectedFee - originalFee))
throw new PayjoinSenderException("The payjoin receiver increased the fee rate we are paying too much");
}