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improve(SpokePool): Apply rounding consistently to partial and full fills #268

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Merged
merged 1 commit into from
Apr 11, 2023
Merged

improve(SpokePool): Apply rounding consistently to partial and full fills #268

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17 changes: 8 additions & 9 deletions contracts/SpokePool.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -1148,20 +1148,19 @@ abstract contract SpokePool is

// If user's specified max amount to send is greater than the amount of the relay remaining pre-fees,
// we'll pull exactly enough tokens to complete the relay.
uint256 amountToSend = relayExecution.maxTokensToSend;
uint256 amountRemainingInRelay = relayData.amount - relayFills[relayExecution.relayHash];
if (amountRemainingInRelay < fillAmountPreFees) {
fillAmountPreFees = amountRemainingInRelay;

// The user will fulfill the remainder of the relay, so we need to compute exactly how many tokens post-fees
// that they need to send to the recipient. Note that if the relayer is filled using contract funds then
// this is a slow relay.
amountToSend = _computeAmountPostFees(
fillAmountPreFees,
relayData.realizedLpFeePct + relayExecution.updatedRelayerFeePct
);
}

// Apply post-fees computation to amount that relayer will send to user. Rounding errors are possible
// when computing fillAmountPreFees and then amountToSend, and we just want to enforce that
// the error added to amountToSend is consistently applied to partial and full fills.
uint256 amountToSend = _computeAmountPostFees(
fillAmountPreFees,
relayData.realizedLpFeePct + relayExecution.updatedRelayerFeePct
);

// This can only happen in a slow fill, where the contract is funding the relay.
if (relayExecution.payoutAdjustmentPct != 0) {
// If payoutAdjustmentPct is positive, then the recipient will receive more than the amount they
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13 changes: 11 additions & 2 deletions test/SpokePool.Relay.ts
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Expand Up @@ -647,8 +647,17 @@ async function testfillRelayWithUpdatedDeposit(depositorAddress: string) {
);

// The collateral should have transferred from relayer to recipient.
expect(await destErc20.balanceOf(relayer.address)).to.equal(consts.amountToSeedWallets.sub(consts.amountToRelay));
expect(await destErc20.balanceOf(recipient.address)).to.equal(consts.amountToRelay);
const relayerBalance = await destErc20.balanceOf(relayer.address);
const expectedRelayerBalance = consts.amountToSeedWallets.sub(consts.amountToRelay);

// Note: We need to add an error bound of 1 wei to the expected balance because of the possibility
// of rounding errors with the modified fees. The unmodified fees result in clean numbers but the modified fee does not.
expect(relayerBalance.gte(expectedRelayerBalance.sub(1)) || relayerBalance.lte(expectedRelayerBalance.add(1))).to.be
.true;
const recipientBalance = await destErc20.balanceOf(recipient.address);
const expectedRecipientBalance = consts.amountToRelay;
expect(recipientBalance.gte(expectedRecipientBalance.sub(1)) || recipientBalance.lte(expectedRecipientBalance.add(1)))
.to.be.true;

// Fill amount should be be set taking into account modified fees.
expect(await spokePool.relayFills(relayHash)).to.equal(consts.amountToRelayPreModifiedFees);
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