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Submission Details
Severity: gas
Valid

refinance function could be modified to save gas

ni8mare

Summary

refinance function could be modified to save gas

Vulnerability Details

In the current implementation, note the position of the line where loan array is initialised.

Loan memory loan = loans[loanId];

Its initialised on line 606. But, it can be initialised before line 595 to save on gas.
As this would save the function from a couple of SLOADs in the form of loans[loanId].lender, loans[loanId].loanToken, loans[loanId].collateralToken. These would no longer be read from storage if the array is initialised before and these values are read from memory.

Impact

In the current implementation the gas cost for the test function test_refinance is 850199.
In the new implementation, the gas cost for the test function now becomes 849228.

Tools Used

Manual review

Recommendations

Recommend to implement the functions as follows:

function refinance(Refinance[] calldata refinances) public {
for (uint256 i = 0; i < refinances.length; i++) {
uint256 loanId = refinances[i].loanId;
bytes32 poolId = refinances[i].poolId;
​
// get the loan info
Loan memory loan = loans[loanId];
​
bytes32 oldPoolId = keccak256(
abi.encode(loan.lender, loan.loanToken, loan.collateralToken)
);
uint256 debt = refinances[i].debt;
uint256 collateral = refinances[i].collateral;
​
// validate the loan
if (msg.sender != loan.borrower) revert Unauthorized();
​
// get the pool info
Pool memory pool = pools[poolId];
// validate the new loan
if (pool.loanToken != loan.loanToken) revert TokenMismatch();
if (pool.collateralToken != loan.collateralToken) {
revert TokenMismatch();
}
if (pool.poolBalance < debt) revert LoanTooLarge();
if (debt < pool.minLoanSize) revert LoanTooSmall();
uint256 loanRatio = (debt * 10 ** 18) / collateral;
if (loanRatio > pool.maxLoanRatio) revert RatioTooHigh();
​
// calculate the interest
(
uint256 lenderInterest,
uint256 protocolInterest
) = _calculateInterest(loan);
uint256 debtToPay = loan.debt + lenderInterest + protocolInterest;
​
// update the old lenders pool
_updatePoolBalance(
oldPoolId,
pools[oldPoolId].poolBalance + loan.debt + lenderInterest
);
pools[oldPoolId].outstandingLoans -= loan.debt;
​
// now lets deduct our tokens from the new pool
_updatePoolBalance(poolId, pools[poolId].poolBalance - debt);
pools[poolId].outstandingLoans += debt;
​
if (debtToPay > debt) {
// we owe more in debt so we need the borrower to give us more loan tokens
// transfer the loan tokens from the borrower to the contract
IERC20(loan.loanToken).transferFrom(
msg.sender,
address(this),
debtToPay - debt
);
} else if (debtToPay < debt) {
// we have excess loan tokens so we give some back to the borrower
// first we take our borrower fee
uint256 fee = (borrowerFee * (debt - debtToPay)) / 10000;
IERC20(loan.loanToken).transfer(feeReceiver, fee);
// transfer the loan tokens from the contract to the borrower
IERC20(loan.loanToken).transfer(
msg.sender,
debt - debtToPay - fee
);
}
// transfer the protocol fee to governance
IERC20(loan.loanToken).transfer(feeReceiver, protocolInterest);
​
// update loan debt
loans[loanId].debt = debt;
// update loan collateral
if (collateral > loan.collateral) {
// transfer the collateral tokens from the borrower to the contract
IERC20(loan.collateralToken).transferFrom(
msg.sender,
address(this),
collateral - loan.collateral
);
} else if (collateral < loan.collateral) {
// transfer the collateral tokens from the contract to the borrower
IERC20(loan.collateralToken).transfer(
msg.sender,
loan.collateral - collateral
);
}
​
emit Repaid(
msg.sender,
loan.lender,
loanId,
debt,
collateral,
loan.interestRate,
loan.startTimestamp
);
​
loans[loanId].collateral = collateral;
// update loan interest rate
loans[loanId].interestRate = pool.interestRate;
// update loan start timestamp
loans[loanId].startTimestamp = block.timestamp;
// update loan auction start timestamp
loans[loanId].auctionStartTimestamp = type(uint256).max;
// update loan auction length
loans[loanId].auctionLength = pool.auctionLength;
// update loan lender
loans[loanId].lender = pool.lender;
// update pool balance
pools[poolId].poolBalance -= debt;
emit Borrowed(
msg.sender,
pool.lender,
loanId,
debt,
collateral,
pool.interestRate,
block.timestamp
);
emit Refinanced(loanId);
}
}

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