Function: redeemCollateral(uint256 _debtAmount, address _firstRedemptionHint, address _upperPartialRedemptionHint, address _lowerPartialRedemptionHint, uint256 _partialRedemptionHintNICR, uint256 _maxIterations, uint256 _maxFeePercentage)

This is the function used to redeem the corresponding amount of collateral from as manytTroves as are needed to fill the redemption request.

Inputs

• _debtAmount

  • Control: Fully controlled.

  • Constraints: Balance of caller should be greater than _debtAmount.

  • Impact: The debt amount to be sent to the system.

• _firstRedemptionHint

  • Control: Fully controlled.

  • Constraints: No constraints.

  • Impact: Hints at the position of the first trove that will be redeemed from.

• _upperPartialRedemptionHint

  • Control: Fully controlled.

  • Constraints: No constraints.

  • Impact: Hints at the prevId neighbor of the last redeemed trove upon reinsertion, if it is partially redeemed.

• _lowerPartialRedemptionHint

  • Control: Fully controlled.

  • Constraints: No constraints.

  • Impact: Hints at the nextId neighbor of the last redeemed trove upon reinsertion, if it is partially redeemed.

• _partialRedemptionHintNICR

  • Control: Fully controlled.

  • Constraints: No constraints.

  • Impact: Ensures that the transaction will not run out of gas if neither _lowerPartialRedemptionHint nor _upperPartialRedemptionHint are valid anymore.

• _maxIterations

  • Control: Fully controlled.

  • Constraints: No constraints.

  • Impact: The number of troves redeemed from is capped by _maxIterations.

• _maxFeePercentage

  • Control: Fully controlled.

  • Constraints: _maxFeePercentage >= redemptionFeeFloor && _maxFeePercentage <= maxRedemptionFee.

  • Impact: The borrower has to provide a _maxFeePercentage that they are willing to accept in case of a fee slippage.

Branches and code coverage (including function calls)

Intended branches

• If the provided redemption hint is valid, set current borrower to the given first redemption hint.

  Test coverage

• If the provided redemption hint is invalid, find the first trove with ICR >= MCR.

  Test coverage

• If _maxIterations is set to a nonzero value, the loop is capped to the provided value.

  Test coverage

• If _maxIterations is set to 0, the value should be ignored.

  Test coverage

• The amount to be redeemed should be capped by the entire debt of the trove minus the liquidation reserve.

  Test coverage

• If the remaining debt is equal to DEBT_GAS_COMPENSATION, close the trove.

  Test coverage

• If partial redemption was cancelled (out-of-date hint or new net debt < minimum), do not redeem from the last trove and break out of the loop.

  Test coverage

• Collateral fee should be zero when sunsetting; otherwise, check if the user accepts the fee.

  Test coverage

• If the trove length becomes zero after redemptions, reset the state of the system.

  Test coverage

Negative behavior

• Revert if _maxFeePercentage is not in acceptable range.

  Test coverage

• Revert if collateral drawn is zero.

  Test coverage

Function call analysis

• debtToken.balanceOf(msg.sender)

  • What is controllable? msg.sender.

  • If return value controllable, how is it used and how can it go wrong? Return value is the balance of caller's debtToken.

  • What happens if it reverts, reenters, or does other unusual control flow? No reentrancy scenarios.