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🩹 cap pool utilisation to 100% #137

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Feb 29, 2024
Merged

🩹 cap pool utilisation to 100% #137

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2 changes: 2 additions & 0 deletions src/LendingPool.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -812,6 +812,8 @@ contract LendingPool is LendingPoolGuardian, Creditor, DebtToken, ILendingPool {
// This doesn't overflow since totalDebt is a uint128: uint128 * 10_000 < type(uint256).max.
if (totalLiquidity_ > 0) utilisation = totalDebt * ONE_4 / totalLiquidity_;
}
// Cap utilisation to 100%.
utilisation = utilisation <= ONE_4 ? utilisation : ONE_4;

emit PoolStateUpdated(totalDebt, totalLiquidity_, interestRate = _calculateInterestRate(utilisation));
}
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73 changes: 54 additions & 19 deletions test/fuzz/LendingPool/UpdateInterestRate.fuzz.t.sol
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Expand Up @@ -29,12 +29,14 @@ contract UpdateInterestRate_LendingPool_Fuzz_Test is LendingPool_Fuzz_Test {
uint80 interestRate
) public {
// realisedDebt smaller than equal to than 3402823669209384912995114146594816
vm.assume(deltaTimestamp <= 5 * 365 * 24 * 60 * 60);
//5 year
vm.assume(interestRate <= 10 * 10 ** 18);
vm.assume(deltaTimestamp <= 5 * 365 * 24 * 60 * 60);
//1000%
vm.assume(realisedDebt <= type(uint128).max / (10 ** 5));
vm.assume(interestRate <= 10 * 10 ** 18);
//highest possible debt at 1000% over 5 years: 3402823669209384912995114146594816
vm.assume(realisedDebt <= type(uint128).max / (10 ** 5));

// Given: Utilisation below 100% (test-case).
vm.assume(realisedDebt <= realisedLiquidity);

pool.setTotalRealisedLiquidity(realisedLiquidity);
Expand All @@ -57,44 +59,41 @@ contract UpdateInterestRate_LendingPool_Fuzz_Test is LendingPool_Fuzz_Test {
assertEq(pool.totalLiquidity(), realisedLiquidity + interest);
}

function testFuzz_Success_updateInterestRate_totalRealisedLiquidityMoreThanZero(
function testFuzz_Success_updateInterestRate_totalRealisedLiquidityMoreThanZero_UtilizationBelow100Percent(
uint128 realisedDebt_,
uint128 totalRealisedLiquidity_,
uint72 baseRate_,
uint72 highSlope_,
uint72 lowSlope_,
uint16 utilisationThreshold_
) public {
// Given: totalRealisedLiquidity_ is more than equal to 0, baseRate_ is less than 100000, highSlope_ is bigger than lowSlope_
vm.assume(totalRealisedLiquidity_ > 0);
vm.assume(realisedDebt_ <= type(uint128).max / ONE_4);
vm.assume(realisedDebt_ <= totalRealisedLiquidity_);
vm.assume(utilisationThreshold_ <= ONE_4);
// Given: totalRealisedLiquidity_ is more than equal to 0.
totalRealisedLiquidity_ = uint128(bound(totalRealisedLiquidity_, 1, type(uint128).max));

// When: The InterestConfiguration is set
// And: Utilisation is below 100% (test-case).
// And: utilisation does not overflow.
realisedDebt_ = uint128(bound(realisedDebt_, 0, type(uint128).max / ONE_4));
realisedDebt_ = uint128(bound(realisedDebt_, 0, totalRealisedLiquidity_));

// And: The InterestConfiguration is set.
vm.prank(users.creatorAddress);
utilisationThreshold_ = uint16(bound(utilisationThreshold_, 0, ONE_4));
pool.setInterestParameters(baseRate_, lowSlope_, highSlope_, utilisationThreshold_);

// And: utilisation is 10_000 multiplied by realisedDebt_ and divided by totalRealisedLiquidity_
uint256 utilisation = (ONE_4 * realisedDebt_) / totalRealisedLiquidity_;

// Calculate expectedInterestRate.
uint256 expectedInterestRate;

uint256 utilisation = (ONE_4 * realisedDebt_) / totalRealisedLiquidity_;
if (utilisation <= utilisationThreshold_) {
// And: expectedInterestRate is lowSlope multiplied by utilisation, divided by 10_000 and added to baseRate
expectedInterestRate = uint256(baseRate_) + uint256(lowSlope_) * utilisation / ONE_4;
} else {
// And: lowSlopeInterest is utilisationThreshold multiplied by lowSlope,
// highSlopeInterest is utilisation minus utilisationThreshold multiplied by highSlope
uint256 lowSlopeInterest = uint256(utilisationThreshold_) * lowSlope_;
uint256 highSlopeInterest = uint256(utilisation - utilisationThreshold_) * highSlope_;

// And: expectedInterestRate is baseRate added to lowSlopeInterest added to highSlopeInterest divided by 10_000
expectedInterestRate = uint256(baseRate_) + (lowSlopeInterest + highSlopeInterest) / ONE_4;
}

assertTrue(expectedInterestRate <= type(uint80).max);

// When: interest rate is updated.
vm.expectEmit();
emit PoolStateUpdated(uint256(realisedDebt_), uint256(totalRealisedLiquidity_), uint80(expectedInterestRate));
pool.updateInterestRate(realisedDebt_, totalRealisedLiquidity_);
Expand All @@ -104,6 +103,42 @@ contract UpdateInterestRate_LendingPool_Fuzz_Test is LendingPool_Fuzz_Test {
assertEq(actualInterestRate, expectedInterestRate);
}

function testFuzz_Success_updateInterestRate_totalRealisedLiquidityMoreThanZero_UtilizationAbove100Percent(
uint128 realisedDebt_,
uint128 totalRealisedLiquidity_,
uint72 baseRate_,
uint72 highSlope_,
uint72 lowSlope_,
uint16 utilisationThreshold_
) public {
// Given: Utilisation is above 100% (test-case).
// And: utilisation does not overflow.
realisedDebt_ = uint128(bound(realisedDebt_, 2, type(uint128).max / ONE_4));
// And: totalRealisedLiquidity_ is more than equal to 0.
totalRealisedLiquidity_ = uint128(bound(totalRealisedLiquidity_, 1, realisedDebt_ - 1));

// And: The InterestConfiguration is set.
vm.prank(users.creatorAddress);
utilisationThreshold_ = uint16(bound(utilisationThreshold_, 0, ONE_4));
pool.setInterestParameters(baseRate_, lowSlope_, highSlope_, utilisationThreshold_);

// Calculate expectedInterestRate.
uint256 lowSlopeInterest = uint256(utilisationThreshold_) * lowSlope_;
uint256 highSlopeInterest = uint256(ONE_4 - utilisationThreshold_) * highSlope_;
uint256 expectedInterestRate = uint256(baseRate_) + (lowSlopeInterest + highSlopeInterest) / ONE_4;

assertTrue(expectedInterestRate <= type(uint80).max);

// When: interest rate is updated.
vm.expectEmit();
emit PoolStateUpdated(uint256(realisedDebt_), uint256(totalRealisedLiquidity_), uint80(expectedInterestRate));
pool.updateInterestRate(realisedDebt_, totalRealisedLiquidity_);
uint256 actualInterestRate = pool.interestRate();

// Then: actualInterestRate should be equal to expectedInterestRate.
assertEq(actualInterestRate, expectedInterestRate);
}

function testFuzz_Success_updateInterestRate_totalRealisedLiquidityZero(
uint256 realisedDebt_,
uint72 baseRate_,
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