Merge pull request #36 from euler-xyz/fix/min-amount-to-gulp

Fix: Minimum amount to gulp

src/core/EulerAggregationVault.sol

@@ -50,8 +50,10 @@ contract EulerAggregationVault is
     bytes32 public constant AGGREGATION_LAYER_MANAGER = keccak256("AGGREGATION_LAYER_MANAGER");
     bytes32 public constant AGGREGATION_LAYER_MANAGER_ADMIN = keccak256("AGGREGATION_LAYER_MANAGER_ADMIN");
 
-    /// @dev interest rate smearing period
+    /// @dev Interest rate smearing period
     uint256 public constant INTEREST_SMEAR = 2 weeks;
+    /// @dev Minimum amount of shares to exist for gulp to be enabled
+    uint256 public constant MIN_SHARES_FOR_GULP = 1e7;
 
     constructor(address _rewardsModule, address _hooksModule, address _feeModule, address _allocationPointsModule)
         Dispatch(_rewardsModule, _hooksModule, _feeModule, _allocationPointsModule)
@@ -475,7 +477,8 @@ contract EulerAggregationVault is
 
         AggregationVaultStorage storage $ = StorageLib._getAggregationVaultStorage();
 
-        if (totalSupply() == 0) return;
+        // Do not gulp if total supply is too low
+        if (totalSupply() < MIN_SHARES_FOR_GULP) return;
 
         uint256 toGulp = totalAssetsAllocatable() - $.totalAssetsDeposited - $.interestLeft;
         if (toGulp == 0) return;

test/fuzz/GulpFuzzTest.t.sol

@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+pragma solidity ^0.8.0;
+
+import {
+    EulerAggregationVaultBase,
+    EulerAggregationVault,
+    IEulerAggregationVault
+} from "../common/EulerAggregationVaultBase.t.sol";
+
+contract GulpFuzzTest is EulerAggregationVaultBase {
+    function setUp() public virtual override {
+        super.setUp();
+
+        uint256 initialStrategyAllocationPoints = 500e18;
+        _addStrategy(manager, address(eTST), initialStrategyAllocationPoints);
+    }
+
+    function testFuzz_interestAccrued_under_uint168(
+        uint256 _interestAmount,
+        uint256 _depositAmount,
+        uint256 _timePassed
+    ) public {
+        _depositAmount = bound(_depositAmount, 0, type(uint112).max);
+        // this makes sure that the mint won't cause overflow in token accounting
+        _interestAmount = bound(_interestAmount, 0, type(uint112).max - _depositAmount);
+        _timePassed = bound(_timePassed, block.timestamp, type(uint40).max);
+
+        assetTST.mint(user1, _depositAmount);
+        vm.startPrank(user1);
+        assetTST.approve(address(eulerAggregationVault), _depositAmount);
+        eulerAggregationVault.deposit(_depositAmount, user1);
+        vm.stopPrank();
+
+        assetTST.mint(address(eulerAggregationVault), _interestAmount);
+        eulerAggregationVault.gulp();
+
+        vm.warp(_timePassed);
+        uint256 interestAccrued = eulerAggregationVault.interestAccrued();
+
+        assertLe(interestAccrued, type(uint168).max);
+    }
+
+    // this tests shows that when you have a very small deposit and a very large interestAmount minted to the contract
+    function testFuzz_gulp_under_uint168(uint256 _interestAmount, uint256 _depositAmount) public {
+        _depositAmount = bound(_depositAmount, 1e7, type(uint112).max);
+        _interestAmount = bound(_interestAmount, 0, type(uint256).max - _depositAmount); // this makes sure that the mint won't cause overflow
+
+        assetTST.mint(address(eulerAggregationVault), _interestAmount);
+
+        assetTST.mint(user1, _depositAmount);
+        vm.startPrank(user1);
+        assetTST.approve(address(eulerAggregationVault), _depositAmount);
+        eulerAggregationVault.deposit(_depositAmount, user1);
+        vm.stopPrank();
+
+        eulerAggregationVault.gulp();
+
+        EulerAggregationVault.AggregationVaultSavingRate memory aggregationVaultSavingRate =
+            eulerAggregationVault.getAggregationVaultSavingRate();
+
+        if (_interestAmount <= type(uint168).max) {
+            assertEq(aggregationVaultSavingRate.interestLeft, _interestAmount);
+        } else {
+            assertEq(aggregationVaultSavingRate.interestLeft, type(uint168).max);
+        }
+    }
+}

test/invariant/EulerAggregationLayerInvariants.t.sol

@@ -124,6 +124,13 @@ contract EulerAggregationVaultInvariants is EulerAggregationVaultBase {
         }
     }
 
+    function invariant_interestLeft() public view {
+        EulerAggregationVault.AggregationVaultSavingRate memory aggregationVaultSavingRate =
+            eulerAggregationVault.getAggregationVaultSavingRate();
+        uint256 accruedInterest = eulerAggregationVault.interestAccrued();
+        assertGe(aggregationVaultSavingRate.interestLeft, accruedInterest);
+    }
+
     function _deployOtherStrategies() private {
         eTSTsecond = IEVault(
             factory.createProxy(address(0), true, abi.encodePacked(address(assetTST), address(oracle), unitOfAccount))