Strategy Contracts

Overview

Strategy contracts implement yield-generating protocols like Aave, Compound, or leverage strategies. All strategies must implement the IStrategy interface.

IStrategy Interface

All strategies must implement these core functions:

interface IStrategy {
    function strategyBalance() external view returns (uint256);
    function invest(uint256 amount) external;
    function withdrawToVault(uint256 amount) external returns (uint256);
    function harvest() external;
    function deleverageAll(uint256 maxLoops) external;
}

Source: contracts/interfaces/IStrategy.sol:4-10

Strategy Architecture

Common Pattern

All strategies follow this architecture:

Immutable References: Vault, router, and protocol addresses
Access Control: onlyRouter modifier for protected functions
Token Approvals: Pre-approve protocol contracts
Bookkeeping: Track deposited amounts and protocol balances

Aave V3 Strategy

Simple yield strategy using Aave V3 lending:

Contract Setup

contract StrategyAaveV3 is IStrategy {
    using SafeERC20 for IERC20;

    IERC20 public immutable token;        // underlying (USDC)
    address public immutable vault;
    address public immutable router;
    IPool public immutable pool;
    IProtocolDataProvider public immutable dataProvider;

    uint256 public deposited; // track principal

    constructor(
        address _asset,
        address _vault,
        address _router,
        address _pool,
        address _dataProvider
    ) {
        token = IERC20(_asset);
        vault = _vault;
        router = _router;
        pool = IPool(_pool);
        dataProvider = IProtocolDataProvider(_dataProvider);
        token.approve(address(pool), type(uint256).max);
    }
}

Source: contracts/strategy/StrategyAave.sol:15-34

Invest Function

Deposit funds into Aave:

function invest(uint256 amount) external override onlyRouter {
    // Vault already transferred tokens to this contract
    pool.supply(address(token), amount, address(this), 0);
    deposited += amount;
}

Source: contracts/strategy/StrategyAave.sol:54-59

Withdraw Function

Withdraw funds back to vault:

function withdrawToVault(uint256 amount) external override onlyRouter returns(uint256) {
    // Withdraw from Aave
    uint256 out = pool.withdraw(address(token), amount, address(this));
    token.safeTransfer(vault, out);

    if (out <= deposited) deposited -= out;
    else deposited = 0;

    return out;
}

Source: contracts/strategy/StrategyAave.sol:61-70

Harvest Function

Collect interest profits:

function harvest() external override onlyRouter {
    // Get aToken address
    (address aTokenAddr, , ) = dataProvider.getReserveTokensAddresses(address(token));
    uint256 aBal = IERC20(aTokenAddr).balanceOf(address(this));
    
    if (aBal > deposited) {
        uint256 profit = aBal - deposited;
        // Withdraw profit and send to vault
        uint256 out = pool.withdraw(address(token), profit, address(this));
        token.safeTransfer(vault, out);
    }
}

Source: contracts/strategy/StrategyAave.sol:72-86

Strategy Balance

Return current strategy value:

function strategyBalance() public view override returns (uint256) {
    return pool.getUnderlyingValue(address(this), address(token));
}

Source: contracts/strategy/StrategyAave.sol:88-90

APY Estimation

function estimateAPY() external view returns (uint256) {
    (address aTokenAddr,,) = dataProvider.getReserveTokensAddresses(address(token));
    uint256 aBal = IERC20(aTokenAddr).balanceOf(address(this));

    if (deposited == 0) return 0;
    uint256 profit = aBal > deposited ? aBal - deposited : 0;

    return (profit * 1e18) / deposited; 
}

Source: contracts/strategy/StrategyAave.sol:41-49

Aave Leverage Strategy

Advanced strategy using leverage to amplify yields:

Contract Setup

contract StrategyAaveLeverage is IStrategy {
    using SafeERC20 for IERC20;

    IERC20 public immutable token; // LINK (underlying)
    address public immutable vault;
    address public immutable router;
    IPool public immutable pool;
    IProtocolDataProvider public immutable dataProvider;
    
    // Swap infrastructure
    ISwapRouterV2 public immutable swapRouter;
    address public immutable WETH;
    
    // Oracle for price feeds
    IPriceOracle public immutable oracle;

    // Bookkeeping
    uint256 public deposited;
    uint256 public borrowedWETH;

    // Leverage parameters
    uint8 public maxDepth = 3;
    uint256 public borrowFactor = 6000; // 60% of collateral
}

Source: contracts/strategy/StrategyAaveLeverage.sol:35-59

Leverage Mechanism

The strategy uses a loop to build leverage:

Supply LINK as collateral
Borrow WETH (60% of collateral value)
Swap WETH for LINK
Supply new LINK as collateral
Repeat up to maxDepth times

Invest with Leverage

function invest(uint256 amount) external override onlyRouter {
    require(!paused, "paused");
    require(amount > 0, "zero amount");

    // Initial supply
    pool.supply(address(token), amount, address(this), 0);
    uint256 totalSupplied = amount;

    uint8 depth = maxDepth;
    uint256 totalBorrowedWETH = 0;

    // Conservative leverage loop
    for (uint8 i = 0; i < depth; i++) {
        // 1. Check WETH liquidity
        uint256 poolWethBal = IERC20(WETH).balanceOf(address(pool));
        if (poolWethBal == 0) break;

        // 2. Calculate safe borrow amount
        uint256 borrowAmountWeth = min(tinyBorrow, poolWethBal / 100);
        if (borrowAmountWeth == 0) break;

        // 3. Borrow WETH
        try pool.borrow(WETH, borrowAmountWeth, 2, 0) {
            // success
        } catch {
            break;
        }
        totalBorrowedWETH += borrowAmountWeth;

        // 4. Swap WETH -> LINK
        address[] memory path = new address[](2);
        path[0] = WETH;
        path[1] = address(token);

        uint256 linkBefore = token.balanceOf(address(this));
        
        try swapRouter.swapExactTokensForTokens(
            borrowAmountWeth, 0, path, address(this), block.timestamp + 300
        ) {
            // success
        } catch {
            break;
        }

        uint256 linkAfter = token.balanceOf(address(this));
        uint256 addedLink = linkAfter - linkBefore;

        // 5. Supply new LINK
        try pool.supply(address(token), addedLink, address(this), 0) {
            totalSupplied += addedLink;
        } catch {
            break;
        }
    }

    deposited += amount;
    borrowedWETH += totalBorrowedWETH;

    emit InvestedLeveraged(amount, depth, totalSupplied, totalBorrowedWETH);
}

Source: contracts/strategy/StrategyAaveLeverage.sol:154-272

Deleverage

Unwind leverage positions:

function deleverageAll(uint256 maxLoops) external onlyRouter {
    require(!paused, "paused");

    for (uint256 i = 0; i < maxLoops; i++) {
        uint256 debt = pool.getUserDebt(address(this), WETH);
        if (debt == 0) break;

        // 1. Calculate LINK needed to repay WETH debt
        uint256 price = oracle.getPrice(WETH); // LINK per WETH
        uint256 linkNeeded = (debt * price * 105) / (1e18 * 100); // 5% buffer
        
        // Get available collateral
        uint256 availableCollateral = pool.getUnderlyingValue(address(this), address(token));
        if (availableCollateral == 0) break;
        
        uint256 withdrawAmt = min(linkNeeded, availableCollateral);
        if (withdrawAmt == 0) break;

        // 2. Withdraw LINK
        uint256 gotLINK = pool.withdraw(address(token), withdrawAmt, address(this));
        if (gotLINK == 0) break;

        // 3. Swap LINK → WETH
        address[] memory path = new address[](2);
        path[0] = address(token);
        path[1] = WETH;

        uint256 wethBefore = IERC20(WETH).balanceOf(address(this));

        try swapRouter.swapExactTokensForTokens(
            gotLINK, 0, path, address(this), block.timestamp + 300
        ) {
            // success
        } catch {
            break;
        }

        uint256 wethOut = IERC20(WETH).balanceOf(address(this)) - wethBefore;
        if (wethOut == 0) break;

        // 4. Repay debt
        IERC20(WETH).approve(address(pool), wethOut);
        uint256 repayAmount = min(wethOut, debt);
        uint256 repaid = pool.repay(WETH, repayAmount, 2, address(this));

        // Update bookkeeping
        if (borrowedWETH <= repaid) borrowedWETH = 0;
        else borrowedWETH -= repaid;

        if (deposited <= gotLINK) deposited = 0;
        else deposited -= gotLINK;
    }
}

Source: contracts/strategy/StrategyAaveLeverage.sol:305-377

Leverage Parameters

Adjust leverage settings:

function setLeverageParams(uint8 _maxDepth, uint256 _borrowFactor) external onlyRouter {
    require(_maxDepth <= 6, "maxDepth too large");
    require(_borrowFactor <= 8000, "borrowFactor too high"); // max 80%
    maxDepth = _maxDepth;
    borrowFactor = _borrowFactor;
    emit LeverageParamsUpdated(_maxDepth, _borrowFactor);
}

Source: contracts/strategy/StrategyAaveLeverage.sol:105-111

Leverage State

function getLeverageState()
    external view
    returns (
        uint256 deposited_,
        uint256 borrowed_,
        uint256 netExposure,
        uint256 loops,
        uint8 maxDepth_
    )
{
    deposited_ = deposited;
    borrowed_ = borrowedWETH;
    netExposure = deposited_ > borrowed_ ? deposited_ - borrowed_ : 0;
    loops = maxDepth;
    maxDepth_ = maxDepth;
}

Source: contracts/strategy/StrategyAaveLeverage.sol:113-128

LTV Monitoring

function getLTV() external view returns (uint256) {
    if (deposited == 0) return 0;
    return (borrowedWETH * 1e18) / deposited; // 1e18 = 100%
}

function isAtRisk(uint256 maxSafeLTV) external view returns (bool) {
    uint256 ltv = (borrowedWETH * 1e18) / deposited;
    return ltv > maxSafeLTV;
}

Source: contracts/strategy/StrategyAaveLeverage.sol:130-138

Strategy Balance with Debt

function strategyBalance() public view override returns (uint256) {
    uint256 collateral = pool.getUnderlyingValue(address(this), address(token));
    uint256 idle = token.balanceOf(address(this));
    uint256 total = collateral + idle;

    if (borrowedWETH == 0) return total;

    uint256 price = oracle.getPrice(WETH); // LINK per WETH
    uint256 debtValue = borrowedWETH * price / 1e18;

    if (debtValue >= total) return 0;
    return total - debtValue;
}

Source: contracts/strategy/StrategyAaveLeverage.sol:381-393

Creating New Strategies

Implementation Checklist

Implement IStrategy Interface
- strategyBalance() - return current strategy value
- invest() - deploy funds into protocol
- withdrawToVault() - return funds to vault
- harvest() - collect and send profits to vault
- deleverageAll() - unwind positions (can be no-op)

Access Control

modifier onlyRouter() {
    require(msg.sender == router, "not router");
    _;
}

Token Approvals

constructor(...) {
    token.approve(address(protocol), type(uint256).max);
}

Safe Transfers

using SafeERC20 for IERC20;
token.safeTransfer(vault, amount);

Error Handling
- Use try-catch for external calls
- Validate amounts and addresses
- Emit events for failures
Bookkeeping
- Track deposited principal
- Track borrowed amounts (if applicable)
- Calculate net value correctly

Protocol Interfaces

Aave V3 Pool

interface IPool {
    function supply(address asset, uint256 amount, address onBehalfOf, uint16 referralCode) external;
    function withdraw(address asset, uint256 amount, address to) external returns (uint256);
    function borrow(address asset, uint256 amount, uint256 interestRateMode, uint16 referralCode) external;
    function repay(address asset, uint256 amount, uint256 rateMode, address onBehalfOf) external returns (uint256);
    function getUnderlyingValue(address user, address token) external view returns (uint256);
    function getUserDebt(address user, address token) external view returns (uint256);
}

Source: contracts/strategy/StrategyAaveLeverage.sol:9-17

Uniswap V2 Router

interface ISwapRouterV2 {
    function swapExactTokensForTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external returns (uint[] memory amounts);
}

Source: contracts/strategy/StrategyAaveLeverage.sol:20-28

Price Oracle

interface IPriceOracle {
    function getPrice(address token) external view returns (uint256);
}

Source: contracts/strategy/StrategyAaveLeverage.sol:31-33

OpenZeppelin Dependencies

import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "../interfaces/IStrategy.sol";
import "../interfaces/IProtocolDataProvider.sol";

Source: contracts/strategy/StrategyAave.sol:4-6

Security Best Practices

Access Control: Always use onlyRouter modifier
Safe Math: Solidity 0.8+ has built-in overflow protection
Safe Transfers: Use OpenZeppelin’s SafeERC20
Error Handling: Wrap external calls in try-catch
Slippage Protection: Set minimum output amounts for swaps
LTV Monitoring: Track leverage ratios for leveraged strategies
Emergency Pause: Include pause functionality for leverage strategies
Conservative Parameters: Use safe borrow factors (e.g., 60% instead of 80%)

Testing Strategies

import { expect } from "chai";
import { ethers } from "hardhat";

describe("Strategy", function () {
  it("Should invest and withdraw", async function () {
    // Deploy contracts
    const strategy = await deployStrategy();
    
    // Test invest
    await token.transfer(strategy.address, amount);
    await strategy.invest(amount);
    
    // Check balance
    const balance = await strategy.strategyBalance();
    expect(balance).to.be.gte(amount);
    
    // Test withdraw
    await strategy.withdrawToVault(amount);
    const vaultBalance = await token.balanceOf(vault.address);
    expect(vaultBalance).to.be.gte(amount);
  });
});

Events

event InvestedLeveraged(uint256 initial, uint8 depth, uint256 finalSupplied, uint256 borrowedWETH);
event Deleveraged(uint256 repaidWETH, uint256 redeemedLINK);
event Harvested(uint256 profit);
event PauseToggled(bool paused);
event LeverageParamsUpdated(uint8 maxDepth, uint256 borrowFactor);

Source: contracts/strategy/StrategyAaveLeverage.sol:70-74

Setup

Smart Contracts

Frontend

AI Agents

Overview

IStrategy Interface

Strategy Architecture

Common Pattern

Aave V3 Strategy

Contract Setup

Invest Function

Withdraw Function

Harvest Function

Strategy Balance

APY Estimation

Aave Leverage Strategy

Contract Setup

Leverage Mechanism

Invest with Leverage

Deleverage

Leverage Parameters

Leverage State

LTV Monitoring

Strategy Balance with Debt

Creating New Strategies

Implementation Checklist

Protocol Interfaces

Aave V3 Pool

Uniswap V2 Router

Price Oracle

OpenZeppelin Dependencies

Security Best Practices

Testing Strategies

Events

Next Steps

Build docs developers (and LLMs) love

Setup

Smart Contracts

Frontend

AI Agents

​Overview

​IStrategy Interface

​Strategy Architecture

​Common Pattern

​Aave V3 Strategy

​Contract Setup

​Invest Function

​Withdraw Function

​Harvest Function

​Strategy Balance

​APY Estimation

​Aave Leverage Strategy

​Contract Setup

​Leverage Mechanism

​Invest with Leverage

​Deleverage

​Leverage Parameters

​Leverage State

​LTV Monitoring

​Strategy Balance with Debt

​Creating New Strategies

​Implementation Checklist

​Protocol Interfaces

​Aave V3 Pool

​Uniswap V2 Router

​Price Oracle

​OpenZeppelin Dependencies

​Security Best Practices

​Testing Strategies

​Events

​Next Steps

Build docs developers (and LLMs) love

Overview

IStrategy Interface

Strategy Architecture

Common Pattern

Aave V3 Strategy

Contract Setup

Invest Function

Withdraw Function

Harvest Function

Strategy Balance

APY Estimation

Aave Leverage Strategy

Contract Setup

Leverage Mechanism

Invest with Leverage

Deleverage

Leverage Parameters

Leverage State

LTV Monitoring

Strategy Balance with Debt

Creating New Strategies

Implementation Checklist

Protocol Interfaces

Aave V3 Pool

Uniswap V2 Router

Price Oracle

OpenZeppelin Dependencies

Security Best Practices

Testing Strategies

Events

Next Steps