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Build Strategy By Example

Strategy Library

We've introduced a library featuring strategies for various DeFi protocols, these strategies are used in Unhosted wallet and might be useful in to get idea or even be built upon them. This library is consistently updated to incorporate new protocols. Each strategy within the library offers key functionalities specific to its associated protocol.


Hardhat, Truffle (npm)

npm install @unhosted/strategies  @openzeppelin/contracts

Foundry (git)

forge install Unhosted-Wallet/unhosted-strategies OpenZeppelin/openzeppelin-contracts

Also add


to remappings.txt.

Swapping Collateral with Compound v3 Strategy


Familiarity with Compound, Aave and Uniswap documentation is recommended for a comprehensive understanding of the integration.


Improperly implemented strategies may lead to wallet malfunctions or potential fund losses. During strategy development, feel free to reach out to our team for a thorough review.

Explore this tutorial to construct a straightforward DeFi strategy for swapping provided collateral to another supported collateral within the Compound v3 protocol. The strategy includes four steps for executing the collateral swap:

  1. Initiate a flash loan for the exact amount of the current collateral from Aave v2.
  2. Execute a swap for the precise amount to the targeted collateral token using Uniswap v3.
  3. Deposit the new collateral into Compound v3 and withdraw the old collateral.
  4. Repay the flash loan to Aave v2 with the withdrawn collateral.

Since the strategy involves a flash loan, a fallback handler contract is also required to modify the default fallback handler of the wallet during the process.

1. Strategy Contract

// SPDX-License-Identifier: MIT
pragma solidity 0.8.20;

import {IComet} from "@unhosted/strategies/compoundV3/CompoundV3Strategy.sol";
import {BaseStrategy, IERC20, SafeERC20} from "@unhosted/strategies/BaseStrategy.sol";
import {AaveV2Strategy, ILendingPoolAddressesProviderV2} from "@unhosted/strategies/aaveV2/AaveV2Strategy.sol";

* @title Compound v3 collateral swap strategy
* @dev Compatible with Unhosted strategy module
contract CompV3CollateralSwap is AaveV2Strategy {
using SafeERC20 for IERC20;

address public immutable fallbackHandler;

constructor(address wethAddress, address aaveV2Provider, address fallbackHandler_, address dataProvider_, address quoter_)
AaveV2Handler(wethAddress, aaveV2Provider, fallbackHandler_, dataProvider_, quoter_)
fallbackHandler = fallbackHandler_;

struct ReceiveData {
address tokenOut;
address comet;

* @dev Executes a collateral swap from the supplied token to another supported collateral token on Compound v3.
* @param comet Address of the Compound contract used for collateral supply and withdrawal.
* @param suppliedCollateralToken, Address of the currently supplied collateral token.
* @param targetCollateralToken, Address of the new collateral token to be supplied.
* @param collateralAmountToSwap, Amount of the current collateral token to be swapped.
* @param debtMode, Flashloan mode for Aave (noDebt=0, stableDebt=1, variableDebt=2).
function collateralSwap(
address comet,
address suppliedCollateralToken,
address targetCollateralToken,
uint256 collateralAmountToSwap,
uint256 debtMode
) public payable {
uint256[] memory mode = new uint256[](1);
uint256[] memory amount = new uint256[](1);
address[] memory token = new address[](1);
ReceiveData memory receiveData = ReceiveData(targetCollateralToken, comet);
mode[0] = debtMode;
amount[0] = collateralAmountToSwap;
token[0] = suppliedCollateralToken;
bytes memory data = abi.encode(receiveData);

IComet(comet).allow(fallbackHandler, true);
IERC20(suppliedCollateralToken).approve(fallbackHandler, collateralAmountToSwap);
flashLoan(token, amount, mode, data);
IComet(comet).allow(fallbackHandler, false);
IERC20(suppliedCollateralToken).approve(fallbackHandler, 0);

function getContractName() public pure override(AaveV2Strategy) returns (string memory) {
return "CollateralSwapStrategy";


To initialize this contract, we initialize the Aave V2 strategy from the library, granting access to its flashloan functionality. The initialization requires the wrapped native token address, the AaveV2 provider address, and the deployed fallback handler (discussed later in this guide). Ensure familiarity with Compound comet contracts via their documentation here to understand how supplying and borrowing works.


comet: The address of the Compound protocol comet contract with which we intend to engage for supplying and withdrawing collateral.

suppliedCollateralToken: Address of the currently supplied collateral to the Comet contract.

targetCollateralToken: Address of the new collateral token to supply.

collateralAmountToSwap: The amount of supplied collateral (should already be supplied to the comet).

mode: Flashloan mode for Aave, learn more here.


The collateralSwap function operates the following steps:

  1. Prepares parameters for the flashloan, including passing the Comet and new collateral token addresses. This informs the fallback handler about the targeted Comet and the token to swap for the new collateral.

  2. Allows the fallback handler to withdraw and transfer on behalf of the Smart Account (SA), approving it for the transfer of the received borrowed token. This is crucial for the subsequent transfer and swap operations.

  3. Calls the flashloan on Aave, triggering a fallback to the SA, which then invokes the fallback handler for executing operations. In this step, we borrow the collateralAmountToSwap from Aave pools.

  4. Revokes the given allowances and approvals from the fallback handler, ensuring proper cleanup after the flashloan operation.

2. Fallback Handler Contract

// SPDX-License-Identifier: MIT
pragma solidity 0.8.20;

/* solhint-disable no-empty-blocks */
import {IFlashLoanReceiver} from "@unhosted/strategies/aaveV2/FallbackHandler.sol";
import {ISwapRouter} from "@unhosted/strategies/uniswapV3/UniswapV3Strategy.sol";
import {IERC20} from "@unhosted/strategies/BaseStrategy.sol";
import {IComet} from "@unhosted/strategies/compoundV3/CompoundV3Strategy.sol";

* @title Collateral swap flashloan fallback handler
* @dev This contract temporarily replaces the default handler of SA during the flashloan process
contract FallbackHandler is IFlashLoanReceiver {
// prettier-ignore
ISwapRouter public immutable router;

struct ReceiveData {
address tokenOut;
address comet;

error InvalidInitiator();
error SwapFailed();

constructor(address router_) {
router = ISwapRouter(router_);

* @dev Called by SA during the executeOperation of a flashloan
* @dev Transfers the borrowed tokens from SA, swaps it for new collateral,
* and supplies the new collateral, then withdraws the previous collateral to repay the loan
function executeOperation(
address[] calldata assets,
uint256[] calldata amounts,
uint256[] calldata,
address initiator,
bytes calldata data
) external virtual returns (bool) {
if (initiator != msg.sender) {
revert InvalidInitiator();
ReceiveData memory decodedData = abi.decode(data, (ReceiveData));
ISwapRouter.ExactInputSingleParams memory params;

params.tokenIn = assets[0];
params.tokenOut = decodedData.tokenOut;
params.fee = 3000;
params.recipient = address(this);
params.amountIn = amounts[0];
params.amountOutMinimum = 1;
params.sqrtPriceLimitX96 = 0;
params.deadline = block.timestamp;

IERC20(assets[0]).transferFrom(msg.sender, address(this), amounts[0]);

IERC20(assets[0]).approve(address(router), amounts[0]);
try router.exactInputSingle(params) {}
catch {
revert SwapFailed();

uint256 newBalance = IERC20(decodedData.tokenOut).balanceOf(address(this));
IERC20(decodedData.tokenOut).approve(decodedData.comet, newBalance);
IComet(decodedData.comet).supplyTo(msg.sender, decodedData.tokenOut, newBalance);

msg.sender, // to

return true;


We initialize this contract with the Uniswap V3 router, which it utilizes for swapping the supplied collateral to the new collateral token.


The executeOperation function operates in the following steps:

  1. Decodes the received data from the flashLoan function to extract the Comet and new collateral token needed for further operations.

  2. Upon successfully receiving the collateralAmountToSwap from the supplied collateral token in the SA, it transfers the received loan from SA to the fallback contract and swaps it using the Uniswap router to the new collateral token.

  3. After the successful swap, it approves Comet for supplying the new collateral on behalf of SA and completes the supply operation.

  4. Finally, it withdraws the previous collateral on behalf of SA and transfers it to SA itself. This enables SA to repay the flash loan with that amount (if the mode is 0 and no debt will be created).


Security considerations:

  • The fallback handler initially verifies that the initiator of the flash loan is the SA address.
  • The fallback handler reinstates the default fallback handler of SA once the flash loan operations are completed.
  • Approvals granted by SA for repaying the loan, allowances given to the fallback handler for withdrawing collateral, and approvals for the fallback handler to transfer borrowed tokens are revoked at the conclusion of executed operations.

Explore additional examples of strategies here to enhance your understanding of various scenarios. Diving into the associated test scripts can provide valuable insights into the logic behind DeFi strategies. For faster development and efficient testing, we used Foundry. If you are unfamiliar with Foundry, read their documentation for additional insights.

Next Step

Now you are prepared to add your strategy to our strategy module and start accumulating fees for it.