custom-swaps

CustomSwaps (Governance Safe Smart Swaps)

name is not final, all suggestions are welcome

These contracts were developed to allow devs to provide a safe, flexible and governable way to handle swaps on their smart contracts. This has synergy with keep3r.network since keep3rs can submit custom dex+data to reduce slippage (and possibly get a bonus for it)

Wishlist

DexHandlers

• Uniswap (swapExactTokensForTokens)
• Sushiswap (swapExactTokensForTokens)
• 0x
• bancor
• paraswap
• crv
• 1inch

Integrations

• yearn strategy
• erc20-dca (TBD)

Run tests

• npm i
• cp example.config.json .config.json
  • add Infura and Alchemy APIs
  • add "accounts.mainnet.publicKey" (should have ETH balance > 3 for tests to run ok)
• npm test
  • use npm run test:gas to get gas report

Contracts

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dex-handlers

DexHandlerAbstract.sol

Abstract contract that should be used to extend from when creating DexHandlers. (see UniswapV2DexHandler.sol)

address public dex;
constructor(address _dex) public {
    require(_dex.isContract(), 'dex-handler::constructor:dex-is-not-a-contract');
    dex = _dex;
}
function isDexHandler() external override view returns (bool) { return true; }
function swap(bytes memory _data, uint256 _amount) public virtual override returns (uint256 _amountOut) {}
function getAmountOut(bytes memory _data, uint256 _amount) public virtual override view returns (uint256 _amountOut) {}
function swapData() external virtual override pure returns (bytes memory) {}
function decodeData(bytes memory _data) public virtual pure;

UniswapV2DexHandler.sol

uniswap verified on etherscan

sushiswap verified on etherscan

UniswapV2 custom DexHandler.

Overrides following DexHandlerAbstract functions:

function swap(bytes memory _data, uint256 _amount) public override returns (uint256 _amountOut)
function getAmountOut(bytes memory _data, uint256 _amount) public override view returns (uint256 _amountOut)
function decodeData(bytes memory _data) public override pure
function swapData() external override pure returns (bytes memory) {

For decodeData it always returns a message pointing to correct custom implementation:

require(false, 'use customDecodeData(bytes memory _data) returns (uint256 _amount, uint256 _min, address[] memory _path, address _to, uint256 _expire)');

For swapData it always returns a message pointing to correct custom implementation:

require(false, 'use customSwapData(uint256 _amount, uint256 _min, address[] memory _path, address _to, uint256 _expire) returns (bytes memory)');

These 2 functions above will return a different message for other DexHandlers (more examples in the future)

customSwap handles decoding and overwriting the data + the UniswapV2 logic for swapExactTokensForTokens

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swap

GovernanceSwap.sol

verified on etherscan

Governance managed mappings for dex and pairs.

// Dex handlers mapping
mapping(address => address) internal dexHandlers;
// in => out defaults
mapping(address => mapping(address => address)) internal defaultPairDex;
mapping(address => mapping(address => bytes)) internal defaultPairData;

This contract and it's governance need to be REALLY secure and trustworthy, since they have the ability to steal funds and/or block custom swaps by introducing an evil handler and/or data into a pair's default.

I need to find a way to incentivize good behaviour and minimize oversight required.

SafeSmartSwapAbstract.sol

Abstract contract that has all the internal functions to safely handle and verify swaps done via GovernanceSwap + DexHandlers.

Contracts that extend SafeSmartSwap should call SafeSmartSwap(_governanceSwap) on construction. (see MockStrategy.sol)

There are only 2 functions that respectively handle default and custom swaps:

// Governance swap
function _swap(uint256 _amount, address _in, address _out) internal returns (uint _amountOut)
// Custom swap
function _swap(uint256 _amount, address _in, address _out, address _dex, bytes memory _data) internal returns (uint _amountOut)

Governance (default) swaps spend less gas since they don't require extra checks (see gas spendage with npm run test:gas)

Custom swaps reverts if the output is less than the estimated output by the current Governance (default) swap for the pair.

require(_amountOut >= _governanceAmountOut, 'custom-swap-is-suboptimal');

Also checks final token balances in case the dex+data used was maliciously returning a higher _amountOut:

require(inBalancePostSwap >= inBalancePreSwap.sub(_amount), 'in-balance-mismatch');
require(outBalancePostSwap >= outBalancePreSwap.add(_governanceAmountOut), 'out-balance-mismatch');

---

mock

MockStrategy.sol

Mocked Strategy based on yearn's StrategyCurveYVoterProxy.sol

Extends SafeSmartSwapAbstract.sol, constructor needs address _governanceSwap.

3 key/test functions are:

// Swaps CRV to DAI by using a custom dex (available on GovernanceSwap) + custom data (can be created by using dex default handler)
function customHarvest(address _dex, bytes memory _data) public returns (uint256 _amountOut)
// New harvest function that uses GovernanceSwap default dex and data
function harvest() public override
// Legacy harvest function that uses uniswap and hardcoded path
function oldHarvest() public