fleupold / milkman

A smart contract system which allows smart contracts, including Gnosis Safes, to route their order flow through the CoW protocol with market orders.

Milkman

Fulfills all of your smart contract's CoW needs. 🐮

A simple way for smart contracts to sell their tokens via the CoW Protocol, reaping the benefits of MEV protection even when tx.origin is malicious (e.g., a liquidator bot in a borrow/lend protocol).

How to use

To swap via Milkman, call milkman.requestSwapExactTokensForTokens, passing in the following parameters:

• amountIn: an amount of tokens to sell
• fromToken: ERC20 you're swapping out of
• toToken: ERC20 you're swapping into
• to: the intended receiver of the bought tokens
• priceChecker: the address of a price checker, or address(0) for none; explained below
• priceCheckerData: encoded data to pass to the price checker; explained below

After you submit a swap request, it should be picked up and executed within 1-2 minutes.

See docs/EXAMPLES for examples.

Price checkers

After token have been sent to Milkman, it functions like a 'conditional signer', only releasing those tokens to CoW protocol under certain conditions. Anyone can generate an off-chain order for an on-chain swap request, but Milkman will only sign off on orders that pass its checks.

Many of these checks are baked into Milkman itself, such as ensuring that the off-chain order is a sell order (not a buy order). However, an important one is not: validating that the bot-supplied minOut approximates the true value of the tokens that a user is swapping. Users who don't want to trust the CoW off-chain system can use price checkers. Price checkers verify that a minOut is in-line with some on-chain price feed. For example, one price checker could verify that minOut is at least 90% of what they could get from selling the tokens via SushiSwap.

The only requirement for a price checker is that it needs to be compatible with the IPriceChecker interface. Anyone can create a new one, and new ones don't need to be whitelisted.

Developing new price checkers

To be valid, price checkers need to implement the following function:

function checkPrice(
        uint256 _amountIn,
        address _fromToken,
        address _toToken,
        uint256 _minOut,
        bytes calldata _data
    ) external view returns (bool);

The process of building one is straightforward. Examples can be found in the pricecheckers folder.