Coby's Dutch CoWs integration guide

Integrate

Do these three calls in one transaction, from the contract that holds the sell token. receiver must be that contract and startBlock must be block.number. The interface is src/IDutchCoW.sol.

AuctionParams memory params = AuctionParams({
    sellToken: sellToken,
    buyToken: buyToken,
    sellAmount: sellAmount,
    maxAmount: maxAmount,
    receiver: address(this),
    startBlock: block.number,
    validFor: validFor,
    slippageBps: slippageBps
});

address escrow = auctioneer.predictEscrow(params);

Option A: standard approve. Use this when the token's approve returns a bool, which covers most ERC-20s.

IERC20(sellToken).approve(escrow, sellAmount);
auctioneer.placeOrder(params);

Some tokens, such as USDT, return nothing from approve. Option A reverts on those. Option B accepts both kinds of return, so use it when you have not tested the token.

Option B: low-level approve. Accepts a bool return or no return.

(bool ok, bytes memory data) = sellToken.call(abi.encodeWithSelector(0x095ea7b3, escrow, sellAmount));
require(ok && (data.length == 0 || abi.decode(data, (bool))), "approve");
auctioneer.placeOrder(params);

How it works

Your contract calls the auctioneer. The auctioneer deploys a small escrow, pulls the sell token into it, and registers the order with ComposableCoW. The CoW watch tower posts the order to the orderbook. A solver fills it by paying the buy token to your contract and taking the sell token from the escrow.

The price stays at maxAmount for the first 5 blocks, then falls. slippageBps is the total drop in basis points of maxAmount. validFor is how many Base blocks that drop takes. Base blocks are 200ms. The floor is maxAmount * (10_000 - slippageBps) / 10_000.

If nobody fills it, anyone can call releaseFunds on the escrow once block.number is greater than startBlock + validFor. The sell tokens go back to your contract. When the balance is at least 1000 raw units, the caller keeps balance / 1000. The full behavior is in the reference.

Base Deployment Addresses