Executing custom bytecode before and after order fill?

[andr11111]

I know the LimitOrder has pre- and post- interaction capabilities. How do I achieve the same here. I tried to modify the underlying LimitOrder object, but no luck so far. My use case is this. I'm integrating swap from a contract. First, in the pre-interaction I'd like to verify that swap is between whitelisted assets and only then give approval to pull makerToken. Second, once the swap is complete, I'd like to perform additional code to finalize the transaction on our side. Do you have an example on how to do it?

[krboktv]

First of all, you need to implement isValidSignature method on your smart contract according to EIP-1271. This will allow to set smart contract address to order.maker. In such scenario, you don't necessary need to use preInteraction, because in the signature field you can provide any data that would be accessible inside isValidSignature method. Usually, you write to storage some address over which you have a control. Sign the order with controlled private key. And isValidSignature will validate the signature against the address in storage. In such case, you can safely give approval in advance and control which assets do you sign by your private key.

As for custom postInteraction, this functionality hasn't implemented yet for FusionSDK. In a nutshell, the custom post interaction should follow after the end of extension in a format ${interaction_target}${interaction_data}

[andr11111]

Yes I'm already using isValidSignature. The problem is that since it only passes the hash of the order I have no way to verify the order on the contract side. E.g. if someone gets access to the signer EOA they could potentially steal funds by exchanging into a token they control, so I'd like to implement additional checks on contract side.

[andr11111]

Regarding the interaction I see it is not implemented in the SDK. Is there a custom code to make this possible still? I've been trying to "hack" it by modifying the underlying LimitOrder, but no luck so far. The API says it cannot verify signature, even though I sign after modifying it (in sumbitOrder)