How to bubble up meaningful 0x contract revert data?

Question

I'm fairly new to solidity so thanks in advance for your patience with this question.

I'm trying to implement a contract that uses the following line from the 0x sample provided here: https://github.com/0xProject/0x-api-starter-guide-code/blob/master/contracts/SimpleTokenSwap.sol#L90

I understand that the call won't revert itself, but will return a boolean "success" depending on whether or not it worked. However, the next line doesn't provide anything useful, as it has a hardcoded "SWAP_CALL_FAILED" string.

I'd like to bubble up the reason why it failed. According to the 0x documentation, the 0x protocol uses "rich revert" reasons that are not simply strings, but custom errors with custom params: https://0x.org/docs/guides/v3-specification#rich-reverts

My problem: How am I supposed to decode the bytes memory response without knowing in advance which error profile is in there? Is there any way to get meaningful error data from the swapTarget.call{value: msg.value}(swapCallData); call?

I should mention that I'm using a hardhat local fork, if that makes a difference.

Answer 1

The Solidity devs are working on supporting this more natively (you can read up on this on the try/catch docs).

Until then you would have to parse the response bytes similar how you parse a method id. An example for this can also be found on the array slices docs

Basically you would do the following:

// Check if the call failed
if (!success) {
  if (bytes4(response) == bytes4(keccak256("OrderStatus(bytes32,uint8)"))) {
     (bytes32 orderHash, uint8 orderStatus) = abi.decode(response[4:], (bytes32,uint8));
    // Custom error handling
  } else {
    revert("Unknown error");
  }
}

Answer 2

For 0x V3 these can be decoded with RevertError.decode(bytes) in the @0x/utils package. This will look at the Error bytes4 selector and decode the reason.