The low-level functions call, delegatecall and staticcall return true as their first return value if the account called is non-existent

Question

According to the official Solidity documentation:

The low-level functions call, delegatecall and staticcall return true as their first return value if the account called is non-existent, as part of the design of the EVM. Account existence must be checked prior to calling if needed.

Does that mean that if I use call (/delegatecall/staticcall) in my contract, I should first check that the address is a contract?

For this example code:

function swap(
    IERC20 _asset,
    uint256 _amount,
    address _routingContract,
    bytes calldata _routingPayload)
internal
{
    IERC20(_asset).safeApprove(_routingContract, _amount);
    (bool success,) = _routingContract.call(_routingPayload);
    if (!success) revert SwapFailed();
}

Would call return true if the address is not a contract?

Which in this case I'm assuming the best practice will be to add the line:

if (_routingContract.code.length == 0) revert InvalidRoutingContract();

And also is there a way to know if the call actually passed to the contract's fallback function?

Answer 1

You could use Address.isContract() from the OpenZeppelin contracts.

There's no way to determine if the callback was executed or no. It shouldn't be too important since many important contracts use a proxy contract as a "frontend".