def lookup_online(byte_sig: str, timeout: int, proxies=None) -> List[str]:
        """Lookup function signatures from 4byte.directory.

        :param byte_sig: function signature hash as hexstr
        :param timeout: optional timeout for online lookup
        :param proxies: optional proxy servers for online lookup
        :return: a list of matching function signatures for this hash
        """
        if not ethereum_input_decoder:
            return []
        return list(
            ethereum_input_decoder.decoder.FourByteDirectory.lookup_signatures(
                byte_sig, timeout=timeout, proxies=proxies
            )
        )