- case unknown_error: return "unknown_err";
- case arg_error: return "invalid_arg";
- case mismatch_error: return "mismatch";
- case not_found_error: return "not found";
- case system_error: return "system_err";
- case network_error: return "network_err";
- case timeout_error: return "timeout";
- case thread_error: return "thread_err";
- default: return "INVALID_ERR";