Re: [PATCH v1 2/2] daemon: telegram: Handle MySQL error

[Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>]

On Sat, Oct 29, 2022 at 1:10 AM Muhammad Rizki wrote:
> On 28/10/22 23.46, Alviro Iskandar Setiawan wrote:
>> Even this part is also problematic, if you hit an error before
>> utils.remove_patch(), the patch file won't get removed because
>> exception will stop the current execution and throw the exception to
>> the previous call stack.
>
> You are right. So we just check every value from the DB method and if
> it's None just return like goto?

You don't use goto in Python. In an OOP style, the cleanup usually
happens in the destructor, or in a "try with finally" statement.

>>
>> I hate try and catch style, because it's very easy to miss an error
>> like this. I prefer the way C handles error manually via return value
>> like:
>>
>>          ret = func_call();
>>          if (ret < 0)
>>                  goto clean_up;
>>
>
> I've improved the remove_patch() earlier using the glob UNIX style path
> to check if all temp dirs is exists then remove them all. What do you think?

It doesn't address the issue. You still don't understand the
underlying issue behind your remove_patch() placement.

You have this:

        for d, f in files:
                await m.reply_document(f"{d}/{f}", file_name=f)
                await asyncio.sleep(1)

        utils.remove_patch(files)

What happens if you follow that for loop, then m.reply_document()
throws an exception?

The answer is:
utils.remove_patch(files) will *not* be executed because it will throw
the exception to the previous call stack, and if the previous call
stack doesn't have a "try and except" statement, it will throw the
exception to the previous call stack again, until at some point it is
handled by and "try and except". If it never hits a "try and except"
statement, the application will terminate.

You don't do the cleanup if:
    - An error happens *after you create the patch file*.
    - But before the remove_patch() is executed.

There are 2 possible solutions, either using a "try with finally"
statement, or using a destructor wrapped in a class.