fix EventLoggerPlugin.__getattr__

[edenhaus]

The EventLoggerPlugin is implementing wrong the method __getattr__, which lead to an incorrect check in

amqtt/amqtt/plugins/manager.py

Lines 193 to 199 in 8961b8f

	async def _call_coro(plugin, coro_name, *args, **kwargs):
	if not hasattr(plugin.object, coro_name):
	# Plugin doesn't implement coro_name
	return None
	coro = getattr(plugin.object, coro_name)(*args, **kwargs)
	return await coro

Before the fix the method hasattr would return True for name like 'topic_filtering' and the method is not returning None. This then will lead to an 'NoneType' object is not callable in line 199.
On version 0.10.0 this creates an infinite wait for the client to subscribe on topics. Bug was find during migration from hbmqtt to amqtt. Probably this PR fixes also #83

The python docs says for object.__getattr__(self, name):

This method should either return the (computed) attribute value or raise an AttributeError exception.

@FlorianLudwig I think we should cherry pick this PR also for the 0.10.x branch as I cannot use the 0.10 without this fix and probably others, if they have disabled topic_check.

[FlorianLudwig]

@edenhaus Thank you very much for your detailed investigation.

I will need to take a detailed look before merging this. The handling of plugins has interesting edge cases. Especially this is of interest to me:

Bug was find during migration from hbmqtt to amqtt

So you didn't have this bug with hbmqtt?

One of the reasons why I am hesitant to merge this is breaking compatiblity - but it seems we already have.

[edenhaus]

Hbmqtt has implemented the method __getattr__ wrong and I would fix this correctly. Also to mention this is not a breaking change, it's only a bugfix

@FlorianLudwig The bug was introduces by the following commit a69ef81
As you can see in the diff, the 'NoneType' object is not callable is in hbmqtt catched by except TypeError

[FlorianLudwig]

@edenhaus Thank you very much! Nice find and investigative work.

The commit introducing the bug actually solved another bug - so this is the right course of action - including for the compatibility branch 0.10.x.

[edmaher]

as mentioned in this thread, can we get this cherry-picked to the current major version, the bug is quite a big time-waster