Authenticator class errors get lost

[harmon]

I had a custom authenticator that was misconfigured, and it tried to import a settings.SOME_NAME when SOME_NAME did not exist in my settings module. This caused an AttributeError, so when the APIView tried to authenticate and called request.user, the Python property call swallowed this error, and gave me a "'WSGIRequest' object has no attribute 'successful_authenticator'" error instead, masking the real issue in my code.

I've got a pull request that demos this issue. It seems to happen on bad module references. I don't have a good solution, but maybe not having an authentication side effect inside a property definition might do the trick.

I'm happy to take a stab at a solution, but could use some guidance!

Pull Request: #1938

[tomchristie]

Probably specific to AttributeError and something to do with how our Request attempts to proxy attributes not on that class to Django's underlying HTTPRequest instance.

Needs further investigation.

[tomchristie]

Still seems valid to me, but not clear how we'd resolve.
Possible that we'd need to do something weird like inspecting the call stack when an AttributeError is raised, but unsure.

[harmon]

Hi Tom,

I've updated my pull request #1938 with a potential fix. I catch any AttributeErrors raised by the _authenticate() method and bubble up a RuntimeError with the details of the AttributeError. It's not the most error-prone approach (might be some odd edge cases for this odd edge-case), but I think it would help developers get to the bottom of the issue a lot quicker.

I thought about adding another catch for AttributeError here instead (https://github.com/harmon/django-rest-framework/blob/python-swallows-errors-in-properties/rest_framework/request.py#L405), which might be better, since it would cover the other properties that call _authenticate() internally within Request, but I didn't run into issues with those :P

It seems this is a problem some others have:

https://groups.google.com/forum/#!topic/comp.lang.python/BZf-d0rLP8U
http://blog.devork.be/2011/06/using-getattr-and-property_17.html

Thanks for your consideration. I'd be happy to try a different approach. I'm not the most experienced Python dev, so your thoughts are greatly appreciated.

[tomchristie]

Assuming this report on the discussion group is for the same issue: https://groups.google.com/forum/#!topic/django-rest-framework/emldSe_gxfI

[tomchristie]

Closing in favor of #2108.