Return 404 at SubdomainMiddleware level if project doesn't exist

[humitos]

While deploying .com we found that SubdomainMiddleware doesn't check the existence of the project that it's injecting at request.slug.

So, any middleware that relies on this to do some extra work, will probably do something like Project.objects.get(slug=request.slug) and will fail.

We workarounded it by adding try/except block in the middleware that uses this, but we should probably just raise a 404 inside the SubdomainMiddleware itself instead of continue with the flow.

Code: https://github.com/rtfd/readthedocs.org/blob/74bbb3ac23b6b06a70517bc1b301961db6821e32/readthedocs/core/middleware.py#L72

[dojutsu-user]

@humitos I would like to take this issue up.
If I'm not wrong, you probably want something like this

# Checking if the project exist or not
from django.shortcuts import get_object_or_404
get_object_or_404(Project, slug=subdomain)

request.subdomain = True
request.slug = subdomain
request.urlconf = SUBDOMAIN_URLCONF
return None

With get_object_or_404, it will show error and does not go further.

[humitos]

@dojutsu-user since this is a code that it's executed a lot, retrieving the whole Project object it may be overkilling since we not going to use that data anyway. You may just need to check if the project does exist with .exists() and using an if in this case.