set_cookie timezone naive vs aware

[James Addison]

I appear to be unable to set a cookie when using the following in my settings and code:

from django.utils import timezone

TIME_ZONE = 'America/Vancouver'
USE_TZ=True

I get the following traceback:

Traceback (most recent call last):
  File "/Users/jaddison/projects/testproj/src/django/django/core/handlers/base.py", line 111, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/Users/jaddison/projects/testproj/src/django/django/views/decorators/csrf.py", line 77, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/jaddison/projects/testproj/project/apps/facebookapp/views.py", line 61, in tab
    response.set_cookie('referral_data', "page-%s" % page.id, expires=timezone.now() + datetime.timedelta(days=settings.SIGNUP_REFERRAL_COOKIE_DURATION))
  File "/Users/jaddison/projects/testproj/src/django/django/http/__init__.py", line 651, in set_cookie
    delta = expires - expires.utcnow()
TypeError: can't subtract offset-naive and offset-aware datetimes

I *think* that set_cookie needs to be checked for aware vs naive datetime handling, but I'm not sure. Am willing to provide more information upon request.

[Aymeric Augustin]

set_cookie is a bit of a special case already -- its expires argument must be "a naive datetime in UTC", while everything else happens (well, used to happen) in local time in Django. If you use it, you probably have either TIME_ZONE = "UTC" or some conversion code.

Anyway, with aware datetimes being the standard when USE_TZ = True, and the general recommendation to use timezone.now() (as facebookapp does in the traceback above), it makes sense to accept them in set_cookie. Does the attached patch fix your problem?

[Aymeric Augustin]

I just checked that there are no other uses of utcnow in Django, except in code related to time zone support.

[James Addison]

Yes, the code now works - and it makes sense that it needs to work with naive datetimes internally when setting the cookie. Nice work.

Not sure if I should resolve the bug as fixed or not... I'll leave that for others as I don't want to step on toes.

[Aymeric Augustin]

In [17766]:

Fixed #17931 -- Accepted aware datetimes to set cookies expiry dates. Thanks jaddison for the report.