Add session backend for Google's App Engine

[Jannis Leidel]

Now that the cheering stopped I started implementing a session backend for Google's App Engine, obviously the easiest part in creating more compatibility between Django and GAE.

[Jannis Leidel]

first implementation, including documentation and tests

[colinramsay]

I think line 107 on your patch should be "if s:" rather than "if not s:", otherwise when a matching entry is found it will still raise SuspiciousOperation and reset the session.

[Jannis Leidel]

Fixed stupid conditional error

[ribrdb <ribrdb@…>]

It would be more efficient to use the session_key as the key_name, and then use Session.get_by_key_name() instead of querying through Session.all()

[Jannis Leidel]

Yes, I think so, too.

I had it implemented that way first but got "BadArgumentError: Names may not begin with a digit; received 838deafcd209c60564b730bb8b4f8fd1." exceptions from appengine and didn't want to change the way the session IDs are generated by Django.

What do you think?

[ribrdb <ribrdb@…>]

You could add a prefix string like 'session_key:' to the django generated id.

[ribrdb <ribrdb@…>]

Couldn't someone set settings.SESSION_COOKIE_NAME to something that starts with a number? That seems to be allowed by the RFC.

[Jannis Leidel]

Uses session_key as key_name and Session.get_by_key_name() for better performance. Added session_key_prefix to circumvent BadArgumentError.

[Jannis Leidel]

Replying to ribrdb <ribrdb@gmail.com>:

Couldn't someone set settings.SESSION_COOKIE_NAME to something that starts with a number? That seems to be allowed by the RFC.

Right, I fixed that now :)

[ribrdb]

I like it. It might be good though to add a test case to make sure you get the data back when you save and then load a session.

[makovick]

AFAIK the App Engine has currently no equivalent of cron, so it would be nice if SessionStore.load is able to purge all expired sessions every once a while.
The purge timeout could be handled by the memcache API - after the cleanup, one can set some "sessions_purged" flag with 1 hour/day/whatever expiration, and then skip the purge until the flag disappears. This would avoid unnecessary datastore lookups.

[Marc Fargas]

Brought to django-developers (​here) for discussion.

[Jannis Leidel]

Maby better alternatives:

​http://code.google.com/p/django-ae-utils/
​http://code.google.com/p/django-gae-helpers/
​http://code.google.com/p/django-gae-tools/

[Marc Fargas]

I take this as a "Close this until one of those alternatives requests inclusion as a contrib app" ;)