Django: signal when user logs in?

Question

In my Django app, I need to start running a few periodic background jobs when a user logs in and stop running them when the user logs out, so I am looking for an elegant way

Answer 1

One option might be to wrap Django's login/logout views with your own. For example:

from django.contrib.auth.views import login, logout

def my_login(request, *args, **kwargs):
    response = login(request, *args, **kwargs)
    #fire a signal, or equivalent
    return response

def my_logout(request, *args, **kwargs):
    #fire a signal, or equivalent
    return logout(request, *args, **kwargs)

You then use these views in your code rather than Django's, and voila.

With regards to querying login status, it's pretty simple if you have access to the request object; simply check request's user attribute to see if they're a registered user or the anonymous user, and bingo. To quote the Django documentation:

if request.user.is_authenticated():
    # Do something for logged-in users.
else:
    # Do something for anonymous users.

If you don't have access to the request object, then determining if the current user is logged in is going to be difficult.

Edit:

Unfortunately, you'll never be able to get User.is_logged_in() functionality - it's a limitation of the HTTP protocol. If you make a few assumptions, however, you might be able to get close to what you want.

First, why can't you get that functionality? Well, you can't tell the difference between someone closing the browser, or someone spending a while on a page before fetching a new one. There's no way to tell over HTTP when someone actually leaves the site or closes the browser.

So you have two options here that aren't perfect:

1. Use Javascript's unload event to catch when a user is leaving a page. You'd have to write some careful logic to make sure you aren't logging out a user when they're still navigating your site, however.
2. Fire the logout signal whenever a user logs in, just to be sure. Also create a cron job that runs fairly often to flush out expired sessions -- when an expired session is deleted, check that the session's user (if it's not anonymous) has no more active sessions, in which case you fire the logout signal.

These solutions are messy and not ideal, but they're the best you can do, unfortunately.