We recently uncovered a bug in our code, which was pretty confusing, and is explainable only via the fine-print of http://docs.djangoproject.com/en/dev/topics/http/middleware/ -- and reading through the Django source. So I thought I'd share, and maybe a Django developer might comment on whether the current behaviour is really desirable, and if so perhaps consider improving the docs.
We have some Middleware that updates the user's session, from a process_response method. Sometimes this would fail, because the request object had no session. It turns out this would happen because the Common middleware had issued a redirect (specifically, APPEND_SLASH was redirecting us to correct the view's URL). In a case like this, the current behaviour is not like the 'onion' as illustrated in the docs, because whilst the redirect meant that *only* the Common middleware had its process_request function executed, every loaded middleware's process_response is executed. (This is mentioned in the docs, it turns out, in the process_request section but not in the process_response section.) What this means is that even though it seems, and is the case 99% of the time, that middleware listed later can rely totally on middleware further up the list (i.e. the 'onion' model), this is in fact not the case, for processing responses. So response processing code is either subject to rare bugs, or has to contain extra checks to make sure of its preconditions (in our case a check for hasattr(request, 'session') ). Personally I think this is confusing enough that it would be better if the program logic could be changed, so that later-listed middleware would definitely only either run, or not run, depending on whether the earlier middleware allows the request to proceed or not. But I guess such a change could break existing code, so at the very least the docs could use a bit more explanation and or highlighting in bold! thanks George Lund --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
