CachedStaticFilesMixin lags in updating hashed names of other static files referenced in CSS
|Reported by:||woodlee||Owned by:||Marc Egli|
|Has patch:||yes||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||yes|
Procedure to replicate:
- Be using staticfiles with CachedStaticFilesStorage.
- Have a CSS file such as 'abc.css' which refers to an image file such as 'xyz.png' (via either "url()" or "@import").
- Do an initial run of collectstatic. Observe correct substitution of the path to 'xyz.png' to its hashed name within abc.css.
- Change the contents of xyz.png (maybe it's a sprites file... so changes aren't unheard of!).
- Rerun collectstatic (without the --clear option).
- Observe that abc.css still refers to the old hashed name of xyz.png; this is the bug.
- Run collectstatic a third time.
- Observe that abc.css now refers to the correct, newer hashed name of xyz.png.
I believe this is happening because during post_process, when the url_converter calls url() (see https://github.com/django/django/blob/1.6.2/django/contrib/staticfiles/storage.py#L195), url() gets the hashed name out of the staticfiles cache... which has not yet been updated with the new hashed-name value for the image file, since said cache updating doesn't happen until the end of post_process.
I think the best solution may be to add a kwarg of 'use_cache=True' to url(), which url_converter can set to False when it calls url(). When False, the cache will simply be evaded (not updated) and hashed_name can be called directly. In this way, url_converter is always substituting to the most up-to-date hash, but actually updating the cache is still delayed until the end of post_process, which seems desirable since I think updating that cache should happen as closely as possible in time to the moment when the new static assets are placed wherever they'll be served from (bit of a race condition, there).
Unrelated: it would be nice to warn in documentation that if you define a separate 'staticfiles' cache in CACHES, it might be desirable to set its TIMEOUT option to None. I kept wondering why lookups were coming back empty and eventually realized it was because my staticfiles cache was using the default 5 minute timeout.