id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
29277	Add a bust_browser_cache flag to the static template tag	David Kerkeslager	nobody	"The proposal is to add a `bust_browser_cache` flag to the `static` template tag using a similar syntax to passing context variables to the `include` template tag. It would look something like this:

{{{
{% static 'css/style.css' with bust_browser_cache=True %}
}}}

The flag would default to `False` to avoid breaking existing usages of the `static` tag.

What flag does is add a `cache_hash` get parameter to the URL of the static file, with a hash of the static file. So if the content of `css/style.css` looks like:

{{{
p {
    color: magenta;
}
}}}

The generated URL will look like `/static/css/style.css?cache_hash=0756793258f5ea00cda3e445de6bb595`.

If the content of `css/style.css` changes to:

{{{
p {
    color: magenta;
}
p::after {
    content: ""Sorry about this awful color."";
}
}}}

Then the link would be `/static/css/style.css?cache_hash=c3aebd6286841ce8f4d76aa8d3eba487`.

This is not a security feature, so I think it would be best to use MD5 because it is fast.

Instead, the purpose of this is to allow us to serve static files with `Cache-Control: immutable` or `Cache-Control: max-age=<some large number>` without fear. As long as the content of the file does not change, the URL's `cache_hash` will not change, so the browser will use the cached version. But if the content of the static file changes, the `cache_hash` parameter will change, causing the browser to request the new version of the file. This gets us the best of both worlds: we maximize usage of browser cache for static files, while never having to worry that our users are seeing stale versions of static files.

It may make sense to store the MD5 hash in Django's cache so that it doesn't get calculated every time."	New feature	new	Template system	2.0	Normal		browser-cache-busting static-files		Unreviewed	0	0	0	0	0	0