Middleware order is important hence docs for third party libraries advise this should come before x or after y. Some middleware read headers that others set. Some set headers that affect caching. Some perform some action on the rendered response content such as gzip.
Over a long-lived codebase itβs easy for middlware to fall out of order. During my time reviewing pull requests I give this feedback:
Below is the order the built-in Django middlware should conform to.
Near the start
CommonMiddleware
As the name implies, this performs common operations we expect Django to do such as redirecting according to APPEND_SLASH
and PREPEND_WWW
setting. If Django is redirecting based on the URL, we want that
to happen as soon as possible, hence this middlware comes at the start. The middleware also sets content-length, which other middlwares may rely on.
LocaleMiddleware
This handles internationalization of content. It customizes content for each user. We would not want any part of our website to miss that language-specific and user-specific customization and have the header in English the footer in German. Nien! Hence this comes early.
SecurityMiddleware
Another well named middleware that hardens security. We would not want security to be handled near the end of the request.
Near the end
There are two built in fallback middlwares that perform some operation if all else fails:
RedirectFallbackMiddleware
This middleware handles 404s by redirecting somewhere according to redirect records set in Django admin. We would not want this to happen at the start otherwise database records would take precedence over code in urls.py, and also the database lookup would slow down the response that do not need a fallback.
FlatpageFallbackMiddleware
Very similar to RedirectFallbackMiddleware
but it serves flat pages instead of redirecting the user somewhere.
Relative to each other
And then the spider web begins:
UpdateCacheMiddleware
before SessionMiddleware
UpdateCacheMiddleware
before GZipMiddleware
UpdateCacheMiddleware
before LocaleMiddleware
SessionMiddleware
before LocaleMiddleware
GZipMiddleware
before ConditionalGetMiddleware
SessionMiddleware
before AuthenticationMiddleware
SessionMiddleware
before MessageMiddleware
CsrfViewMiddleware
before RemoteUserMiddleware
FetchFromCacheMiddleware
before SessionMiddleware
FetchFromCacheMiddleware
before GZipMiddleware
FetchFromCacheMiddleware
before LocaleMiddleware
Does your codebase order middleware correctly?
Itβs easy to miss something. I can check that for you at django.doctor, or can review your GitHub PRs:
Or try out Django refactor challenges.
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