Bug 1258700 - Use WhiteNoise as middleware rather than as a WSGI app

WhiteNoise now supports being used as Django middleware, rather than
having to wrap the Django app with the standalone WSGI WhiteNoise app:
http://whitenoise.evans.io/en/latest/changelog.html#simpler-cleaner-django-middleware-integration
http://whitenoise.evans.io/en/latest/django.html#enable-whitenoise

In addition to reducing the complexity of the WGSI configuration, it
means that Django's security middleware can soon be used to perform
HTTPS redirection (and more), rather than having to rely on yet another
(and less featureful) standalone WSGI app: wsgi-sslify.

treeherder/config/settings.py

@@ -31,6 +31,7 @@
 USE_L10N = True
 
 SERVE_MINIFIED_UI = env.bool("SERVE_MINIFIED_UI", default=False)
+# Files in this directory will be served by WhiteNoise at the site root.
 WHITENOISE_ROOT = path("..", "dist" if SERVE_MINIFIED_UI else "ui")
 
 STATIC_ROOT = path("static")
@@ -65,6 +66,9 @@
 )
 
 MIDDLEWARE_CLASSES = [
+    # Allows both Django static files and those specified via `WHITENOISE_ROOT`
+    # to be served by WhiteNoise, avoiding the need for Apache/nginx on Heroku.
+    'treeherder.config.whitenoise_custom.CustomWhiteNoise',
     'django.middleware.gzip.GZipMiddleware',
     'django.middleware.common.CommonMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',

treeherder/config/whitenoise_custom.py

@@ -1,9 +1,9 @@
 import re
 
-from whitenoise.django import DjangoWhiteNoise
+from whitenoise.middleware import WhiteNoiseMiddleware
 
 
-class CustomWhiteNoise(DjangoWhiteNoise):
+class CustomWhiteNoise(WhiteNoiseMiddleware):
 
     # Matches grunt-cache-busting's style of hash filenames.
     IMMUTABLE_FILE_RE = re.compile(r'\.min-[a-f0-9]{32}\.(js|css)$')

treeherder/config/wsgi.py

@@ -19,15 +19,9 @@
 from django.core.wsgi import get_wsgi_application as django_app
 from wsgi_sslify import sslify
 
-from treeherder.config.whitenoise_custom import CustomWhiteNoise
-
 env = environ.Env()
 
-# Wrap the Django WSGI app with WhiteNoise so the UI can be served by gunicorn
-# in production, avoiding the need for Apache/nginx on Heroku. WhiteNoise will
-# serve the Django static files at /static/ and also those in the directory
-# referenced by WHITENOISE_ROOT at the site root.
-application = CustomWhiteNoise(django_app())
+application = django_app()
 
 if env.bool('IS_HEROKU', default=False):
     # Redirect HTTP requests to HTTPS and set an HSTS header.