Fix Django "consume iterator" warning

[Archmonger]

Description

There are some circumstances where Django >4.2 would show the following warning: Warning: StreamingHttpResponse must consume synchronous iterators in order to serve them asynchronously. Use an asynchronous iterator instead.

There are two culprits are that caused these warnings:

• "304 file unchanged" file responses were being sent to Django with an empty tuple as the file content, which is technically not asynchronous.
• Django's sync/async middleware auto selection prefers middleware to run in sync mode, even when it didn't make sense. This prevented ServeStatic from generating async file responses.

Changelog

• Prevent responses with no body from creating a warning by providing Django a "placeholder" empty async iterable as the file content.
• Force Django>=3.2 to try using async file responses, even if the middleware is not running in async mode.

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

_{By submitting this pull request I agree that all contributions comply with this project's open source license(s).}

[brianglass]

@Archmonger, I tried this out this morning. First, thank you for finding a solution for this issue and getting a fix out so promptly! Second, I do have a potential issue to report. I haven't dug into this yet, but I'm getting a new error from a middleware lower in the stack that looks like the following:

Traceback (most recent call last):
web-1  |   File "/usr/local/lib/python3.12/site-packages/django/core/handlers/exception.py", line 55, in inner
web-1  |     response = get_response(request)
web-1  |                ^^^^^^^^^^^^^^^^^^^^^
web-1  |   File "/usr/local/lib/python3.12/site-packages/google/cloud/logging_v2/handlers/middleware/request.py", line 48, in middleware
web-1  |     return get_response(request)
web-1  |            ^^^^^^^^^^^^^^^^^^^^^
web-1  |   File "/usr/local/lib/python3.12/site-packages/asgiref/sync.py", line 187, in __call__
web-1  |     raise RuntimeError(
web-1  | RuntimeError: You cannot use AsyncToSync in the same thread as an async event loop - just await the async function directly.

My MIDDLEWARE setting looks like this:

MIDDLEWARE = [
    'orthocal.middleware.request_queueing',
    'corsheaders.middleware.CorsMiddleware',
    'servestatic.middleware.ServeStaticMiddleware',
    'django.middleware.gzip.GZipMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.locale.LocaleMiddleware',
    'django.middleware.common.CommonMiddleware',
    'google.cloud.logging_v2.handlers.middleware.RequestMiddleware',
    'orthocal.middleware.cache_control',
]

If I remove the Google cloud logging middleware, the error goes away. Also, if I downgrade to ServeStatic 1.0.0, the error goes away. I don't know which package is the root cause of the error. I hope to dig into this a little more tonight after work.

[Archmonger]

I will create a test branch to draft potential solutions to this.