Channels: Channels + rest framework: exception after file upload causes endless exception loop

[alexmnazarenko]

I've encountered a very annoying bug that seems directly related to channels.AsgiRequest.

• Channels + asgi_redis
• Django debug turned on
• Have a django/rest_framework handler accepting a file upload
• raise from this handler
• While attempting to return 500 response page, Django will raise exception again
• Catches exception, and tries to return 500 again...

---

• OS, runtime environment,browser: Ubuntu 16.04, Python 3.6, curl )
• Library versions: channels-1.1.8, daphne-1.3.0, django-1.11.5, twisted-17.9.0, asgi_redis-1.4.3, rest_framework-3.6.4
• Django debug turned on (important)
• Expected behavior: show an exception message in log, return 500 to the client
• Actual behavior: exception loops in the server, client hangs
• How you're running Channels: runserver + redis. Same situation with daphne.
• Console logs and full tracebacks of any errors:
  This exception repeats in the 'loop':

Traceback (most recent call last):
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/core/handlers/exception.py", line 41, in inner
    response = get_response(request)
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/utils/deprecation.py", line 140, in __call__
    response = self.get_response(request)
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/core/handlers/exception.py", line 43, in inner
    response = response_for_exception(request, exc)
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/core/handlers/exception.py", line 93, in response_for_exception
    response = handle_uncaught_exception(request, get_resolver(get_urlconf()), sys.exc_info())
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/core/handlers/exception.py", line 139, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/views/debug.py", line 81, in technical_500_response
    text = reporter.get_traceback_text()
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/views/debug.py", line 333, in get_traceback_text
    c = Context(self.get_traceback_data(), autoescape=False, use_l10n=False)
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/views/debug.py", line 300, in get_traceback_data
    'filtered_POST_items': list(self.filter.get_post_parameters(self.request).items()),
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/views/debug.py", line 167, in get_post_parameters
    return request.POST
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/channels/handler.py", line 160, in _get_post
    self._load_post_and_files()
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/http/request.py", line 299, in _load_post_and_files
    self._post, self._files = self.parse_file_upload(self.META, data)
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/http/request.py", line 255, in parse_file_upload
    warning="You cannot alter upload handlers after the upload has been processed."
  File "/home/alexey.nazarenko/.pyenv/versions/p7reloaded_py/lib/python3.6/site-packages/django/http/request.py", line 248, in upload_handlers
    raise AttributeError("You cannot set the upload handlers after the upload has been processed.")
AttributeError: You cannot set the upload handlers after the upload has been processed.

[alexmnazarenko]

Simple (probably, not minimal) example app:

rest_upload_fail.zip

Offending request:

curl -F "inputs=@$HOME/tmp/test.txt" http://127.0.0.1:8000/users/1/oppana/

[andrewgodwin]

Yup, looks like something about the 500 handling is slightly off, which is weird, as the request handling code is basically copied from Django.

[alexmnazarenko]

That's one quick response )

It looks like we're missing something like hasattr(self, '_files') check somewhere, but I can't be sure.

[mkdk]

I have same problem with DRF. Any suggestion?

[taikikazuo66]

Same here with DRF. General http 500 exception gives me this.

[vladimirmyshkovski]

I get the same error when using DRF

[mkdk]

I found that this error occurs for me when serializer use UniqueTogether validator, so I replaced it on custom validate field e.g:
def validate(self, data):
post = data['post']
if SavedPost.objects.filter(user_id=self.context['request'].user.id, post_id=post).exists():
raise ValidationError("This post was already saved")
return data

maybe it will help someone.

[rpkilby]

Hi everyone. I believe this has been fixed by encode/django-rest-framework#5590.

If anyone has the time, it'd be appreciated if you could verify the fix by testing your code against the DRF master branch.

[mark-mishyn]

@rpkilby
Hello Ryan.
Yes, now issue is fixed. But I've tested only one case.

channels==1.1.8 + djangorestframework==3.7.3 (master)

Thank you!

[SHohentanner]

Hello, are there any updates on this issue? I am using the same configuration as @mark-mishyn , but I still get the error

[rpkilby]

Hi @SHohentanner - have you tried installing the latest release (3.7.7)? It should no longer be necessary to install DRF from the master branch.

[andrewgodwin]

Closing as it's been fixed on the DRF end (thanks for that!)