Django async support with ASGI.

[marcinocto]

I'm converting my project to be deployed under ASGI with daphne with the Django channels library. I have the IPRestrictMiddleware hooked up in my middleware and after turning on the channels app I started getting this issue

Traceback (most recent call last):
django_1    |   File "/usr/local/lib/python3.8/site-packages/channels/staticfiles.py", line 40, in __call__
django_1    |     return await self.staticfiles_handler_class()(
django_1    |   File "/usr/local/lib/python3.8/site-packages/channels/http.py", line 179, in __init__
django_1    |     self.load_middleware()
django_1    |   File "/usr/local/lib/python3.8/site-packages/channels/http.py", line 294, in load_middleware
django_1    |     super(AsgiHandler, self).load_middleware()
django_1    |   File "/usr/local/lib/python3.8/site-packages/django/core/handlers/base.py", line 58, in load_middleware
django_1    |     mw_instance = middleware(adapted_handler)
django_1    |   File "/code/project/middlewares/ejn_ip_restrict.py", line 7, in __init__
django_1    |     self.ip_restrict = IPRestrictMiddleware(get_response)
django_1    |   File "/usr/local/lib/python3.8/site-packages/iprestrict/middleware.py", line 17, in __init__
django_1    |     self.restrictor = IPRestrictor()
django_1    |   File "/usr/local/lib/python3.8/site-packages/iprestrict/restrictor.py", line 12, in __init__
django_1    |     self.load_rules()
django_1    |   File "/usr/local/lib/python3.8/site-packages/iprestrict/restrictor.py", line 24, in load_rules
django_1    |     self.rules = list(Rule.objects.all())
django_1    |   File "/usr/local/lib/python3.8/site-packages/django/db/models/query.py", line 262, in __len__
django_1    |     self._fetch_all()
django_1    |   File "/usr/local/lib/python3.8/site-packages/django/db/models/query.py", line 1324, in _fetch_all
django_1    |     self._result_cache = list(self._iterable_class(self))
django_1    |   File "/usr/local/lib/python3.8/site-packages/django/db/models/query.py", line 51, in __iter__
django_1    |     results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
django_1    |   File "/usr/local/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1173, in execute_sql
django_1    |     cursor = self.connection.cursor()
django_1    |   File "/usr/local/lib/python3.8/site-packages/django/utils/asyncio.py", line 24, in inner
django_1    |     raise SynchronousOnlyOperation(message)
django_1    | django.core.exceptions.SynchronousOnlyOperation: You cannot call this from an async context - use a thread or sync_to_async.

This happens because of the DB call in the __init__ of the IPRestrictMiddleware when instantiating the IPRestrictor.

    def load_rules(self):
        # We are caching the rules, to avoid DB lookup on each request
        from .models import Rule

        self.rules = list(Rule.objects.all())
        self.last_reload = timezone.now()

I can't see anything specific here about middleware https://docs.djangoproject.com/en/4.0/topics/async/ but I assume that any call like DB call is not ideal in the async scope.

I implemented this workaround which delays the instantiation of the class to the process_request instead which with the help of the django's MiddlewareMixin is implemented to run with the sync_to_async wrapper.

from django.utils.deprecation import MiddlewareMixin
from iprestrict.middleware import IPRestrictMiddleware


class CustomIPRestrictMiddleware(MiddlewareMixin):
    ip_restrict: IPRestrictMiddleware = None

    def process_request(self, request):
        if self.ip_restrict is None:
            self.ip_restrict = IPRestrictMiddleware(self.get_response)
        return self.ip_restrict(request)

Any thoughts on moving the DB call away from the __init__ call in the IPRestrictMiddleware and having some similar solution to what I've done?

[zhixuan-loh]

Hi. I'm working on something similar involving using IP restrict redux (which is a more updated version of IPRestrict) in the django channels. I notice that their middleware are not compatible because channels middleware has a call method with signature async def __call__(self, scope, receive, send): while django channels middleware has method signature def __call__(self, request): I get error because of the mismatch in number of arguments (which is expected).

May I know if there is a way to incorporate iprestrict redux into django channels middleware?