async get_response can be a regular function too

[abetkin]

Here is what we have in MiddlewareMixin:

    def _async_check(self):
        """
        If get_response is a coroutine function, turns us into async mode so
        a thread is not consumed during a whole request.
        """
        if asyncio.iscoroutinefunction(self.get_response):
            # Mark the class as async-capable, but do the actual switch
            # inside __call__ to avoid swapping out dunder methods
            self._is_coroutine = asyncio.coroutines._is_coroutine
        else:
            self._is_coroutine = None

This checks if the next middleware is a coroutine, and if not fallbacks to sync mode. However, we already mark all async-capable middleware as such, why the redundancy?

A common usecase that is currently not supported:

def MyMiddleware(get_response):

    def middleware(request):
        # Do some stuff with request that does not involve I/O
        request.vip_user = True
        return get_response(request)

    return middleware

MyMiddleware.async_capable=True

middleware(request) will return the response in sync case and a coroutine in the async case, despite being a regular function (because get_response is a coroutine function in the latter case).

So I propose to remove the redundant _async_check

Github project to see the error: ​https://github.com/pwtail/django_bug