id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
33716	async get_response can be a regular function too	abetkin	nobody	"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, I think this check is redundant: if the middleware is async-capable, and we have an ASGI request, what else we need ti check?

The downside of _async_check is that this common usecase is 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).

Here is a patch that I use that explains a possible way to fix it:


{{{
def call_mw(mw, request, _call_mw=MiddlewareMixin.__call__):
    if isinstance(request, ASGIRequest) and mw.async_capable:
        return mw.__acall__(request)
    return _call_mw(mw, request)


MiddlewareMixin.__call__ = call_mw
}}}


Github project that shows the error: https://github.com/pwtail/django_bug"	Bug	new	Uncategorized	4.0	Normal				Accepted	0	0	0	0	0	0