#34174: async process_exception being called as sync from async view/middleware
-------------------------------------+-------------------------------------
               Reporter:  Gabriel    |          Owner:  nobody
  Rado                               |
                   Type:             |         Status:  new
  Cleanup/optimization               |
              Component:             |        Version:  4.1
  Documentation                      |       Keywords:  middleware async
               Severity:  Normal     |  process_exception
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 following this bold part of the
 docs[https://docs.djangoproject.com/en/4.1/topics/http/middleware
 /#asynchronous-support]:


 process_view, process_template_response and process_exception methods, if
 they are provided, **should also be adapted to match the sync/async
 mode**. However, Django will individually adapt them as required if you do
 not, at an additional performance penalty.

 I' using this middleware to parse errors from sync and async views:


 {{{
 @sync_and_async_middleware
 def custom_error(get_response):
     if asyncio.iscoroutinefunction(get_response):

         async def middleware(request):
             response = await get_response(request)
             return response

         async def _process_exception(request, exception):
             return my_custom_process_exception(exception)

     else:

         def middleware(request):
             response = get_response(request)
             return response

         def _process_exception(request, exception):
             return my_custom_process_exception(exception)

     middleware.process_exception = _process_exception
     return middleware
 }}}

 and I'm getting "ValueError: The view my_view.view_func didn't return an
 HttpResponse object. It returned an unawaited coroutine instead. You may
 need to add an 'await' into your view." from
 
here[https://github.com/django/django/blob/main/django/core/handlers/base.py#L257]

 i thought that with an async middleware + async view, all my hooks
 (process_view, process_template_response and process_exception) should be
 also async, but it appears that is mandatory to use sync process_exception
 with async capable middlewares. if this is intended, could the official
 docs be changed to expose this mandatory behavior?

-- 
Ticket URL: <https://code.djangoproject.com/ticket/34174>
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