decorator_from_middleware can cause middleware hooks to run out of correct order.

[Jeremy Dunck]

cache_page, gzip_page, and conditional_page all use decorator_from_middleware.

decorator_from_middleware wraps the view function to simulate middleware being run on a per-view basis.

Here's the interesting bit:

        def _wrapped_view(request, *args, **kwargs):
            if hasattr(middleware, 'process_request'):
                result = middleware.process_request(request)
                if result is not None:
                    return result
            if hasattr(middleware, 'process_view'):
                result = middleware.process_view(request, view_func, *args, **kwargs)
                if result is not None:
                    return result
            try:
                response = view_func(request, *args, **kwargs)
            except Exception, e:
                if hasattr(middleware, 'process_exception'):
                    result = middleware.process_exception(request, e)
                    if result is not None:
                        return result
                raise
            if hasattr(middleware, 'process_response'):
                result = middleware.process_response(request, response)
                if result is not None:
                    return result
            return response

The problem is that middleware's order is important. Suppose two middleware decorators, A and B, are applied to the same view.

The normal flow of middleware processing would be: A.process_request, B.process_request, A.process_view, B.process_view, view, B.process_response, A.process_response.

The flow of the *decorated execution* is this: A.process_request, A.process_view, B.process_request, B.process_view, view, B.process_response, A.process_response.

This is not yet a real-world issue as far as I know, but seems to be a lurking problem. I think the only reason it hasn't surfaced is that view decorators are fairly uncommon. I don't see a simple way to fix this.

[Gary Wilson]

One solution would be to have a decorator that takes in middleware classes, something like:

@middleware(CacheMiddleware, TransactionMiddleware)
def myview(request)
   ...

The middleware decorator would combine each type of middleware method and run each type at the appropriate time.

But next you'll be telling me that you want to order the middleware differently for process_request and process_response :)

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Hiroki Kiyohara]

I fixed decorator_from_middleware to support multiple arguments caused by gwilson's idea,
here this (​https://github.com/hirokiky/django/commit/2db135897f7dcc86861d4e3d6328e8d86a3ecf4c) .

It passed the existing tests by Python2.7.1 and Python 3.3.
But, It needs more testes, and documentation.

[Hiroki Kiyohara]

I send the pull-request here (​https://github.com/django/django/pull/659).

[Hiroki Kiyohara]

The pull-requelt doesn't work current master brunch. (​https://github.com/django/django/pull/659)

[Asif Saifuddin Auvi]

Replying to hirokiky:

The pull-requelt doesn't work current master brunch. (​https://github.com/django/django/pull/659)

so to make it properly need to rework based on this ​https://github.com/hirokiky/django/commit/2db135897f7dcc86861d4e3d6328e8d86a3ecf4c against master right?