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
29427	RequestDataTooBig raised in request.py prevents Middleware from returning a valid response	S. Paquette	Claude Paroz	"This is effectively a request to re-open #28106, which was closed because the original author never replied to a request for more information. 

We need a way to return a response from a Middleware which is handling the RequestDataTooBig exception, but Middlewares intercepting this exception never generate a valid response. This seems due to how the exception causes self._body to never be created in request.py.

In django.http.request, a check of the content length is done against settings.DATA_UPLOAD_MAX_MEMORY_SIZE at line 267. 
{{{
            # Limit the maximum request data size that will be handled in-memory.
            if (settings.DATA_UPLOAD_MAX_MEMORY_SIZE is not None and
                    int(self.META.get('CONTENT_LENGTH') or 0) > settings.DATA_UPLOAD_MAX_MEMORY_SIZE):
                raise RequestDataTooBig('Request body exceeded settings.DATA_UPLOAD_MAX_MEMORY_SIZE.')

}}}

If the content length exceeds DATA_UPLOAD_MAX_MEMORY_SIZE, no request body is generated, and a RequestDataTooBig exception is raised. 

In order to detect this error and return a useful response to our users' browsers, we created a Middleware to catch the exception and supply an informative JsonResponse. However, despite the status setting correctly, the response itself was never being returned. Our Middleware:
{{{
from django.http import JsonResponse
from django.core.exceptions import RequestDataTooBig


class CheckSize(object):

    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):

        try:
            body = request.body
        except RequestDataTooBig:
            return JsonResponse({""msg"": ""The file provided is too large. Please reduce its size and try again.""}, status=400)

        response = self.get_response(request)
        return response
}}}
We tried placing the Middleware anywhere in the chain, and making it the only Middleware, but nothing worked.

Per the author of #28106, we then added in an empty body to the request when the exception is raised, and that solved the problem:
{{{
            # Limit the maximum request data size that will be handled in-memory.
            if (settings.DATA_UPLOAD_MAX_MEMORY_SIZE is not None and
                    int(self.META.get('CONTENT_LENGTH') or 0) > settings.DATA_UPLOAD_MAX_MEMORY_SIZE):
                self._body = self.read(None)
                raise RequestDataTooBig('Request body exceeded settings.DATA_UPLOAD_MAX_MEMORY_SIZE.')

}}}

After doing this, our response is returned. This can be reproduced on Django 1.11."	Bug	closed	HTTP handling	dev	Normal	needsinfo		Herbert Fortes	Accepted	1	0	0	1	0	0