Request does not raise UnsupportedMediaType exception

[Feverfew]

Checklist

• I have reduced the issue to the simplest possible case.

With the following view:

@api_view(['POST'])
@parser_classes([JSONParser])
def my_view(request):
    request.data['change_me'] = 'MyValue'

By sending a request with Content-Type: multipart/form-data (with at least one key/value pair, if it's empty it still goes through but doesn't trip up weirdly enough) one will observe the following behaviour:
AttributeError at $myViewsURL This QueryDict instance is immutable

What surprises me is that as I've specified the use of only the JSONParser, I should expect request.data to be a dict. I've tried other content-types and they are correctly rejected before parsing, but this one goes through.

[tomchristie]

Guiding you kindly towards discussions... :)

I'm not able to replicate this...

urls.py

from django.urls import path
from rest_framework.decorators import api_view, parser_classes
from rest_framework.parsers import JSONParser


@api_view(['POST'])
@parser_classes([JSONParser])
def homepage(request):
    request.data['change_me'] = 'MyValue'


urlpatterns = [
    path('', homepage),
]

client.py:

import httpx

r = httpx.post("http://127.0.0.1:8000", data={"a":"b"})
print(r)

shell:

$ python client.py 
<Response [415 Unsupported Media Type]>

[Feverfew]

I'm able to replicate this with the following (i.e. make sure Content-Type == 'multipart/form-data', your test case likely sets it to application/x-www-form-urlencoded):

>>> import requests
>>> r = requests.post("http://127.0.0.1:8000", files={"a":"b"})
>>> print(r)
<Response [500]>

The issues occurs in request.py, in particular in def _parse(self). IMO this should also return a 415 before it gets to my code in the view.

[Feverfew]

Further debugging indicates that in def _parse(self) a RawPostDataException is raised (which is caught appropriately). Interestingly in tests/test_response.py a similar test (UnsupportedMediaTypeExists.test_should_not_allow_posting_a_form) already exists but the exception isn't raised, leading to the expected behaviour.

[Feverfew]

Ok, I believe I have figured out the issue. This is not a bug in Django Rest Framework but actually a bug in my code!

For debugging purposes we have a special middleware that we use, which modifies/accesses request.POST, which is explicitly prohibited and is why the RawPostDataException is raised.

[tomchristie]

Fanastic, thanks for following up on that.