Django REST framework, content negotiation - django

Question

I am trying to get my endpoint to return a uri-list when asked for that and a json string as default. I am testing this in a unit test looking a bit like:
[...]
headers = {'Accept': 'text/uri-list'}
response = self.client.get('/api/v1/licenses/', headers=headers)
[...]
I have written a URIListRenderer like this:
from rest_framework import renderers
class URIListRenderer(renderers.BaseRenderer):
media_type = 'text/uri-list'
def render(self, data, media_type='None', renderer_context=None):
return "\n".join(data).encode()
Next I am trying to get my Response in my View to be rendered using my renderer:
class RestLicenses(APIView):
"""
List all licenses, or create a new license
"""
permission_classes = (IsAuthenticated,)
parser_classes = (MultiPartParser,)
renderer_classes = (JSONRenderer, URIListRenderer,)
def get(self, request, format=None,):
models = LicenseModel.objects.all()
if len(models) == 0 :
return Response('[]',status=204)
if request.META.get('headers') is not None :
if request.META.get('headers').get('Accept') == 'text/uri-list' :
result = [];
for m in models :
result.append(reverse('downloadLicense', args=[m.pk], request=request))
return Response(result, status=200)
serializer = LicenseJSONSerializer(request, models, many=True)
serializer.is_valid()
return HttpResponse(JSONRenderer().render(serializer.data), content_type='application/json', status=200)
But it seems impossible to get it to choose any other renderer than the first one in the list. How do I make it choose my URIListRenderer and not the json one?

Answer 1

Your unit test is not setting the headers correctly. As described here, you should use CGI style headers when using the Django test client:
response = self.client.get('/api/v1/licenses/', HTTP_ACCEPT='text/uri-list')
The content negotiation uses the real HTTP Accept header. In your code, you check that "headers" is set, but that's not the real HTTP Accept header. It should be:
if request.META.get('HTTP_ACCEPT') == "text/uri-list":
...

Answer 2

This is a block of code from the method finalize_response:
if isinstance(response, Response):
if not getattr(request, 'accepted_renderer', None):
neg = self.perform_content_negotiation(request, force=True)
request.accepted_renderer, request.accepted_media_type = neg
response.accepted_renderer = request.accepted_renderer
response.accepted_media_type = request.accepted_media_type
response.renderer_context = self.get_renderer_context()
As you can see, before it performs content negotiaton, it checks to see if the view has already set the renderer needed and if not tries to perform the negotiation by itself.
So you can do this in your get method:
if request.META.get('headers') is not None :
if request.META.get('headers').get('Accept') == 'text/uri-list' :
request.accepted_renderer = URIListRenderer
result = [];
for m in models :
result.append(reverse('downloadLicense', args=[m.pk], request=request))
return Response(result, status=200)
Another thing you should probably do is to place your custom renderer class before JSONRenderer in the renderer_classes list. In that way, it will first check the special case before the more general case during content negotiation. Is suspect that the request format also matches JSOnRender and it overshadows the custom renderer. Hope this helps