Question

In order to provide progress feedback of file uploads I need to install a custom upload handler for a specific view. This is documented for “classical” Django views at

https://docs.djangoproject.com/en/dev/topics/http/file-uploads/#modifying-upload-handlers-on-the-fly

For generic views, however, I could not find any instructions and I came up with the following:

from django.utils import importlib
from django.core.exceptions import ImproperlyConfigured
from django.views.decorators.csrf import csrf_protect

class UploadHandlerMixin(object):
    '''
        A mixin for Django generic views that installs a custom upload handler in front of
        the current chain of upload handlers.

        You specify the handler to install by overriding the 'upload_handler' attribute of
        the class, specifying the module and class name in the form 'path.to.module.class':

            class MyView(UploadHandlerMixin, View):
                upload_handler = 'path.to.module.MyUploadHandler'

        If you do not override 'upload_handler', no additional upload handler will be
        installed.

        If the CsrfViewMiddleware is installed (which is the default) then you must use
        your view as follows in your urls.py:

            from django.views.decorators.csrf import csrf_exempt
            url(r'^.../$', csrf_exempt(MyView.as_view()), ...),

        Internally, the UploadHandlerMixin mixin will install the upload handler and then
        perform the CSRF check. (This is necessary because the CSRF check inspects
        request.POST, and afterwards upload handlers cannot be changed, see documentation
        link given below.)

        The handler is installed as described in the Django documentation "Modifying upload handlers
        on the fly", see https://docs.djangoproject.com/en/dev/topics/http/file-uploads/#modifying-upload-handlers-on-the-fly
    '''

    upload_handler = None

    def dispatch(self, request, *args, **kwargs):
        if not self.upload_handler is None:
            request.upload_handlers.insert(0, UploadHandlerMixin._instantiate_upload_handler(self.upload_handler, request))
        return _uploadhandler_dispatch(request, self, *args, **kwargs)

    @staticmethod
    def _instantiate_upload_handler(path, *args, **kwargs):
        i = path.rfind('.')
        module, attr = path[:i], path[i+1:]
        try:
            mod = importlib.import_module(module)
        except ImportError, e:
            raise ImproperlyConfigured('Error importing upload handler module %s: "%s"' % (module, e))
        except ValueError, e:
            raise ImproperlyConfigured('Error importing upload handler module. Is FILE_UPLOAD_HANDLERS a correctly defined list or tuple?')
        try:
            cls = getattr(mod, attr)
        except AttributeError:
            raise ImproperlyConfigured('Module "%s" does not define a "%s" upload handler backend' % (module, attr))
        return cls(*args, **kwargs)

@csrf_protect
def _uploadhandler_dispatch(request, view, *args, **kwargs):
    return super(UploadHandlerMixin, view).dispatch(request, *args, **kwargs)

Is this the “recommended way” to accomplish the task? Is it okay security-wise?

Answer 1

Answering myself, an alternative to a service-side solution (like Django with a custom upload handler) is a client-side solution like JQuery File Upload. It uses the fact that more recent browsers allow the upload progress to be read on the client. In my case, this was much simpler to implement and causes no additional server load.