django-oscar-api conflict with Django's UpdateCacheMiddleware: {TypeError}cannot pickle '

I implemented django's per site cache in a django-oscar project with django-oscar-api. I use LocMemCache as a cache backend.

Before adding django.middleware.cache.UpdateCacheMiddleware to my middlewares, everything worked fine and I could make a request to the "basket" endpoint like this and it returned a 200 response:

import requests

session = session.Session()
r_basket = session.get("http://127.0.0.1:8000/api/basket/")

After adding the per-site caching the response has the status code 500. I debugged it and it fails in the UpdateCacheMiddleware with the following error: {TypeError}cannot pickle '_io.BufferedReader' object.

Other endpoints seem to work fine, but I haven't tested them all yet. The error can also be reproduced on a freshly installed django-oscar sandbox. I pip-installed the django-oscar-api and added it to the installed apps, and the MIDDLEWARE setting looks like this:

MIDDLEWARE = [
    'debug_toolbar.middleware.DebugToolbarMiddleware',

    'django.middleware.security.SecurityMiddleware',
    'whitenoise.middleware.WhiteNoiseMiddleware',

    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.contrib.flatpages.middleware.FlatpageFallbackMiddleware',

    # Allow languages to be selected
    'django.middleware.locale.LocaleMiddleware',
    'django.middleware.http.ConditionalGetMiddleware',
    'django.middleware.common.CommonMiddleware',

    # per site caching
    'django.middleware.cache.UpdateCacheMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.cache.FetchFromCacheMiddleware',

    # Ensure a valid basket is added to the request instance for every request
    'oscar.apps.basket.middleware.BasketMiddleware',
]

My package versions are Django v.3.2.9, django-oscar v.2.2 or 3.0, django-oscar-api v.2.1.1.

What object can not be pickled? Or is the order of the middlewares possibly wrong?

Traceback:

[2021-11-13 08:43:33,256] Internal Server Error: /api/basket/
Traceback (most recent call last):
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/django/utils/deprecation.py", line 119, in __call__
    response = self.process_response(request, response)
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/django/middleware/cache.py", line 111, in process_response
    response.add_post_render_callback(
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/django/template/response.py", line 92, in add_post_render_callback
    callback(self)
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/django/middleware/cache.py", line 112, in <lambda>
    lambda r: self.cache.set(cache_key, r, timeout)
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/debug_toolbar/panels/cache.py", line 39, in wrapped
    value = method(self, *args, **kwargs)
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/debug_toolbar/panels/cache.py", line 94, in set
    return self.cache.set(*args, **kwargs)
  File "/home/victor/PycharmProjects/virtual_environments/django-oscar-sandbox/lib/python3.8/site-packages/django/core/cache/backends/locmem.py", line 56, in set
    pickled = pickle.dumps(value, self.pickle_protocol)
TypeError: cannot pickle '_io.BufferedReader' object

expected response

{'id': 1,
 'owner': None,
 'status': 'Open',
 'lines': 'http://127.0.0.1:8000/api/baskets/1/lines/',
 'url': 'http://127.0.0.1:8000/api/baskets/1/',
 'total_excl_tax': '0.00',
 'total_excl_tax_excl_discounts': '0.00',
 'total_incl_tax': '0.00',
 'total_incl_tax_excl_discounts': '0.00',
 'total_tax': '0.00',
 'currency': None,
 'voucher_discounts': [],
 'offer_discounts': [],
 'is_tax_known': True}

View: oscarapi.views.basket.BasketView

CodePudding user response：

You need to ensure that UpdateCacheMiddleware is before SessionMiddleware and LocaleMiddleware in your settings. DOCS

FetchFromCacheMiddleware needs to be after those middleware, can be left where it is

MIDDLEWARE = [
    'debug_toolbar.middleware.DebugToolbarMiddleware',

    'django.middleware.security.SecurityMiddleware',
    'whitenoise.middleware.WhiteNoiseMiddleware',

    # Moved UpdateCacheMiddleware to here
    'django.middleware.cache.UpdateCacheMiddleware',

    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.contrib.flatpages.middleware.FlatpageFallbackMiddleware',

    # Allow languages to be selected
    'django.middleware.locale.LocaleMiddleware',
    'django.middleware.http.ConditionalGetMiddleware',
    'django.middleware.common.CommonMiddleware',

    # per site caching
    'django.middleware.cache.FetchFromCacheMiddleware',

    # Ensure a valid basket is added to the request instance for every request
    'oscar.apps.basket.middleware.BasketMiddleware',
]