Django middleware learning - Cache middleware

Django middleware learning - Cache

The middleware cache code is in the django/middleware/cache.py file

When using cache middleware, you must configure the following

    MIDDLEWARE = [
        'django.middleware.cache.UpdateCacheMiddleware',
        ...
        'django.middleware.cache.FetchFromCacheMiddleware'
    ]

UpdateCacheMiddleware
caches the response FetchFromCacheMiddleware takes out the cached response

UpdateCacheMiddleware function logic

To determine whether request._cache_update_cache is True, the value of _cache_update_cache is set in FetchFromCacheMiddleware

if not self._should_update_cache(request, response):
    # We don't need to update the cache, just return.
    return response

def _should_update_cache(self, request, response):
    return hasattr(request, '_cache_update_cache') and request._cache_update_cache

The status of the response is not 200 and 304, the request and response have cookies and are not cached, and the Cache-Control in the response is not private
and not cached

if response.streaming or response.status_code not in (200, 304):
    return response

# Don't cache responses that set a user-specific (and maybe security
# sensitive) cookie in response to a cookie-less request.
if not request.COOKIES and response.cookies and has_vary_header(response, 'Cookie'):
    return response

# Don't cache a response with 'Cache-Control: private'
if 'private' in response.get('Cache-Control', ()):
    return response

The next step is to set the response header ETag Expires max_age

patch_response_headers(response, timeout)

Finally, set the cache

if timeout and response.status_code == 200:
    cache_key = learn_cache_key(request, response, timeout, self.key_prefix, cache=self.cache)
    if hasattr(response, 'render') and callable(response.render):
        response.add_post_render_callback(
            lambda r: self.cache.set(cache_key, r, timeout)
        )
    else:
        self.cache.set(cache_key, response, timeout)

FetchFromCacheMiddleware

Use request to generate the corresponding cache_key
If cache_key is None, set _cache_update_cache = True, this attribute will be used in UpdateCacheMiddleware to fetch cache
according to cache_key

 # try and get the cached GET response
 cache_key = get_cache_key(request, self.key_prefix, 'GET', cache=self.cache)
 if cache_key is None:
     request._cache_update_cache = True
     return None  # No cache information available, need to rebuild.
 response = self.cache.get(cache_key)