from django.conf import settings from django.contrib.sessions.backends.base import ( CreateError, SessionBase, UpdateError, ) from django.core.cache import caches KEY_PREFIX = "django.contrib.sessions.cache" class SessionStore(SessionBase): """ A cache-based session store. """ cache_key_prefix = KEY_PREFIX def __init__(self, session_key=None): self._cache = caches[settings.SESSION_CACHE_ALIAS] super().__init__(session_key) @property def cache_key(self): return self.cache_key_prefix + self._get_or_create_session_key() def load(self): try: session_data = self._cache.get(self.cache_key) except Exception: # Some backends (e.g. memcache) raise an exception on invalid # cache keys. If this happens, reset the session. See #17810. session_data = None if session_data is not None: return session_data self._session_key = None return {} def create(self): # Because a cache can fail silently (e.g. memcache), we don't know if # we are failing to create a new session because of a key collision or # because the cache is missing. So we try for a (large) number of times # and then raise an exception. That's the risk you shoulder if using # cache backing. for i in range(10000): self._session_key = self._get_new_session_key() try: self.save(must_create=True) except CreateError: continue self.modified = True return raise RuntimeError( "Unable to create a new session key. " "It is likely that the cache is unavailable.") def save(self, must_create=False): if self.session_key is None: return self.create() if must_create: func = self._cache.add elif self._cache.get(self.cache_key) is not None: func = self._cache.set else: raise UpdateError result = func(self.cache_key, self._get_session(no_load=must_create), self.get_expiry_age()) if must_create and not result: raise CreateError def exists(self, session_key): return bool(session_key) and (self.cache_key_prefix + session_key) in self._cache def delete(self, session_key=None): if session_key is None: if self.session_key is None: return session_key = self.session_key self._cache.delete(self.cache_key_prefix + session_key) @classmethod def clear_expired(cls): pass