Hi, stepping in to add some code as @carltongibson mentioned a “prototype”
We’ve been using this session backend successfully in a FastAPI/Django hybrid application on a small scale for half a year now. (As a note, I’m the founder of the company, wrote the below code, and expressly allow the Django community to modify this freely. Anyway…). The “hybrid-ness” is that I use the Django ORM under the hood for db ops, my django-async-redis package for caching, and FastAPI for my API framework:
base.py:
#
# Copyright (c) 2022-2023. Lazify, Inc. and its affiliates - All Rights Reserved
#
# This file is part of the Lazify project.
#
# Unauthorized copying of this file in source and binary
# forms, via any medium, is strictly prohibited.
# Proprietary and confidential
#
import logging
from datetime import datetime, timedelta
from asgiref.sync import sync_to_async
from django.conf import settings
from django.contrib.sessions.backends.base import VALID_KEY_CHARS
from django.contrib.sessions.backends.base import SessionBase as DjangoSessionBase
from django.core import signing
from django.utils import timezone
from django.utils.crypto import get_random_string
class SessionBase(DjangoSessionBase):
"""
Base class for all Session classes.
"""
TEST_COOKIE_NAME = "testcookie"
TEST_COOKIE_VALUE = "worked"
__not_given = object()
def __contains__(self, key):
return key in self._session
def __getitem__(self, key):
return self._session[key]
def __setitem__(self, key, value):
self.set(key, value)
def __delitem__(self, key):
del self._session[key]
self.modified = True
@property
def key_salt(self):
return "django.contrib.sessions." + self.__class__.__qualname__
def get(self, key, default=None):
return self._session.get(key, default)
async def aget(self, key, default=None):
return (await self._aget_session()).get(key, default)
def set(self, key, value):
self._session[key] = value
self.modified = True
async def aset(self, key, value):
(await self._aget_session())[key] = value
self.modified = True
def pop(self, key, default=__not_given):
self.modified = self.modified or key in self._session
args = () if default is self.__not_given else (default,)
return self._session.pop(key, *args)
async def apop(self, key, default=__not_given):
self.modified = self.modified or key in (await self._aget_session())
args = () if default is self.__not_given else (default,)
return (await self._aget_session()).pop(key, *args)
def setdefault(self, key, value):
if key in self._session:
return self._session[key]
else:
self.set(key, value)
return value
async def asetdefault(self, key, value):
if key in (await self._aget_session()):
return (await self._aget_session())[key]
else:
await self.aset(key, value)
return value
def set_test_cookie(self):
self[self.TEST_COOKIE_NAME] = self.TEST_COOKIE_VALUE
async def aset_test_cookie(self):
await self.aset(self.TEST_COOKIE_NAME, self.TEST_COOKIE_VALUE)
def test_cookie_worked(self):
return self.get(self.TEST_COOKIE_NAME) == self.TEST_COOKIE_VALUE
async def atest_cookie_worked(self):
return (await self.aget(self.TEST_COOKIE_NAME)) == self.TEST_COOKIE_VALUE
def delete_test_cookie(self):
del self[self.TEST_COOKIE_NAME]
async def adelete_test_cookie(self):
del (await self._aget_session())[self.TEST_COOKIE_NAME]
self.modified = True
def encode(self, session_dict):
"Return the given session dictionary serialized and encoded as a string."
return signing.dumps(
session_dict,
salt=self.key_salt,
serializer=self.serializer,
compress=True,
)
def decode(self, session_data):
try:
return signing.loads(
session_data, salt=self.key_salt, serializer=self.serializer
)
except signing.BadSignature:
logger = logging.getLogger("django.security.SuspiciousSession")
logger.warning("Session data corrupted")
except Exception:
# ValueError, unpickling exceptions. If any of these happen, just
# return an empty dictionary (an empty session).
pass
return {}
def update(self, dict_):
self._session.update(dict_)
self.modified = True
async def aupdate(self, dict_):
(await self._aget_session()).update(dict_)
self.modified = True
def has_key(self, key):
return key in self._session
async def ahas_key(self, key):
return key in (await self._aget_session())
def keys(self):
return self._session.keys()
async def akeys(self):
return (await self._aget_session()).keys()
def values(self):
return self._session.values()
async def avalues(self):
return (await self._aget_session()).values()
def items(self):
return self._session.items()
async def aitems(self):
return (await self._aget_session()).items()
def clear(self):
# To avoid unnecessary persistent storage accesses, we set up the
# internals directly (loading data wastes time, since we are going to
# set it to an empty dict anyway).
self._session_cache = {}
self.accessed = True
self.modified = True
def is_empty(self):
"Return True when there is no session_key and the session is empty."
try:
return not self._session_key and not self._session_cache
except AttributeError:
return True
def _get_new_session_key(self):
"Return session key that isn't being used."
while True:
session_key = get_random_string(32, VALID_KEY_CHARS)
if not self.exists(session_key):
return session_key
async def _aget_new_session_key(self):
while True:
session_key = get_random_string(32, VALID_KEY_CHARS)
if not await self.aexists(session_key):
return session_key
def _get_or_create_session_key(self):
if self._session_key is None:
self._session_key = self._get_new_session_key()
return self._session_key
async def _aget_or_create_session_key(self):
if self._session_key is None:
self._session_key = await self._aget_new_session_key()
return self._session_key
def _validate_session_key(self, key):
"""
Key must be truthy and at least 8 characters long. 8 characters is an
arbitrary lower bound for some minimal key security.
"""
return key and len(key) >= 8
def _get_session_key(self):
return self.__session_key
def _set_session_key(self, value):
"""
Validate session key on assignment. Invalid values will set to None.
"""
if self._validate_session_key(value):
self.__session_key = value
else:
self.__session_key = None
session_key = property(_get_session_key)
_session_key = property(_get_session_key, _set_session_key)
def _get_session(self, no_load=False):
"""
Lazily load session from storage (unless "no_load" is True, when only
an empty dict is stored) and store it in the current instance.
"""
self.accessed = True
try:
return self._session_cache
except AttributeError:
if self.session_key is None or no_load:
self._session_cache = {}
else:
self._session_cache = self.load()
return self._session_cache
async def _aget_session(self, no_load=False):
self.accessed = True
try:
return self._session_cache
except AttributeError:
if self.session_key is None or no_load:
self._session_cache = {}
else:
self._session_cache = await self.aload()
return self._session_cache
_session = property(_get_session)
def get_session_cookie_age(self):
return settings.SESSION_COOKIE_AGE
def get_expiry_age(self, **kwargs):
"""Get the number of seconds until the session expires.
Optionally, this function accepts `modification` and `expiry` keyword
arguments specifying the modification and expiry of the session.
"""
try:
modification = kwargs["modification"]
except KeyError:
modification = timezone.now()
# Make the difference between "expiry=None passed in kwargs" and
# "expiry not passed in kwargs", in order to guarantee not to trigger
# self.load() when expiry is provided.
try:
expiry = kwargs["expiry"]
except KeyError:
expiry = self.get("_session_expiry")
if not expiry: # Checks both None and 0 cases
return self.get_session_cookie_age()
if not isinstance(expiry, (datetime, str)):
return expiry
if isinstance(expiry, str):
expiry = datetime.fromisoformat(expiry)
delta = expiry - modification
return delta.days * 86400 + delta.seconds
async def aget_expiry_age(self, **kwargs):
try:
modification = kwargs["modification"]
except KeyError:
modification = timezone.now()
try:
expiry = kwargs["expiry"]
except KeyError:
expiry = await self.aget("_session_expiry")
if not expiry: # Checks both None and 0 cases
return self.get_session_cookie_age()
if not isinstance(expiry, (datetime, str)):
return expiry
if isinstance(expiry, str):
expiry = datetime.fromisoformat(expiry)
delta = expiry - modification
return delta.days * 86400 + delta.seconds
def get_expiry_date(self, **kwargs):
"""Get session the expiry date (as a datetime object).
Optionally, this function accepts `modification` and `expiry` keyword
arguments specifying the modification and expiry of the session.
"""
try:
modification = kwargs["modification"]
except KeyError:
modification = timezone.now()
# Same comment as in get_expiry_age
try:
expiry = kwargs["expiry"]
except KeyError:
expiry = self.get("_session_expiry")
if isinstance(expiry, datetime):
return expiry
elif isinstance(expiry, str):
return datetime.fromisoformat(expiry)
expiry = expiry or self.get_session_cookie_age()
return modification + timedelta(seconds=expiry)
async def aget_expiry_date(self, **kwargs):
try:
modification = kwargs["modification"]
except KeyError:
modification = timezone.now()
try:
expiry = kwargs["expiry"]
except KeyError:
expiry = await self.aget("_session_expiry")
if isinstance(expiry, datetime):
return expiry
elif isinstance(expiry, str):
return datetime.fromisoformat(expiry)
expiry = expiry or self.get_session_cookie_age()
return modification + timedelta(seconds=expiry)
def set_expiry(self, value):
"""
Set a custom expiration for the session. ``value`` can be an integer,
a Python ``datetime`` or ``timedelta`` object or ``None``.
If ``value`` is an integer, the session will expire after that many
seconds of inactivity. If set to ``0`` then the session will expire on
browser close.
If ``value`` is a ``datetime`` or ``timedelta`` object, the session
will expire at that specific future time.
If ``value`` is ``None``, the session uses the global session expiry
policy.
"""
if value is None:
# Remove any custom expiration for this session.
try:
del self["_session_expiry"]
except KeyError:
pass
return
if isinstance(value, timedelta):
value = timezone.now() + value
if isinstance(value, datetime):
value = value.isoformat()
self["_session_expiry"] = value
async def aset_expiry(self, value):
if value is None:
# Remove any custom expiration for this session.
try:
await self.adelete("_session_expiry")
except KeyError:
pass
return
if isinstance(value, timedelta):
value = timezone.now() + value
if isinstance(value, datetime):
value = value.isoformat()
await self.aset("_session_expiry", value)
def get_expire_at_browser_close(self):
"""
Return ``True`` if the session is set to expire when the browser
closes, and ``False`` if there's an expiry date. Use
``get_expiry_date()`` or ``get_expiry_age()`` to find the actual expiry
date/age, if there is one.
"""
if (expiry := self.get("_session_expiry")) is None:
return settings.SESSION_EXPIRE_AT_BROWSER_CLOSE
return expiry == 0
async def aget_expire_at_browser_close(self):
if (expiry := await self.aget("_session_expiry")) is None:
return settings.SESSION_EXPIRE_AT_BROWSER_CLOSE
return expiry == 0
def flush(self):
"""
Remove the current session data from the database and regenerate the
key.
"""
self.clear()
self.delete()
self._session_key = None
async def aflush(self):
self.clear()
await self.adelete()
self._session_key = None
def cycle_key(self):
"""
Create a new session key, while retaining the current session data.
"""
data = self._session
key = self.session_key
self.create()
self._session_cache = data
if key:
self.delete(key)
async def acycle_key(self):
"""
Create a new session key, while retaining the current session data.
"""
data = self._session
key = self.session_key
await self.acreate()
self._session_cache = data
if key:
await self.adelete(key)
# Methods that child classes must implement.
def exists(self, session_key):
"""
Return True if the given session_key already exists.
"""
raise NotImplementedError(
"subclasses of SessionBase must provide an exists() method"
)
async def aexists(self, session_key):
return await sync_to_async(self.exists, thread_sensitive=True)(session_key)
def create(self):
"""
Create a new session instance. Guaranteed to create a new object with
a unique key and will have saved the result once (with empty data)
before the method returns.
"""
raise NotImplementedError(
"subclasses of SessionBase must provide a create() method"
)
async def acreate(self):
return await sync_to_async(self.create, thread_sensitive=True)()
def save(self, must_create=False):
"""
Save the session data. If 'must_create' is True, create a new session
object (or raise CreateError). Otherwise, only update an existing
object and don't create one (raise UpdateError if needed).
"""
raise NotImplementedError(
"subclasses of SessionBase must provide a save() method"
)
async def asave(self, must_create=False):
return await sync_to_async(self.save, thread_sensitive=True)(must_create)
def delete(self, session_key=None):
"""
Delete the session data under this key. If the key is None, use the
current session key value.
"""
raise NotImplementedError(
"subclasses of SessionBase must provide a delete() method"
)
async def adelete(self, session_key=None):
return await sync_to_async(self.delete, thread_sensitive=True)(session_key)
def load(self):
"""
Load the session data and return a dictionary.
"""
raise NotImplementedError(
"subclasses of SessionBase must provide a load() method"
)
async def aload(self):
return await sync_to_async(self.load, thread_sensitive=True)()
@classmethod
def clear_expired(cls):
"""
Remove expired sessions from the session store.
If this operation isn't possible on a given backend, it should raise
NotImplementedError. If it isn't necessary, because the backend has
a built-in expiration mechanism, it should be a no-op.
"""
raise NotImplementedError("This backend does not support clear_expired().")
@classmethod
async def aclear_expired(cls):
return await sync_to_async(cls.clear_expired, thread_sensitive=True)()
cache.py
#
# Copyright (c) 2022-2023. Lazify, Inc. and its affiliates - All Rights Reserved
#
# This file is part of the Lazify project.
#
# Unauthorized copying of this file in source and binary
# forms, via any medium, is strictly prohibited.
# Proprietary and confidential
#
from django.conf import settings
from django.contrib.sessions.backends.base import CreateError, UpdateError
from django.core.cache import caches
from app.vendor.django.contrib.sessions.backends.base import SessionBase
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()
async def acache_key(self):
return self.cache_key_prefix + await self._aget_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 {}
async def aload(self):
try:
session_data = await self._cache.aget(await self.acache_key())
except Exception:
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."
)
async def acreate(self):
for i in range(10000):
self._session_key = await self._aget_new_session_key()
try:
await self.asave(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
async def asave(self, must_create=False):
if self.session_key is None:
return await self.acreate()
if must_create:
func = self._cache.aadd
elif await self._cache.ahas_key(self.cache_key):
func = self._cache.aset
else:
raise UpdateError
result = await func(
self.cache_key,
await self._aget_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
)
async def aexists(self, session_key):
return bool(session_key) and await self._cache.ahas_key(
self.cache_key_prefix + session_key
)
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)
async def adelete(self, session_key=None):
if session_key is None:
if self.session_key is None:
return
session_key = self.session_key
await self._cache.adelete(self.cache_key_prefix + session_key)
@classmethod
def clear_expired(cls):
pass
@classmethod
async def aclear_expired(cls):
pass
middleware (it’s a Starlette middleware but incorporates the beef of Django’s session middleware):
#
# Copyright (c) 2022-2023. Lazify, Inc. and its affiliates - All Rights Reserved
#
# This file is part of the Lazify project.
#
# Unauthorized copying of this file in source and binary
# forms, via any medium, is strictly prohibited.
# Proprietary and confidential
#
import asyncio
import time
from django.conf import settings
from django.contrib.sessions.backends.base import UpdateError
from django.utils.http import http_date
from starlette.datastructures import MutableHeaders
from starlette.exceptions import HTTPException
from starlette.types import ASGIApp, Message, Receive, Scope, Send
from app.api.views.client.session import ClientChatSessionStore
from app.core.utils.django.cache import patch_vary_headers
from app.core.utils.django.request import delete_cookie, set_cookie
from app.request import Request, WebSocket
from app.vendor.django.contrib.sessions.backends.cache import SessionStore
class SessionMiddleware:
def __init__(self, app: ASGIApp):
self.app = app
async def _process_response(
self,
message: Message,
scope: Scope,
receive: Receive,
send: Send,
prefix: str = "",
):
request = Request(scope, receive, send)
message.setdefault("headers", [])
setting_prefix = prefix.upper()
headers = MutableHeaders(scope=message)
def session() -> SessionStore:
return getattr(request, f"{prefix}session")
def setting(_setting_name: str):
return getattr(settings, f"{setting_prefix}{_setting_name}")
try:
accessed = session().accessed
modified = session().modified
empty = session().is_empty()
except AttributeError:
await self.app(scope, receive, send)
return
if prefix == "chat_":
if (modified or setting("SESSION_SAVE_EVERY_REQUEST")) and not empty:
try:
await session().asave()
except UpdateError:
# originally django.contrib.sessions.exceptions.SessionInterrupted
raise HTTPException(
status_code=400,
detail="The request's session was deleted before the "
"request completed. The user may have logged "
"out in a concurrent request, for example.",
)
return
# First check if we need to delete this cookie.
# The session should be deleted only if the session is entirely empty.
if setting("SESSION_COOKIE_NAME") in request.cookies and empty:
delete_cookie(
headers,
setting("SESSION_COOKIE_NAME"),
path=setting("SESSION_COOKIE_PATH"),
domain=setting("SESSION_COOKIE_DOMAIN"),
samesite=setting("SESSION_COOKIE_SAMESITE"),
)
delete_cookie(headers, "user")
patch_vary_headers(headers, ("Cookie",))
else:
if accessed:
patch_vary_headers(headers, ("Cookie",))
if (modified or setting("SESSION_SAVE_EVERY_REQUEST")) and not empty:
if await session().aget_expire_at_browser_close():
max_age = None
expires = None
else:
max_age = await session().aget_expiry_age()
expires_time = time.time() + max_age
expires = http_date(expires_time)
# Save the session data and refresh the client cookie.
# Skip session save for 500 responses, refs #3881.
# if response.status_code != 500:
try:
await session().asave()
except UpdateError:
# originally django.contrib.sessions.exceptions.SessionInterrupted
raise HTTPException(
status_code=400,
detail="The request's session was deleted before the "
"request completed. The user may have logged "
"out in a concurrent request, for example.",
)
set_cookie(
headers,
setting("SESSION_COOKIE_NAME"),
session().session_key,
max_age=max_age,
expires=expires,
domain=setting("SESSION_COOKIE_DOMAIN"),
path=setting("SESSION_COOKIE_PATH"),
secure=setting("SESSION_COOKIE_SECURE") or None,
httponly=setting("SESSION_COOKIE_HTTPONLY") or None,
samesite=setting("SESSION_COOKIE_SAMESITE"),
)
