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import hashlib
import typing as t
import warnings
from collections.abc import MutableMapping
from datetime import datetime
from datetime import timezone
from itsdangerous import BadSignature
from itsdangerous import URLSafeTimedSerializer
from werkzeug.datastructures import CallbackDict
from .helpers import is_ip
from .json.tag import TaggedJSONSerializer
if t.TYPE_CHECKING: # pragma: no cover
import typing_extensions as te
from .app import Flask
from .wrappers import Request, Response
class SessionMixin(MutableMapping):
"""Expands a basic dictionary with session attributes."""
@property
def permanent(self) -> bool:
"""This reflects the ``'_permanent'`` key in the dict."""
return self.get("_permanent", False)
@permanent.setter
def permanent(self, value: bool) -> None:
self["_permanent"] = bool(value)
#: Some implementations can detect whether a session is newly
#: created, but that is not guaranteed. Use with caution. The mixin
# default is hard-coded ``False``.
new = False
#: Some implementations can detect changes to the session and set
#: this when that happens. The mixin default is hard coded to
#: ``True``.
modified = True
#: Some implementations can detect when session data is read or
#: written and set this when that happens. The mixin default is hard
#: coded to ``True``.
accessed = True
class SecureCookieSession(CallbackDict, SessionMixin):
"""Base class for sessions based on signed cookies.
This session backend will set the :attr:`modified` and
:attr:`accessed` attributes. It cannot reliably track whether a
session is new (vs. empty), so :attr:`new` remains hard coded to
``False``.
"""
#: When data is changed, this is set to ``True``. Only the session
#: dictionary itself is tracked; if the session contains mutable
#: data (for example a nested dict) then this must be set to
#: ``True`` manually when modifying that data. The session cookie
#: will only be written to the response if this is ``True``.
modified = False
#: When data is read or written, this is set to ``True``. Used by
# :class:`.SecureCookieSessionInterface` to add a ``Vary: Cookie``
#: header, which allows caching proxies to cache different pages for
#: different users.
accessed = False
def __init__(self, initial: t.Any = None) -> None:
def on_update(self) -> None:
self.modified = True
self.accessed = True
super().__init__(initial, on_update)
def __getitem__(self, key: str) -> t.Any:
self.accessed = True
return super().__getitem__(key)
def get(self, key: str, default: t.Any = None) -> t.Any:
self.accessed = True
return super().get(key, default)
def setdefault(self, key: str, default: t.Any = None) -> t.Any:
self.accessed = True
return super().setdefault(key, default)
class NullSession(SecureCookieSession):
"""Class used to generate nicer error messages if sessions are not
available. Will still allow read-only access to the empty session
but fail on setting.
"""
def _fail(self, *args: t.Any, **kwargs: t.Any) -> "te.NoReturn":
raise RuntimeError(
"The session is unavailable because no secret "
"key was set. Set the secret_key on the "
"application to something unique and secret."
)
__setitem__ = __delitem__ = clear = pop = popitem = update = setdefault = _fail # type: ignore # noqa: B950
del _fail
class SessionInterface:
"""The basic interface you have to implement in order to replace the
default session interface which uses werkzeug's securecookie
implementation. The only methods you have to implement are
:meth:`open_session` and :meth:`save_session`, the others have
useful defaults which you don't need to change.
The session object returned by the :meth:`open_session` method has to
provide a dictionary like interface plus the properties and methods
from the :class:`SessionMixin`. We recommend just subclassing a dict
and adding that mixin::
class Session(dict, SessionMixin):
pass
If :meth:`open_session` returns ``None`` Flask will call into
:meth:`make_null_session` to create a session that acts as replacement
if the session support cannot work because some requirement is not
fulfilled. The default :class:`NullSession` class that is created
will complain that the secret key was not set.
To replace the session interface on an application all you have to do
is to assign :attr:`flask.Flask.session_interface`::
app = Flask(__name__)
app.session_interface = MySessionInterface()
Multiple requests with the same session may be sent and handled
concurrently. When implementing a new session interface, consider
whether reads or writes to the backing store must be synchronized.
There is no guarantee on the order in which the session for each
request is opened or saved, it will occur in the order that requests
begin and end processing.
.. versionadded:: 0.8
"""
#: :meth:`make_null_session` will look here for the class that should
#: be created when a null session is requested. Likewise the
#: :meth:`is_null_session` method will perform a typecheck against
#: this type.
null_session_class = NullSession
#: A flag that indicates if the session interface is pickle based.
#: This can be used by Flask extensions to make a decision in regards
#: to how to deal with the session object.
#:
#: .. versionadded:: 0.10
pickle_based = False
def make_null_session(self, app: "Flask") -> NullSession:
"""Creates a null session which acts as a replacement object if the
real session support could not be loaded due to a configuration
error. This mainly aids the user experience because the job of the
null session is to still support lookup without complaining but
modifications are answered with a helpful error message of what
failed.
This creates an instance of :attr:`null_session_class` by default.
"""
return self.null_session_class()
def is_null_session(self, obj: object) -> bool:
"""Checks if a given object is a null session. Null sessions are
not asked to be saved.
This checks if the object is an instance of :attr:`null_session_class`
by default.
"""
return isinstance(obj, self.null_session_class)
def get_cookie_name(self, app: "Flask") -> str:
"""The name of the session cookie. Uses``app.config["SESSION_COOKIE_NAME"]``."""
return app.config["SESSION_COOKIE_NAME"]
def get_cookie_domain(self, app: "Flask") -> t.Optional[str]:
"""Returns the domain that should be set for the session cookie.
Uses ``SESSION_COOKIE_DOMAIN`` if it is configured, otherwise
falls back to detecting the domain based on ``SERVER_NAME``.
Once detected (or if not set at all), ``SESSION_COOKIE_DOMAIN`` is
updated to avoid re-running the logic.
"""
rv = app.config["SESSION_COOKIE_DOMAIN"]
# set explicitly, or cached from SERVER_NAME detection
# if False, return None
if rv is not None:
return rv if rv else None
rv = app.config["SERVER_NAME"]
# server name not set, cache False to return none next time
if not rv:
app.config["SESSION_COOKIE_DOMAIN"] = False
return None
# chop off the port which is usually not supported by browsers
# remove any leading '.' since we'll add that later
rv = rv.rsplit(":", 1)[0].lstrip(".")
if "." not in rv:
# Chrome doesn't allow names without a '.'. This should only
# come up with localhost. Hack around this by not setting
# the name, and show a warning.
warnings.warn(
f"{rv!r} is not a valid cookie domain, it must contain"
" a '.'. Add an entry to your hosts file, for example"
f" '{rv}.localdomain', and use that instead."
)
app.config["SESSION_COOKIE_DOMAIN"] = False
return None
ip = is_ip(rv)
if ip:
warnings.warn(
"The session cookie domain is an IP address. This may not work"
" as intended in some browsers. Add an entry to your hosts"
' file, for example "localhost.localdomain", and use that'
" instead."
)
# if this is not an ip and app is mounted at the root, allow subdomain
# matching by adding a '.' prefix
if self.get_cookie_path(app) == "/" and not ip:
rv = f".{rv}"
app.config["SESSION_COOKIE_DOMAIN"] = rv
return rv
def get_cookie_path(self, app: "Flask") -> str:
"""Returns the path for which the cookie should be valid. The
default implementation uses the value from the ``SESSION_COOKIE_PATH``
config var if it's set, and falls back to ``APPLICATION_ROOT`` or
uses ``/`` if it's ``None``.
"""
return app.config["SESSION_COOKIE_PATH"] or app.config["APPLICATION_ROOT"]
def get_cookie_httponly(self, app: "Flask") -> bool:
"""Returns True if the session cookie should be httponly. This
currently just returns the value of the ``SESSION_COOKIE_HTTPONLY``
config var.
"""
return app.config["SESSION_COOKIE_HTTPONLY"]
def get_cookie_secure(self, app: "Flask") -> bool:
"""Returns True if the cookie should be secure. This currently
just returns the value of the ``SESSION_COOKIE_SECURE`` setting.
"""
return app.config["SESSION_COOKIE_SECURE"]
def get_cookie_samesite(self, app: "Flask") -> str:
"""Return ``'Strict'`` or ``'Lax'`` if the cookie should use the
``SameSite`` attribute. This currently just returns the value of
the :data:`SESSION_COOKIE_SAMESITE` setting.
"""
return app.config["SESSION_COOKIE_SAMESITE"]
def get_expiration_time(
self, app: "Flask", session: SessionMixin
) -> t.Optional[datetime]:
"""A helper method that returns an expiration date for the session
or ``None`` if the session is linked to the browser session. The
default implementation returns now + the permanent session
lifetime configured on the application.
"""
if session.permanent:
return datetime.now(timezone.utc) + app.permanent_session_lifetime
return None
def should_set_cookie(self, app: "Flask", session: SessionMixin) -> bool:
"""Used by session backends to determine if a ``Set-Cookie`` header
should be set for this session cookie for this response. If the session
has been modified, the cookie is set. If the session is permanent and
the ``SESSION_REFRESH_EACH_REQUEST`` config is true, the cookie is
always set.
This check is usually skipped if the session was deleted.
.. versionadded:: 0.11
"""
return session.modified or (
session.permanent and app.config["SESSION_REFRESH_EACH_REQUEST"]
)
def open_session(
self, app: "Flask", request: "Request"
) -> t.Optional[SessionMixin]:
"""This is called at the beginning of each request, after
pushing the request context, before matching the URL.
This must return an object which implements a dictionary-like
interface as well as the :class:`SessionMixin` interface.
This will return ``None`` to indicate that loading failed in
some way that is not immediately an error. The request
context will fall back to using :meth:`make_null_session`
in this case.
"""
raise NotImplementedError()
def save_session(
self, app: "Flask", session: SessionMixin, response: "Response"
) -> None:
"""This is called at the end of each request, after generating
a response, before removing the request context. It is skipped
if :meth:`is_null_session` returns ``True``.
"""
raise NotImplementedError()
session_json_serializer = TaggedJSONSerializer()
class SecureCookieSessionInterface(SessionInterface):
"""The default session interface that stores sessions in signed cookies
through the :mod:`itsdangerous` module.
"""
#: the salt that should be applied on top of the secret key for the
#: signing of cookie based sessions.
salt = "cookie-session"
#: the hash function to use for the signature. The default is sha1
digest_method = staticmethod(hashlib.sha1)
#: the name of the itsdangerous supported key derivation. The default
#: is hmac.
key_derivation = "hmac"
#: A python serializer for the payload. The default is a compact
#: JSON derived serializer with support for some extra Python types
#: such as datetime objects or tuples.
serializer = session_json_serializer
session_class = SecureCookieSession
def get_signing_serializer(
self, app: "Flask"
) -> t.Optional[URLSafeTimedSerializer]:
if not app.secret_key:
return None
signer_kwargs = dict(
key_derivation=self.key_derivation, digest_method=self.digest_method
)
return URLSafeTimedSerializer(
app.secret_key,
salt=self.salt,
serializer=self.serializer,
signer_kwargs=signer_kwargs,
)
def open_session(
self, app: "Flask", request: "Request"
) -> t.Optional[SecureCookieSession]:
s = self.get_signing_serializer(app)
if s is None:
return None
val = request.cookies.get(self.get_cookie_name(app))
if not val:
return self.session_class()
max_age = int(app.permanent_session_lifetime.total_seconds())
try:
data = s.loads(val, max_age=max_age)
return self.session_class(data)
except BadSignature:
return self.session_class()
def save_session(
self, app: "Flask", session: SessionMixin, response: "Response"
) -> None:
name = self.get_cookie_name(app)
domain = self.get_cookie_domain(app)
path = self.get_cookie_path(app)
secure = self.get_cookie_secure(app)
samesite = self.get_cookie_samesite(app)
httponly = self.get_cookie_httponly(app)
# If the session is modified to be empty, remove the cookie.
# If the session is empty, return without setting the cookie.
if not session:
if session.modified:
response.delete_cookie(
name,
domain=domain,
path=path,
secure=secure,
samesite=samesite,
httponly=httponly,
)
return
# Add a "Vary: Cookie" header if the session was accessed at all.
if session.accessed:
response.vary.add("Cookie")
if not self.should_set_cookie(app, session):
return
expires = self.get_expiration_time(app, session)
val = self.get_signing_serializer(app).dumps(dict(session)) # type: ignore
response.set_cookie(
name,
val, # type: ignore
expires=expires,
httponly=httponly,
domain=domain,
path=path,
secure=secure,
samesite=samesite,
)