363 lines (302 sloc) 14 KB
# -*- coding: utf-8 -*-
Implements cookie based sessions based on itsdangerous.
:copyright: (c) 2015 by Armin Ronacher.
:license: BSD, see LICENSE for more details.
import uuid
import hashlib
from base64 import b64encode, b64decode
from datetime import datetime
from werkzeug.http import http_date, parse_date
from werkzeug.datastructures import CallbackDict
from . import Markup, json
from ._compat import iteritems, text_type
from .helpers import total_seconds
from itsdangerous import URLSafeTimedSerializer, BadSignature
class SessionMixin(object):
"""Expands a basic dictionary with an accessors that are expected
by Flask extensions and users for the session.
def _get_permanent(self):
return self.get('_permanent', False)
def _set_permanent(self, value):
self['_permanent'] = bool(value)
#: this reflects the ``'_permanent'`` key in the dict.
permanent = property(_get_permanent, _set_permanent)
del _get_permanent, _set_permanent
#: some session backends can tell you if a session is new, but that is
#: not necessarily guaranteed. Use with caution. The default mixin
#: implementation just hardcodes ``False`` in.
new = False
#: for some backends this will always be ``True``, but some backends will
#: default this to false and detect changes in the dictionary for as
#: long as changes do not happen on mutable structures in the session.
#: The default mixin implementation just hardcodes ``True`` in.
modified = True
def _tag(value):
if isinstance(value, tuple):
return {' t': [_tag(x) for x in value]}
elif isinstance(value, uuid.UUID):
return {' u': value.hex}
elif isinstance(value, bytes):
return {' b': b64encode(value).decode('ascii')}
elif callable(getattr(value, '__html__', None)):
return {' m': text_type(value.__html__())}
elif isinstance(value, list):
return [_tag(x) for x in value]
elif isinstance(value, datetime):
return {' d': http_date(value)}
elif isinstance(value, dict):
return dict((k, _tag(v)) for k, v in iteritems(value))
elif isinstance(value, str):
return text_type(value)
except UnicodeError:
from flask.debughelpers import UnexpectedUnicodeError
raise UnexpectedUnicodeError(u'A byte string with '
u'non-ASCII data was passed to the session system '
u'which can only store unicode strings. Consider '
u'base64 encoding your string (String was %r)' % value)
return value
class TaggedJSONSerializer(object):
"""A customized JSON serializer that supports a few extra types that
we take for granted when serializing (tuples, markup objects, datetime).
def dumps(self, value):
return json.dumps(_tag(value), separators=(',', ':'))
def loads(self, value):
def object_hook(obj):
if len(obj) != 1:
return obj
the_key, the_value = next(iteritems(obj))
if the_key == ' t':
return tuple(the_value)
elif the_key == ' u':
return uuid.UUID(the_value)
elif the_key == ' b':
return b64decode(the_value)
elif the_key == ' m':
return Markup(the_value)
elif the_key == ' d':
return parse_date(the_value)
return obj
return json.loads(value, object_hook=object_hook)
session_json_serializer = TaggedJSONSerializer()
class SecureCookieSession(CallbackDict, SessionMixin):
"""Base class for sessions based on signed cookies."""
def __init__(self, initial=None):
def on_update(self):
self.modified = True
CallbackDict.__init__(self, initial, on_update)
self.modified = False
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, **kwargs):
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
del _fail
class SessionInterface(object):
"""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):
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()
.. 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):
"""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
This creates an instance of :attr:`null_session_class` by default.
return self.null_session_class()
def is_null_session(self, obj):
"""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_domain(self, app):
"""Helpful helper method that returns the cookie domain that should
be used for the session cookie if session cookies are used.
if app.config['SESSION_COOKIE_DOMAIN'] is not None:
return app.config['SESSION_COOKIE_DOMAIN']
if app.config['SERVER_NAME'] is not None:
# chop off the port which is usually not supported by browsers
rv = '.' + app.config['SERVER_NAME'].rsplit(':', 1)[0]
# Google chrome does not like cookies set to .localhost, so
# we just go with no domain then. Flask documents anyways that
# cross domain cookies need a fully qualified domain name
if rv == '.localhost':
rv = None
# If we infer the cookie domain from the server name we need
# to check if we are in a subpath. In that case we can't
# set a cross domain cookie.
if rv is not None:
path = self.get_cookie_path(app)
if path != '/':
rv = rv.lstrip('.')
return rv
def get_cookie_path(self, app):
"""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'] or '/'
def get_cookie_httponly(self, app):
"""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):
"""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_expiration_time(self, app, session):
"""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.utcnow() + app.permanent_session_lifetime
def should_set_cookie(self, app, session):
"""Indicates whether a cookie should be set now or not. This is
used by session backends to figure out if they should emit a
set-cookie header or not. The default behavior is controlled by
the ``SESSION_REFRESH_EACH_REQUEST`` config variable. If
it's set to ``False`` then a cookie is only set if the session is
modified, if set to ``True`` it's always set if the session is
This check is usually skipped if sessions get deleted.
.. versionadded:: 0.11
if session.modified:
return True
save_each = app.config['SESSION_REFRESH_EACH_REQUEST']
return save_each and session.permanent
def open_session(self, app, request):
"""This method has to be implemented and must either return ``None``
in case the loading failed because of a configuration error or an
instance of a session object which implements a dictionary like
interface + the methods and attributes on :class:`SessionMixin`.
raise NotImplementedError()
def save_session(self, app, session, response):
"""This is called for actual sessions returned by :meth:`open_session`
at the end of the request. This is still called during a request
context so if you absolutely need access to the request you can do
raise NotImplementedError()
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):
if not app.secret_key:
return None
signer_kwargs = dict(
return URLSafeTimedSerializer(app.secret_key, salt=self.salt,
def open_session(self, app, request):
s = self.get_signing_serializer(app)
if s is None:
return None
val = request.cookies.get(app.session_cookie_name)
if not val:
return self.session_class()
max_age = total_seconds(app.permanent_session_lifetime)
data = s.loads(val, max_age=max_age)
return self.session_class(data)
except BadSignature:
return self.session_class()
def save_session(self, app, session, response):
domain = self.get_cookie_domain(app)
path = self.get_cookie_path(app)
# Delete case. If there is no session we bail early.
# If the session was modified to be empty we remove the
# whole cookie.
if not session:
if session.modified:
domain=domain, path=path)
# Modification case. There are upsides and downsides to
# emitting a set-cookie header each request. The behavior
# is controlled by the :meth:`should_set_cookie` method
# which performs a quick check to figure out if the cookie
# should be set or not. This is controlled by the
# SESSION_REFRESH_EACH_REQUEST config flag as well as
# the permanent flag on the session itself.
if not self.should_set_cookie(app, session):
httponly = self.get_cookie_httponly(app)
secure = self.get_cookie_secure(app)
expires = self.get_expiration_time(app, session)
val = self.get_signing_serializer(app).dumps(dict(session))
response.set_cookie(app.session_cookie_name, val,
expires=expires, httponly=httponly,
domain=domain, path=path, secure=secure)