386 lines
14 KiB
Python
386 lines
14 KiB
Python
# -*- coding: utf-8 -*-
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"""
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flask.sessions
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~~~~~~~~~~~~~~
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Implements cookie based sessions based on itsdangerous.
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:copyright: © 2010 by the Pallets team.
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:license: BSD, see LICENSE for more details.
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"""
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import hashlib
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import warnings
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from collections import MutableMapping
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from datetime import datetime
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from itsdangerous import BadSignature, URLSafeTimedSerializer
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from werkzeug.datastructures import CallbackDict
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from flask.helpers import is_ip, total_seconds
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from flask.json.tag import TaggedJSONSerializer
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class SessionMixin(MutableMapping):
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"""Expands a basic dictionary with session attributes."""
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@property
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def permanent(self):
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"""This reflects the ``'_permanent'`` key in the dict."""
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return self.get('_permanent', False)
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@permanent.setter
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def permanent(self, value):
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self['_permanent'] = bool(value)
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#: Some implementations can detect whether a session is newly
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#: created, but that is not guaranteed. Use with caution. The mixin
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# default is hard-coded ``False``.
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new = False
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#: Some implementations can detect changes to the session and set
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#: this when that happens. The mixin default is hard coded to
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#: ``True``.
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modified = True
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#: Some implementations can detect when session data is read or
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#: written and set this when that happens. The mixin default is hard
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#: coded to ``True``.
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accessed = True
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class SecureCookieSession(CallbackDict, SessionMixin):
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"""Base class for sessions based on signed cookies.
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This session backend will set the :attr:`modified` and
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:attr:`accessed` attributes. It cannot reliably track whether a
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session is new (vs. empty), so :attr:`new` remains hard coded to
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``False``.
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"""
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#: When data is changed, this is set to ``True``. Only the session
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#: dictionary itself is tracked; if the session contains mutable
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#: data (for example a nested dict) then this must be set to
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#: ``True`` manually when modifying that data. The session cookie
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#: will only be written to the response if this is ``True``.
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modified = False
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#: When data is read or written, this is set to ``True``. Used by
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# :class:`.SecureCookieSessionInterface` to add a ``Vary: Cookie``
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#: header, which allows caching proxies to cache different pages for
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#: different users.
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accessed = False
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def __init__(self, initial=None):
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def on_update(self):
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self.modified = True
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self.accessed = True
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super(SecureCookieSession, self).__init__(initial, on_update)
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def __getitem__(self, key):
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self.accessed = True
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return super(SecureCookieSession, self).__getitem__(key)
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def get(self, key, default=None):
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self.accessed = True
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return super(SecureCookieSession, self).get(key, default)
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def setdefault(self, key, default=None):
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self.accessed = True
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return super(SecureCookieSession, self).setdefault(key, default)
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class NullSession(SecureCookieSession):
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"""Class used to generate nicer error messages if sessions are not
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available. Will still allow read-only access to the empty session
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but fail on setting.
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"""
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def _fail(self, *args, **kwargs):
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raise RuntimeError('The session is unavailable because no secret '
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'key was set. Set the secret_key on the '
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'application to something unique and secret.')
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__setitem__ = __delitem__ = clear = pop = popitem = \
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update = setdefault = _fail
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del _fail
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class SessionInterface(object):
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"""The basic interface you have to implement in order to replace the
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default session interface which uses werkzeug's securecookie
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implementation. The only methods you have to implement are
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:meth:`open_session` and :meth:`save_session`, the others have
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useful defaults which you don't need to change.
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The session object returned by the :meth:`open_session` method has to
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provide a dictionary like interface plus the properties and methods
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from the :class:`SessionMixin`. We recommend just subclassing a dict
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and adding that mixin::
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class Session(dict, SessionMixin):
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pass
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If :meth:`open_session` returns ``None`` Flask will call into
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:meth:`make_null_session` to create a session that acts as replacement
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if the session support cannot work because some requirement is not
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fulfilled. The default :class:`NullSession` class that is created
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will complain that the secret key was not set.
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To replace the session interface on an application all you have to do
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is to assign :attr:`flask.Flask.session_interface`::
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app = Flask(__name__)
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app.session_interface = MySessionInterface()
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.. versionadded:: 0.8
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"""
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#: :meth:`make_null_session` will look here for the class that should
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#: be created when a null session is requested. Likewise the
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#: :meth:`is_null_session` method will perform a typecheck against
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#: this type.
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null_session_class = NullSession
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#: A flag that indicates if the session interface is pickle based.
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#: This can be used by Flask extensions to make a decision in regards
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#: to how to deal with the session object.
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#:
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#: .. versionadded:: 0.10
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pickle_based = False
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def make_null_session(self, app):
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"""Creates a null session which acts as a replacement object if the
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real session support could not be loaded due to a configuration
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error. This mainly aids the user experience because the job of the
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null session is to still support lookup without complaining but
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modifications are answered with a helpful error message of what
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failed.
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This creates an instance of :attr:`null_session_class` by default.
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"""
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return self.null_session_class()
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def is_null_session(self, obj):
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"""Checks if a given object is a null session. Null sessions are
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not asked to be saved.
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This checks if the object is an instance of :attr:`null_session_class`
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by default.
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"""
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return isinstance(obj, self.null_session_class)
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def get_cookie_domain(self, app):
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"""Returns the domain that should be set for the session cookie.
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Uses ``SESSION_COOKIE_DOMAIN`` if it is configured, otherwise
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falls back to detecting the domain based on ``SERVER_NAME``.
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Once detected (or if not set at all), ``SESSION_COOKIE_DOMAIN`` is
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updated to avoid re-running the logic.
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"""
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rv = app.config['SESSION_COOKIE_DOMAIN']
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# set explicitly, or cached from SERVER_NAME detection
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# if False, return None
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if rv is not None:
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return rv if rv else None
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rv = app.config['SERVER_NAME']
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# server name not set, cache False to return none next time
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if not rv:
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app.config['SESSION_COOKIE_DOMAIN'] = False
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return None
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# chop off the port which is usually not supported by browsers
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# remove any leading '.' since we'll add that later
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rv = rv.rsplit(':', 1)[0].lstrip('.')
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if '.' not in rv:
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# Chrome doesn't allow names without a '.'
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# this should only come up with localhost
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# hack around this by not setting the name, and show a warning
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warnings.warn(
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'"{rv}" is not a valid cookie domain, it must contain a ".".'
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' Add an entry to your hosts file, for example'
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' "{rv}.localdomain", and use that instead.'.format(rv=rv)
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)
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app.config['SESSION_COOKIE_DOMAIN'] = False
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return None
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ip = is_ip(rv)
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if ip:
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warnings.warn(
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'The session cookie domain is an IP address. This may not work'
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' as intended in some browsers. Add an entry to your hosts'
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' file, for example "localhost.localdomain", and use that'
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' instead.'
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)
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# if this is not an ip and app is mounted at the root, allow subdomain
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# matching by adding a '.' prefix
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if self.get_cookie_path(app) == '/' and not ip:
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rv = '.' + rv
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app.config['SESSION_COOKIE_DOMAIN'] = rv
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return rv
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def get_cookie_path(self, app):
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"""Returns the path for which the cookie should be valid. The
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default implementation uses the value from the ``SESSION_COOKIE_PATH``
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config var if it's set, and falls back to ``APPLICATION_ROOT`` or
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uses ``/`` if it's ``None``.
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"""
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return app.config['SESSION_COOKIE_PATH'] \
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or app.config['APPLICATION_ROOT']
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def get_cookie_httponly(self, app):
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"""Returns True if the session cookie should be httponly. This
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currently just returns the value of the ``SESSION_COOKIE_HTTPONLY``
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config var.
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"""
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return app.config['SESSION_COOKIE_HTTPONLY']
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def get_cookie_secure(self, app):
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"""Returns True if the cookie should be secure. This currently
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just returns the value of the ``SESSION_COOKIE_SECURE`` setting.
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"""
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return app.config['SESSION_COOKIE_SECURE']
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def get_cookie_samesite(self, app):
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"""Return ``'Strict'`` or ``'Lax'`` if the cookie should use the
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``SameSite`` attribute. This currently just returns the value of
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the :data:`SESSION_COOKIE_SAMESITE` setting.
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"""
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return app.config['SESSION_COOKIE_SAMESITE']
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def get_expiration_time(self, app, session):
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"""A helper method that returns an expiration date for the session
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or ``None`` if the session is linked to the browser session. The
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default implementation returns now + the permanent session
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lifetime configured on the application.
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"""
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if session.permanent:
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return datetime.utcnow() + app.permanent_session_lifetime
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def should_set_cookie(self, app, session):
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"""Used by session backends to determine if a ``Set-Cookie`` header
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should be set for this session cookie for this response. If the session
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has been modified, the cookie is set. If the session is permanent and
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the ``SESSION_REFRESH_EACH_REQUEST`` config is true, the cookie is
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always set.
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This check is usually skipped if the session was deleted.
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.. versionadded:: 0.11
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"""
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return session.modified or (
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session.permanent and app.config['SESSION_REFRESH_EACH_REQUEST']
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)
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def open_session(self, app, request):
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"""This method has to be implemented and must either return ``None``
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in case the loading failed because of a configuration error or an
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instance of a session object which implements a dictionary like
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interface + the methods and attributes on :class:`SessionMixin`.
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"""
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raise NotImplementedError()
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def save_session(self, app, session, response):
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"""This is called for actual sessions returned by :meth:`open_session`
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at the end of the request. This is still called during a request
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context so if you absolutely need access to the request you can do
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that.
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"""
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raise NotImplementedError()
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session_json_serializer = TaggedJSONSerializer()
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class SecureCookieSessionInterface(SessionInterface):
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"""The default session interface that stores sessions in signed cookies
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through the :mod:`itsdangerous` module.
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"""
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#: the salt that should be applied on top of the secret key for the
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#: signing of cookie based sessions.
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salt = 'cookie-session'
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#: the hash function to use for the signature. The default is sha1
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digest_method = staticmethod(hashlib.sha1)
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#: the name of the itsdangerous supported key derivation. The default
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#: is hmac.
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key_derivation = 'hmac'
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#: A python serializer for the payload. The default is a compact
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#: JSON derived serializer with support for some extra Python types
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#: such as datetime objects or tuples.
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serializer = session_json_serializer
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session_class = SecureCookieSession
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def get_signing_serializer(self, app):
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if not app.secret_key:
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return None
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signer_kwargs = dict(
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key_derivation=self.key_derivation,
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digest_method=self.digest_method
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)
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return URLSafeTimedSerializer(app.secret_key, salt=self.salt,
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serializer=self.serializer,
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signer_kwargs=signer_kwargs)
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def open_session(self, app, request):
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s = self.get_signing_serializer(app)
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if s is None:
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return None
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val = request.cookies.get(app.session_cookie_name)
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if not val:
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return self.session_class()
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max_age = total_seconds(app.permanent_session_lifetime)
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try:
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data = s.loads(val, max_age=max_age)
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return self.session_class(data)
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except BadSignature:
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return self.session_class()
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def save_session(self, app, session, response):
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domain = self.get_cookie_domain(app)
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path = self.get_cookie_path(app)
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# If the session is modified to be empty, remove the cookie.
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# If the session is empty, return without setting the cookie.
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if not session:
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if session.modified:
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response.delete_cookie(
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app.session_cookie_name,
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domain=domain,
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path=path
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)
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return
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# Add a "Vary: Cookie" header if the session was accessed at all.
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if session.accessed:
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response.vary.add('Cookie')
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if not self.should_set_cookie(app, session):
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return
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httponly = self.get_cookie_httponly(app)
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secure = self.get_cookie_secure(app)
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samesite = self.get_cookie_samesite(app)
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expires = self.get_expiration_time(app, session)
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val = self.get_signing_serializer(app).dumps(dict(session))
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response.set_cookie(
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app.session_cookie_name,
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val,
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expires=expires,
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httponly=httponly,
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domain=domain,
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path=path,
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secure=secure,
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samesite=samesite
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)
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