350 lines
12 KiB
Python
350 lines
12 KiB
Python
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import base64
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import logging
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import string
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from datetime import datetime, timedelta
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from django.conf import settings
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from django.contrib.sessions.exceptions import SuspiciousSession
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from django.core.exceptions import SuspiciousOperation
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from django.utils import timezone
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from django.utils.crypto import (
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constant_time_compare, get_random_string, salted_hmac,
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)
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from django.utils.encoding import force_bytes
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from django.utils.module_loading import import_string
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# session_key should not be case sensitive because some backends can store it
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# on case insensitive file systems.
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VALID_KEY_CHARS = string.ascii_lowercase + string.digits
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class CreateError(Exception):
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"""
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Used internally as a consistent exception type to catch from save (see the
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docstring for SessionBase.save() for details).
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"""
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pass
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class UpdateError(Exception):
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"""
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Occurs if Django tries to update a session that was deleted.
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"""
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pass
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class SessionBase:
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"""
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Base class for all Session classes.
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"""
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TEST_COOKIE_NAME = 'testcookie'
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TEST_COOKIE_VALUE = 'worked'
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__not_given = object()
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def __init__(self, session_key=None):
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self._session_key = session_key
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self.accessed = False
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self.modified = False
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self.serializer = import_string(settings.SESSION_SERIALIZER)
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def __contains__(self, key):
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return key in self._session
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def __getitem__(self, key):
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return self._session[key]
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def __setitem__(self, key, value):
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self._session[key] = value
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self.modified = True
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def __delitem__(self, key):
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del self._session[key]
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self.modified = True
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def get(self, key, default=None):
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return self._session.get(key, default)
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def pop(self, key, default=__not_given):
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self.modified = self.modified or key in self._session
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args = () if default is self.__not_given else (default,)
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return self._session.pop(key, *args)
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def setdefault(self, key, value):
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if key in self._session:
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return self._session[key]
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else:
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self.modified = True
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self._session[key] = value
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return value
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def set_test_cookie(self):
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self[self.TEST_COOKIE_NAME] = self.TEST_COOKIE_VALUE
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def test_cookie_worked(self):
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return self.get(self.TEST_COOKIE_NAME) == self.TEST_COOKIE_VALUE
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def delete_test_cookie(self):
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del self[self.TEST_COOKIE_NAME]
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def _hash(self, value):
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key_salt = "django.contrib.sessions" + self.__class__.__name__
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return salted_hmac(key_salt, value).hexdigest()
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def encode(self, session_dict):
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"Return the given session dictionary serialized and encoded as a string."
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serialized = self.serializer().dumps(session_dict)
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hash = self._hash(serialized)
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return base64.b64encode(hash.encode() + b":" + serialized).decode('ascii')
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def decode(self, session_data):
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encoded_data = base64.b64decode(force_bytes(session_data))
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try:
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# could produce ValueError if there is no ':'
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hash, serialized = encoded_data.split(b':', 1)
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expected_hash = self._hash(serialized)
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if not constant_time_compare(hash.decode(), expected_hash):
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raise SuspiciousSession("Session data corrupted")
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else:
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return self.serializer().loads(serialized)
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except Exception as e:
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# ValueError, SuspiciousOperation, unpickling exceptions. If any of
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# these happen, just return an empty dictionary (an empty session).
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if isinstance(e, SuspiciousOperation):
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logger = logging.getLogger('django.security.%s' % e.__class__.__name__)
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logger.warning(str(e))
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return {}
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def update(self, dict_):
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self._session.update(dict_)
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self.modified = True
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def has_key(self, key):
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return key in self._session
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def keys(self):
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return self._session.keys()
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def values(self):
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return self._session.values()
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def items(self):
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return self._session.items()
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def clear(self):
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# To avoid unnecessary persistent storage accesses, we set up the
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# internals directly (loading data wastes time, since we are going to
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# set it to an empty dict anyway).
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self._session_cache = {}
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self.accessed = True
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self.modified = True
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def is_empty(self):
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"Return True when there is no session_key and the session is empty."
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try:
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return not self._session_key and not self._session_cache
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except AttributeError:
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return True
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def _get_new_session_key(self):
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"Return session key that isn't being used."
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while True:
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session_key = get_random_string(32, VALID_KEY_CHARS)
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if not self.exists(session_key):
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return session_key
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def _get_or_create_session_key(self):
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if self._session_key is None:
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self._session_key = self._get_new_session_key()
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return self._session_key
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def _validate_session_key(self, key):
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"""
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Key must be truthy and at least 8 characters long. 8 characters is an
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arbitrary lower bound for some minimal key security.
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"""
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return key and len(key) >= 8
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def _get_session_key(self):
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return self.__session_key
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def _set_session_key(self, value):
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"""
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Validate session key on assignment. Invalid values will set to None.
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"""
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if self._validate_session_key(value):
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self.__session_key = value
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else:
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self.__session_key = None
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session_key = property(_get_session_key)
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_session_key = property(_get_session_key, _set_session_key)
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def _get_session(self, no_load=False):
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"""
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Lazily load session from storage (unless "no_load" is True, when only
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an empty dict is stored) and store it in the current instance.
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"""
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self.accessed = True
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try:
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return self._session_cache
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except AttributeError:
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if self.session_key is None or no_load:
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self._session_cache = {}
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else:
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self._session_cache = self.load()
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return self._session_cache
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_session = property(_get_session)
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def get_expiry_age(self, **kwargs):
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"""Get the number of seconds until the session expires.
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Optionally, this function accepts `modification` and `expiry` keyword
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arguments specifying the modification and expiry of the session.
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"""
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try:
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modification = kwargs['modification']
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except KeyError:
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modification = timezone.now()
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# Make the difference between "expiry=None passed in kwargs" and
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# "expiry not passed in kwargs", in order to guarantee not to trigger
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# self.load() when expiry is provided.
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try:
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expiry = kwargs['expiry']
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except KeyError:
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expiry = self.get('_session_expiry')
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if not expiry: # Checks both None and 0 cases
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return settings.SESSION_COOKIE_AGE
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if not isinstance(expiry, datetime):
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return expiry
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delta = expiry - modification
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return delta.days * 86400 + delta.seconds
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def get_expiry_date(self, **kwargs):
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"""Get session the expiry date (as a datetime object).
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Optionally, this function accepts `modification` and `expiry` keyword
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arguments specifying the modification and expiry of the session.
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"""
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try:
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modification = kwargs['modification']
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except KeyError:
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modification = timezone.now()
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# Same comment as in get_expiry_age
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try:
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expiry = kwargs['expiry']
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except KeyError:
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expiry = self.get('_session_expiry')
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if isinstance(expiry, datetime):
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return expiry
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expiry = expiry or settings.SESSION_COOKIE_AGE # Checks both None and 0 cases
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return modification + timedelta(seconds=expiry)
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def set_expiry(self, value):
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"""
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Set a custom expiration for the session. ``value`` can be an integer,
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a Python ``datetime`` or ``timedelta`` object or ``None``.
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If ``value`` is an integer, the session will expire after that many
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seconds of inactivity. If set to ``0`` then the session will expire on
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browser close.
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If ``value`` is a ``datetime`` or ``timedelta`` object, the session
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will expire at that specific future time.
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If ``value`` is ``None``, the session uses the global session expiry
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policy.
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"""
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if value is None:
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# Remove any custom expiration for this session.
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try:
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del self['_session_expiry']
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except KeyError:
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pass
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return
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if isinstance(value, timedelta):
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value = timezone.now() + value
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self['_session_expiry'] = value
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def get_expire_at_browser_close(self):
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"""
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Return ``True`` if the session is set to expire when the browser
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closes, and ``False`` if there's an expiry date. Use
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``get_expiry_date()`` or ``get_expiry_age()`` to find the actual expiry
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date/age, if there is one.
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"""
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if self.get('_session_expiry') is None:
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return settings.SESSION_EXPIRE_AT_BROWSER_CLOSE
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return self.get('_session_expiry') == 0
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def flush(self):
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"""
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Remove the current session data from the database and regenerate the
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key.
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"""
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self.clear()
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self.delete()
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self._session_key = None
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def cycle_key(self):
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"""
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Create a new session key, while retaining the current session data.
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"""
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data = self._session
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key = self.session_key
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self.create()
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self._session_cache = data
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if key:
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self.delete(key)
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# Methods that child classes must implement.
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def exists(self, session_key):
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"""
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Return True if the given session_key already exists.
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"""
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raise NotImplementedError('subclasses of SessionBase must provide an exists() method')
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def create(self):
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"""
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Create a new session instance. Guaranteed to create a new object with
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a unique key and will have saved the result once (with empty data)
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before the method returns.
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"""
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raise NotImplementedError('subclasses of SessionBase must provide a create() method')
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def save(self, must_create=False):
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"""
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Save the session data. If 'must_create' is True, create a new session
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object (or raise CreateError). Otherwise, only update an existing
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object and don't create one (raise UpdateError if needed).
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"""
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raise NotImplementedError('subclasses of SessionBase must provide a save() method')
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def delete(self, session_key=None):
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"""
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Delete the session data under this key. If the key is None, use the
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current session key value.
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"""
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raise NotImplementedError('subclasses of SessionBase must provide a delete() method')
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def load(self):
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"""
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Load the session data and return a dictionary.
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"""
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raise NotImplementedError('subclasses of SessionBase must provide a load() method')
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@classmethod
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def clear_expired(cls):
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"""
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Remove expired sessions from the session store.
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If this operation isn't possible on a given backend, it should raise
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NotImplementedError. If it isn't necessary, because the backend has
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a built-in expiration mechanism, it should be a no-op.
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"""
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raise NotImplementedError('This backend does not support clear_expired().')
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