from __future__ import unicode_literals import base64 import logging import string from datetime import datetime, timedelta from django.conf import settings from django.contrib.sessions.exceptions import SuspiciousSession from django.core.exceptions import SuspiciousOperation from django.utils import timezone from django.utils.crypto import ( constant_time_compare, get_random_string, salted_hmac, ) from django.utils.encoding import force_bytes, force_text from django.utils.module_loading import import_string # session_key should not be case sensitive because some backends can store it # on case insensitive file systems. VALID_KEY_CHARS = string.ascii_lowercase + string.digits class CreateError(Exception): """ Used internally as a consistent exception type to catch from save (see the docstring for SessionBase.save() for details). """ pass class SessionBase(object): """ Base class for all Session classes. """ TEST_COOKIE_NAME = 'testcookie' TEST_COOKIE_VALUE = 'worked' def __init__(self, session_key=None): self._session_key = session_key self.accessed = False self.modified = False self.serializer = import_string(settings.SESSION_SERIALIZER) def __contains__(self, key): return key in self._session def __getitem__(self, key): return self._session[key] def __setitem__(self, key, value): self._session[key] = value self.modified = True def __delitem__(self, key): del self._session[key] self.modified = True def get(self, key, default=None): return self._session.get(key, default) def pop(self, key, default=None): self.modified = self.modified or key in self._session return self._session.pop(key, default) def setdefault(self, key, value): if key in self._session: return self._session[key] else: self.modified = True self._session[key] = value return value def set_test_cookie(self): self[self.TEST_COOKIE_NAME] = self.TEST_COOKIE_VALUE def test_cookie_worked(self): return self.get(self.TEST_COOKIE_NAME) == self.TEST_COOKIE_VALUE def delete_test_cookie(self): del self[self.TEST_COOKIE_NAME] def _hash(self, value): key_salt = "django.contrib.sessions" + self.__class__.__name__ return salted_hmac(key_salt, value).hexdigest() def encode(self, session_dict): "Returns the given session dictionary serialized and encoded as a string." serialized = self.serializer().dumps(session_dict) hash = self._hash(serialized) return base64.b64encode(hash.encode() + b":" + serialized).decode('ascii') def decode(self, session_data): encoded_data = base64.b64decode(force_bytes(session_data)) try: # could produce ValueError if there is no ':' hash, serialized = encoded_data.split(b':', 1) expected_hash = self._hash(serialized) if not constant_time_compare(hash.decode(), expected_hash): raise SuspiciousSession("Session data corrupted") else: return self.serializer().loads(serialized) except Exception as e: # ValueError, SuspiciousOperation, unpickling exceptions. If any of # these happen, just return an empty dictionary (an empty session). if isinstance(e, SuspiciousOperation): logger = logging.getLogger('django.security.%s' % e.__class__.__name__) logger.warning(force_text(e)) return {} def update(self, dict_): self._session.update(dict_) self.modified = True def has_key(self, key): return key in self._session def keys(self): return self._session.keys() def values(self): return self._session.values() def items(self): return self._session.items() def iterkeys(self): return self._session.iterkeys() def itervalues(self): return self._session.itervalues() def iteritems(self): return self._session.iteritems() 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): "Returns True when there is no session_key and the session is empty" try: return not bool(self._session_key) and not self._session_cache except AttributeError: return True def _get_new_session_key(self): "Returns session key that isn't being used." while True: session_key = get_random_string(32, VALID_KEY_CHARS) if not self.exists(session_key): break 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 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 loads session from storage (unless "no_load" is True, when only an empty dict is stored) and stores 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 _session = property(_get_session) 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 settings.SESSION_COOKIE_AGE if not isinstance(expiry, datetime): return 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 if not expiry: # Checks both None and 0 cases expiry = settings.SESSION_COOKIE_AGE return modification + timedelta(seconds=expiry) def set_expiry(self, value): """ Sets 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 self['_session_expiry'] = value def get_expire_at_browser_close(self): """ Returns ``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 self.get('_session_expiry') is None: return settings.SESSION_EXPIRE_AT_BROWSER_CLOSE return self.get('_session_expiry') == 0 def flush(self): """ Removes the current session data from the database and regenerates the key. """ self.clear() self.delete() self._session_key = None def cycle_key(self): """ Creates a new session key, while retaining the current session data. """ data = self._session_cache key = self.session_key self.create() self._session_cache = data self.delete(key) # Methods that child classes must implement. def exists(self, session_key): """ Returns True if the given session_key already exists. """ raise NotImplementedError('subclasses of SessionBase must provide an exists() method') def create(self): """ Creates 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') def save(self, must_create=False): """ Saves the session data. If 'must_create' is True, a new session object is created (otherwise a CreateError exception is raised). Otherwise, save() can update an existing object with the same key. """ raise NotImplementedError('subclasses of SessionBase must provide a save() method') def delete(self, session_key=None): """ Deletes the session data under this key. If the key is None, the current session key value is used. """ raise NotImplementedError('subclasses of SessionBase must provide a delete() method') def load(self): """ Loads the session data and returns a dictionary. """ raise NotImplementedError('subclasses of SessionBase must provide a load() method') @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().')