Django session 源码流程
流程
Django session源码流程 首先执行的是SessionMiddleware的init方法 import_module(settings.SESSION_ENGINE) 导入了一个 django.contrib.sessions.backends.db的包 将db中SessionStore 赋值给self.SessionStore 执行process_request 方法 获取存放于cookie中的session_id,赋值为session_key 实例化session仓库session_key作为参数，赋值给request.sessions 执行SessionStore 的init方法 执行父类SessionBase的init方法 self._session_key = session_key 将参数session_key 赋值给 self._session_key self.accessed = False 存取 session self.modified = False 修改session 修改_session_key会执行下面 _session_key = property(_get_session_key, _set_session_key) 然后执行_set_session_key方法 判断_session_key是否存在 T:将其赋值给__session_key F:__session_key为None 如果此时没有用户登录会执行__getitem__ def __getitem__(self, key): return self._session[key] #self._session = _session_cache 如果用户登录会给session赋值，执行__setitem__方法 一键值对存放于self._session中 self.modified = True 修改session 因为self.session执行 _session = property(_get_session) 执行_get_session方法 self.accessed = True #获取session 如果self._session_cache 存在或者 no_load存在 self._session_cache = {} 否则 self._session_cache = self.load() return self._session_cache 执行process_response方法 accessed = request.session.accessed modified = request.session.modified 判断session是否为空 empty = request.session.is_empty() 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 return True 如果此时self既有session_key又有session返回F，不为空（说明此时已经存在cookie与session） 此时self如果没有属性_session_cache报错 为空 判断sessionID是否存在于cookie中和 session是否存在（有cookie，没session）（绝对是注销操作） True，就删除并重新赋值cookie 否则 判断 accessed 存储是否为空（是否获取了session） 判断session是否赋值和session不为空 保存session并给cookie赋值 保存session request.session.save() 获取sessionID 获取那个字典 生成model实例 写入到数据库 给cookie赋值 session_id : fsufuhakjfhkuahfkdahkfhakfhakfhka 1.一直处于未登录 1.获取到cookie的session_id 为空 2.获取session的某个值，为空 3.session没有被赋值，不执行 2.从未登录到登陆 1.获取到cookie的session_id 为空 2.给session赋值 3.把session存放到数据库 sessionkey sessiondata 过期时间 4.把sessionkey 存放到cookie sessionID 32位随机字符串 认证原理：获取sessionkey 与数据库的sessionkey是否一致 一致就可取到 session data数据，然后取出判断此数据是否存在与数据库中 3.一直登陆 1.获取到cookie的session_id 为32位随机字符串 2.获取session某值，不为空 3.session没有被赋值，不执行 4.注销 1.获取到cookie的session_id 为32位随机字符串 2.给session赋值 3.把session存放到数据库 sessionkey sessiondata 过期时间 （sessiondata会被修改） 4.把sessionkey 存放到cookie sessionID 32位随机字符串 认证原理：获取cookie 的sessionkey 和 服务器的sessionkey字段 作比较 一致为 同一浏览器，但sessiondata 中的数据 向user表中查看
SessionMiddleware源码
import time from importlib import import_module from django.conf import settings from django.contrib.sessions.backends.base import UpdateError from django.core.exceptions import SuspiciousOperation from django.utils.cache import patch_vary_headers from django.utils.deprecation import MiddlewareMixin from django.utils.http import cookie_date class SessionMiddleware(MiddlewareMixin): def __init__(self, get_response=None): self.get_response = get_response engine = import_module(settings.SESSION_ENGINE) #settings.SESSION_ENGINE = django.contrib.sessions.backends.db self.SessionStore = engine.SessionStore # class SessionStore(SessionBase): 实现数据库会话存储的类 def process_request(self, request): session_key = request.COOKIES.get(settings.SESSION_COOKIE_NAME) #SESSION_COOKIE_NAME = 'sessionid' request.session = self.SessionStore(session_key) #实例化 SessionStore def process_response(self, request, response): """ If request.session was modified, or if the configuration is to save the session every time, save the changes and set a session cookie or delete the session cookie if the session has been emptied. """ try: accessed = request.session.accessed #存取 modified = request.session.modified #修改 empty = request.session.is_empty() except AttributeError: pass else: # First check if we need to delete this cookie. # The session should be deleted only if the session is entirely empty if settings.SESSION_COOKIE_NAME in request.COOKIES and empty: #cookie上的sessionkey sessiondata都为空 时执行这个 response.delete_cookie( settings.SESSION_COOKIE_NAME, path=settings.SESSION_COOKIE_PATH, #SESSION_COOKIE_PATH = '/' domain=settings.SESSION_COOKIE_DOMAIN,#SESSION_COOKIE_DOMAIN = None ) else: if accessed: patch_vary_headers(response, ('Cookie',)) if (modified or settings.SESSION_SAVE_EVERY_REQUEST) and not empty: if request.session.get_expire_at_browser_close(): max_age = None expires = None else: max_age = request.session.get_expiry_age() expires_time = time.time() + max_age expires = cookie_date(expires_time) # Save the session data and refresh the client cookie. # Skip session save for 500 responses, refs #3881. if response.status_code != 500: try: request.session.save() except UpdateError: raise SuspiciousOperation( "The request's session was deleted before the " "request completed. The user may have logged " "out in a concurrent request, for example." ) response.set_cookie( settings.SESSION_COOKIE_NAME, request.session.session_key, max_age=max_age, expires=expires, domain=settings.SESSION_COOKIE_DOMAIN, path=settings.SESSION_COOKIE_PATH, secure=settings.SESSION_COOKIE_SECURE or None, httponly=settings.SESSION_COOKIE_HTTPONLY or None, ) return response
SessionStore
import logging from django.contrib.sessions.backends.base import ( CreateError, SessionBase, UpdateError, ) from django.core.exceptions import SuspiciousOperation from django.db import DatabaseError, IntegrityError, router, transaction from django.utils import timezone from django.utils.encoding import force_text from django.utils.functional import cached_property class SessionStore(SessionBase): """ Implements database session store. """ def __init__(self, session_key=None): super(SessionStore, self).__init__(session_key) @classmethod def get_model_class(cls): # Avoids a circular import and allows importing SessionStore when # django.contrib.sessions is not in INSTALLED_APPS. from django.contrib.sessions.models import Session return Session @cached_property def model(self): return self.get_model_class() def load(self): try: s = self.model.objects.get( session_key=self.session_key, expire_date__gt=timezone.now() ) return self.decode(s.session_data) except (self.model.DoesNotExist, SuspiciousOperation) as e: if isinstance(e, SuspiciousOperation): logger = logging.getLogger('django.security.%s' % e.__class__.__name__) logger.warning(force_text(e)) self._session_key = None return {} def exists(self, session_key): return self.model.objects.filter(session_key=session_key).exists() def create(self): while True: self._session_key = self._get_new_session_key() try: # Save immediately to ensure we have a unique entry in the # database. self.save(must_create=True) except CreateError: # Key wasn't unique. Try again. continue self.modified = True return def create_model_instance(self, data): """ Return a new instance of the session model object, which represents the current session state. Intended to be used for saving the session data to the database. """ return self.model( session_key=self._get_or_create_session_key(), #获取session_key session_data=self.encode(data), #那个字典 expire_date=self.get_expiry_date(), ) def save(self, must_create=False): """ Saves the current session data to the database. If 'must_create' is True, a database error will be raised if the saving operation doesn't create a *new* entry (as opposed to possibly updating an existing entry). """ if self.session_key is None: return self.create() data = self._get_session(no_load=must_create) #此时已经存在值了 obj = self.create_model_instance(data) #model实例 using = router.db_for_write(self.model, instance=obj) #from django.contrib.sessions.models import Session try: with transaction.atomic(using=using): #写入数据库 obj.save(force_insert=must_create, force_update=not must_create, using=using) except IntegrityError: if must_create: raise CreateError raise except DatabaseError: if not must_create: raise UpdateError raise def delete(self, session_key=None): if session_key is None: if self.session_key is None: return session_key = self.session_key try: self.model.objects.get(session_key=session_key).delete() except self.model.DoesNotExist: pass @classmethod def clear_expired(cls): cls.get_model_class().objects.filter(expire_date__lt=timezone.now()).delete()
session
class SessionBase(object): """ Base class for all Session classes. """ TEST_COOKIE_NAME = 'testcookie' TEST_COOKIE_VALUE = 'worked' __not_given = object() def __init__(self, session_key=None): self._session_key = session_key self.accessed = False self.modified = False self.serializer = import_string(settings.SESSION_SERIALIZER) #django.contrib.sessions.serializers.JSONSerializer #self.serializer = class JSONSerializer(object): 实现序列化方法的类 def __contains__(self, key): return key in self._session def __getitem__(self, key): return self._session[key] def __setitem__(self, key, value): #self._session = _session_cache = {'name':'ldq'} self._session[key] = value #因为字典是可变类型，所以当_session改变的时候_session_cache也随之改变 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=__not_given): self.modified = self.modified or key in self._session args = () if default is self.__not_given else (default,) return self._session.pop(key, *args) 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 #如果此时self既有session_key又有session返回F：不为空（说明此时已经存在cookie与session） 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) #32位的随机字符串 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): #对象实例化时执行这个方法 """ 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) #None _session_key = property(_get_session_key, _set_session_key) #self._session_key = self._get_new_session_key() #32位的随机字符串 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 #正在获取session 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 #SESSION_COOKIE_AGE = 60 * 60 * 24 * 7 * 2 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 key = self.session_key self.create() self._session_cache = data if key: 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() only updates an existing object and does not create one (an UpdateError is raised). """ 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().')
