Flask---session源码分析

本文主要是介绍Flask---session源码分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

我在Flask—上下文源码分析这篇笔记中，简单分析了下Flask的上下文管理源码分析，今天我单拎出来session来，并且结合flask-session保存到redis进行分析，先抛出一张图

当我们在项目中构造app = Flask(__name__)实例时，在发起request请求时，会执行app的__call__方法

 def __call__(self, environ, start_response):"""Shortcut for :attr:`wsgi_app`."""return self.wsgi_app(environ, start_response)

跟踪方法wsgi_app参看如下代码

ctx = self.request_context(environ)

在RequestContext(self, environ)中封装了session

    def __init__(self, app, environ, request=None):self.app = appif request is None:request = app.request_class(environ)self.request = requestself.url_adapter = app.create_url_adapter(self.request)self.flashes = Noneself.session = None、、、省略部分代码、、、

然后继续回到wsgi_app方法中，在ctx = self.request_context(environ)中封装了session属性之后，在下一行代码中

 ctx.push()

进行了如下操作

self.session = self.app.open_session(self.request)

继而跟踪到class SecureCookieSessionInterface(SessionInterface)类的如下代码

  def open_session(self, app, request):s = self.get_signing_serializer(app)if s is None:return Noneval = request.cookies.get(app.session_cookie_name)if not val:return self.session_class()max_age = total_seconds(app.permanent_session_lifetime)try:data = s.loads(val, max_age=max_age)return self.session_class(data)except BadSignature:return self.session_class()

上述代码中通过get_signing_serializer拿到序列化器，通过val = request.cookies.get(app.session_cookie_name)获取浏览器Cookie的session键对应的值，然后通过data = s.loads(val, max_age=max_age)获取session数据，以下是数据格式

我们通过如下代码进行设置

session['k1'] = 123session['k2'] = 456

然后如下是输出格式：
val
eyJrMSI6MTIzLCJrMiI6NDU2fQ.DcrHQQ.WGPBpjRyamwNVxWKU7CM_YB8w4

data
{‘k1’: 123, ‘k2’: 456}

浏览器Cookie的键值对

session=eyJrMSI6MTIzLCJrMiI6NDU2fQ.DcrHQQ.WGPBpjRyamwNVxWKU7CM_YB8w4A

然后在open_session中进行如下操作

return self.session_class(data)

session_class = SecureCookieSession

是构造了一个SecureCookieSession对象，跟踪代码如下

class SecureCookieSession(CallbackDict, SessionMixin):"""Base class for sessions based on signed cookies."""def __init__(self, initial=None):def on_update(self):self.modified = TrueCallbackDict.__init__(self, initial, on_update)self.modified = False

打印出来这个对象输出如下：<SecureCookieSession {'k1': 123, 'k2': 456}>

以上就是self.session = self.app.open_session(self.request)的流程

接下来继续看wsgi_app方法，去看如下代码

response = self.full_dispatch_request()

定位到如下代码

return self.finalize_request(rv)

response = self.process_response(response)

然后在process_response方法中看看如何进行保存session的

self.save_session(ctx.session, response)

    def save_session(self, session, response):return self.session_interface.save_session(self, session, response)

最后执行如下的方法

   def save_session(self, app, session, response):domain = self.get_cookie_domain(app)path = self.get_cookie_path(app)if not session:if session.modified:response.delete_cookie(app.session_cookie_name,domain=domain, path=path)returnif not self.should_set_cookie(app, session):returnhttponly = 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)

通过not self.should_set_cookie(app, session)进行判断是不是进行了session.modified可以修改操作
然后通过后，执行保存

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)

序列化dict(session)，然后写回set_cookie即可

以上是flask的session源码部分的分析

接下里我们结合flask-session,保存redis进行简单分析

通过pip3 install redis 和pip3 install flask_session安装

我们通过如下代码进行使用

def create_app():app = Flask(__name__)app.config.from_object('settings.DevelopmentConfig')app.register_blueprint(account.account)app.register_blueprint(home.home)# 将session替换成redis sessionSession(app)return app

在 Session(app)这句代码中，进行了如下的初始化操作

    def __init__(self, app=None):self.app = appif app is not None:self.init_app(app)def init_app(self, app):app.session_interface = self._get_interface(app)

然后在_get_interface方法中去设置自己的配置
如下是_get_interface方法全部代码

    def _get_interface(self, app):config = app.config.copy()config.setdefault('SESSION_TYPE', 'null')config.setdefault('SESSION_PERMANENT', True)config.setdefault('SESSION_USE_SIGNER', False)config.setdefault('SESSION_KEY_PREFIX', 'session:')config.setdefault('SESSION_REDIS', None)config.setdefault('SESSION_MEMCACHED', None)config.setdefault('SESSION_FILE_DIR',os.path.join(os.getcwd(), 'flask_session'))config.setdefault('SESSION_FILE_THRESHOLD', 500)config.setdefault('SESSION_FILE_MODE', 384)config.setdefault('SESSION_MONGODB', None)config.setdefault('SESSION_MONGODB_DB', 'flask_session')config.setdefault('SESSION_MONGODB_COLLECT', 'sessions')config.setdefault('SESSION_SQLALCHEMY', None)config.setdefault('SESSION_SQLALCHEMY_TABLE', 'sessions')if config['SESSION_TYPE'] == 'redis':session_interface = RedisSessionInterface(config['SESSION_REDIS'], config['SESSION_KEY_PREFIX'],config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])elif config['SESSION_TYPE'] == 'memcached':session_interface = MemcachedSessionInterface(config['SESSION_MEMCACHED'], config['SESSION_KEY_PREFIX'],config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])elif config['SESSION_TYPE'] == 'filesystem':session_interface = FileSystemSessionInterface(config['SESSION_FILE_DIR'], config['SESSION_FILE_THRESHOLD'],config['SESSION_FILE_MODE'], config['SESSION_KEY_PREFIX'],config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])elif config['SESSION_TYPE'] == 'mongodb':session_interface = MongoDBSessionInterface(config['SESSION_MONGODB'], config['SESSION_MONGODB_DB'],config['SESSION_MONGODB_COLLECT'],config['SESSION_KEY_PREFIX'], config['SESSION_USE_SIGNER'],config['SESSION_PERMANENT'])elif config['SESSION_TYPE'] == 'sqlalchemy':session_interface = SqlAlchemySessionInterface(app, config['SESSION_SQLALCHEMY'],config['SESSION_SQLALCHEMY_TABLE'],config['SESSION_KEY_PREFIX'], config['SESSION_USE_SIGNER'],config['SESSION_PERMANENT'])else:session_interface = NullSessionInterface()return session_interface

看如下这几句代码，我们在项目中配置的

SESSION_TYPE = "redis"
SESSION_REDIS = Redis(host='192.168.0.94', port='6379')

会生成RedisSessionInterface实例对象，如下是代码

        if config['SESSION_TYPE'] == 'redis':session_interface = RedisSessionInterface(config['SESSION_REDIS'], config['SESSION_KEY_PREFIX'],config['SESSION_USE_SIGNER'], config['SESSION_PERMANENT'])

然后flask_session库构造了自己的方法，去open_session和save_session

   def open_session(self, app, request):sid = request.cookies.get(app.session_cookie_name)if not sid:sid = self._generate_sid()return self.session_class(sid=sid, permanent=self.permanent)if self.use_signer:signer = self._get_signer(app)if signer is None:return Nonetry:sid_as_bytes = signer.unsign(sid)sid = sid_as_bytes.decode()except BadSignature:sid = self._generate_sid()return self.session_class(sid=sid, permanent=self.permanent)if not PY2 and not isinstance(sid, text_type):sid = sid.decode('utf-8', 'strict')val = self.redis.get(self.key_prefix + sid)if val is not None:try:data = self.serializer.loads(val)return self.session_class(data, sid=sid)except:return self.session_class(sid=sid, permanent=self.permanent)return self.session_class(sid=sid, permanent=self.permanent)def save_session(self, app, session, response):domain = self.get_cookie_domain(app)path = self.get_cookie_path(app)if not session:if session.modified:self.redis.delete(self.key_prefix + session.sid)response.delete_cookie(app.session_cookie_name,domain=domain, path=path)returnhttponly = self.get_cookie_httponly(app)secure = self.get_cookie_secure(app)expires = self.get_expiration_time(app, session)val = self.serializer.dumps(dict(session))self.redis.setex(name=self.key_prefix + session.sid, value=val,time=total_seconds(app.permanent_session_lifetime))if self.use_signer:session_id = self._get_signer(app).sign(want_bytes(session.sid))else:session_id = session.sidresponse.set_cookie(app.session_cookie_name, session_id,expires=expires, httponly=httponly,domain=domain, path=path, secure=secure)

这篇关于Flask---session源码分析的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！

---