源码如下

class NullSession(SecureCookieSession):
    """Class used to generate nicer error messages if sessions are not
    available.  Will still allow read-only access to the empty session
    but fail on setting.
    """

    def _fail(self, *args, **kwargs):
        raise RuntimeError(
            "The session is unavailable because no secret "
            "key was set.  Set the secret_key on the "
            "application to something unique and secret."
        )

    __setitem__ = __delitem__ = clear = pop = popitem = update = setdefault = _fail
    del _fail

_fial是检查是否设置了secret，这个一般在app.py中设置

这个secret类似于对session的一个加密的salt，泄露这个攻击者可以通过使用相同的盐来构造cookie来进行攻击。

app.config["SECRET_KEY"] = "SECRET_WRITE_HERE"

顺便看了

class SecureCookieSessionInterface(SessionInterface):
    """The default session interface that stores sessions in signed cookies
    through the :mod:`itsdangerous` module.
    """

    #: the salt that should be applied on top of the secret key for the
    #: signing of cookie based sessions.
    salt = "cookie-session"
    #: the hash function to use for the signature.  The default is sha1
    digest_method = staticmethod(hashlib.sha1)
    #: the name of the itsdangerous supported key derivation.  The default
    #: is hmac.
    key_derivation = "hmac"
    #: A python serializer for the payload.  The default is a compact
    #: JSON derived serializer with support for some extra Python types
    #: such as datetime objects or tuples.
    serializer = session_json_serializer
    session_class = SecureCookieSession

    def get_signing_serializer(self, app):
        if not app.secret_key:
            return None
        signer_kwargs = dict(
            key_derivation=self.key_derivation, digest_method=self.digest_method
        )
        return URLSafeTimedSerializer(
            app.secret_key,
            salt=self.salt,
            serializer=self.serializer,
            signer_kwargs=signer_kwargs,
        )

    def open_session(self, app, request):
        s = self.get_signing_serializer(app)
        if s is None:
            return None
        val = 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()

    def save_session(self, app, session, response):
        domain = self.get_cookie_domain(app)
        path = self.get_cookie_path(app)

        # If the session is modified to be empty, remove the cookie.
        # If the session is empty, return without setting the cookie.
        if not session:
            if session.modified:
                response.delete_cookie(
                    app.session_cookie_name, domain=domain, path=path
                )

            return

        # Add a "Vary: Cookie" header if the session was accessed at all.
        if session.accessed:
            response.vary.add("Cookie")

        if not self.should_set_cookie(app, session):
            return

        httponly = self.get_cookie_httponly(app)
        secure = self.get_cookie_secure(app)
        samesite = self.get_cookie_samesite(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,
            samesite=samesite,
        )

由于开发过很多次了，这段源码还是比较浅显易懂的。

自卑

什么时候才能写代码和大佬一样让人赏心悦目(x