如何在运行时替换装饰器？

Question

I'm trying to adapt another StackOverflow answer on conditionally applying a decorator to only require login for a specific environment (eventually a staging environment, but development until I get this working). Toward that end, I started with the following

auth = HTTPDigestAuth()

def login_required(dec, condition):
    def decorator(func):
        if not condition:
            return func
        return dec(func)
    return decorator

@bp.route('/auth')
@login_required(auth.login_required, current_app.config['ENV'] != 'development')
def auth_route():
    return current_app.config['ENV']

When I launch the server, I get a RuntimeError: Working outside of application context error. After trying a few suggestions from an earlier version of this question, I got the RuntimeError to disappear, but the decorator still isn't being correctly applied when I want. Here's the current version:

def login_required(dec):
    def decorator(func):
        if not os.environ.get('ENV') != 'development':
            return func
        return dec(func)
    return decorator

@bp.route('/auth')
@login_required(auth.login_required)
def auth_route():
    return current_app.config['ENV']

This never returns the auth.login_reqired function. It always lets the browser in without authentication.

So, I tried changing the condition to

if not os.environ.get('ENV') is not None:

and then the authentication shows up.

Yes, I've done an export ENV=development in the shell and confirmed it with the env command. But even then it's not reading the environment variable as I would expect.

Perhaps this is simply the wrong way to go about it? My final goal is to require authentication on one particular environment. Is this possible with the path I'm on? Is it possible at all?

Answer 1

current_app is a context local proxy that only has meaning during a request. This means you can't use it before a request, ie as part of a decorator.

Using current_app is generally good practice because Flask allows multiple apps to be configured. In your specific case however, it isn't actually necessary. For instance, the following would work, because it uses the app object directly instead of the current_app proxy:

from yourpackage import app

@bp.route('/auth')
@login_required(auth.login_required, app.config['ENV'] != 'development')
def auth():
    return current_app.config['ENV']

Answer 2

Let me paste something from documentation of Flask

Lifetime of the Context The application context is created and destroyed as necessary. When a Flask application begins handling a request, it pushes an application context and a request context. When the request ends it pops the request context then the application context. Typically, an application context will have the same lifetime as a request.

Now let's consider how decorators work. It is just a syntactic sugar see this answer .

So the login_required decorator is called while the module is loaded and the current app is not available yet because it's not handling request.

I would do this way, move condition to the decorator function (relating to your example). It will be called while the request will be handled so you should have access to current_app.