Detecting whether a Flask app handles a URL

Question

I have a case for having a preliminary frontend Flask app before continuing to my main app.

I've implemented it using a "middleware" pattern:

class MyMiddleware(object):
    def __init__(self, main_app, pre_app):
        self.main_app = main_app
        self.pre_app = pre_app

    def __call__(self, environ, start_response):
        # check whether pre_app has a rule for this URL
        with self.pre_app.request_context(environ) as ctx:
            if ctx.request.url_rule is None:
                return self.main_app(environ, start_response)

        return self.pre_app(environ, start_response)

Is there a more idiomatic way of doing this, without creating a context just to check whether the URL is handled by the app? I want to maintain the flexibility of keeping two apps.

Answer 1

Each flask.Flask app has a url_map property - which is a werkzeug.routing.Map. You could just run bind_to_environ and use the test method from MapAdapter:

if self.pre_app.url_map.bind_to_environ(environ).test(environ['PATH_INFO']):
    return self.pre_app(environ, start_response)

return self.main_app(environ, start_response)

I don't know that I'd call it "more idiomatic" but it is another way of handling your use case.