Exceptions in before_request methods prevent later before_request methods from running

[skylerberg]

Expected Behavior

All methods added with @app.before_request should be run.

Paste a minimal example that causes the problem.

Actual Behavior

If an exception occurs in a single @app.before_request method, all following @app.before_request methods will not run.

Context

For a detailed example of this causing an issue, see GoogleCloudPlatform/flask-talisman#22.

In summary, Flask-Talisman does setup in an @app.before_request method which is expected to be done by the time it runs an @app.after_request method. However, if an exception occurs in an @app.before_request method that runs before Flask-Talisman's, and that exception is caught by an @app.errorhandler, then Flask-Talisman's @app.after_request method can be run without the setup work ever being done.

[davidism]

Changing Flask's behavior would be incorrect, as before request handlers are allowed to exit early and return a response (an exception is a response). This would just cause all the before handlers that expect earlier handlers to run to fail too.