How to handle exception that is generated in rack middleware before it reach rails app?

[drchanimal]

I know that we can use config.exception_app to set up custom exception handling and also use rescue_from. However, I have an issue that there is malformed request (testing generated request) that caused Rails Rack middleware to throw an exception when Rack's parse_query method.  Here is the detail of the problem: http://stackoverflow.com/questions/17796878/how-to-handle-exception-generated-from-rack-before-reaching-your-rails-app

The issue is that it failed in rails Rack::MethodOverride with is before ActionDispatch::ShowExceptions middleware and way before it even got to the rails app.

So how do we handle the exception gracefully without showing the stack trace?

Thanks for your help.