Rails: how can I access the request object outside a helper or controller?

In my application_helper.rb file I have a function like this:

def internal_request?
  server_name = request.env['SERVER_NAME']
  [plus more code...]
end

This function is needed in controllers, models, and views. So, I put this code in a utility function file in the lib/ directory. However, this did not work: I got complaints about request not being defined.

How can I access the request object in a file in the lib/ directory?