rescue_from ActionController::RoutingError doesn't work

Question

I'm trying to rescue from ActionController::RoutingError and I can't get it to work. I tried almost everything that I could find online, including rescue_from ActionController::RoutingError in Rails 4. I have an errors controller and error pages. I got to work cancan access denied and RecordNotFound, but I can solve the RoutingError.

For cancan I use this inside application_controller.rb

rescue_from CanCan::AccessDenied do
    render template: 'errors/error_403', status: 403
  end

and I have this in my routes:

match "/404", to: "errors#error_404", via: :all

If I do the same thing for RoutingError it won't work.

I've also tried match '*path', :to => "errors#error_404" but I get erors.

How can I solve this?

Edit: If I do the same thing for RoutingError as for access denied:

    rescue_from ActionController::RoutingError do
       render template: 'errors/error_404', status: 404
    end

it won't work.

Answer 1

The ActionController::RoutingError is raised when Rails tries to match the request with a route. This happens before Rails even initializes a controller - thus your ApplicationController never has a chance to rescue the exception.

Instead the Rails default exceptions_app kicks in - note that this is an app in the Rack sense - it takes a ENV hash with a request and returns a response - in this case the static /public/404.html file.

What you can do is have your Rails app handle rendering the error pages dynamically instead:

# config/application.rb
config.exceptions_app = self.routes # a Rack Application

# config/routes.rb
match "/404", :to => "errors#not_found", :via => :all
match "/500", :to => "errors#internal_server_error", :via => :all

You would then setup a specific controller to handle the error pages - don't do this in your ApplicationController class as you would be adding a not_found and internal_server_error method to all your controllers!

class ErrorsController < ActionController::Base
  protect_from_forgery with: :null_session

  def not_found
    render(status: 404)
  end

  def internal_server_error
    render(status: 500)
  end
end

Code borrowed from Matt Brictson: Dynamic Rails Error Pages - read it for the full rundown.