Action and controller are lost when an error is handled by ActionDispatch::ShowExceptions

[fsateler]

When ActionDispatch::ShowExceptions captures an error, it renders the appropriate error page and then sets the correct exit status. To do this, it reuses the rack env (wrapped in a Request), and resets the path_info to /#{status} and runs that request with an exceptions_app. This may[1] result in the controller and action being overriden, since the exceptions_app will parse the path info and route to a different controller/action. This results in the wrong labels being added to the prometheus metrics.

[1] At least, when an exception app is configured with config.exceptions_app = routes.

We have worked around this locally by re-parsing the path when setting the labels:

  def default_labels(env, result)
    labels = super
    if labels[:controller] == "errors"
      params = begin
        Rails.application.routes.recognize_path(env["REQUEST_PATH"])
      rescue ActionController::RoutingError
        nil # Si no podemos parsear no reemplazamos nomas
      end
      if params
        labels[:controller] = params[:controller]
        labels[:action] = params[:action]
      end
    end
    labels
  end

I don't know how to cleanly fix this. This only works for us because we know the "errors" controller is only used for error routing.