gistfile1.rb

class BridgeController < ApplicationController
  rescue_from YouShallNotPassException, :status => 403, :error_code => 'no_way' do |exception, response|
    response[:where] = exception.backtrace.first
  end

  # Assuming a route like this:
  #   map.connect "/khazad_dum/bridge/cross", :controller => :bridge, :action => :cross, :format => :json
  # then this will return a HTTP 403 error with the following JSON object as body:
  #   {"error_code": "no_way", "message": "No balrogs past this point please",
  #    "where": "bridge_controller.rb:12:in `cross'"}
  def cross
    raise YouShallNotPassException, "No balrogs past this point please" if current_user.is_a?(Balrog)
  end
end