rescue.rb

module ActionController #:nodoc:
  # Actions that fail to perform as expected throw exceptions. These exceptions can either be rescued for the public view 
  # (with a nice user-friendly explanation) or for the developers view (with tons of debugging information). The developers view
  # is already implemented by the Action Controller, but the public view should be tailored to your specific application. So too
  # could the decision on whether something is a public or a developer request.
  #
  # You can tailor the rescuing behavior and appearance by overwriting the following two stub methods.
  module Rescue
    def self.included(base) #:nodoc:
      base.extend(ClassMethods)
      base.class_eval do
        alias_method :perform_action_without_rescue, :perform_action
        alias_method :perform_action, :perform_action_with_rescue
      end
    end

    module ClassMethods #:nodoc:
      def process_with_exception(request, response, exception)
        new.process(request, response, :rescue_action, exception)
      end
    end

    protected
      # Exception handler called when the performance of an action raises an exception.
      def rescue_action(exception)
        log_error(exception) if logger
        erase_results if performed?

        if consider_all_requests_local || local_request?
          rescue_action_locally(exception)
        else
          rescue_action_in_public(exception)
        end
      end

      # Overwrite to implement custom logging of errors. By default logs as fatal.
      def log_error(exception) #:doc:
        if ActionView::TemplateError === exception
          logger.fatal(exception.to_s)
        else
          logger.fatal(
            "\n\n#{exception.class} (#{exception.message}):\n    " + 
            clean_backtrace(exception).join("\n    ") + 
            "\n\n"
          )
        end
      end

      # Overwrite to implement public exception handling (for requests answering false to <tt>local_request?</tt>).
      def rescue_action_in_public(exception) #:doc:
        case exception
          when RoutingError, UnknownAction then
            render_text(IO.read(File.join(RAILS_ROOT, 'public', '404.html')), "404 Not Found")
          else render_text "<html><body><h1>Application error (Rails)</h1></body></html>"
        end
      end

      # Overwrite to expand the meaning of a local request in order to show local rescues on other occurrences than
      # the remote IP being 127.0.0.1. For example, this could include the IP of the developer machine when debugging
      # remotely.
      def local_request? #:doc:
        [@request.remote_addr, @request.remote_ip] == ["127.0.0.1"] * 2
      end

      # Renders a detailed diagnostics screen on action exceptions. 
      def rescue_action_locally(exception)
        add_variables_to_assigns
        @template.instance_variable_set("@exception", exception)
        @template.instance_variable_set("@rescues_path", File.dirname(__FILE__) + "/templates/rescues/")    
        @template.send(:assign_variables_from_controller)

        @template.instance_variable_set("@contents", @template.render_file(template_path_for_local_rescue(exception), false))
    
        @headers["Content-Type"] = "text/html"
        render_file(rescues_path("layout"), response_code_for_rescue(exception))
      end
    
    private
      def perform_action_with_rescue #:nodoc:
        begin
          perform_action_without_rescue
        rescue Object => exception
          if defined?(Breakpoint) && @params["BP-RETRY"]
            msg = exception.backtrace.first
            if md = /^(.+?):(\d+)(?::in `(.+)')?$/.match(msg) then
              origin_file, origin_line = md[1], md[2].to_i

              set_trace_func(lambda do |type, file, line, method, context, klass|
                if file == origin_file and line == origin_line then
                  set_trace_func(nil)
                  @params["BP-RETRY"] = false

                  callstack = caller
                  callstack.slice!(0) if callstack.first["rescue.rb"]
                  file, line, method = *callstack.first.match(/^(.+?):(\d+)(?::in `(.*?)')?/).captures

                  message = "Exception at #{file}:#{line}#{" in `#{method}'" if method}." # `´ ( for ruby-mode)

                  Breakpoint.handle_breakpoint(context, message, file, line)
                end
              end)

              retry
            end
          end

          rescue_action(exception)
        end
      end

      def rescues_path(template_name)
        File.dirname(__FILE__) + "/templates/rescues/#{template_name}.rhtml"
      end

      def template_path_for_local_rescue(exception)
        rescues_path(
          case exception
            when MissingTemplate then "missing_template"
            when RoutingError then "routing_error"
            when UnknownAction   then "unknown_action"
            when ActionView::TemplateError then "template_error"
            else "diagnostics"
          end
        )
      end
      
      def response_code_for_rescue(exception)
        case exception
          when UnknownAction, RoutingError then "404 Page Not Found"
          else "500 Internal Error"
        end
      end
      
      def clean_backtrace(exception)
        exception.backtrace.collect { |line| Object.const_defined?(:RAILS_ROOT) ? line.gsub(RAILS_ROOT, "") : line }
      end
  end
end