base.rb

require 'action_controller/mime_type'
require 'action_controller/request'
require 'action_controller/response'
require 'action_controller/routing'
require 'action_controller/resources'
require 'action_controller/url_rewriter'
require 'action_controller/status_codes'
require 'action_view/template_finder'
require 'drb'
require 'set'

module ActionController #:nodoc:
  class ActionControllerError < StandardError #:nodoc:
  end

  class SessionRestoreError < ActionControllerError #:nodoc:
  end

  class MissingTemplate < ActionControllerError #:nodoc:
  end

  class RenderError < ActionControllerError #:nodoc:
  end

  class RoutingError < ActionControllerError #:nodoc:
    attr_reader :failures
    def initialize(message, failures=[])
      super(message)
      @failures = failures
    end
  end

  class MethodNotAllowed < ActionControllerError #:nodoc:
    attr_reader :allowed_methods

    def initialize(*allowed_methods)
      super("Only #{allowed_methods.to_sentence} requests are allowed.")
      @allowed_methods = allowed_methods
    end

    def allowed_methods_header
      allowed_methods.map { |method_symbol| method_symbol.to_s.upcase } * ', '
    end

    def handle_response!(response)
      response.headers['Allow'] ||= allowed_methods_header
    end
  end

  class NotImplemented < MethodNotAllowed #:nodoc:
  end

  class UnknownController < ActionControllerError #:nodoc:
  end

  class UnknownAction < ActionControllerError #:nodoc:
  end

  class MissingFile < ActionControllerError #:nodoc:
  end

  class RenderError < ActionControllerError #:nodoc:
  end

  class SessionOverflowError < ActionControllerError #:nodoc:
    DEFAULT_MESSAGE = 'Your session data is larger than the data column in which it is to be stored. You must increase the size of your data column if you intend to store large data.'

    def initialize(message = nil)
      super(message || DEFAULT_MESSAGE)
    end
  end

  class DoubleRenderError < ActionControllerError #:nodoc:
    DEFAULT_MESSAGE = "Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like \"redirect_to(...) and return\"."

    def initialize(message = nil)
      super(message || DEFAULT_MESSAGE)
    end
  end

  class RedirectBackError < ActionControllerError #:nodoc:
    DEFAULT_MESSAGE = 'No HTTP_REFERER was set in the request to this action, so redirect_to :back could not be called successfully. If this is a test, make sure to specify request.env["HTTP_REFERER"].'

    def initialize(message = nil)
      super(message || DEFAULT_MESSAGE)
    end
  end

  class UnknownHttpMethod < ActionControllerError #:nodoc:
  end

  # Action Controllers are the core of a web request in Rails. They are made up of one or more actions that are executed
  # on request and then either render a template or redirect to another action. An action is defined as a public method
  # on the controller, which will automatically be made accessible to the web-server through Rails Routes.
  #
  # A sample controller could look like this:
  #
  #   class GuestBookController < ActionController::Base
  #     def index
  #       @entries = Entry.find(:all)
  #     end
  #
  #     def sign
  #       Entry.create(params[:entry])
  #       redirect_to :action => "index"
  #     end
  #   end
  #
  # Actions, by default, render a template in the <tt>app/views</tt> directory corresponding to the name of the controller and action
  # after executing code in the action. For example, the +index+ action of the +GuestBookController+  would render the
  # template <tt>app/views/guestbook/index.erb</tt> by default after populating the <tt>@entries</tt> instance variable.
  #
  # Unlike index, the sign action will not render a template. After performing its main purpose (creating a
  # new entry in the guest book), it initiates a redirect instead. This redirect works by returning an external
  # "302 Moved" HTTP response that takes the user to the index action.
  #
  # The index and sign represent the two basic action archetypes used in Action Controllers. Get-and-show and do-and-redirect.
  # Most actions are variations of these themes.
  #
  # == Requests
  #
  # Requests are processed by the Action Controller framework by extracting the value of the "action" key in the request parameters.
  # This value should hold the name of the action to be performed. Once the action has been identified, the remaining
  # request parameters, the session (if one is available), and the full request with all the http headers are made available to
  # the action through instance variables. Then the action is performed.
  #
  # The full request object is available with the request accessor and is primarily used to query for http headers. These queries
  # are made by accessing the environment hash, like this:
  #
  #   def server_ip
  #     location = request.env["SERVER_ADDR"]
  #     render :text => "This server hosted at #{location}"
  #   end
  #
  # == Parameters
  #
  # All request parameters, whether they come from a GET or POST request, or from the URL, are available through the params method
  # which returns a hash. For example, an action that was performed through <tt>/weblog/list?category=All&limit=5</tt> will include
  # <tt>{ "category" => "All", "limit" => 5 }</tt> in params.
  #
  # It's also possible to construct multi-dimensional parameter hashes by specifying keys using brackets, such as:
  #
  #   <input type="text" name="post[name]" value="david">
  #   <input type="text" name="post[address]" value="hyacintvej">
  #
  # A request stemming from a form holding these inputs will include <tt>{ "post" => { "name" => "david", "address" => "hyacintvej" } }</tt>.
  # If the address input had been named "post[address][street]", the params would have included
  # <tt>{ "post" => { "address" => { "street" => "hyacintvej" } } }</tt>. There's no limit to the depth of the nesting.
  #
  # == Sessions
  #
  # Sessions allows you to store objects in between requests. This is useful for objects that are not yet ready to be persisted,
  # such as a Signup object constructed in a multi-paged process, or objects that don't change much and are needed all the time, such
  # as a User object for a system that requires login. The session should not be used, however, as a cache for objects where it's likely
  # they could be changed unknowingly. It's usually too much work to keep it all synchronized -- something databases already excel at.
  #
  # You can place objects in the session by using the <tt>session</tt> method, which accesses a hash:
  #
  #   session[:person] = Person.authenticate(user_name, password)
  #
  # And retrieved again through the same hash:
  #
  #   Hello #{session[:person]}
  #
  # For removing objects from the session, you can either assign a single key to nil, like <tt>session[:person] = nil</tt>, or you can
  # remove the entire session with reset_session.
  #
  # Sessions are stored in a browser cookie that's cryptographically signed, but unencrypted, by default. This prevents
  # the user from tampering with the session but also allows him to see its contents.
  #
  # Do not put secret information in session!
  #
  # Other options for session storage are:
  #
  # ActiveRecordStore: sessions are stored in your database, which works better than PStore with multiple app servers and,
  # unlike CookieStore, hides your session contents from the user. To use ActiveRecordStore, set
  #
  #   config.action_controller.session_store = :active_record_store
  #
  # in your <tt>environment.rb</tt> and run <tt>rake db:sessions:create</tt>.
  #
  # MemCacheStore: sessions are stored as entries in your memcached cache.  Set the session store type in <tt>environment.rb</tt>:
  #
  #   config.action_controller.session_store = :mem_cache_store
  #
  #  This assumes that memcached has been installed and configured properly.  See the MemCacheStore docs for more information.
  #
  # == Responses
  #
  # Each action results in a response, which holds the headers and document to be sent to the user's browser. The actual response
  # object is generated automatically through the use of renders and redirects and requires no user intervention.
  #
  # == Renders
  #
  # Action Controller sends content to the user by using one of five rendering methods. The most versatile and common is the rendering
  # of a template. Included in the Action Pack is the Action View, which enables rendering of ERb templates. It's automatically configured.
  # The controller passes objects to the view by assigning instance variables:
  #
  #   def show
  #     @post = Post.find(params[:id])
  #   end
  #
  # Which are then automatically available to the view:
  #
  #   Title: <%= @post.title %>
  #
  # You don't have to rely on the automated rendering. Especially actions that could result in the rendering of different templates will use
  # the manual rendering methods:
  #
  #   def search
  #     @results = Search.find(params[:query])
  #     case @results
  #       when 0 then render :action => "no_results"
  #       when 1 then render :action => "show"
  #       when 2..10 then render :action => "show_many"
  #     end
  #   end
  #
  # Read more about writing ERb and Builder templates in link:classes/ActionView/Base.html.
  #
  # == Redirects
  #
  # Redirects are used to move from one action to another. For example, after a <tt>create</tt> action, which stores a blog entry to a database,
  # we might like to show the user the new entry. Because we're following good DRY principles (Don't Repeat Yourself), we're going to reuse (and redirect to)
  # a <tt>show</tt> action that we'll assume has already been created. The code might look like this:
  #
  #   def create
  #     @entry = Entry.new(params[:entry])
  #     if @entry.save
  #       # The entry was saved correctly, redirect to show
  #       redirect_to :action => 'show', :id => @entry.id
  #     else
  #       # things didn't go so well, do something else
  #     end
  #   end
  #
  # In this case, after saving our new entry to the database, the user is redirected to the <tt>show</tt> method which is then executed.
  #
  # == Calling multiple redirects or renders
  #
  # An action may contain only a single render or a single redirect. Attempting to try to do either again will result in a DoubleRenderError:
  #
  #   def do_something
  #     redirect_to :action => "elsewhere"
  #     render :action => "overthere" # raises DoubleRenderError
  #   end
  #
  # If you need to redirect on the condition of something, then be sure to add "and return" to halt execution.
  #
  #   def do_something
  #     redirect_to(:action => "elsewhere") and return if monkeys.nil?
  #     render :action => "overthere" # won't be called unless monkeys is nil
  #   end
  #
  class Base
    DEFAULT_RENDER_STATUS_CODE = "200 OK"

    include StatusCodes

    # Determines whether the view has access to controller internals @request, @response, @session, and @template.
    # By default, it does.
    @@view_controller_internals = true
    cattr_accessor :view_controller_internals

    # Protected instance variable cache
    @@protected_variables_cache = nil
    cattr_accessor :protected_variables_cache

    # Prepends all the URL-generating helpers from AssetHelper. This makes it possible to easily move javascripts, stylesheets,
    # and images to a dedicated asset server away from the main web server. Example:
    #   ActionController::Base.asset_host = "http://assets.example.com"
    @@asset_host = ""
    cattr_accessor :asset_host

    # All requests are considered local by default, so everyone will be exposed to detailed debugging screens on errors.
    # When the application is ready to go public, this should be set to false, and the protected method <tt>local_request?</tt>
    # should instead be implemented in the controller to determine when debugging screens should be shown.
    @@consider_all_requests_local = true
    cattr_accessor :consider_all_requests_local

    # Enable or disable the collection of failure information for RoutingErrors.
    # This information can be extremely useful when tweaking custom routes, but is
    # pointless once routes have been tested and verified.
    @@debug_routes = true
    cattr_accessor :debug_routes

    # Controls whether the application is thread-safe, so multi-threaded servers like WEBrick know whether to apply a mutex
    # around the performance of each action. Action Pack and Active Record are by default thread-safe, but many applications
    # may not be. Turned off by default.
    @@allow_concurrency = false
    cattr_accessor :allow_concurrency

    # Modern REST web services often need to submit complex data to the web application.
    # The param_parsers hash lets you register handlers which will process the http body and add parameters to the
    # <tt>params</tt> hash. These handlers are invoked for post and put requests.
    #
    # By default application/xml is enabled. A XmlSimple class with the same param name as the root will be instantiated
    # in the <tt>params</tt>. This allows XML requests to mask themselves as regular form submissions, so you can have one
    # action serve both regular forms and web service requests.
    #
    # Example of doing your own parser for a custom content type:
    #
    #   ActionController::Base.param_parsers[Mime::Type.lookup('application/atom+xml')] = Proc.new do |data|
    #      node = REXML::Document.new(post)
    #     { node.root.name => node.root }
    #   end
    #
    # Note: Up until release 1.1 of Rails, Action Controller would default to using XmlSimple configured to discard the
    # root node for such requests. The new default is to keep the root, such that "<r><name>David</name></r>" results
    # in params[:r][:name] for "David" instead of params[:name]. To get the old behavior, you can
    # re-register XmlSimple as application/xml handler ike this:
    #
    #   ActionController::Base.param_parsers[Mime::XML] =
    #     Proc.new { |data| XmlSimple.xml_in(data, 'ForceArray' => false) }
    #
    # A YAML parser is also available and can be turned on with:
    #
    #   ActionController::Base.param_parsers[Mime::YAML] = :yaml
    @@param_parsers = { Mime::MULTIPART_FORM => :multipart_form,
                        Mime::URL_ENCODED_FORM => :url_encoded_form,
                        Mime::XML => :xml_simple }
    cattr_accessor :param_parsers

    # Controls the default charset for all renders.
    @@default_charset = "utf-8"
    cattr_accessor :default_charset
    
    # The logger is used for generating information on the action run-time (including benchmarking) if available.
    # Can be set to nil for no logging. Compatible with both Ruby's own Logger and Log4r loggers.
    cattr_accessor :logger

    # Determines which template class should be used by ActionController.
    cattr_accessor :template_class

    # Turn on +ignore_missing_templates+ if you want to unit test actions without making the associated templates.
    cattr_accessor :ignore_missing_templates

    # Controls the resource action separator
    @@resource_action_separator = "/"
    cattr_accessor :resource_action_separator
    
    # Sets the token parameter name for RequestForgery.  Calling #protect_from_forgery sets it to :authenticity_token by default
    cattr_accessor :request_forgery_protection_token

    # Indicates whether or not optimise the generated named
    # route helper methods
    cattr_accessor :optimise_named_routes
    self.optimise_named_routes = true

    # Controls whether request forgergy protection is turned on or not. Turned off by default only in test mode.
    class_inheritable_accessor :allow_forgery_protection
    self.allow_forgery_protection = true

    # Holds the request object that's primarily used to get environment variables through access like
    # <tt>request.env["REQUEST_URI"]</tt>.
    attr_internal :request

    # Holds a hash of all the GET, POST, and Url parameters passed to the action. Accessed like <tt>params["post_id"]</tt>
    # to get the post_id. No type casts are made, so all values are returned as strings.
    attr_internal :params

    # Holds the response object that's primarily used to set additional HTTP headers through access like
    # <tt>response.headers["Cache-Control"] = "no-cache"</tt>. Can also be used to access the final body HTML after a template
    # has been rendered through response.body -- useful for <tt>after_filter</tt>s that wants to manipulate the output,
    # such as a OutputCompressionFilter.
    attr_internal :response

    # Holds a hash of objects in the session. Accessed like <tt>session[:person]</tt> to get the object tied to the "person"
    # key. The session will hold any type of object as values, but the key should be a string or symbol.
    attr_internal :session

    # Holds a hash of header names and values. Accessed like <tt>headers["Cache-Control"]</tt> to get the value of the Cache-Control
    # directive. Values should always be specified as strings.
    attr_internal :headers

    # Holds the hash of variables that are passed on to the template class to be made available to the view. This hash
    # is generated by taking a snapshot of all the instance variables in the current scope just before a template is rendered.
    attr_accessor :assigns

    # Returns the name of the action this controller is processing.
    attr_accessor :action_name

    # Templates that are exempt from layouts
    @@exempt_from_layout = Set.new([/\.rjs$/])

    class << self
      # Factory for the standard create, process loop where the controller is discarded after processing.
      def process(request, response) #:nodoc:
        new.process(request, response)
      end

      # Converts the class name from something like "OneModule::TwoModule::NeatController" to "NeatController".
      def controller_class_name
        @controller_class_name ||= name.demodulize
      end

      # Converts the class name from something like "OneModule::TwoModule::NeatController" to "neat".
      def controller_name
        @controller_name ||= controller_class_name.sub(/Controller$/, '').underscore
      end

      # Converts the class name from something like "OneModule::TwoModule::NeatController" to "one_module/two_module/neat".
      def controller_path
        @controller_path ||= name.gsub(/Controller$/, '').underscore
      end

      # Return an array containing the names of public methods that have been marked hidden from the action processor.
      # By default, all methods defined in ActionController::Base and included modules are hidden.
      # More methods can be hidden using <tt>hide_actions</tt>.
      def hidden_actions
        unless read_inheritable_attribute(:hidden_actions)
          write_inheritable_attribute(:hidden_actions, ActionController::Base.public_instance_methods.map(&:to_s))
        end

        read_inheritable_attribute(:hidden_actions)
      end

      # Hide each of the given methods from being callable as actions.
      def hide_action(*names)
        write_inheritable_attribute(:hidden_actions, hidden_actions | names.map(&:to_s))
      end

      ## View load paths determine the bases from which template references can be made. So a call to
      ## render("test/template") will be looked up in the view load paths array and the closest match will be
      ## returned.
      def view_paths
        @view_paths || superclass.view_paths
      end

      def view_paths=(value)
        @view_paths = value
        ActionView::TemplateFinder.process_view_paths(value)
      end

      # Adds a view_path to the front of the view_paths array.
      # If the current class has no view paths, copy them from 
      # the superclass.  This change will be visible for all future requests.
      #
      #   ArticleController.prepend_view_path("views/default")
      #   ArticleController.prepend_view_path(["views/default", "views/custom"])
      #
      def prepend_view_path(path)
        @view_paths = superclass.view_paths.dup if @view_paths.nil?
        view_paths.unshift(*path)
        ActionView::TemplateFinder.process_view_paths(path)
      end
      
      # Adds a view_path to the end of the view_paths array.
      # If the current class has no view paths, copy them from 
      # the superclass. This change will be visible for all future requests.
      #
      #   ArticleController.append_view_path("views/default")
      #   ArticleController.append_view_path(["views/default", "views/custom"])
      #
      def append_view_path(path)
        @view_paths = superclass.view_paths.dup if @view_paths.nil?
        view_paths.push(*path)
        ActionView::TemplateFinder.process_view_paths(path)
      end
      
      # Replace sensitive parameter data from the request log.
      # Filters parameters that have any of the arguments as a substring.
      # Looks in all subhashes of the param hash for keys to filter.
      # If a block is given, each key and value of the parameter hash and all
      # subhashes is passed to it, the value or key
      # can be replaced using String#replace or similar method.
      #
      # Examples:
      #   filter_parameter_logging
      #   => Does nothing, just slows the logging process down
      #
      #   filter_parameter_logging :password
      #   => replaces the value to all keys matching /password/i with "[FILTERED]"
      #
      #   filter_parameter_logging :foo, "bar"
      #   => replaces the value to all keys matching /foo|bar/i with "[FILTERED]"
      #
      #   filter_parameter_logging { |k,v| v.reverse! if k =~ /secret/i }
      #   => reverses the value to all keys matching /secret/i
      #
      #   filter_parameter_logging(:foo, "bar") { |k,v| v.reverse! if k =~ /secret/i }
      #   => reverses the value to all keys matching /secret/i, and
      #      replaces the value to all keys matching /foo|bar/i with "[FILTERED]"
      def filter_parameter_logging(*filter_words, &block)
        parameter_filter = Regexp.new(filter_words.collect{ |s| s.to_s }.join('|'), true) if filter_words.length > 0

        define_method(:filter_parameters) do |unfiltered_parameters|
          filtered_parameters = {}

          unfiltered_parameters.each do |key, value|
            if key =~ parameter_filter
              filtered_parameters[key] = '[FILTERED]'
            elsif value.is_a?(Hash)
              filtered_parameters[key] = filter_parameters(value)
            elsif block_given?
              key = key.dup
              value = value.dup if value
              yield key, value
              filtered_parameters[key] = value
            else
              filtered_parameters[key] = value
            end
          end

          filtered_parameters
        end
      end

      # Don't render layouts for templates with the given extensions.
      def exempt_from_layout(*extensions)
        regexps = extensions.collect do |extension|
          extension.is_a?(Regexp) ? extension : /\.#{Regexp.escape(extension.to_s)}$/
        end
        @@exempt_from_layout.merge regexps
      end
    end

    public
      # Extracts the action_name from the request parameters and performs that action.
      def process(request, response, method = :perform_action, *arguments) #:nodoc:
        initialize_template_class(response)
        assign_shortcuts(request, response)
        initialize_current_url
        assign_names
        forget_variables_added_to_assigns

        log_processing
        send(method, *arguments)

        assign_default_content_type_and_charset

        response.request = request
        response.prepare! unless component_request?
        response
      ensure
        process_cleanup
      end

      # Returns a URL that has been rewritten according to the options hash and the defined Routes.
      # (For doing a complete redirect, use redirect_to).
      #  
      # <tt>url_for</tt> is used to:
      #  
      # All keys given to url_for are forwarded to the Route module, save for the following:
      # * <tt>:anchor</tt> -- specifies the anchor name to be appended to the path. For example,
      #   <tt>url_for :controller => 'posts', :action => 'show', :id => 10, :anchor => 'comments'</tt>
      #   will produce "/posts/show/10#comments".
      # * <tt>:only_path</tt> --  if true, returns the relative URL (omitting the protocol, host name, and port) (<tt>false</tt> by default)
      # * <tt>:trailing_slash</tt> --  if true, adds a trailing slash, as in "/archive/2005/". Note that this
      #   is currently not recommended since it breaks caching.
      # * <tt>:host</tt> -- overrides the default (current) host if provided.
      # * <tt>:protocol</tt> -- overrides the default (current) protocol if provided.
      # * <tt>:port</tt> -- optionally specify the port to connect to.
      # * <tt>:user</tt> -- Inline HTTP authentication (only plucked out if :password is also present).
      # * <tt>:password</tt> -- Inline HTTP authentication (only plucked out if :user is also present).
      # * <tt>:skip_relative_url_root</tt> -- if true, the url is not constructed using the relative_url_root of the request so the path
      #   will include the web server relative installation directory.
      #
      # The URL is generated from the remaining keys in the hash. A URL contains two key parts: the <base> and a query string.
      # Routes composes a query string as the key/value pairs not included in the <base>.
      #
      # The default Routes setup supports a typical Rails path of "controller/action/id" where action and id are optional, with
      # action defaulting to 'index' when not given. Here are some typical url_for statements and their corresponding URLs:
      #
      #   url_for :controller => 'posts', :action => 'recent'                # => 'proto://host.com/posts/recent'
      #   url_for :controller => 'posts', :action => 'index'                 # => 'proto://host.com/posts'
      #   url_for :controller => 'posts', :action => 'index', :port=>'8033'  # => 'proto://host.com:8033/posts'
      #   url_for :controller => 'posts', :action => 'show', :id => 10       # => 'proto://host.com/posts/show/10'
      #   url_for :controller => 'posts', :user => 'd', :password => '123'   # => 'proto://d:123@host.com/posts'
      #
      # When generating a new URL, missing values may be filled in from the current request's parameters. For example,
      # <tt>url_for :action => 'some_action'</tt> will retain the current controller, as expected. This behavior extends to
      # other parameters, including <tt>:controller</tt>, <tt>:id</tt>, and any other parameters that are placed into a Route's
      # path.
      #  
      # The URL helpers such as <tt>url_for</tt> have a limited form of memory: when generating a new URL, they can look for
      # missing values in the current request's parameters. Routes attempts to guess when a value should and should not be
      # taken from the defaults. There are a few simple rules on how this is performed:
      #
      # * If the controller name begins with a slash, no defaults are used: <tt>url_for :controller => '/home'</tt>
      # * If the controller changes, the action will default to index unless provided
      #
      # The final rule is applied while the URL is being generated and is best illustrated by an example. Let us consider the
      # route given by <tt>map.connect 'people/:last/:first/:action', :action => 'bio', :controller => 'people'</tt>.
      #
      # Suppose that the current URL is "people/hh/david/contacts". Let's consider a few different cases of URLs which are generated
      # from this page.
      #
      # * <tt>url_for :action => 'bio'</tt> -- During the generation of this URL, default values will be used for the first and
      # last components, and the action shall change. The generated URL will be, "people/hh/david/bio".
      # * <tt>url_for :first => 'davids-little-brother'</tt> This generates the URL 'people/hh/davids-little-brother' -- note
      #   that this URL leaves out the assumed action of 'bio'.
      #
      # However, you might ask why the action from the current request, 'contacts', isn't carried over into the new URL. The
      # answer has to do with the order in which the parameters appear in the generated path. In a nutshell, since the
      # value that appears in the slot for <tt>:first</tt> is not equal to default value for <tt>:first</tt> we stop using
      # defaults. On its own, this rule can account for much of the typical Rails URL behavior.
      #  
      # Although a convenience, defaults can occasionally get in your way. In some cases a default persists longer than desired.
      # The default may be cleared by adding <tt>:name => nil</tt> to <tt>url_for</tt>'s options.
      # This is often required when writing form helpers, since the defaults in play may vary greatly depending upon where the
      # helper is used from. The following line will redirect to PostController's default action, regardless of the page it is
      # displayed on:
      #
      #   url_for :controller => 'posts', :action => nil
      #
      # If you explicitly want to create a URL that's almost the same as the current URL, you can do so using the
      # :overwrite_params options. Say for your posts you have different views for showing and printing them.
      # Then, in the show view, you get the URL for the print view like this
      #
      #   url_for :overwrite_params => { :action => 'print' }
      #
      # This takes the current URL as is and only exchanges the action. In contrast, <tt>url_for :action => 'print'</tt>
      # would have slashed-off the path components after the changed action.
      def url_for(options = nil) #:doc:
        case options || {}
          when String
            options
          when Hash
            @url.rewrite(rewrite_options(options))
          else
            polymorphic_url(options)
        end
      end

      # Converts the class name from something like "OneModule::TwoModule::NeatController" to "NeatController".
      def controller_class_name
        self.class.controller_class_name
      end

      # Converts the class name from something like "OneModule::TwoModule::NeatController" to "neat".
      def controller_name
        self.class.controller_name
      end

      # Converts the class name from something like "OneModule::TwoModule::NeatController" to "one_module/two_module/neat".
      def controller_path
        self.class.controller_path
      end

      def session_enabled?
        request.session_options && request.session_options[:disabled] != false
      end

      self.view_paths = []
      
      # View load paths for controller.
      def view_paths
        @template.finder.view_paths
      end
    
      def view_paths=(value)
        @template.finder.view_paths = value  # Mutex needed
      end

      # Adds a view_path to the front of the view_paths array.
      # This change affects the current request only.
      #
      #   self.prepend_view_path("views/default")
      #   self.prepend_view_path(["views/default", "views/custom"])
      #
      def prepend_view_path(path)
        @template.finder.prepend_view_path(path)  # Mutex needed
      end
      
      # Adds a view_path to the end of the view_paths array.
      # This change affects the current request only.
      #
      #   self.append_view_path("views/default")
      #   self.append_view_path(["views/default", "views/custom"])
      #
      def append_view_path(path)
        @template.finder.append_view_path(path)  # Mutex needed
      end

    protected
      # Renders the content that will be returned to the browser as the response body.
      #
      # === Rendering an action
      #
      # Action rendering is the most common form and the type used automatically by Action Controller when nothing else is
      # specified. By default, actions are rendered within the current layout (if one exists).
      #
      #   # Renders the template for the action "goal" within the current controller
      #   render :action => "goal"
      #
      #   # Renders the template for the action "short_goal" within the current controller,
      #   # but without the current active layout
      #   render :action => "short_goal", :layout => false
      #
      #   # Renders the template for the action "long_goal" within the current controller,
      #   # but with a custom layout
      #   render :action => "long_goal", :layout => "spectacular"
      #
      # === Rendering partials
      #
      # Partial rendering in a controller is most commonly used together with Ajax calls that only update one or a few elements on a page
      # without reloading. Rendering of partials from the controller makes it possible to use the same partial template in
      # both the full-page rendering (by calling it from within the template) and when sub-page updates happen (from the
      # controller action responding to Ajax calls). By default, the current layout is not used.
      #
      #   # Renders the same partial with a local variable.
      #   render :partial => "person", :locals => { :name => "david" }
      #
      #   # Renders the partial, making @new_person available through
      #   # the local variable 'person'
      #   render :partial => "person", :object => @new_person
      #
      #   # Renders a collection of the same partial by making each element
      #   # of @winners available through the local variable "person" as it
      #   # builds the complete response.
      #   render :partial => "person", :collection => @winners
      #
      #   # Renders the same collection of partials, but also renders the
      #   # person_divider partial between each person partial.
      #   render :partial => "person", :collection => @winners, :spacer_template => "person_divider"
      #
      #   # Renders a collection of partials located in a view subfolder
      #   # outside of our current controller.  In this example we will be
      #   # rendering app/views/shared/_note.r(html|xml)  Inside the partial
      #   # each element of @new_notes is available as the local var "note".
      #   render :partial => "shared/note", :collection => @new_notes
      #
      #   # Renders the partial with a status code of 500 (internal error).
      #   render :partial => "broken", :status => 500
      #
      # Note that the partial filename must also be a valid Ruby variable name,
      # so e.g. 2005 and register-user are invalid.
      #
      #
      # == Automatic etagging
      #
      # Rendering will automatically insert the etag header on 200 OK responses. The etag is calculated using MD5 of the
      # response body. If a request comes in that has a matching etag, the response will be changed to a 304 Not Modified
      # and the response body will be set to an empty string. No etag header will be inserted if it's already set.
      #
      # === Rendering a template
      #
      # Template rendering works just like action rendering except that it takes a path relative to the template root.
      # The current layout is automatically applied.
      #
      #   # Renders the template located in [TEMPLATE_ROOT]/weblog/show.r(html|xml) (in Rails, app/views/weblog/show.erb)
      #   render :template => "weblog/show"
      #
      # === Rendering a file
      #
      # File rendering works just like action rendering except that it takes a filesystem path. By default, the path
      # is assumed to be absolute, and the current layout is not applied.
      #
      #   # Renders the template located at the absolute filesystem path
      #   render :file => "/path/to/some/template.erb"
      #   render :file => "c:/path/to/some/template.erb"
      #
      #   # Renders a template within the current layout, and with a 404 status code
      #   render :file => "/path/to/some/template.erb", :layout => true, :status => 404
      #   render :file => "c:/path/to/some/template.erb", :layout => true, :status => 404
      #
      #   # Renders a template relative to the template root and chooses the proper file extension
      #   render :file => "some/template", :use_full_path => true
      #
      # === Rendering text
      #
      # Rendering of text is usually used for tests or for rendering prepared content, such as a cache. By default, text
      # rendering is not done within the active layout.
      #
      #   # Renders the clear text "hello world" with status code 200
      #   render :text => "hello world!"
      #
      #   # Renders the clear text "Explosion!"  with status code 500
      #   render :text => "Explosion!", :status => 500
      #
      #   # Renders the clear text "Hi there!" within the current active layout (if one exists)
      #   render :text => "Hi there!", :layout => true
      #
      #   # Renders the clear text "Hi there!" within the layout
      #   # placed in "app/views/layouts/special.r(html|xml)"
      #   render :text => "Hi there!", :layout => "special"
      #
      # The :text option can also accept a Proc object, which can be used to manually control the page generation. This should
      # generally be avoided, as it violates the separation between code and content, and because almost everything that can be
      # done with this method can also be done more cleanly using one of the other rendering methods, most notably templates.
      #
      #   # Renders "Hello from code!"
      #   render :text => proc { |response, output| output.write("Hello from code!") }
      #
      # === Rendering JSON
      #
      # Rendering JSON sets the content type to application/json and optionally wraps the JSON in a callback. It is expected
      # that the response will be parsed (or eval'd) for use as a data structure.
      #
      #   # Renders '{"name": "David"}'
      #   render :json => {:name => "David"}.to_json
      #
      # It's not necessary to call <tt>to_json</tt> on the object you want to render, since <tt>render</tt> will
      # automatically do that for you:
      #
      #   # Also renders '{"name": "David"}'
      #   render :json => {:name => "David"}
      #
      # Sometimes the result isn't handled directly by a script (such as when the request comes from a SCRIPT tag),
      # so the <tt>:callback</tt> option is provided for these cases.
      #
      #   # Renders 'show({"name": "David"})'
      #   render :json => {:name => "David"}.to_json, :callback => 'show'
      #
      # === Rendering an inline template
      #
      # Rendering of an inline template works as a cross between text and action rendering where the source for the template
      # is supplied inline, like text, but its interpreted with ERb or Builder, like action. By default, ERb is used for rendering
      # and the current layout is not used.
      #
      #   # Renders "hello, hello, hello, again"
      #   render :inline => "<%= 'hello, ' * 3 + 'again' %>"
      #
      #   # Renders "<p>Good seeing you!</p>" using Builder
      #   render :inline => "xml.p { 'Good seeing you!' }", :type => :builder
      #
      #   # Renders "hello david"
      #   render :inline => "<%= 'hello ' + name %>", :locals => { :name => "david" }
      #
      # === Rendering inline JavaScriptGenerator page updates
      #
      # In addition to rendering JavaScriptGenerator page updates with Ajax in RJS templates (see ActionView::Base for details),
      # you can also pass the <tt>:update</tt> parameter to +render+, along with a block, to render page updates inline.
      #
      #   render :update do |page|
      #     page.replace_html  'user_list', :partial => 'user', :collection => @users
      #     page.visual_effect :highlight, 'user_list'
      #   end
      #
      # === Rendering with status and location headers
      #
      # All renders take the :status and :location options and turn them into headers. They can even be used together:
      #
      #   render :xml => post.to_xml, :status => :created, :location => post_url(post)
      def render(options = nil, &block) #:doc:
        raise DoubleRenderError, "Can only render or redirect once per action" if performed?

        if options.nil?
          return render_for_file(default_template_name, nil, true)
        else
          if options == :update
            options = { :update => true }
          elsif !options.is_a?(Hash)
            raise RenderError, "You called render with invalid options : #{options}"
          end
        end

        if content_type = options[:content_type]
          response.content_type = content_type.to_s
        end

        if location = options[:location]
          response.headers["Location"] = url_for(location)
        end

        if options.has_key?(:text)
          render_for_text(options[:text], options[:status])

        else
          if file = options[:file]
            render_for_file(file, options[:status], options[:use_full_path], options[:locals] || {})

          elsif template = options[:template]
            render_for_file(template, options[:status], true)

          elsif inline = options[:inline]
            add_variables_to_assigns
            render_for_text(@template.render_template(options[:type], inline, nil, options[:locals] || {}), options[:status])

          elsif action_name = options[:action]
            template = default_template_name(action_name.to_s)
            if options[:layout] && !template_exempt_from_layout?(template)
              render_with_a_layout(:file => template, :status => options[:status], :use_full_path => true, :layout => true)              
            else
              render_with_no_layout(:file => template, :status => options[:status], :use_full_path => true)
            end            

          elsif xml = options[:xml]
            response.content_type ||= Mime::XML
            render_for_text(xml.respond_to?(:to_xml) ? xml.to_xml : xml, options[:status])

          elsif json = options[:json]
            json = json.to_json unless json.is_a?(String)
            json = "#{options[:callback]}(#{json})" unless options[:callback].blank?
            response.content_type ||= Mime::JSON
            render_for_text(json, options[:status])

          elsif partial = options[:partial]
            partial = default_template_name if partial == true
            add_variables_to_assigns

            if collection = options[:collection]
              render_for_text(
                @template.send!(:render_partial_collection, partial, collection, 
                options[:spacer_template], options[:locals]), options[:status]
              )
            else
              render_for_text(
                @template.send!(:render_partial, partial, 
                ActionView::Base::ObjectWrapper.new(options[:object]), options[:locals]), options[:status]
              )
            end

          elsif options[:update]
            add_variables_to_assigns
            @template.send! :evaluate_assigns

            generator = ActionView::Helpers::PrototypeHelper::JavaScriptGenerator.new(@template, &block)
            response.content_type = Mime::JS
            render_for_text(generator.to_s)

          elsif options[:nothing]
            # Safari doesn't pass the headers of the return if the response is zero length
            render_for_text(" ", options[:status])

          else
            render_for_file(default_template_name, options[:status], true)
          end
        end
      end

      # Renders according to the same rules as <tt>render</tt>, but returns the result in a string instead
      # of sending it as the response body to the browser.
      def render_to_string(options = nil, &block) #:doc:
        render(options, &block)
      ensure
        erase_render_results
        forget_variables_added_to_assigns
        reset_variables_added_to_assigns
      end

      # Return a response that has no content (merely headers). The options
      # argument is interpreted to be a hash of header names and values.
      # This allows you to easily return a response that consists only of
      # significant headers:
      #
      #   head :created, :location => person_path(@person)
      #
      # It can also be used to return exceptional conditions:
      #
      #   return head(:method_not_allowed) unless request.post?
      #   return head(:bad_request) unless valid_request?
      #   render
      def head(*args)
        if args.length > 2
          raise ArgumentError, "too many arguments to head"
        elsif args.empty?
          raise ArgumentError, "too few arguments to head"
        end
        options = args.extract_options!
        status = interpret_status(args.shift || options.delete(:status) || :ok)

        options.each do |key, value|
          headers[key.to_s.dasherize.split(/-/).map { |v| v.capitalize }.join("-")] = value.to_s
        end

        render :nothing => true, :status => status
      end


      # Clears the rendered results, allowing for another render to be performed.
      def erase_render_results #:nodoc:
        response.body = nil
        @performed_render = false
      end

      # Clears the redirected results from the headers, resets the status to 200 and returns
      # the URL that was used to redirect or nil if there was no redirected URL
      # Note that +redirect_to+ will change the body of the response to indicate a redirection.
      # The response body is not reset here, see +erase_render_results+
      def erase_redirect_results #:nodoc:
        @performed_redirect = false
        response.redirected_to = nil
        response.redirected_to_method_params = nil
        response.headers['Status'] = DEFAULT_RENDER_STATUS_CODE
        response.headers.delete('Location')
      end

      # Erase both render and redirect results
      def erase_results #:nodoc:
        erase_render_results
        erase_redirect_results
      end

      def rewrite_options(options) #:nodoc:
        if defaults = default_url_options(options)
          defaults.merge(options)
        else
          options
        end
      end

      # Overwrite to implement a number of default options that all url_for-based methods will use. The default options should come in
      # the form of a hash, just like the one you would use for url_for directly. Example:
      #
      #   def default_url_options(options)
      #     { :project => @project.active? ? @project.url_name : "unknown" }
      #   end
      #
      # As you can infer from the example, this is mostly useful for situations where you want to centralize dynamic decisions about the
      # urls as they stem from the business domain. Please note that any individual url_for call can always override the defaults set
      # by this method.
      def default_url_options(options) #:doc:
      end

      # Redirects the browser to the target specified in +options+. This parameter can take one of three forms:
      #
      # * <tt>Hash</tt> - The URL will be generated by calling url_for with the +options+.
      # * <tt>Record</tt> - The URL will be generated by calling url_for with the +options+, which will reference a named URL for that record.
      # * <tt>String starting with protocol:// (like http://)</tt> - Is passed straight through as the target for redirection.
      # * <tt>String not containing a protocol</tt> - The current protocol and host is prepended to the string.
      # * <tt>:back</tt> - Back to the page that issued the request. Useful for forms that are triggered from multiple places.
      #   Short-hand for redirect_to(request.env["HTTP_REFERER"])
      #
      # Examples:
      #   redirect_to :action => "show", :id => 5
      #   redirect_to post
      #   redirect_to "http://www.rubyonrails.org"
      #   redirect_to "/images/screenshot.jpg"
      #   redirect_to articles_url
      #   redirect_to :back
      #
      # The redirection happens as a "302 Moved" header unless otherwise specified. 
      #
      # Examples:
      #   redirect_to post_url(@post), :status=>:found
      #   redirect_to :action=>'atom', :status=>:moved_permanently
      #   redirect_to post_url(@post), :status=>301
      #   redirect_to :action=>'atom', :status=>302
      #
      # When using <tt>redirect_to :back</tt>, if there is no referrer,
      # RedirectBackError will be raised. You may specify some fallback
      # behavior for this case by rescuing RedirectBackError.
      def redirect_to(options = {}, response_status = {}) #:doc: 
        raise ActionControllerError.new("Cannot redirect to nil!") if options.nil?

        if options.is_a?(Hash) && options[:status] 
          status = options.delete(:status) 
        elsif response_status[:status] 
          status = response_status[:status] 
        else 
          status = 302 
        end
        
        case options
          when %r{^\w+://.*}
            raise DoubleRenderError if performed?
            logger.info("Redirected to #{options}") if logger && logger.info?
            response.redirect(options, interpret_status(status))
            response.redirected_to = options
            @performed_redirect = true

          when String
            redirect_to(request.protocol + request.host_with_port + options, :status=>status)

          when :back
            request.env["HTTP_REFERER"] ? redirect_to(request.env["HTTP_REFERER"], :status=>status) : raise(RedirectBackError)

          when Hash
            redirect_to(url_for(options), :status=>status)
            response.redirected_to = options

          else
            redirect_to(url_for(options), :status=>status)
        end
      end

      # Sets a HTTP 1.1 Cache-Control header. Defaults to issuing a "private" instruction, so that
      # intermediate caches shouldn't cache the response.
      #
      # Examples:
      #   expires_in 20.minutes
      #   expires_in 3.hours, :private => false
      #   expires in 3.hours, 'max-stale' => 5.hours, :private => nil, :public => true
      #
      # This method will overwrite an existing Cache-Control header.
      # See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html for more possibilities.
      def expires_in(seconds, options = {}) #:doc:
        cache_options = { 'max-age' => seconds, 'private' => true }.symbolize_keys.merge!(options.symbolize_keys)
        cache_options.delete_if { |k,v| v.nil? or v == false }
        cache_control = cache_options.map{ |k,v| v == true ? k.to_s : "#{k.to_s}=#{v.to_s}"}
        response.headers["Cache-Control"] = cache_control.join(', ')
      end

      # Sets a HTTP 1.1 Cache-Control header of "no-cache" so no caching should occur by the browser or
      # intermediate caches (like caching proxy servers).
      def expires_now #:doc:
        response.headers["Cache-Control"] = "no-cache"
      end

      # Resets the session by clearing out all the objects stored within and initializing a new session object.
      def reset_session #:doc:
        request.reset_session
        @_session = request.session
        response.session = @_session
      end


    private
      def render_for_file(template_path, status = nil, use_full_path = false, locals = {}) #:nodoc:
        add_variables_to_assigns
        assert_existence_of_template_file(template_path) if use_full_path
        logger.info("Rendering #{template_path}" + (status ? " (#{status})" : '')) if logger
        render_for_text(@template.render_file(template_path, use_full_path, locals), status)
      end

      def render_for_text(text = nil, status = nil, append_response = false) #:nodoc:
        @performed_render = true

        response.headers['Status'] = interpret_status(status || DEFAULT_RENDER_STATUS_CODE)

        if append_response
          response.body ||= ''
          response.body << text.to_s
        else
          response.body = text.is_a?(Proc) ? text : text.to_s
        end
      end
      
      def initialize_template_class(response)
        unless @@template_class
          raise "You must assign a template class through ActionController.template_class= before processing a request"
        end

        response.template = ActionView::Base.new(self.class.view_paths, {}, self)
        response.template.extend self.class.master_helper_module
        response.redirected_to = nil
        @performed_render = @performed_redirect = false
      end

      def assign_shortcuts(request, response)
        @_request, @_params, @_cookies = request, request.parameters, request.cookies

        @_response         = response
        @_response.session = request.session

        @_session = @_response.session
        @template = @_response.template
        @assigns  = @_response.template.assigns

        @_headers = @_response.headers
      end

      def initialize_current_url
        @url = UrlRewriter.new(request, params.clone)
      end

      def log_processing
        if logger && logger.info?
          logger.info "\n\nProcessing #{controller_class_name}\##{action_name} (for #{request_origin}) [#{request.method.to_s.upcase}]"
          logger.info "  Session ID: #{@_session.session_id}" if @_session and @_session.respond_to?(:session_id)
          logger.info "  Parameters: #{respond_to?(:filter_parameters) ? filter_parameters(params).inspect : params.inspect}"
        end
      end

      def default_render #:nodoc:
        render
      end

      def perform_action
        if self.class.action_methods.include?(action_name)
          send(action_name)
          default_render unless performed?
        elsif respond_to? :method_missing
          method_missing action_name
          default_render unless performed?
        elsif template_exists? && template_public?
          default_render
        else
          raise UnknownAction, "No action responded to #{action_name}", caller
        end
      end

      def performed?
        @performed_render || @performed_redirect
      end

      def assign_names
        @action_name = (params['action'] || 'index')
      end

      def assign_default_content_type_and_charset
        response.content_type ||= Mime::HTML
        response.charset      ||= self.class.default_charset unless sending_file?
      end

      def sending_file?
        response.headers["Content-Transfer-Encoding"] == "binary"
      end

      def action_methods
        self.class.action_methods
      end

      def self.action_methods
        @action_methods ||= Set.new(public_instance_methods.map(&:to_s)) - hidden_actions
      end

      def add_variables_to_assigns
        unless @variables_added
          add_instance_variables_to_assigns
          add_class_variables_to_assigns if view_controller_internals
          @variables_added = true
        end
      end

      def forget_variables_added_to_assigns
        @variables_added = nil
      end

      def reset_variables_added_to_assigns
        @template.instance_variable_set("@assigns_added", nil)
      end

      def add_instance_variables_to_assigns
        @@protected_variables_cache ||= Set.new(protected_instance_variables)
        instance_variable_names.each do |var|
          next if @@protected_variables_cache.include?(var)
          @assigns[var[1..-1]] = instance_variable_get(var)
        end
      end

      def add_class_variables_to_assigns
        %w(view_paths logger template_class ignore_missing_templates).each do |cvar|
          @assigns[cvar] = self.send(cvar)
        end
      end

      def protected_instance_variables
        if view_controller_internals
          %w(@assigns @performed_redirect @performed_render)
        else
          %w(@assigns @performed_redirect @performed_render
             @_request @request @_response @response @_params @params
             @_session @session @_cookies @cookies
             @template @request_origin @parent_controller)
        end
      end

      def request_origin
        # this *needs* to be cached!
        # otherwise you'd get different results if calling it more than once
        @request_origin ||= "#{request.remote_ip} at #{Time.now.to_s(:db)}"
      end

      def complete_request_uri
        "#{request.protocol}#{request.host}#{request.request_uri}"
      end

      def close_session
        @_session.close if @_session && @_session.respond_to?(:close)
      end

      def template_exists?(template_name = default_template_name)
        @template.finder.file_exists?(template_name)
      end

      def template_public?(template_name = default_template_name)
        @template.file_public?(template_name)
      end

      def template_exempt_from_layout?(template_name = default_template_name)
        extension = @template && @template.finder.pick_template_extension(template_name)
        name_with_extension = !template_name.include?('.') && extension ? "#{template_name}.#{extension}" : template_name
        @@exempt_from_layout.any? { |ext| name_with_extension =~ ext }
      end

      def assert_existence_of_template_file(template_name)
        unless template_exists?(template_name) || ignore_missing_templates
          full_template_path = template_name.include?('.') ? template_name : "#{template_name}.#{@template.template_format}.erb"
          display_paths = view_paths.join(':')
          template_type = (template_name =~ /layouts/i) ? 'layout' : 'template'
          raise(MissingTemplate, "Missing #{template_type} #{full_template_path} in view path #{display_paths}")
        end
      end

      def default_template_name(action_name = self.action_name)
        if action_name
          action_name = action_name.to_s
          if action_name.include?('/') && template_path_includes_controller?(action_name)
            action_name = strip_out_controller(action_name)
          end
        end
        "#{self.class.controller_path}/#{action_name}"
      end

      def strip_out_controller(path)
        path.split('/', 2).last
      end

      def template_path_includes_controller?(path)
        self.class.controller_path.split('/')[-1] == path.split('/')[0]
      end

      def process_cleanup
        close_session
      end
  end
end