3 files changed, 112 insertions, 0 deletions
diff --git a/actionpack/lib/action_controller.rb b/actionpack/lib/action_controller.rb
index e977bbce99..7667e469d3 100644
--- a/actionpack/lib/action_controller.rb
+++ b/actionpack/lib/action_controller.rb
@@ -11,6 +11,7 @@ module ActionController
   autoload :Caching
   autoload :Metal
   autoload :Middleware
+  autoload :Renderer
 
   autoload_under "metal" do
     autoload :Compatibility
diff --git a/actionpack/lib/action_controller/metal/rendering.rb b/actionpack/lib/action_controller/metal/rendering.rb
index 7bbff0450a..2370c607ed 100644
--- a/actionpack/lib/action_controller/metal/rendering.rb
+++ b/actionpack/lib/action_controller/metal/rendering.rb
@@ -4,6 +4,14 @@ module ActionController
 
     RENDER_FORMATS_IN_PRIORITY = [:body, :text, :plain, :html]
 
+    module ClassMethods
+      # Returns a renderer class (inherited from ActionController::Renderer)
+      # for the controller.
+      def renderer
+        @renderer ||= Renderer.for(self)
+      end
+    end
+
     # Before processing, set the request formats in current controller formats.
     def process_action(*) #:nodoc:
       self.formats = request.formats.map(&:ref).compact
diff --git a/actionpack/lib/action_controller/renderer.rb b/actionpack/lib/action_controller/renderer.rb
new file mode 100644
index 0000000000..a122954968
--- /dev/null
+++ b/actionpack/lib/action_controller/renderer.rb
@@ -0,0 +1,103 @@
+module ActionController
+  # ActionController::Renderer allows to render arbitrary templates
+  # without requirement of being in controller actions.
+  #
+  # You get a concrete renderer class by invoking ActionController::Base#renderer.
+  # For example,
+  #
+  #   ApplicationController.renderer
+  #
+  # It allows you to call method #render directly.
+  #
+  #   ApplicationController.renderer.render template: '...'
+  #
+  # You can use a shortcut on controller to replace previous example with:
+  #
+  #   ApplicationController.render template: '...'
+  #
+  # #render method allows you to use any options as when rendering in controller.
+  # For example,
+  #
+  #   FooController.render :action, locals: { ... }, assigns: { ... }
+  #
+  # The template will be rendered in a Rack environment which is accessible through
+  # ActionController::Renderer#env. You can set it up in two ways:
+  #
+  # *  by changing renderer defaults, like
+  #
+  #       ApplicationController.renderer.defaults # => hash with default Rack environment
+  #
+  # *  by initializing an instance of renderer by passing it a custom environment.
+  #
+  #       ApplicationController.renderer.new(method: 'post', https: true)
+  #
+  class Renderer
+    class_attribute :controller, :defaults
+    # Rack environment to render templates in.
+    attr_reader :env
+
+    class << self
+      delegate :render, to: :new
+
+      # Create a new renderer class for a specific controller class.
+      def for(controller)
+        Class.new self do
+          self.controller = controller
+          self.defaults = {
+            http_host: 'example.org',
+            https: false,
+            method: 'get',
+            script_name: '',
+            'rack.input' => ''
+          }
+        end
+      end
+    end
+
+    # Accepts a custom Rack environment to render templates in.
+    # It will be merged with ActionController::Renderer.defaults
+    def initialize(env = {})
+      @env = normalize_keys(defaults).merge normalize_keys(env)
+      @env['action_dispatch.routes'] = controller._routes
+    end
+
+    # Render templates with any options from ActionController::Base#render_to_string.
+    def render(*args)
+      raise 'missing controller' unless controller?
+
+      instance = controller.build_with_env(env)
+      instance.render_to_string(*args)
+    end
+
+    private
+      def normalize_keys(env)
+        env.dup.tap do |new_env|
+          convert_symbols!   new_env
+          handle_method_key! new_env
+          handle_https_key!  new_env
+        end
+      end
+
+      def convert_symbols!(env)
+        env.keys.each do |key|
+          if key.is_a? Symbol
+            value = env.delete key
+            key = key.to_s.upcase 
+            env[key] = value
+          end
+        end
+      end
+
+      def handle_method_key!(env)
+        if method = env.delete('METHOD')
+          env['REQUEST_METHOD'] = method.upcase
+        end
+      end
+
+      def handle_https_key!(env)
+        if env.has_key? 'HTTPS'
+          env['HTTPS'] = env['HTTPS'] ? 'on' : 'off'
+        end
+      end
+  end
+end