1 files changed, 100 insertions, 0 deletions
diff --git a/actionpack/lib/action_controller/renderer.rb b/actionpack/lib/action_controller/renderer.rb
new file mode 100644
index 0000000000..e8b29c5b5e
--- /dev/null
+++ b/actionpack/lib/action_controller/renderer.rb
@@ -0,0 +1,100 @@
+require 'active_support/core_ext/hash/keys'
+
+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)
+        http_header_format(env).tap do |new_env|
+          handle_method_key! new_env
+          handle_https_key!  new_env
+        end
+      end
+
+      def http_header_format(env)
+        env.transform_keys do |key|
+          key.is_a?(Symbol) ? key.to_s.upcase : key
+        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