Action Pack Variants

By default, variants in the templates will be picked up if a variant is set
and there's a match. The format will be:

  app/views/projects/show.html.erb
  app/views/projects/show.html+tablet.erb
  app/views/projects/show.html+phone.erb

If request.variant = :tablet is set, we'll automatically be rendering the
html+tablet template.

In the controller, we can also tailer to the variants with this syntax:

  class ProjectsController < ActionController::Base
    def show
      respond_to do |format|
        format.html do |html|
          @stars = @project.stars

          html.tablet { @notifications = @project.notifications }
          html.phone  { @chat_heads    = @project.chat_heads }
        end

        format.js
        format.atom
      end
    end
  end

The variant itself is nil by default, but can be set in before filters, like
so:

  class ApplicationController < ActionController::Base
    before_action do
      if request.user_agent =~ /iPad/
        request.variant = :tablet
      end
    end
  end

This is modeled loosely on custom mime types, but it's specifically not
intended to be used together. If you're going to make a custom mime type,
you don't need a variant. Variants are for variations on a single mime
types.

1 files changed, 14 insertions, 0 deletions

diff --git a/actionpack/lib/action_dispatch/http/mime_negotiation.rb b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
index 40bb060d52..41e6727315 100644
--- a/actionpack/lib/action_dispatch/http/mime_negotiation.rb
+++ b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
@@ -10,6 +10,8 @@ module ActionDispatch
         self.ignore_accept_header = false
       end
 
+      attr_reader :variant
+
       # The MIME type of the HTTP request, such as Mime::XML.
       #
       # For backward compatibility, the post \format is extracted from the
@@ -64,6 +66,18 @@ module ActionDispatch
           end
       end
 
+      # Sets the \variant for template
+      def variant=(variant)
+        if variant.is_a? Symbol
+          @variant = variant
+        else
+          raise ArgumentError, "request.variant must be set to a Symbol, not a #{variant.class}. For security reasons," +
+                               "never directly set the variant to a user-provided value, like params[:variant].to_sym." +
+                               "Check user-provided value against a whitelist first, then set the variant:"+
+                               "request.variant = :tablet if params[:some_param] == 'tablet'"
+        end
+      end
+
       # Sets the \format by string extension, which can be used to force custom formats
       # that are not controlled by the extension.
       #