PERF: missing caching on CSS and Site Customizations

app/controllers/site_customizations_controller.rb

@@ -2,6 +2,13 @@ class SiteCustomizationsController < ApplicationController
   skip_before_filter :preload_json, :check_xhr, :redirect_to_login_if_required
 
   def show
+    version = params["v"]
+
+    if version && version == request.headers['If-None-Match']
+      return render nothing: true, status: 304
+    end
+
+    response.headers["ETag"] = version if version
     expires_in 1.year, public: true
     render text: SiteCustomization.stylesheet_contents(params[:key], params[:target] == "mobile" ? :mobile : :desktop),
            content_type: "text/css"

app/controllers/stylesheets_controller.rb

@@ -4,8 +4,12 @@ class StylesheetsController < ApplicationController
   def show
 
     target,digest = params[:name].split("_")
-
     digest_orig = digest
+
+    if digest_orig && digest_orig == request.headers['If-None-Match']
+      return render nothing: true, status: 304
+    end
+
     digest = "_" + digest if digest
 
     # Security note, safe due to route constraint
@@ -26,6 +30,7 @@ class StylesheetsController < ApplicationController
       end
     end
 
+    response.headers['ETag'] = digest_orig if digest_orig
     expires_in 1.year, public: true unless Rails.env == "development"
     send_file(location, disposition: :inline)