Add default charset config to ActionDispatch

actionpack/lib/action_dispatch/railtie.rb

@@ -11,6 +11,7 @@ class Railtie < Rails::Railtie
     config.action_dispatch.ignore_accept_header = false
     config.action_dispatch.rescue_templates = { }
     config.action_dispatch.rescue_responses = { }
+    config.action_dispatch.default_charset = nil
 
     config.action_dispatch.rack_cache = {
       :metastore => "rails:/",
@@ -21,7 +22,7 @@ class Railtie < Rails::Railtie
     initializer "action_dispatch.configure" do |app|
       ActionDispatch::Http::URL.tld_length = app.config.action_dispatch.tld_length
       ActionDispatch::Request.ignore_accept_header = app.config.action_dispatch.ignore_accept_header
-      ActionDispatch::Response.default_charset = app.config.encoding
+      ActionDispatch::Response.default_charset = app.config.action_dispatch.default_charset || app.config.encoding
 
       ActionDispatch::ExceptionWrapper.rescue_responses.merge!(config.action_dispatch.rescue_responses)
       ActionDispatch::ExceptionWrapper.rescue_templates.merge!(config.action_dispatch.rescue_templates)

railties/test/application/configuration_test.rb

@@ -286,6 +286,14 @@ def index
       assert_equal res, last_response.body # value should be unchanged
     end
 
+    test "sets ActionDispatch::Response.default_charset" do
+      make_basic_app do |app|
+        app.config.action_dispatch.default_charset = "utf-16"
+      end
+
+      assert_equal "utf-16", ActionDispatch::Response.default_charset
+    end
+
     test "sets all Active Record models to whitelist all attributes by default" do
       add_to_config <<-RUBY
         config.active_record.whitelist_attributes = true