3 files changed, 7 insertions, 8 deletions
diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index f875aa5e6b..b9088e6d86 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -26,10 +26,10 @@ module ActionController
       end
     end
 
-    def build(action, app = Proc.new)
+    def build(action, app = nil, &block)
       action = action.to_s
 
-      middlewares.reverse.inject(app) do |a, middleware|
+      middlewares.reverse.inject(app || block) do |a, middleware|
         middleware.valid?(action) ? middleware.build(a) : a
       end
     end
diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 1d38942a31..69798f99e0 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -82,6 +82,7 @@ module ActionDispatch # :nodoc:
     SET_COOKIE   = "Set-Cookie"
     LOCATION     = "Location"
     NO_CONTENT_CODES = [100, 101, 102, 204, 205, 304]
+    CONTENT_TYPE_PARSER = /\A(?<type>[^;\s]+)?(?:.*;\s*charset=(?<quote>"?)(?<charset>[^;\s]+)\k<quote>)?/ # :nodoc:
 
     cattr_accessor :default_charset, default: "utf-8"
     cattr_accessor :default_headers
@@ -409,10 +410,8 @@ module ActionDispatch # :nodoc:
     NullContentTypeHeader = ContentTypeHeader.new nil, nil
 
     def parse_content_type(content_type)
-      if content_type
-        type, charset = content_type.split(/;\s*charset=/)
-        type = nil if type && type.empty?
-        ContentTypeHeader.new(type, charset)
+      if content_type && match = CONTENT_TYPE_PARSER.match(content_type)
+        ContentTypeHeader.new(match[:type], match[:charset])
       else
         NullContentTypeHeader
       end
diff --git a/actionpack/lib/action_dispatch/middleware/stack.rb b/actionpack/lib/action_dispatch/middleware/stack.rb
index b82f8aa3a3..7a2fcd6db7 100644
--- a/actionpack/lib/action_dispatch/middleware/stack.rb
+++ b/actionpack/lib/action_dispatch/middleware/stack.rb
@@ -97,8 +97,8 @@ module ActionDispatch
       middlewares.push(build_middleware(klass, args, block))
     end
 
-    def build(app = Proc.new)
-      middlewares.freeze.reverse.inject(app) { |a, e| e.build(a) }
+    def build(app = nil, &block)
+      middlewares.freeze.reverse.inject(app || block) { |a, e| e.build(a) }
     end
 
     private