charset should not be appended for `head` responses

      1) Failure:
    test_head_created_with_image_png_content_type(RenderTest) [test/controller/render_test.rb:1238]:
    Expected: "image/png"
      Actual: "image/png; charset=utf-8"

1 files changed, 6 insertions, 2 deletions

diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 0f808ac9cf..91cf4784db 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -260,14 +260,18 @@ module ActionDispatch # :nodoc:
       return if headers[CONTENT_TYPE].present?
 
       @content_type ||= Mime::HTML
-      @charset      ||= self.class.default_charset
+      @charset      ||= self.class.default_charset unless @charset == false
 
       type = @content_type.to_s.dup
-      type << "; charset=#{@charset}" unless @sending_file
+      type << "; charset=#{@charset}" if append_charset?
 
       headers[CONTENT_TYPE] = type
     end
 
+    def append_charset?
+      !@sending_file && @charset != false
+    end
+
     def rack_response(status, header)
       assign_default_content_type_and_charset!(header)
       handle_conditional_get!