Change `ActionDispatch::Response#content_type` returning Content-Type header as it is

Since #35709, `Response#conten_type` returns only MIME type correctly.
It is a documented behavior that this method only returns MIME type, so
this change seems appropriate.
https://github.com/rails/rails/blob/39de7fac0507070e3c5f8b33fbad6fced84d97ed/actionpack/lib/action_dispatch/http/response.rb#L245-L249

But unfortunately, some users expect this method to return all
Content-Type that does not contain charset. This seems to be breaking
changes.

We can change this behavior with the deprecate cycle.
But, in that case, a method needs that include Content-Type with
additional parameters. And that method name is probably the
`content_type` seems to properly.

So I changed the new behavior to more appropriate `media_type` method.
And `Response#content_type` changed (as the method name) to return Content-Type
header as it is.

Fixes #35709.

[Rafael Mendonça França & Yuuji Yaginuma ]

3 files changed, 9 insertions, 4 deletions

diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 69798f99e0..61e3a870ab 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -243,8 +243,13 @@ module ActionDispatch # :nodoc:
     end
 
     # Content type of response.
-    # It returns just MIME type and does NOT contain charset part.
     def content_type
+      type = super
+      type&.empty? ? nil : type
+    end
+
+    # Media type of response.
+    def media_type
       parsed_content_type_header.mime_type
     end
 
@@ -458,7 +463,7 @@ module ActionDispatch # :nodoc:
     end
 
     def assign_default_content_type_and_charset!
-      return if content_type
+      return if media_type
 
       ct = parsed_content_type_header
       set_content_type(ct.mime_type || Mime[:html].to_s,
diff --git a/actionpack/lib/action_dispatch/testing/assertions.rb b/actionpack/lib/action_dispatch/testing/assertions.rb
index 08c2969685..dcaf914ac9 100644
--- a/actionpack/lib/action_dispatch/testing/assertions.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions.rb
@@ -14,7 +14,7 @@ module ActionDispatch
     include Rails::Dom::Testing::Assertions
 
     def html_document
-      @html_document ||= if @response.content_type.to_s.end_with?("xml")
+      @html_document ||= if @response.media_type.to_s.end_with?("xml")
         Nokogiri::XML::Document.parse(@response.body)
       else
         Nokogiri::HTML::Document.parse(@response.body)
diff --git a/actionpack/lib/action_dispatch/testing/test_response.rb b/actionpack/lib/action_dispatch/testing/test_response.rb
index 6f7c86fdcf..f1dd4099c5 100644
--- a/actionpack/lib/action_dispatch/testing/test_response.rb
+++ b/actionpack/lib/action_dispatch/testing/test_response.rb
@@ -19,7 +19,7 @@ module ActionDispatch
     end
 
     def response_parser
-      @response_parser ||= RequestEncoder.parser(content_type)
+      @response_parser ||= RequestEncoder.parser(media_type)
     end
   end
 end