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.
39de7fac05/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 ]
