Ah, before this change:

>> stub_request('CONTENT_TYPE' => 'application/xml; charset=UTF-8').content_charset
# => nil
>> stub_request('CONTENT_TYPE' => 'application/xml; charset=UTF-8').media_type_params
# => {}

👍

Agreed in theory, but deprecation is impossible for a return-value behavior change like this. It'll cause many subtle bugs in engines, apps, etc.

May be better to find a new way forward, like providing a ContentTypeHeader object that with params, charset, mime_type, etc. And patch the other Request methods that rely on content_type returning the full header to use an internal content_type_header.

Not sure if it is worth to patch the Request method, this will only become a endless race for rack compatibility. If they add a new method using content_type we will have to override it here again. The best thing to do in my opinion is stop to override this rack method.

Maybe in Rails 5 we can merge this patch as it is?

Giving up