In Rails 4.2, How Does One Set the Response Content-Type Header With Media Type Parameters?

Question

In earlier versions, this would work:

ActionController::Renderers.add(:foo) do | data, options |
  self.content_type = 'application/foo; bar=1'
end

In 4.2.4, this causes the Content-Type header to be blank. However, the following works, i.e., sets the Content-Type header to the string assigned to content_type:

ActionController::Renderers.add(:foo) do | data, options |
  self.content_type = 'application/foo'
end

The other approach I know of, setting content_type on the render, seems to have no result anymore, i.e., render('foo', content_type: 'application/foo') doesn't set the header (never mind trying application/foo; bar=1.)

Answer 1

First take a look at the documentation (Section 2.2.13.1):

http://guides.rubyonrails.org/layouts_and_rendering.html#using-render

The example they give there uses your alternative approach, setting content_type when using render:

render file: filename, content_type: "application/rss"

I tested this strategy in a vanilla Rails 4.2.4 application. This is how I defined the controller:

class WelcomeController < ApplicationController
  def index
    render inline: 'Hello World', content_type: 'application/foo; bar=1'
  end
end

And here is what I see in Chrome's network inspector when I hit that action, note the Content-Type under Response Headers:

General

Remote Address:[::1]:3000
Request URL:http://localhost:3000/
Request Method:GET
Status Code:200 OK

Response Headers

Cache-Control:max-age=0, private, must-revalidate
Connection:Keep-Alive
Content-Length:11
Content-Type:application/foo; bar=1; charset=utf-8
Date:Tue, 29 Sep 2015 02:53:39 GMT
Etag:W/"b10a8db164e0754105b7a99be72e3fe5"
Server:WEBrick/1.3.1 (Ruby/2.2.2/2015-04-13)
X-Content-Type-Options:nosniff
X-Frame-Options:SAMEORIGIN
X-Request-Id:3825d446-44dc-46fa-8aed-630dc7f001ae
X-Runtime:0.022774
X-Xss-Protection:1; mode=block

Answer 2

Sean Huber is correct and the code in the question is correct. Except in the case of having registered a MIME type and then rendering files of that type, e.g.,

Mime::Type.register('application/foobar', :foobar)

render('view') # where view is actually view.foobar.jbuilder

In this case, the type string registered appears to always override the approaches available for setting content type explicitly. This can lead to thinking that the media type parameters are being stripped because, coincidentally, ParamsParser selection appears to "break" when media type parameters are specified for a default parser, i.e., a parser registered for 'application/foo; bar=1' will not parse content provided with that content type, leading one to use a parameterless string for the mime type string and then attempting to override with one including the parameters.

So, to get around that in 4.2, I've removed the ParamsParser and Render registrations and moved to a before_filter on a parent controller and the content type header to an after_filter, e.g.,

class BaseController < ApplicationController
  before_filter :parse_body
  after_filter :set_content_type

  attr_accessor :parsed

  def parse_body
    self.parsed = JSON.load(request.body)
  end

  def set_content_type
    self.content_type = "application/foo; bar=1; charset=utf-8"
  end
end

Note: this is quite the hack/workaround; not recommended for long-term use.