Rails Metal DataStreaming broken?!

tracking_controller.rb

class Api::V1::OpenRateController < ActionController::Metal
  include ActionController::DataStreaming

  def show
    tracking_gif = "GIF89a\x03\x00\x02\x00\x80\x00\x00\xC0\xC0\xC0\x00\x00\x00!\xF9\x04\x01\x00\x00\x00\x00,\x00\x00\x00\x00\x03\x00\x02\x00\x00\x02\x02\x84_\x00;".freeze
    send_data tracking_gif
  end
end

undefined method `sending_file=' for nil:NilClass

Trace
actionpack (3.2.1) lib/action_controller/metal/data_streaming.rb:146:in send_file_headers!' actionpack (3.2.1) lib/action_controller/metal/data_streaming.rb:111:insend_data'
app/controllers/api/v1/open_rate_controller.rb:9:in show' actionpack (3.2.1) lib/abstract_controller/base.rb:167:inprocess_action'
actionpack (3.2.1) lib/action_controller/metal/rendering.rb:10:in process_action' actionpack (3.2.1) lib/abstract_controller/base.rb:121:inprocess'
actionpack (3.2.1) lib/abstract_controller/rendering.rb:45:in process' actionpack (3.2.1) lib/action_controller/metal.rb:203:indispatch'
actionpack (3.2.1) lib/action_controller/metal.rb:246:in block in action' actionpack (3.2.1) lib/action_dispatch/routing/route_set.rb:66:incall'
actionpack (3.2.1) lib/action_dispatch/routing/route_set.rb:66:in dispatch' actionpack (3.2.1) lib/action_dispatch/routing/route_set.rb:30:incall'
journey (1.0.1) lib/journey/router.rb:68:in block in call' journey (1.0.1) lib/journey/router.rb:56:ineach'
journey (1.0.1) lib/journey/router.rb:56:in `call'

i also meet this error , rails version is 3.2.2

do u have solved?

haven't solved this, i'm using a ActionController::Base now

Including include ActionController::RackDelegation solves this.