我用 Rails 5.2 和 carrierwave-qiniu

现在我可以通过 carrierwave-qiniu 上传文件到服务器，但是我下载时，提示：

Cannot read file http://pczd3l6pu.bkt.clouddn.com/document/129/railsguides-5.0.2.1.pdf,

完整错误内容为：

Processing by DocumentsController#download as HTML
  Parameters: {"id"=>"129"}
  User Load (0.3ms)  SELECT  `users`.* FROM `users` WHERE `users`.`id` = 2 LIMIT 1
  Document Load (0.3ms)  SELECT  `documents`.* FROM `documents` WHERE `documents`.`id` = 129 LIMIT 1
Sent file http://pczd3l6pu.bkt.clouddn.com/document/129/railsguides-5.0.2.1.pdf (0.3ms)
Completed 500 Internal Server Error in 4ms (ActiveRecord: 0.7ms)



ActionController::MissingFile - Cannot read file http://pczd3l6pu.bkt.clouddn.com/document/129/railsguides-5.0.2.1.pdf:
  app/controllers/documents_controller.rb:35:in `download'

但是单独访问 上述链接，是可以在线浏览文件的。

我的 document_controllers 如下：

def create

  @document = Document.new
  @document.file_name = params[:file]
  if @document.file_name.blank?
    render json: { ok: false }, status: 400
    return
  end

  @document.user_id = current_user.id
  if @document.save
    render json: { url: @document.file_name.url, id:@document.id }
  else
    flash[:warning] = "文件上传失败"
  end
end

def destroy
  @document = Document.find(params[:id])
  @document.destroy
  redirect_to session[:back_path].pop
  flash[:success] = '文件已删除，请重新上传'
end

def download
  @document = Document.find(params[:id])
  response.headers['Content-Type'] = "application/octet-stream"
  response.headers['Content-Disposition'] = "attachment; filename=#{@document.file_name}"
  response.headers['Cache-Control'] =  "private"
  response.headers['X-Accel-Redirect'] = @document.file_name.url
  send_file(@document.file_name.url, disposition: 'attachment')
end

document的 表内容：

def change
    create_table :documents do |t|
      t.string :file_name
      t.string :file_type
      t.integer :user_id

      t.timestamps
    end
    add_index :documents, [:user_id, :created_at]
  end

routes.rb如下：

resources :documents, only: [:create,:destroy] do
    member do
      get :download
    end
  end

请问，我该怎么下载远程文件呢？非常感谢。