generic_file.rb

  CHUNK = 1024**2
  
  def add_file(file, dsid, file_name)
    return add_external_file(file, file_name) if dsid == 'content'
    super
  end

  def add_external_file(file, original_filename)
    external_file_path = generate_external_file_path

    if file.respond_to? :read
      File.open(external_file_path, "wb") do |f|
        f.write(file.read(CHUNK)) until file.eof?
        file.rewind
      end
    elsif File.exists? file
      FileUtils.mv file, external_file_path
    else
      raise ArgumentError, "File not found: #{file.inspect}"
    end

    content.dsLocation = URI.escape("file://#{external_file_path}")

    mime = MIME::Types.type_for(original_filename).first
    content.mimeType = mime.content_type if mime # mime can't always be detected by filename                                           

    self.label = original_filename

    save!
  end

  private

  # Generates a random filename                                                                                                        
  def generate_external_file_path
    filename = SecureRandom.uuid
    dir = File.join CourseAssets.external_datastore_base, filename[0], filename[1]
    FileUtils.mkdir_p dir unless Dir.exists? dir
    File.join dir, filename
  end