class Rack::Multipart::Generator

def dump
  return nil if @first && !multipart?
  return flattened_params unless @first
  flattened_params.map do |name, file|
    if file.respond_to?(:original_filename)
      if file.path
        ::File.open(file.path, 'rb') do |f|
          f.set_encoding(Encoding::BINARY)
          content_for_tempfile(f, file, name)
        end
      else
        content_for_tempfile(file, file, name)
      end
    else
      content_for_other(file, name)
    end
  end.join << "--#{MULTIPART_BOUNDARY}--\r"
end