class Zip::OutputStream

def write_buffer(io = ::StringIO.new(''), encrypter = nil)

Same as #open but writes to a filestream instead 
def write_buffer(io = ::StringIO.new(''), encrypter = nil)
  io.binmode if io.respond_to?(:binmode)
  zos = new(io, true, encrypter)
  yield zos
  zos.close_buffer
end