class Zip::OutputStream

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

Same as #open but writes to a filestream instead 
def write_buffer(io = ::StringIO.new, dep_encrypter = nil, encrypter: nil)
  Zip.warn_about_v3_api('Zip::OutputStream.write_buffer') unless dep_encrypter.nil?
  io.binmode if io.respond_to?(:binmode)
  zos = new(io, stream: true, encrypter: (encrypter || dep_encrypter))
  yield zos
  zos.close_buffer
end