class Zip::InputStream

def get_io(io_or_file, offset = 0)
  if io_or_file.respond_to?(:seek)
    io = io_or_file.dup
    io.seek(offset, ::IO::SEEK_SET)
    io
  else
    file = ::File.open(io_or_file, 'rb')
    file.seek(offset, ::IO::SEEK_SET)
    file
  end
end