class IO

def readline_nonblock(sep = $INPUT_RECORD_SEPARATOR)
  line = +''
  buffer = +''
  loop do
    break if buffer == sep
    read_nonblock(1, buffer)
    line.concat(buffer)
  end
  line.freeze
rescue IO::WaitReadable, EOFError => e
  raise e if line.empty?
  line.freeze
end