@property
def in_waiting(self):
    """Return the number of bytes currently in the input buffer."""
    if not self.is_open:
        raise PortNotOpenError()
    # Poll the socket to see if it is ready for reading.
    # If ready, at least one byte will be to read.
    lr, lw, lx = select.select([self._socket], [], [], 0)
    return len(lr)

while len(read) < size:
    try:
        ready, _, _ = select.select([self._socket], [], [], timeout.time_left())

  @property
  def in_waiting(self):
    """Return the number of bytes currently in the input buffer."""
    if not self.is_open:
        raise PortNotOpenError()
        
    if os.name == 'nt':  # Windows
        return len(sock.recv(4096, socket.MSG_PEEK))
        
    else:  # POSIX (Unix-like)
        import fcntl
        import struct
        import termios
        
        buf = fcntl.ioctl(self._socket, termios.FIONREAD, struct.pack("I", 0))
        nbytes = struct.unpack("I", buf)[0]
        return nbytes