def dns_encode(x, check_built=False):
    """Encodes a bytes string into the DNS format

    :param x: the string
    :param check_built: detect already-built strings and ignore them
    :returns: the encoded bytes string
    """
    if not x or x == b".":
        return b"\x00"

    if check_built and b"." not in x and (
        orb(x[-1]) == 0 or (orb(x[-2]) & 0xc0) == 0xc0
    ):
        # The value has already been processed. Do not process it again
        return x

    # Truncate chunks that cannot be encoded (more than 63 bytes..)
    x = b"".join(chb(len(y)) + y for y in (k[:63] for k in x.split(b".")))
    if x[-1:] != b"\x00":
        x += b"\x00"
    return x