Class StrLenField

scapy/fields.py:1970–2003

StrField with a length :param length_from: a function that returns the size of the string :param max_length: max size to use as randval

class StrLenField(StrField):
    """
    StrField with a length

    :param length_from: a function that returns the size of the string
    :param max_length: max size to use as randval
    """
    __slots__ = ["length_from", "max_length"]
    ON_WIRE_SIZE_UTF16 = True

    def __init__(
            self,
            name,  # type: str
            default,  # type: bytes
            length_from=None,  # type: Optional[Callable[[Packet], int]]
            max_length=None,  # type: Optional[Any]
    ):
        # type: (...) -> None
        super(StrLenField, self).__init__(name, default)
        self.length_from = length_from
        self.max_length = max_length

    def getfield(self, pkt, s):
        # type: (Any, bytes) -> Tuple[bytes, bytes]
        len_pkt = (self.length_from or (lambda x: 0))(pkt)
        if not self.ON_WIRE_SIZE_UTF16:
            len_pkt *= 2
        if len_pkt == 0:
            return s, b""
        return s[len_pkt:], self.m2i(pkt, s[:len_pkt])

    def randval(self):
        # type: () -> RandBin
        return RandBin(RandNum(0, self.max_length or 1200))


class _XStrField(Field[bytes, bytes]):