Class PacketLenField

scapy/fields.py:1592–1619

class PacketLenField(_PacketFieldSingle[Optional[BasePacket]]):
    __slots__ = ["length_from"]

    def __init__(self,
                 name,  # type: str
                 default,  # type: Packet
                 cls,  # type: Union[Callable[[bytes], Packet], Type[Packet]]  # noqa: E501
                 length_from=None  # type: Optional[Callable[[Packet], int]]  # noqa: E501
                 ):
        # type: (...) -> None
        super(PacketLenField, self).__init__(name, default, cls)
        self.length_from = length_from or (lambda x: 0)

    def getfield(self,
                 pkt,  # type: Packet
                 s,  # type: bytes
                 ):
        # type: (...) -> Tuple[bytes, Optional[BasePacket]]
        len_pkt = self.length_from(pkt)
        i = None
        if len_pkt:
            try:
                i = self.m2i(pkt, s[:len_pkt])
            except Exception:
                if conf.debug_dissector:
                    raise
                i = conf.raw_layer(load=s[:len_pkt])
        return s[len_pkt:], i


class PacketListField(_PacketField[List[BasePacket]]):