Class PacketListField

scapy/fields.py:1622–1857

PacketListField represents a list containing a series of Packet instances that might occur right in the middle of another Packet field. This field type may also be used to indicate that a series of Packet instances have a sibling semantic instead of a parent/child relationship (i.e.

class PacketListField(_PacketField[List[BasePacket]]):
    """PacketListField represents a list containing a series of Packet instances
    that might occur right in the middle of another Packet field.
    This field type may also be used to indicate that a series of Packet
    instances have a sibling semantic instead of a parent/child relationship
    (i.e. a stack of layers). All elements in PacketListField have current
    packet referenced in parent field.
    """
    __slots__ = ["count_from", "length_from", "next_cls_cb", "max_count"]
    islist = 1

    def __init__(
            self,
            name,  # type: str
            default,  # type: Optional[List[BasePacket]]
            pkt_cls=None,  # type: Optional[Union[Callable[[bytes], Packet], Type[Packet]]]  # noqa: E501
            count_from=None,  # type: Optional[Callable[[Packet], int]]
            length_from=None,  # type: Optional[Callable[[Packet], int]]
            next_cls_cb=None,  # type: Optional[Callable[[Packet, List[BasePacket], Optional[Packet], bytes], Optional[Type[Packet]]]]  # noqa: E501
            max_count=None,  # type: Optional[int]
    ):
        # type: (...) -> None
        """
        The number of Packet instances that are dissected by this field can
        be parametrized using one of three different mechanisms/parameters:

            * count_from: a callback that returns the number of Packet
              instances to dissect. The callback prototype is::

                count_from(pkt:Packet) -> int

            * length_from: a callback that returns the number of bytes that
              must be dissected by this field. The callback prototype is::

                length_from(pkt:Packet) -> int

            * next_cls_cb: a callback that enables a Scapy developer to
              dynamically discover if another Packet instance should be
              dissected or not. See below for this callback prototype.

        The bytes that are not consumed during the dissection of this field
        are passed to the next field of the current packet.

        For the serialization of such a field, the list of Packets that are
        contained in a PacketListField can be heterogeneous and is
        unrestricted.

        The type of the Packet instances that are dissected with this field is
        specified or discovered using one of the following mechanism:

            * the pkt_cls parameter may contain a callable that returns an
              instance of the dissected Packet. This may either be a
              reference of a Packet subclass (e.g. DNSRROPT in layers/dns.py)
              to generate an homogeneous PacketListField or a function
              deciding the type of the Packet instance
              (e.g. _CDPGuessAddrRecord in contrib/cdp.py)

            * the pkt_cls parameter may contain a class object with a defined