Class FieldUVarLenField

scapy/contrib/http2.py:555–633

class FieldUVarLenField(AbstractUVarIntField):
    __slots__ = ['_length_of', '_adjust']

    def __init__(self, name, default, size, length_of, adjust=lambda x: x):
        # type: (str, Optional[int], int, str, Callable[[int], int]) -> None
        """ Initializes a FieldUVarLenField

        :param str name: The name of this field instance.
        :param int|None default: the default value of this field instance.
        :param int size: the number of bits that are occupied by this field in the first byte of a binary string.  # noqa: E501
          size must be in the range ]0;8].
        :param str length_of: The name of the field this field value is measuring/representing.  # noqa: E501
        :param callable adjust: A function that modifies the value computed from the "length_of" field.  # noqa: E501

        adjust can be used for instance to add a constant to the length_of field  # noqa: E501
         length. For instance, let's say that i2len of the length_of field
         returns 2. If adjust is lambda x: x+1 In that case, this field will
         value 3 at build time.
        :return: None
        :raises: AssertionError
        """
        assert default is None or default >= 0
        assert 0 < size <= 8

        super(FieldUVarLenField, self).__init__(name, default, size)
        self._length_of = length_of
        self._adjust = adjust

    def addfield(self, pkt, s, val):
        # type: (Optional[packet.Packet], Union[str, Tuple[str, int, int]], Optional[int]) -> str  # noqa: E501
        """
        :param packet.Packet|None pkt: the packet instance containing this field instance. This parameter must not be  # noqa: E501
          None if the val parameter is.
        :param str|(str, int, long) s: the string to append this field to. A tuple indicates that some bits were already  # noqa: E501
          generated by another bitfield-compatible field. This MUST be the case if "size" is not 8. The int is the  # noqa: E501
          number of bits already generated in the first byte of the str. The long is the value that was generated by the  # noqa: E501
          previous bitfield-compatible fields.
        :param int|None val: the positive or null value to be added. If None, the value is computed from pkt.  # noqa: E501
        :return: str: s concatenated with the machine representation of this field.  # noqa: E501
        :raises: AssertionError
        """
        if val is None:
            assert isinstance(pkt, packet.Packet), \
                'EINVAL: pkt: Packet expected when val is None; received {}'.format(type(pkt))  # noqa: E501
            val = self._compute_value(pkt)
        return super(FieldUVarLenField, self).addfield(pkt, s, val)

    def i2m(self, pkt, x):
        # type: (Optional[packet.Packet], Optional[int]) -> str
        """
        :param packet.Packet|None pkt: the packet instance containing this field instance. This parameter must not be  # noqa: E501
          None if the x parameter is.
        :param int|None x: the positive or null value to be added. If None, the value is computed from pkt.  # noqa: E501
        :return: str
        :raises: AssertionError
        """
        if x is None:
            assert isinstance(pkt, packet.Packet), \