Class H2PaddedPushPromiseFrame

scapy/contrib/http2.py:1807–1859

H2PaddedPushPromiseFrame implements RFC7540 par6.6. This packet is the variant to use when the underlayer padding flag is set

class H2PaddedPushPromiseFrame(H2PushPromiseFrame):
    """ H2PaddedPushPromiseFrame implements RFC7540 par6.6. This
    packet is the variant to use when the underlayer padding flag is set
    """
    __slots__ = ['s_len']

    name = 'HTTP/2 Padded Push Promise Frame'
    fields_desc = [
        fields.FieldLenField('padlen', None, length_of='padding', fmt='B'),
        fields.BitField('reserved', 0, 1),
        fields.BitField('stream_id', 0, 31),
        fields.PacketListField('hdrs', [], HPackHeaders,
                               length_from=lambda pkt: pkt.get_hdrs_len()
                               ),
        fields.StrLenField('padding', '',
                           length_from=lambda pkt: pkt.getfieldval('padlen')
                           )
    ]

    def get_hdrs_len(self):
        # type: () -> int
        """ get_hdrs_len computes the length of the hdrs field

        To do this computation, the length of the padlen field, reserved,
        stream_id and the actual padding is subtracted to the string that was
        provided to the pre_dissect fun of the pkt parameter.
        :return: int: the length of the hdrs field
        :raises: AssertionError
        """
        fld, padding_len = self.getfield_and_val('padlen')
        padding_len_len = fld.i2len(self, padding_len)
        bit_len = self.get_field('reserved').size
        bit_len += self.get_field('stream_id').size

        ret = int(self.s_len -
                  padding_len_len -
                  padding_len -
                  (bit_len / 8)
                  )
        assert ret >= 0
        return ret

    def pre_dissect(self, s):
        # type: (str) -> str
        """pre_dissect is filling the s_len property of this instance. This
        property is later used during the parsing of the hdrs PacketListField
        when trying to evaluate the length of the PacketListField! This "trick"
        works because the underlayer packet (H2Frame) is assumed to override the  # noqa: E501
        "extract_padding" method and to only provide to this packet the data
        necessary for this packet. Tricky, tricky, will break some day probably!  # noqa: E501
        """
        self.s_len = len(s)
        return s

#                                               HTTP/2 Ping Frame Packets                                              #  # noqa: E501