Class H2PaddedHeadersFrame

scapy/contrib/http2.py:1525–1570

H2PaddedHeadersFrame is the variant of H2HeadersFrame where padding flag is set and priority flag is cleared

class H2PaddedHeadersFrame(H2AbstractHeadersFrame):
    """ H2PaddedHeadersFrame is the variant of H2HeadersFrame where padding flag
    is set and priority flag is cleared
    """
    __slots__ = ['s_len']

    name = 'HTTP/2 Headers Frame with Padding'
    fields_desc = [
        fields.FieldLenField('padlen', None, length_of='padding', fmt='B'),
        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 and the actual
        padding is subtracted to the string that was provided to the pre_dissect  # noqa: E501
        fun of the pkt parameter.
        :return: int; length of the data part of the HTTP/2 frame packet provided as parameter  # noqa: E501
        :raises: AssertionError
        """
        padding_len = self.getfieldval('padlen')
        fld, fval = self.getfield_and_val('padlen')
        padding_len_len = fld.i2len(self, fval)

        ret = self.s_len - padding_len_len - padding_len
        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


class H2PriorityHeadersFrame(H2AbstractHeadersFrame):