docs: 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
          @raise 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