code: def get_data_len(self):
          # type: () -> int
          
          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
docs: get_data_len computes the length of the data 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
          @raise AssertionError