code: def pre_dissect(self, s):
          
          if len(s) < 5:
              raise Exception("Invalid record: header is too short.")
  
          if isinstance(self.tls_session.rcs.cipher, Cipher_NULL):
              self.deciphered_len = None
              return s
          else:
              msglen = struct.unpack('!H', s[3:5])[0]
              hdr, efrag, r = s[:5], s[5:5 + msglen], s[msglen + 5:]
              frag, auth_tag = self._tls_auth_decrypt(efrag)
              self.deciphered_len = len(frag)
              return hdr + frag + auth_tag + r
docs: Decrypt, verify and decompress the message.