code: private void validateRSV(byte opcodeByte) throws ProtocolDecoderException {
          if ((opcodeByte & 0x70) != 0) {
              // We don't support negotiated extensions that deal with RSV bits
              if ((opcodeByte & 0x40) != 0) {
                  throw new ProtocolDecoderException("RSV1 is set");
              }
              if ((opcodeByte & 0x20) != 0) {
                  throw new ProtocolDecoderException("RSV2 is set");
              }
              if ((opcodeByte & 0x10) != 0) {
                  throw new ProtocolDecoderException("RSV3 is set");
              }
          }
      }
docs: Validates RSV bits