code: private static FullHttpResponse createUpgradeResponse(CharSequence upgradeProtocol) {
          DefaultFullHttpResponse res = new DefaultFullHttpResponse(HTTP_1_1, SWITCHING_PROTOCOLS,
                  Unpooled.EMPTY_BUFFER, false);
          res.headers().add(HttpHeaderNames.CONNECTION, HttpHeaderValues.UPGRADE);
          res.headers().add(HttpHeaderNames.UPGRADE, upgradeProtocol);
          return res;
      }
docs: Creates the 101 Switching Protocols response message.