聊聊nacos config的doPollingConfig

序

本文主要研究一下nacos config的doPollingConfig

ConfigController

nacos-1.1.3/config/src/main/java/com/alibaba/nacos/config/server/controller/ConfigController.java

@Controller
@RequestMapping(Constants.CONFIG_CONTROLLER_PATH)
public class ConfigController {

    private static final Logger log = LoggerFactory.getLogger(ConfigController.class);

    private static final String NAMESPACE_PUBLIC_KEY = "public";

    public static final String EXPORT_CONFIG_FILE_NAME = "nacos_config_export_";

    public static final String EXPORT_CONFIG_FILE_NAME_EXT = ".zip";

    public static final String EXPORT_CONFIG_FILE_NAME_DATE_FORMAT = "yyyy-MM-dd HH:mm:ss";

    private final transient ConfigServletInner inner;

    private final transient PersistService persistService;

    private final transient ConfigSubService configSubService;

    //......

    @RequestMapping(value = "/listener", method = RequestMethod.POST)
    public void listener(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        request.setAttribute("org.apache.catalina.ASYNC_SUPPORTED", true);
        String probeModify = request.getParameter("Listening-Configs");
        if (StringUtils.isBlank(probeModify)) {
            throw new IllegalArgumentException("invalid probeModify");
        }

        probeModify = URLDecoder.decode(probeModify, Constants.ENCODE);

        Map<String, String> clientMd5Map;
        try {
            clientMd5Map = MD5Util.getClientMd5Map(probeModify);
        } catch (Throwable e) {
            throw new IllegalArgumentException("invalid probeModify");
        }

        // do long-polling
        inner.doPollingConfig(request, response, clientMd5Map, probeModify.length());
    }

    //......
}

ConfigController的listener方法会从request中读取Listening-Configs参数，然后decode，计算clientMd5Map，最后执行inner.doPollingConfig

ConfigServletInner

nacos-1.1.3/config/src/main/java/com/alibaba/nacos/config/server/controller/ConfigServletInner.java

@Service
public class ConfigServletInner {

    @Autowired
    private LongPollingService longPollingService;

    @Autowired
    private PersistService persistService;

    private static final int TRY_GET_LOCK_TIMES = 9;

    private static final int START_LONGPOLLING_VERSION_NUM = 204;

    /**
     * 轮询接口
     */
    public String doPollingConfig(HttpServletRequest request, HttpServletResponse response,
                                  Map<String, String> clientMd5Map, int probeRequestSize)
        throws IOException, ServletException {

        // 长轮询
        if (LongPollingService.isSupportLongPolling(request)) {
            longPollingService.addLongPollingClient(request, response, clientMd5Map, probeRequestSize);
            return HttpServletResponse.SC_OK + "";
        }

        // else 兼容短轮询逻辑
        List<String> changedGroups = MD5Util.compareMd5(request, response, clientMd5Map);

        // 兼容短轮询result
        String oldResult = MD5Util.compareMd5OldResult(changedGroups);
        String newResult = MD5Util.compareMd5ResultString(changedGroups);

        String version = request.getHeader(Constants.CLIENT_VERSION_HEADER);
        if (version == null) {
            version = "2.0.0";
        }
        int versionNum = Protocol.getVersionNumber(version);

        /**
         * 2.0.4版本以前, 返回值放入header中
         */
        if (versionNum < START_LONGPOLLING_VERSION_NUM) {
            response.addHeader(Constants.PROBE_MODIFY_RESPONSE, oldResult);
            response.addHeader(Constants.PROBE_MODIFY_RESPONSE_NEW, newResult);
        } else {
            request.setAttribute("content", newResult);
        }

        // 禁用缓存
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setHeader("Cache-Control", "no-cache,no-store");
        response.setStatus(HttpServletResponse.SC_OK);
        return HttpServletResponse.SC_OK + "";
    }

    //......
}

ConfigServletInner的doPollingConfig方法首先判断request是否支持long polling，支持的话则执行longPollingService.addLongPollingClient；不支持的话则将newResult放入content中，然后返回

LongPollingService

nacos-1.1.3/config/src/main/java/com/alibaba/nacos/config/server/service/LongPollingService.java

@Service
public class LongPollingService extends AbstractEventListener {

    private static final int FIXED_POLLING_INTERVAL_MS = 10000;

    private static final int SAMPLE_PERIOD = 100;

    private static final int SAMPLE_TIMES = 3;

    private static final String TRUE_STR = "true";

    private Map<String, Long> retainIps = new ConcurrentHashMap<String, Long>();

    private static boolean isFixedPolling() {
        return SwitchService.getSwitchBoolean(SwitchService.FIXED_POLLING, false);
    }

    //......

    static public boolean isSupportLongPolling(HttpServletRequest req) {
        return null != req.getHeader(LONG_POLLING_HEADER);
    }

    public void addLongPollingClient(HttpServletRequest req, HttpServletResponse rsp, Map<String, String> clientMd5Map,
                                     int probeRequestSize) {

        String str = req.getHeader(LongPollingService.LONG_POLLING_HEADER);
        String noHangUpFlag = req.getHeader(LongPollingService.LONG_POLLING_NO_HANG_UP_HEADER);
        String appName = req.getHeader(RequestUtil.CLIENT_APPNAME_HEADER);
        String tag = req.getHeader("Vipserver-Tag");
        int delayTime = SwitchService.getSwitchInteger(SwitchService.FIXED_DELAY_TIME, 500);
        /**
         * 提前500ms返回响应，为避免客户端超时 @qiaoyi.dingqy 2013.10.22改动  add delay time for LoadBalance
         */
        long timeout = Math.max(10000, Long.parseLong(str) - delayTime);
        if (isFixedPolling()) {
            timeout = Math.max(10000, getFixedPollingInterval());
            // do nothing but set fix polling timeout
        } else {
            long start = System.currentTimeMillis();
            List<String> changedGroups = MD5Util.compareMd5(req, rsp, clientMd5Map);
            if (changedGroups.size() > 0) {
                generateResponse(req, rsp, changedGroups);
                LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}|{}",
                    System.currentTimeMillis() - start, "instant", RequestUtil.getRemoteIp(req), "polling",
                    clientMd5Map.size(), probeRequestSize, changedGroups.size());
                return;
            } else if (noHangUpFlag != null && noHangUpFlag.equalsIgnoreCase(TRUE_STR)) {
                LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}|{}", System.currentTimeMillis() - start, "nohangup",
                    RequestUtil.getRemoteIp(req), "polling", clientMd5Map.size(), probeRequestSize,
                    changedGroups.size());
                return;
            }
        }
        String ip = RequestUtil.getRemoteIp(req);
        // 一定要由HTTP线程调用，否则离开后容器会立即发送响应
        final AsyncContext asyncContext = req.startAsync();
        // AsyncContext.setTimeout()的超时时间不准，所以只能自己控制
        asyncContext.setTimeout(0L);

        scheduler.execute(
            new ClientLongPolling(asyncContext, clientMd5Map, ip, probeRequestSize, timeout, appName, tag));
    }

    //......
}

LongPollingService的isSupportLongPolling是通过判断request是否有LONG_POLLING_HEADER的header来实现的；addLongPollingClient方法主要是创建ClientLongPolling，然后提交到scheduler执行

ClientLongPolling