MQTT---HiveMQ源码详解(十一)Netty-Throttling

实现功能

• 读取用户throttling配置，对broker的连接、消息进行限制，以保证broker在最健康、最效率的时间去serve

类图

• 它的流量限制是使用GlobalTrafficShapingHandler去完成的，由GlobalTrafficShapingHandlerProvider来提供。

public class GlobalTrafficShapingHandlerProvider
        implements Provider<GlobalTrafficShapingHandler> {
    private static final Logger LOGGER = LoggerFactory.getLogger(GlobalTrafficShapingHandlerProvider.class);
    private final ShutdownRegistry shutdownRegistry;
    private final ThrottlingConfigurationService throttlingConfigurationService;

    @Inject
    GlobalTrafficShapingHandlerProvider(ShutdownRegistry shutdownRegistry,
                                        ThrottlingConfigurationService throttlingConfigurationService) {
        this.shutdownRegistry = shutdownRegistry;
        this.throttlingConfigurationService = throttlingConfigurationService;
    }

    @Override
    public GlobalTrafficShapingHandler get() {
        ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("global-traffic-shaping-executor-%d").build();
        ScheduledExecutorService globalTrafficShapingExecutorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
        GlobalTrafficShapingExecutorShutdown shutdown = new GlobalTrafficShapingExecutorShutdown(globalTrafficShapingExecutorService);
        this.shutdownRegistry.register(shutdown);
        long incomingLimit = this.throttlingConfigurationService.incomingLimit();
        LOGGER.debug("Throttling incoming traffic to {} B/s", incomingLimit);
        long outgoingLimit = this.throttlingConfigurationService.outgoingLimit();
        LOGGER.debug("Throttling outgoing traffic to {} B/s", outgoingLimit);
        GlobalTrafficShapingHandler handler = new GlobalTrafficShapingHandler(globalTrafficShapingExecutorService, outgoingLimit, incomingLimit, 1000L);
        ValueChangedCallback changedCallback = createValueChangedCallback(handler);
        this.throttlingConfigurationService.incomingLimitChanged(changedCallback);
        this.throttlingConfigurationService.outgoingLimitChanged(changedCallback);
        return handler;
    }


    @NotNull
    private ValueChangedCallback<Long> createValueChangedCallback(GlobalTrafficShapingHandler handler) {
        return new ThrottlingTrafficLimitValueChangedCallback(handler, this.throttlingConfigurationService);
    }

    private static class ThrottlingTrafficLimitValueChangedCallback
            implements ValueChangedCallback<Long> {
        private final GlobalTrafficShapingHandler globalTrafficShapingHandler;
        private final ThrottlingConfigurationService throttlingConfigurationService;

        public ThrottlingTrafficLimitValueChangedCallback(GlobalTrafficShapingHandler globalTrafficShapingHandler,
                                                          ThrottlingConfigurationService throttlingConfigurationService) {
            this.globalTrafficShapingHandler = globalTrafficShapingHandler;
            this.throttlingConfigurationService = throttlingConfigurationService;
        }

        @Override
        public void valueChanged(Long newValue) {
            this.globalTrafficShapingHandler.configure(
                    this.throttlingConfigurationService.outgoingLimit(),
                    this.throttlingConfigurationService.incomingLimit());
        }
    }
}

• GlobalTrafficShapingHandlerProvider通过使用ThrottlingConfigurationService读取用户配置，来限制incoming和outgoing。

• 同时给ShutdownRegistry注册一个GlobalTrafficShapingExecutorShutdown，以当broker关闭时，能够关闭GlobalTrafficShapingHandler中的ScheduledExecutorService。

• 由于MQTT协议中对remainingLength的限制在256m，如此大的数据，如果发到服务端，如果数量再一多，再优秀的mqtt broker都扛不住，所以它还提供了自定义最大消息长度，以保证broker稳定运行，以及攻击，是一个阻拦。 在MqttMessageDecoder中，来判断最大消息长度，来限制连接。

• LicenseConnectionLimiter是它读取license之后，根据license限制做的一个连接数限制，以及连接数占最大连接数限制的报警百分比限制。具体的license读取、license验证、license加密这一块由于不属于本章内容，所以不做过多细节介绍，并且由于它是商用软件，所以细节以后也不会不做透漏，请各位朋友谅解；因为本系列只是协助大家了解企业级的broker如何实现的，它考虑的思路是什么，而不是破坏别人知识产权的。

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