追赶错过的消息 [英] Catch-up missed messages

问题描述

据我了解，当消息发布到某个主题时，只有当前订阅该主题的客户端才能接收到该消息.如果客户端在消息发布后出现，它将不会收到该消息.

As far as my understanding goes, when a message is published to a topic, it is received by only the clients currently subscribed to that topic. If a client turns up after the message is published, it won't receive that message.

假设客户端暂时断开连接，有什么方法可以帮助客户端赶上再次连接时丢失的消息?

Suppose a client is disconnected momentarily, is there a way to help the client catch-up with the messages missed when it is connected again?

谢谢

推荐答案

如果客户端订阅了主题，则与代理的连接将被断开，客户端将需要重新连接.

If a client subscribes to a topic then the connection to the broker is dropped, the client will need to reconnect.

只要客户端在连接上设置cleanSession = false标志并重新订阅相同的主题，代理就应重播所有丢失的消息.

As long as client sets the cleanSession=false flag on the connection and resubscribes to the same topics the broker should replay any missed messages.

有关持久订阅的更详细说明，请参见:

A more detailed description of durable subscriptions can be found here:

http://www.hivemq.com /mqtt-essentials-part-7-persistent-session-queuing-messages/

在这里:

http://www.thingsprime.com/?p=2897

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