MQTT 客户端自动重连机制

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Paho 客户端的 python 实现：
https://pypi.org/project/paho-mqtt/

进入 client 的事件循环之后，Paho client 内部将会自动处理掉线重连。但是重连后的状态变化，重连的重试次数等，需要小心处理。

以下几个参数与函数接口需要特别留意。

• loop_start()、loop_forever() 接口进入 client 事件循环，此时开始将自动处理掉线重连的问题。

It automatically handles reconnecting.

• Client 对象构造的参数 clean_session，默认为 True，在重连后，该 client 在 broker 的状态将会被清除。

a boolean that determines the client type. If True, the broker will remove all information about this client when it disconnects. If False, the client is a durable client and subscription information and queued messages will be retained when the client disconnects.Note that a client will never discard its own outgoing messages on disconnect. Calling connect() or reconnect() will cause the messages to be resent. Use reinitialise() to reset a client to its original state.

• reconnect_delay_set(min_delay=1, max_delay=120) 接口决定掉线重连时的重试次数，在网络较差的情况下不妨把 max 值设置大一点。

The client will automatically retry connection. Between each attempt it will wait a number of seconds between min_delay and max_delay.
When the connection is lost, initially the reconnection attempt is delayed of min_delay seconds. It’s doubled between subsequent attempt up to max_delay.

• on_connect(client, userdata, flags, rc) 回调中的 flags 参数也需要注意，他提示了此时 broker 中是否还保留有 client 先前相关信息。如果前面的 clean_session 设置为 True 的话，这个 flags 不用理会。否则，就要考虑重新订阅相应的主题等问题了。

using clean session set to 0 only. If a client with clean session=0, that reconnects to a broker that it has previously connected to, this flag indicates whether the broker still has the session information for the client. If 1, the session still exists.

MQTT 客户端自动重连机制

标签：rev   his   flag   data   对象   事件   _for   提示   sub   

原文地址：https://www.cnblogs.com/liaojieliang/p/mqtt-paho-reconnect.html