October 2019
Intermediate to advanced
350 pages
9h 5m
English
Content preview from Hands-On Internet of Things with MQTT
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Last will messages
Network connections can be volatile, and there are many things that can lead to them being disconnected—temporarily or permanently. Not only can a connection fail, but a device might run out of power (blackout or empty batteries). MQTT has an option called last will/testament, which makes it possible to publish a message when a device goes offline: a protocol or I/O error occurs when the device does not call back in a certain amount of time (the keep-alive time), or the application gets terminated without being disconnected from the server properly.
Similar to a regular MQTT message, a last will message is sent to a certain channel. A very good use case for the last will feature is posting an update to a status channel. ...
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