So if I understand correctly if I set the retain option to true on and MQTT node each time a client subscribes to a topic the server should send the last retained value. If this is correct I'm doing something wrong. Because on an Arduino Mega on a GSM module I don't seem to recieve these "initial" …

I've just done a quick test created mosca broker and set mqtt explorer to monitor it sent a retained msg using qos1 on topic mosca [image] msg arrives [image] if I disconnect Mqtt Explorer and re-connect - no mosca topic visible [image] So i'd say it doesn't retain messages

I don't understand. The steps I followed are: 1- Set the retain flag to true on the broker's output node (this was done literally weeks ago) 2- Subscribe to that topic What am I doing wrong?

I haven't used mqtt explorer, but it looks as if you are publishing to /down/tsetACS and subscribing to /down/deltaTACS. On a side note I thought it was not recommended to start topics with /

[image] Colin: On a side note I thought it was not recommended to start topics with / Good to know [image] Colin: I haven't used mqtt explorer, but it looks as if you are publishing to /down/tsetACS and subscribing to /down/deltaTACS. Sorry, my mistake. This was the first try where I …

If you publish a value to the topic (with retain still set) with explorer open does explorer then see it? If yes then what happens if you close the explorer and re-open it? What mqtt broker are you using?

[image] mbc99: 1- Set the retain flag to true on the broker's output node (this was done literally weeks ago) Something might help a bit. Node-Red is not the broker. Your MQTT server (aDDNSAdressToTheServer) is your broker. Node-Red is either a publisher or a subscriber. Flags set on your mes…

Understood. But that doesn't change anything does it? I mean, I think I understand correctly how the retain option works and I still don't get de desired/expected results.

You haven't answered the questions in my last post.

[image] Colin: You haven't answered the questions in my last post. Sorry [image] Colin: What mqtt broker are you using? I'm using node-red-contrib-mqtt-broker [image] node-red-contrib-mqtt-broker MQTT Broker server on Node-RED [image] Colin: …

What version of node.js are you using? Assuming it is 8.x 10.x or 12.x then it looks as if the broker is not working. I don't use that broker so can't check out myself. Perhaps someone who does use it can confirm whether it does work for them. Just one thought, try it with a topic that does not st…

MQTT retain option

General

dceejay 29 October 2019 19:07 2

You PUBLISH messages with the retain flag set to your broker. You then subscribe to that topic and if there is retained data for it it will be delivered with the retain flag set. If you are already subscribed before you publish then the flag won’t be set as it indicates if the data is “live” or not.

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MQTT retain option

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