onMessage called every time that subscribe to a topic

[alirezaimi]

Hi When my esp8266 subscribe to topic if there is value in it, onMessage() function called ! Why !? is this right behavior ?

[256dpi]

Every subscription to a topic will cause the last retained message to be sent to the client.

[alirezaimi]

Thx, but how can I subscribe to a topic on my esp board that does not call onMessage method ?

[David-2D3FE9]

Hello,

I am not sure to understand you want to do:

• You want your ESP to suscribe to a topic of an mqtt broker
• But you don't want the .onMessage() method

I am right ?

[alirezaimi]

Hi, I want my esp to subscribe to a topic and after that subscription the .onMessage method does not called for this subscription ./ as you said before : Every subscription to a topic will cause the last retained message to be sent to the client. ,, in esp board this will cause to calling onMessage method after that subscription that in some case not important .

if i want to only 1- subscribe to topic 2- write a message 3- unsubscribe i want only this, not read last retain message or another this come to esp board .

[David-2D3FE9]

You don't need to suscribe to a topic to be able to publish somthing in it .

• Suscrire is to read a topic
• Publish is to write in a topic

In other words you can comment or delete client.subscribe("/hello"); in your test script. Doing this, wil still publish the dataworld in the hello topic without any return for your board

@256dpi Does an exemple publishing at an interval of 1s on a WAN public server is respectfull ? Should we/you update the exemples to 2s or more ? I can make a pull request on each examples if you wish

[alirezaimi]

@David-2D3FE9 Hi and thanks for your reply, but when esp doesn't subscribe to a topic doesn't read message come from other side of mqtt server, i mean mqtt client, the onMessage does not work at all and i can't command to my esp from outside .

the real problem is every time that i subscribe to a topic, the onMessage called that i think this is wrong behavior .

And some other thing, every time that I make connect again because of disconnection I have to subscribe again to every topic again .

[256dpi]

As I suggested in my first comment, this behaviour sounds like there is a message retained on your topic that is sent every time you subscribe. That behaviour is correct and documented in the specification. Also note: This library cannot produce MQTT messages out of thin air, if onMessage is called, it's because the server has sent a message.

To your other problem: The library does not store subscriptions and resubscribe them when reconnecting. You either need to resubscribe or use a persistent MQTT session if the broker allows it.

[David-2D3FE9]

maybe you can paste your code, I will try to help you we may start a discussion I think, we will came back here if the problem persist or to close this issue
Because as sayed by 256dpi the problem sounds being outhere ;-)

[256dpi]

I'm closing this for now as the issue was probably in user code.

[alirezaimi]

There is no issue in my code, after every publish on server, the onMessage` called ! why !? When my esp8266 publish a message to mqtt server, the onMessage get same message comes from server ! this is odd ! if there is a way that i could get message sender info i maybe could turn around issue for now but should be a better logical way to call onMessage function .