mqtt连接上的更改将

Question

We are using the mqtt.js ( https://www.npmjs.com/package/mqtt ) client to connect to AWS IoT service.

We can connect no problem and pass in last will with the following code

var clientOptions = {
    will: {
        topic: "logout",
        payload: JSON.stringify({ _id: User.me._id, viewing: User.me.viewing })
    }
};  

client = mqtt.connect(signedUrl, clientOptions);

Now I want to update the will portion of the options--change the payload to have a new viewing property.

Is there a way to update the will without disconnecting and triggering the old will?

Answer 1

There is no way to change the Last Will and Testament, it can only be set in the connect packet.

But the Last Will and Testament should only fire if the client times out, not on a clean disconnect. This means you should be able to tell the client to disconnect and reconnect with a new LWT without triggering the old one to be published.

It you use clean session false and subscribe at QOS1 or better then you should not miss any messages when you reconnect as the broker should queue and deliver them on reconnect.