LWT sent on normal disconnection

[nrbrook]

I have the following typescript code, using MQTT.js 4.3.7:

private init():void {
        this.client = mqtt.connect(`mqtt://${process.env.BROKER_API}`, {
            will: {
                topic: "kfobdmsg/server/status",
                payload: "offline-unexpected",
                qos: 1,
                retain: true
            },
            clean: false,
            clientId: "kfobdmsg-server",
            username: process.env.BROKER_USERNAME,
            password: process.env.BROKER_PASSWORD
        });
        this.client.on("connect",()=>{
            console.log("Connected to broker!")
            this.client.publish("kfobdmsg/server/status", "online", {qos:1, retain:true});
        });
        this.client.on("error", (error:any) => {
            console.error("MQTT connection error:", error);
        });
    }
    
    public shutdown(complete: (result: boolean) => void): void {
        let success = true;
        console.log("Shutting down MQTT connection...");
        this.client.publish("kfobdmsg/server/status", "offline", {qos:1, retain:true}, (error:any)=>{
            if(error) {
                console.error("Error publishing offline message:", error);
                success = false;
            }
            console.log("Published offline message!");
            this.client.end(false, {
                reasonCode: 0,
                properties: {
                    reasonString: "Server shutting down"
                }
            }, (error:any)=>{
                if(error) {
                    console.error("Error disconnecting from broker:", error);
                    success = false;
                }
                console.log("Disconnected from broker!");
                complete(success);
            });
        });
        
    }

When shutdown is called, I get the following console output:

Shutting down MQTT connection...
Published offline message!
Disconnected from broker!

However, observing the published messages shows "offline" is published (correct) followed by "offline-unexpected"? Why is the LWT sent on normal connection close? I've attached a Wireshark trace.

mqtt capture.pcapng.zip

[nrbrook]

For clarity, attached another capture with no active subscribers. I can't see a disconnect message?

mqtt capture no observer.pcapng.zip

[robertsLando]

Try reproduce this with also broker in the same script. You can use Aedes broker for example. Once you reproduce it in a simple script you can also try to do a debug on mqttjs side. The LWT is sent by the broker when he detects an unexpected close of connection by the client (disconnect packet isn't received and ack)