Mosquitto doesn't publish Last Will when LWT Delay interval is specified (MQTT v5.0)

[HamzaHajeir]

Hi there,

I've noticed that Mosquitto doesn't publish Last Will & Testament when I set LWT Delay Interval.

• OS: Windows 11
• Version: 2.0.15
• MQTT Version: 5

Wireshark ensures setting the LWT within CONNECT packet, and here's a hexdump:

0x00000000     0:  10 8F 01 00 04 4D 51 54 54 05 36 00 12 39 11 00   .....MQTT.6..9..
0x00000010    16:  00 0E 10 21 00 19 27 00 00 14 50 22 00 32 17 01   ...!..'...P".2..
0x00000020    32:  19 01 26 00 0A 55 73 65 72 2D 41 67 65 6E 74 00   ..&..User-Agent.
0x00000030    48:  16 48 34 41 73 79 6E 63 4D 51 54 54 20 76 31 2E   .H4AsyncMQTT v1.
0x00000040    64:  30 2E 30 2D 72 63 36 00 18 53 53 54 2D 53 6D 61   0.0-rc6..SST-Sma
0x00000050    80:  72 74 53 6F 63 6B 65 74 33 41 2D 30 30 30 30 32   rtSocket3A-00002
0x00000060    96:  30 07 01 01 18 00 00 00 19 00 1E 53 53 54 2D 53   0..........SST-S
0x00000070   112:  6D 61 72 74 53 6F 63 6B 65 74 33 41 2D 30 30 30   martSocket3A-000
0x00000080   128:  30 32 30 2F 73 74 61 74 65 00 07 6F 66 66 6C 69   020/state..offli
0x00000090   144:  6E 65                                             ne

Image from Wireshark to dump the CONNECT Packet:

* There's a LWT Delay interval of 25 seconds
* Retain is enabled for the LW, QoS2.
* keepalive: 18 seconds

Mosquitto configuration file:

per_listener_settings true

listener 1883
allow_anonymous true

listener 8883 0.0.0.0
allow_anonymous true

# Path to the PEM encoded server certificate.
certfile C:\Program Files\mosquitto-2-0-15\certs\mqtt.crt

# Path to the PEM encoded keyfile.
keyfile C:\Program Files\mosquitto-2-0-15\certs\mqtt.key

The client sends "online" to "SST-SmartSocketA3-000020/state" (Retain, QoS2) topic when connected.
Never received the "offline" LWT.

Eliminated the LW Delay Interval, and the LWT is published immediately.

1696107762: Client SST-SmartSocket3A-000020 has exceeded timeout, disconnecting.
1696107762: Sending PUBLISH to mqtt-explorer-4a8cd6fd (d0, q0, r0, m0, 'SST-SmartSocket3A-000020/state', ... (7 bytes))
1696107762: Sending PUBLISH to mqttx_4e47ea97 (d0, q2, r0, m7, 'SST-SmartSocket3A-000020/state', ... (7 bytes))