MQTT-Client BP-Node "Connect" Event-Dispatcher "OnConnect" does not fire.

[brugr9]

Steps to Reproduce:

A. As Is

1. Startup Mosquitto Brocker
2. Startup UE Project "Heartbeat51", Launch PIE
3. MQTT-Client BP-Node "Connect" works, see Fig. Wireshark dissection
4. MQTT-Client BP-Node "Connect" Event-Dispatcher "OnConnect" does not fire, see Fig.

Fig.: Wireshark Dissecting MQTT Connect Command

Fig.: MQTT-Client BP-Node "Connect" Event-Dispatcher "OnConnect" does not fire

B. Workaround

1. Startup Mosquitto Brocker
2. Startup UE Project "Heartbeat51"
   • To enable the subscription, wire the "Connect" and "Subscribe" nodes temporarily, see Fig.
   • Launch PIE
3. Startup MQTT Explorer
   • connect to mqtt://127.0.0.1:1883
   • publish a message using topic psl/hr
4. The Editor crashes

Fig.: "Connect" and "Subscribe" nodes temporarily wired

Fig.: MQTT-Explorer Connection

Fig.: MQTT-Explorer Publish

Listing: Topic psl/hr, example Payload in JSON

{
  "clientId": "MyPSL-01",
  "deviceId": "12345678",
  "sessionId": 1234567890,
  "timeStamp": 1234567890123,
  "hr": 64,
  "rr": [
    833
  ]
}

Fig.: Wireshark Dissecting MQTT Explorer Publication

---

• See also snippet "MQTT Plugin" by DrYannick1: https://dev.epicgames.com/community/snippets/EoX/unreal-engine-mqtt-plugin; says: "Event 'OnConnect' is not working. Some received payloads make the engine crash."
• reported bug to https://www.unrealengine.com/en-US/support/report-a-bug
• https://issues.unrealengine.com/issue/search?q=MQTT