MQTT (Developer View)
A publish/subscribe messaging protocol. Everything is organized around subscribed topics (receiving) and published topics (sending); parameters live in the request's MQTT settings.
How to Configure in the UI
Fill in the MQTT request's connection settings:
| Setting | Meaning |
|---|---|
| Client ID (clientId) | This connection's identity |
| Subscription list | A set of topics + QoS, auto-subscribed after connecting |
| Publish topic | The default topic messages are sent to |
| Publish QoS / retain | Quality of service and retain flag when sending |
- Topic wildcards:
#matches multiple levels,+matches a single level (e.g.qr/manual/#). - QoS: 0 (at most once) / 1 (at least once) / 2 (exactly once).
- Host takes the broker address, port is separate (e.g.
127.0.0.1:18884);mqtts://uses TLS.
Core Flow
How to Use
- Create an MQTT request and configure clientId, subscriptions and the publish topic per the table above.
- Connect: the session auto-subscribes per your configuration and remembers the default publish topic.
- Publish: send content to the publish topic (topic/QoS/retain can be changed per message); empty payloads are valid.
- Receive: incoming messages display in real time — both your own loopback messages hitting subscriptions and other messages the broker pushes to subscribed topics.
- You can subscribe / unsubscribe during the session; close the session when done.
Verified Behavior
Pre-subscribed qr/manual/# + publishing {"evt":"auto-sub"} to qr/manual/hello → returns PUBACK (QoS1 acknowledged) and the loopback message body arrives — a closed send/receive loop.
Gotchas
- Not receiving your own publish: confirm the publish topic matches one of your subscriptions (e.g. both under
qr/manual/#). - Subscriptions added or removed at runtime only last for the current session — put long-lived subscriptions in the request's configuration.
- Long connections occupy quota and are reclaimed when idle; close them after debugging.
Related: subscription wildcards and QoS are explained above; the connection comes from the environment's mqtt Pre-URL (see concepts).