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mqtt publish

Publishes each message's payload to an MQTT topic.

Properties

  • topic — the topic to publish to. Required. It is fixed: a message's topic is ignored. To publish to several topics, use one node for each.
  • retain — ask the broker to keep the message and give it to later subscribers. Default off.
  • QoS — 0 or 1. Default 0. QoS 2 isn't supported.
  • MQTT Broker — the flow's MQTT broker, shared by every MQTT node in the flow: change it on one and it changes on all (see Editor in depth). Required.
  • WiFi — the flow's WiFi network, shared by every WiFi node in the flow. unmanaged isn't accepted in a flow with MQTT nodes, because they manage the connection themselves.

Wiring

Input — any message. payload is the message sent: bytes as they are, a string as UTF-8, and anything else converted to text first. None sends the text None.

This node has no output.

Behavior

Nodes on the same broker share one connection. The node connects when the first message reaches it, so its status dot stays blank until then (see node status). It shows this node's own view of the connection, even when an mqtt subscribe node shares the broker.

Errors

  • The board can't reach the broker. The dot turns red and the console shows mqtt connect to HOST:PORT failed after 3 attempts, with the reason for each attempt. See MQTT broker unreachable.
  • The publish fails. The console shows mqtt publish to HOST:PORT failed, with the system's error.

These stop the compile: no MQTT broker or no WiFi network in the flow, an empty topic, a QoS other than 0 or 1, an unmanaged WiFi network.