#MqttTopicProvider

#Import

1import { MqttTopicProvider } from "@alepha/mqtt/topic";

#Overview

Topics over MQTT, for device and integration topics.

Opt in per topic, never the app's TopicProvider. The framework's own topics (websocket:broadcast, parameter:sync) stay on memory or Redis; a device topic names this provider:

1status = $topic({2  name: "mcs/v1/{site}/{device}/status",3  provider: MqttTopicProvider,4  schema: {5    params: z.object({ site: z.text(), device: z.text() }),6    payload: deviceStatusSchema,7  },8  mqtt: { qos: 1, share: "mcs" },9});

• Topic names are exact: no prefix unless the prefix atom sets one.
• Params are + wildcards: a subscriber on a templated name receives the params of the topic each message arrived on.
• The wire format is the payload alone, UTF-8 JSON, which is what a device publishes; not the { payload } envelope of memory and Redis.
• QoS 1 by default. At QoS 0 an awaited publish resolves on the socket write and proves nothing; QoS 1 makes the await mean what the memory and Redis providers make it mean. QoS 1 is at-least-once, so a handler on a device topic must be idempotent.

It runs on whichever MqttClientProvider AlephaMqtt selects: the memory broker when MQTT_URL is unset, which is what tests use.