MQTT v5 Connector

Overview

The MQTT v5 connector enables publish/subscribe messaging using the MQTT 5.0 protocol, adding shared subscriptions, user properties, and message expiry on top of MQTT v3.

Connector Types:

MqttV5Reader - Subscribe to MQTT 5.0 topics
MqttV5Writer - Publish to MQTT 5.0 topics

For MQTT 3.1.1 brokers and clients, use the MQTT v3 connector.

MQTT v5 Reader

Subscribe to a topic:

{
  "type": "MqttV5Reader",
  "config": {
    "endpoint": "mqtt://localhost:1883",
    "topic": "sensors/temperature",
    "qos": 1,
    "clientId": "meddle-v5-reader"
  }
}

With Authentication and TLS

{
  "type": "MqttV5Reader",
  "config": {
    "endpoint": "mqtts://mqtt.example.com:8883",
    "topic": "factory/sensors/#",
    "qos": 1,
    "clientId": "meddle-v5-reader",
    "username": "mqtt_user",
    "password": "mqtt_password"
  }
}

Shared Subscription

Distribute messages across multiple readers using sharedGroup. The connector subscribes to $share/<group>/<topic> and the broker load-balances deliveries between members:

{
  "type": "MqttV5Reader",
  "config": {
    "endpoint": "mqtt://broker.example.com:1883",
    "topic": "factory/events",
    "qos": 1,
    "clientId": "meddle-v5-reader-1",
    "sharedGroup": "meddle-workers"
  }
}

MQTT v5 Writer

Publish to a topic:

{
  "type": "MqttV5Writer",
  "config": {
    "endpoint": "mqtt://localhost:1883",
    "topic": "data/output",
    "qos": 1,
    "clientId": "meddle-v5-writer"
  }
}

Retained Message with Expiry and User Properties

{
  "type": "MqttV5Writer",
  "config": {
    "endpoint": "mqtts://mqtt.example.com:8883",
    "topic": "devices/state",
    "qos": 1,
    "clientId": "meddle-v5-writer",
    "username": "mqtt_user",
    "password": "mqtt_password",
    "retain": true,
    "messageExpiry": 3600,
    "userProperties": {
      "source": "meddle",
      "schema": "v1"
    }
  }
}

Configuration Parameters

endpoint: Broker URL with scheme (mqtt://host:port or mqtts://host:port)
topic: Topic to subscribe or publish to (Reader supports + and # wildcards)
qos: Quality of Service: 0, 1, or 2
clientId: (Optional) Client identifier
username: (Optional) MQTT username
password: (Optional) MQTT password
sharedGroup: (Reader) Shared subscription group for load balancing
userProperties: Key/value metadata attached to messages
retain: (Writer) Broker stores the last message and delivers it to new subscribers
messageExpiry: (Writer) Message expiry interval in seconds

QoS Levels

0: At most once (fire and forget)
1: At least once (acknowledged delivery)
2: Exactly once (assured delivery)

Differences from MQTT v3

Shared subscriptions (sharedGroup) let multiple subscribers consume a single topic with broker-side load balancing.
User properties carry arbitrary key/value metadata per message.
Message expiry drops undelivered messages after the configured interval.
Reason codes on connect, subscribe, and publish provide richer error semantics handled by the underlying paho client.

Topic Wildcards (Reader Only)

+ - Single level wildcard (sensors/+/temperature)
# - Multi-level wildcard (sensors/#)

MQTT v3 - Classic MQTT 3.1.1 connector
AMQP - RabbitMQ pub/sub alternative
NATS - Cloud-native pub/sub alternative