MQTT connector buffering

[palexandridis]

When subscribing to topics with retain flag set, the mqtt connector can receive all retained messaged since last connection.
Under the broker section in the mqtt json configuration file, two keys have been introduced for MQTT v5.

• cleanStart which must be false for the buffering to work and
• sessionExpiryInterval which must be greater than 0.

Example configuration for MQTT v5:

"broker": {
    "name": "Default Local Broker",
    "host": "127.0.0.1",
    "port": 1883,
    "clientId": "ThingsBoard_gateway",
    "version": 5,
    "cleanStart": false,
    "sessionExpiryInterval": 604800,
    "maxMessageNumberPerWorker": 10,
    "maxNumberOfWorkers": 100,
    "sendDataOnlyOnChange": false,
    "security": {
      "type": "basic",
      "username": "user",
      "password": "password"
    }

When using MQTT v3, similar behavior can be achieved with:

• cleanSession which must be false for the buffering to work

"broker": {
    "name": "Default Local Broker",
    "host": "127.0.0.1",
    "port": 1883,
    "clientId": "ThingsBoard_gateway",
    "version": 3,
    "cleanSession": false,
    "maxMessageNumberPerWorker": 10,
    "maxNumberOfWorkers": 100,
    "sendDataOnlyOnChange": false,
    "security": {
      "type": "basic",
      "username": "user",
      "password": "password"
    }

The above functionality is relevant for retained mqtt topics that include a timestamp such as:

{"temperature" : 23, "timestamp": 1721233307943}

Please note:
Although the above changes work when executing the gateway locally from source, they do not work when executing the gateway using docker. To my understanding, the issue is related to the mqtt connection of the gateway to thingsboard when publishing received messages.

[CLAassistant]

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