Auto reconnect

[mathankumar-dotworld]

Hi,

The MQTT client works well, but I need to implement auto-reconnect for internet reconnections, server disconnections, and similar issues.

[davidepianca98]

Hello, auto-reconnect is something I want to implement but I am not sure when I will be able to do it. In the meantime it's possible to obtain a similar behaviour by creating a new client object every time.

[qwerty470]

@davidepianca98 Will creating a new publisher client object with the same client ID for each connection cause the broker to discard queued messages from the previous connection for that client? If so, then that's the issue as subscriber client might miss the undelivered messages.
MQTTV5

[davidepianca98]

@qwerty470 it should not if clean start is set to false. From the MQTT specification:

3.1.2.4 Clean Start

Position: bit 1 of the Connect Flags byte.

This bit specifies whether the Connection starts a new Session or is a continuation of an existing Session. Refer to section 4.1 for a definition of the Session State.

If a CONNECT packet is received with Clean Start is set to 1, the Client and Server MUST discard any existing Session and start a new Session [MQTT-3.1.2-4]. Consequently, the Session Present flag in CONNACK is always set to 0 if Clean Start is set to 1.

If a CONNECT packet is received with Clean Start set to 0 and there is a Session associated with the Client Identifier, the Server MUST resume communications with the Client based on state from the existing Session [MQTT-3.1.2-5]. If a CONNECT packet is received with Clean Start set to 0 and there is no Session associated with the Client Identifier, the Server MUST create a new Session [MQTT-3.1.2-6].

The not yet acknowledged packets are part of the session. So if cleans start is set to true, they will be discarded.