MqttClient subscribe: MqttConnectionBase::_onDone - calling disconnected callback

[Rityra]

This seems to be related to this other issue.

I am implementing this in a mobile app.

Everything seems to be working alright, up until this:

client
        ..publishMessage(topic, MqttQos.atLeastOnce, builder.payload!) // SUCCESS
        ..subscribe(topic, MqttQos.atLeastOnce); // SILENT FAILURE

The related logs are:

I/flutter ( 5456): 1-2026-01-26 10:51:59.643427 -- PublishingManager::publish - entered with topic $aws/things/smartThing/shadow/update/documents
I/flutter ( 5456): 1-2026-01-26 10:51:59.652441 -- MqttConnectionHandlerBase::sendMessage
I/flutter ( 5456): 1-2026-01-26 10:51:59.657965 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.publish
I/flutter ( 5456): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 61
I/flutter ( 5456): Publish Variable Header: TopicName={$aws/things/smartThing/shadow/update/documents}, MessageIdentifier={1}, VH Length={0}
I/flutter ( 5456): Payload: {11 bytes={<72><101><108><108><111><32><87><111><114><108><100>
I/flutter ( 5456): 1-2026-01-26 10:52:15.700489 -- MqttConnectionHandlerBase::sendMessage
I/flutter ( 5456): 1-2026-01-26 10:52:15.704027 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.subscribe
I/flutter ( 5456): Header: MessageType = MqttMessageType.subscribe, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 51
I/flutter ( 5456): Subscribe Variable Header: MessageIdentifier={2}
I/flutter ( 5456): Payload: Subscription [{1}]
I/flutter ( 5456): {{ Topic={$aws/things/smartThing/shadow/update/documents}, Qos={MqttQos.atLeastOnce} }}
I/flutter ( 5456): 
I/flutter ( 5456): 1-2026-01-26 10:52:15.712493 -- MqttConnectionKeepAlive::pingRequired
I/flutter ( 5456): 1-2026-01-26 10:52:15.713637 -- MqttConnectionKeepAlive::pingRequired - sending ping request
I/flutter ( 5456): 1-2026-01-26 10:52:15.714032 -- MqttConnectionHandlerBase::sendMessage
I/flutter ( 5456): 1-2026-01-26 10:52:15.714863 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.pingRequest
I/flutter ( 5456): Header: MessageType = MqttMessageType.pingRequest, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter ( 5456): 1-2026-01-26 10:52:15.716181 -- MqttConnectionKeepAlive::pingRequired - restarting ping timer
I/flutter ( 5456): 1-2026-01-26 10:52:15.767738 -- MqttConnectionBase::_onDone - calling disconnected callback
I/flutter ( 5456): 1-2026-01-26 10:52:15.772032 -- MqttConnectionKeepAlive::stop - stopping keep alive

I have tried all possible MqttQos qosLevels, tried different topics, but to no avail.
In AWS I see that the disconnection activity is as follows:

{
  "clientId": "smartThing",
  "timestamp": 1769420715167,
  "eventType": "disconnected",
  "clientInitiatedDisconnect": false,
  "sessionIdentifier": "96d50310-a796-4b2d-9595-4f6244fff843",
  "principalIdentifier": "c145d9c1c7e799778bebbada415dadbd22f16a36b66c333e5a9baa186d0f4414",
  "disconnectReason": "CLIENT_ERROR",
  "versionNumber": 34
}

... but the subscribe method doesn't seem to be throwing any errors.
Thank you for your help

[shamblett]

The issue you refer to is old and known, its fixed by setting the client version to 3.1.1, please check you are doing this though. Disable keep alive for now or set it to a large period so it doesn't spam the logs output.

The AWS disconnection reason is not very helpful, try not subscribing, then try not publishing and just subscribing, see if its the subscription message specifically.

Also, try the same code against test.mosquitto.org to rule out AWS.

[Rityra]

@shamblett the client version is indeed set to 3.1.1, just like in the linked example repository, from your documentation

// Create the client
    final MqttServerClient client = MqttServerClient.withPort(url, clientId, port)
      // Set secure
      ..secure = true
      // Set Keep-Alive
      ..keepAlivePeriod = 20
      // Set the protocol to V3.1.1 for AWS IoT Core, if you fail to do this you will not receive a connect ack with the response code
      ..setProtocolV311()
      // logging if you wish
      ..logging(on: true);

or is it something else?

[shamblett]

Yep, looks good, rule that out then.

[Rityra]

@shamblett when NOT subscribing:

I/flutter ( 9806): 1-2026-01-26 12:42:25.956019 -- PublishingManager::publish - entered with topic $aws/things/smartThing/test/FeelHippo
I/flutter ( 9806): 1-2026-01-26 12:42:25.965610 -- MqttConnectionHandlerBase::sendMessage
I/flutter ( 9806): 1-2026-01-26 12:42:25.971441 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.publish
I/flutter ( 9806): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 52
I/flutter ( 9806): Publish Variable Header: TopicName={$aws/things/smartThing/test/FeelHippo}, MessageIdentifier={1}, VH Length={0}
I/flutter ( 9806): Payload: {11 bytes={<72><101><108><108><111><32><87><111><114><108><100>
I/flutter ( 9806): 1-2026-01-26 12:42:25.980654 -- MqttConnectionKeepAlive::pingRequired
I/flutter ( 9806): 1-2026-01-26 12:42:25.981253 -- MqttConnectionKeepAlive::pingRequired - sending ping request
I/flutter ( 9806): 1-2026-01-26 12:42:25.981482 -- MqttConnectionHandlerBase::sendMessage
I/flutter ( 9806): 1-2026-01-26 12:42:25.982023 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.pingRequest
I/flutter ( 9806): Header: MessageType = MqttMessageType.pingRequest, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter ( 9806): 1-2026-01-26 12:42:25.983170 -- MqttConnectionKeepAlive::pingRequired - restarting ping timer
I/flutter ( 9806): 1-2026-01-26 12:42:26.023625 -- MqttConnectionBase::_onDone - calling disconnected callback
I/flutter ( 9806): 1-2026-01-26 12:42:26.026147 -- MqttConnectionKeepAlive::stop - stopping keep alive

[Rityra]

@shamblett when NOT publishing, only subscribing

I/flutter (10020): 1-2026-01-26 12:44:45.480914 -- MqttConnectionHandlerBase::sendMessage
I/flutter (10020): 1-2026-01-26 12:44:45.484170 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.subscribe
I/flutter (10020): Header: MessageType = MqttMessageType.subscribe, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 42
I/flutter (10020): Subscribe Variable Header: MessageIdentifier={1}
I/flutter (10020): Payload: Subscription [{1}]
I/flutter (10020): {{ Topic={$aws/things/smartThing/test/FeelHippo}, Qos={MqttQos.atLeastOnce} }}
I/flutter (10020): 
I/flutter (10020): 1-2026-01-26 12:44:45.545664 -- MqttConnectionBase::_onDone - calling disconnected callback
I/flutter (10020): 1-2026-01-26 12:44:45.549962 -- MqttConnectionKeepAlive::stop - stopping keep alive

[Rityra]

@shamblett my dependencies:

environment:
  sdk: ^3.8.1

dependencies:
  mqtt_client: ^10.11.9

[shamblett]

Ok, disable keep alive and just publish.

[Rityra]

@shamblett the output is slightly different:

I/flutter (10996): 1-2026-01-26 13:04:31.940193 -- PublishingManager::publish - entered with topic $aws/things/smartThing/test/FeelHippo
I/flutter (10996): 1-2026-01-26 13:04:31.946741 -- MqttConnectionHandlerBase::sendMessage
I/flutter (10996): 1-2026-01-26 13:04:31.952129 -- MqttConnectionHandlerBase::sendMessage = message is MQTTMessage of type MqttMessageType.publish
I/flutter (10996): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 52
I/flutter (10996): Publish Variable Header: TopicName={$aws/things/smartThing/test/FeelHippo}, MessageIdentifier={1}, VH Length={0}
I/flutter (10996): Payload: {11 bytes={<72><101><108><108><111><32><87><111><114><108><100>
I/flutter (10996): 1-2026-01-26 13:04:32.006112 -- MqttConnectionBase::_onDone - calling disconnected callback

... but on AWS I see the client is disconnected:

{
  "clientId": "smartThing",
  "timestamp": 1769429072445,
  "eventType": "disconnected",
  "clientInitiatedDisconnect": false,
  "sessionIdentifier": "4233c2be-d01f-4714-9ebd-1d39e7e2f785",
  "principalIdentifier": "c145d9c1c7e799778bebbada415dadbd22f16a36b66c333e5a9baa186d0f4414",
  "disconnectReason": "CLIENT_ERROR",
  "versionNumber": 10
}

I was skimming through the AWS documentation, I reckon they've moved to MQTT 5 recently.

In here I read:

In MQTT 3, the default value of persistent sessions expiration time is an hour, and this applies to all the sessions in the account.

In MQTT 5, you can set the Session Expiry Interval for each session on CONNECT and DISCONNECT packets.

[shamblett]

You could always try the mqtt5 client, just change mqtt to mqtt5 in your pubspec and code and pub get the package.

Its API compatible except for specific MQTT 5 functions.

[Rityra]

@shamblett the mqtt5 seems to be working perfectly with AWS IoT. Thank you very much for your support