Subject: RangeError in mqtt5_client library - Client-side fix or library update needed?

[RaghuMudem]

Dear Author,

We're incorporating the mqtt5_client library (version ^4.2.2) into our Flutter application (version 3.19.5 with Dart 3.3.3) and experiencing a non-fatal exception reported through Firebase Crashlytics.

Error:

The error message indicates a RangeError (length): Invalid value: Only valid value is 0: 1 within the MqttEnumHelper class's asString method. This suggests an attempt to access an element at an invalid index (1) in a list or similar construct that only has one element (0).

Analysis:

We've analyzed the logs and believe the issue might lie with unexpected values being passed to the asString method in the class MqttEnumHelper.

Request:

We'd appreciate your guidance on how to address this error. Ideally, we'd like to understand:

Are there potential client-side fixes we can implement to handle this unexpected value scenario? Is this a potential bug within the mqtt5_client library that could be addressed in a future update?

Additional Information:

Development Environment: Android Studio (JellyFish) IDE Code Snippet (if applicable): MqttEnumHelper.asString(..) method call. Logs:

Non-fatal Exception: io.flutter.plugins.firebase.crashlytics.FlutterError: RangeError (length): Invalid value: Only valid value is 0: 1.
       at MqttEnumHelper.asString(mqtt_enum_helper.dart)
       at MqttConnectionStatus.toString(mqtt_connection_status.dart:30)
       at _StringBase._interpolate(dart:core)
       at MqttSynchronousServerConnectionHandler.internalConnect(mqtt_synchronous_server_connection_handler.dart:121)
       at MqttConnectionHandlerBase.connect(mqtt_connection_handler_base.dart:108)
       at MqttServerClient.connect(mqtt_server_client.dart:95)

Sincerely, Raghu

[shamblett]

Yes you are correct, the error suggests that the client has received an invalid reason code somehow, I'll have a look at this but as you say this is only in a toString method so if no other solution is found I'll trap this error here and substitute a suitable error string. I should have this done over the next few days.

[shamblett]

OK, try it now, package re released at version 4.2.5

[RaghuMudem]

Hi,

Thank you for your quick response.

Updated Version Behavior:

I tested the updated version (mqtt5_client: ^4.2.5) and observed the following behavior:

Calling connect on MqttServerClient without username and password no longer throws the error I reported earlier. The connection state now simply shows as MqttConnectionState.connected without any error code or message. Previous Version Behavior:

In version 4.2.2, the same scenario correctly threw the error message as i mentioned in my question.

Expected Behavior (May be):

When attempting to connect method (MqttServerClient->connect(..)) without proper credentials, the library should ideally:

Return a descriptive error message or code indicating the issue. Set the connection state to MqttConnectionState.faulted. Attached Screenshots:

Please check the attached screen with my debug values while using version 4.2.5.

Thank you for considering this fix. It would improve the clarity of error handling in the library.

[shamblett]

OK, seems reasonable, I'll have a look at this.

[shamblett]

Just a question, when you say 'without proper credentials...' what do you mean. The client doesn't know you need credentials, lost of brokers work with just a client id say and no username/password, so in this case if theses weren't supplied how would the client know they are needed by the broker and take appropriate action