Amplify PubSub unsubscribe method does not report the status/complete before sign out?

[entest-hai]

Before opening, please confirm:

• I have searched for duplicate or closed issues and discussions.
• I have read the guide for submitting bug reports.
• I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.

JavaScript Framework

React

Amplify APIs

PubSub

Amplify Categories

Not applicable

Environment information

I am using [Amplify PubSub to subscribe to an IoT topic ](https://docs.amplify.aws/lib/pubsub/subunsub/q/platform/js/#subscribe-to-a-topic). I want to stop/unsubscribe before sign out. However, there is no mechanism to check/ensure that unsubscribe completed before sign out.  

Describe the bug

Sign out happens before unsubscribe completed, therefore, the client (web browser) still subscribe the IoT topic even after sign out.

Expected behavior

The unsubscribe method of PubSub should has a mechanism to inform the status of unsubscribe

Reproduction steps

https://docs.amplify.aws/lib/pubsub/subunsub/q/platform/js/#subscribe-to-a-topic

Code Snippet

const sub1 = PubSub.subscribe('myTopicA').subscribe({
    next: data => console.log('Message received', data),
    error: error => console.error(error),
    complete: () => console.log('Done'),
});

sub1.unsubscribe();
// You will no longer get messages for 'myTopicA'

Log output

// Put your logs below this line

aws-exports.js

No response

Manual configuration

No response

Additional configuration

No response

Mobile Device

No response

Mobile Operating System

No response

Mobile Browser

No response

Mobile Browser Version

No response

Additional information and screenshots

No response

[chrisbonifacio]

Hi @entest-hai 👋 thanks for raising this issue. I was able to reproduce consistently and therefore marking as a bug for the team. As far as not being able to tell the success of an unsubscribe, I've referenced this issue in a feature request detailing common issues and pain points with handling subscriptions/websockets with our PubSub library so that we know at a glance where we can improve the developer experience and focus our efforts.

[stocaaro]

Hello @entest-hai ,

I'm not sure the behavior you're expecting is consistent with how subscriptions/observables should work.

Reviewing the zen-observable documentation, I think unsubscribe and complete fit separate use-cases. The two sections from the document that seem most relevant are:

• the subscription's unsubscribe method will be invoked when the subscription has closed
• complete() Terminates the sequence successfully.

In context, unsubscribe is how the client communicates to the back end that it isn't following a given topic any longer where the complete() callback is how the back end communicates to the client that the observed sequence is at an end.

Since the MQTT service topic isn't ending in your example, but instead the client is unsubscribing from further updates, I don't think it would be in line with the observable pattern to send a complete() callback call in this case.

Further, since these MQTT topics on IoT are never closed, I'm not sure they should ever send a complete() callback call. There are cases where errors cause the connection to fail in non-retriable ways, which prompt it to end with an error() callback.

Maybe I'm looking at this incorrectly. Are there other examples of observable interfaces where unsubscribe triggers complete()? Is there a different use-case where complete() makes sense and is missing?

Thanks,
Aaron