Wrong presence channel behavior (Android/IOS)

[Nuclominus]

What is the issue?

Hello there! I found some incorrect behavior of presence channels after restore connection to channel.

Problem step-by-step:

1. Connect to presence channel two or more users
2. Go to in background - pusher disconnected
3. Other users quit from channel
4. Go to in foreground - pusher connected - we resubscribe to channel
5. On onUsersInformationReceived we got old data of users in channel

Notate: Swift SDK has workaround with subscribing on "pusher:subscription_succeeded" and process this event separate from flow logic. In Java SDK we don't have such trick...

In PresenceChannelImpl when channel successfully subscribed we got event SUBSCRIPTION_SUCCESS_EVENT = "pusher_internal:subscription_succeeded" with processing in internal channel body and after that call onUsersInformationReceived for self interface.

Problem in idToUserMap map witch need to clear in this case, because if i'm not wrong with SUBSCRIPTION_SUCCESS_EVENT we getting actual data about users in presence channel but in current realisation we lost users who quit from channel while i was unsubscibed.

Debug of this point shown that problem exist - channel got json with 1 user but idToUserMap not cleared and return wrong users data

...

Is it a crash report? Submit stack traces or anything that you think would help

#class PresenceChannelImpl

@SuppressWarnings({ "rawtypes", "unchecked" })
    private void handleSubscriptionSuccessfulMessage(final String message) {
        final ChannelEventListener listener = getEventListener();

        // extract data from the JSON message
        final PresenceData presenceData = extractPresenceDataFrom(message);
        if (presenceData == null) {
            if (listener != null) {
                listener.onError(
                    "Subscription failed: Presence data not found",
                    null
                );
            }
            return;
        }

        final List<String> ids = presenceData.ids;
        final Map<String, Object> hash = presenceData.hash;

        if (ids != null && !ids.isEmpty()) {
            // build the collection of Users
            for (final String id : ids) {
                final String userData = hash.get(id) != null ? GSON.toJson(hash.get(id)) : null;
                final User user = new User(id, userData);
                idToUserMap.put(id, user);  <--- Problem - is not empty. Suggestion: need clear before process users data
            }
        }

        if (listener != null) {
            final PresenceChannelEventListener presenceListener = (PresenceChannelEventListener)listener;
            presenceListener.onUsersInformationReceived(getName(), getUsers());
        }
    }

...

Any improvements you suggest

In this case clear idToUserMap before process users data. I may be wrong, then tell me the correct scenario for working with this type of channels
...

---

CC @pusher/mobile

[benw-pusher]

I've not been able to replicate this - upon reconnection my app receives the correct presence information. Do you have a small replication app available?

[Nuclominus]

Sorry, but i haven't. NDA etc... :( I can only share debug screen fro this situation

with this debug, it is already clear that one user comes in, and in the map there are two. I don’t see any code for clearing the map, so the result will not be correct. actual data = 1 user, and the channel will return 2

UPD: I checked that handleMemberAddedEvent didn't call in that case, so idToUserMap not modified by that method