How to share a common state between web app and android (Presence?)

[boulaycote]

Hi,

I want to have a common state shared across devices. In this current case, between a web app and an android app. I have tried using Presence and channel.track(state) but the state, when sending from android, seems to be filtered out and the only thing being received on the web app end is the presence_ref field.

First, is this a good use case for Presence? And if so, any idea what's happening?

Thank you

[jan-tennert]

Not sure what you mean with "state", can you describe it a little bit more? Can you show me how you receive these presences? Also make sure both channels have the same id

[jan-tennert]

Okay so assuming you have the same channel id for both clients, can you try to enable logging and see what is says?

[boulaycote]

meViewModel$testMessage  D  Sending PresenceState(test=2, selectedProduct=test, currentPage=test)
ltimeImpl$sendHeartbeat  D  Sending heartbeat
 RealtimeImpl$onMessage  D  Received message {"event":"phx_reply","payload":{"response":{},"status":"ok"},"ref":"23","topic":"realtime:12345"}
                         D  Received event phx_reply for channel realtime:12345
                         D  Received message {"event":"presence_diff","payload":{"joins":{"12345":{"metas":[{"phx_ref":"F1tXOf0DbpQjpaAm","phx_ref_prev":"F1tXONbNnQEjpZGm"}]}},"leaves":{"12345":{"metas":[{"phx_ref":"F1tXONbNnQEjpZGm","phx_ref_prev":"F1tXOL5hLdQjpUZB"}]}}},"ref":null,"topic":"realtime:12345"}
                         D  Received event presence_diff for channel realtime:12345
                         D  Received message {"event":"phx_reply","payload":{"response":{},"status":"ok"},"ref":"24","topic":"phoenix"}
                         I  Heartbeat received

and on the web app side

Prensence sync {"12345":[{"presence_ref":"F1tXOf0DbpQjpaAm"}]}

[jan-tennert]

Okay I may have identified the problem, I'm publishing a dev version for you to test out, give me a few minutes

[jan-tennert]

Can you try out version 0.9.5-dev-1 and tell me if it works now? (Edit: fixed in 0.9.5)

[boulaycote]

Yes this appears to be working!

And now, for the second question: do you think this is a good use case for presence? Maintaining a shared state? If so, I think I have to merge the different presence(s) into one, as the object looks like:

{"12345":[
    {"currentPage":"current-page","currentProductId":"current-product-id","selectedProductId":"selected-product-id","presence_ref":"F1tcQ85B8yqM2qeI"},
    {"currentPage":"current-page","presence_ref":"F1tcTB6pTmkjpUrm"}
]}

In my case I can assume only the relevant clients are connected to the channel (id: 12345).

[jan-tennert]

I see what you mean. Using Presence maybe doesn't fit that well as each client still has an own state and as you said you kinda have to merge them together on each change. Another possibility would be to have a table holding a state for every user and each client listening for changes on a single row. (If you have questions regarding this, feel free to ask me)
I'm not sure, you can try asking in the supabase discord server or in their github discussion for further help.
But I'm glad this was fixed.

[boulaycote]

Yes I guess a table would work. I'll figure it out thanks! I would still use presence for its intended use case, to know if clients are connected.

[boulaycote]

And using broadcast would work as well right? Just not guaranteed delivery?