Tracking online users using Phoenix sockets and Presence?

Does this help Phoenix.Presence — Phoenix v1.8.8? or this Using Phoenix Presence | What did I learn

The second link describes how to track users actively leaving chat rooms. But how to detect disconnected users due to network / internet disconnections?

I want simply to see who is online / offline (who has internet connection on/off).

Any ideas how this can be done?

Found only this https://stackoverflow.com/questions/45350197/how-to-set-and-retrieve-presence-status-online-busy-offline-using-phoenix-pres

Also this https://stackoverflow.com/questions/33934029/how-to-detect-if-a-user-left-a-phoenix-channel-due-to-a-network-disconnect

Everything is done automaticaly, Presence will detect disconnection as well…

This is a simple code I put in my channels

  def join("schedule", _params, socket) do
    send(self(), :after_join)
    {:ok, socket}
  end

  def handle_info(:after_join, socket) do
    user = socket.assigns.user
    {:ok, _} = Presence.track(socket, user.id, %{
      username: user.name,
      online_at: System.system_time(:second)
    })
    push(socket, "presence_state", Presence.list(socket))
    {:noreply, socket}
  end

It does imply the socket is assigned to a user, for this, i extract user from a phoenix token.

You also need a client library supporting Phoenix websocket and channels.

And this library needs to be compliant with the Phoenix version.

It detects, I see that the disconnected client gets removed from the list obtained by Presence.list, but only after some 5 minutes or more.

I cannot tell for the Android client, but using the JS client, it’s almost instantly, when working on my dev machine… Which client do You use?

This one for Android:
https://github.com/eoinsha/JavaPhoenixChannels

You mean when you use the the JS client, if the user disconnects he will be removed from the Presence list immediately?

I think it’s not compatible with Phoenix 1.4 (driver is too old)

Yes, but I know it’s not possible to use old Phoenix JS with new version, it does not work… I think it’s the same for the Java client.

I had to write a driver for ReasonML, because using the previous was not working.