How to Keep the connection alive in phoenix socket for mobile app

Phoenix channels should already provide a keep-alive mechanism. If you do not use channels, you need to implement some kind of heartbeat on your own.

I use Phoenix channel but not it’s js. just elixir code !! does mobile application need js ?

No, just a proper client for the channel. wscat just connects on a websocket and you need to talk raw. If you never send a heartbeat, the phoenix will eventually disconnect you, depending on the timout settings.

after your answer I searched heartbeat and how to send it to my user. but everything I found talk about javascript can you make an example?

"heartbeat" events in the "phoenix" topic - should just emit an OK reply
"phx_join" on any topic - should join the topic
"phx_leave" on any topic - should leave the topic

should I create a handle_in like

  def handle_in("heartbeat", _payload, socket) do
    {:reply, :ok, socket}
  end

or I need to send

send(self, :after_join)

and create a loop with send after like

  def handle_info("heartbeat", socket) do
    broadcast!(socket, "ping", %{}) 
    Process.send_after(self, {:heartbeat}, 2000) 
    {:noreply, socket}
  end

it is right or I need something more?

The JavaScript client already implements sending heartbeats. If you want to write a client in another language, you need to implement the heartbeat there.

The heartbeat is a low level protocol message, you’ll never see it in a way that you could see it in handle_* functions on the server side.

Little word of caution - implementing a client might not be as easy. I was working with a very competent android developer and the channel implementation was a constant source of bugs and problems. Especially if the app is sometimes supposed to sleep keeping the connection alive around OS energy optimization can be pretty rough.

I’ll never forget the joy in the devs eyes when we switched to a simple REST API instead of channels

can you show me an example heartbeats you did on your elixir server side ? I just need a sample code to know how to work

Heartbeat is already built into phoenix channels and pjoenix.js and they do it automatically. Most of us have never sent one manual. You can read their implementation code to see what when and how they do it.

Heartbeats do not need to be implemented server side, they are already there and part of the channel protocol, you need to implement them Clientside if you are writing your own client.

You might look into your client languages ecosystem if there are already clients available.

Ahha, I thought I should do this in elixir. then the mobile developer should do this in mobile app.

Thanks