Where is the state of a WebSocket kept? What object represents it?

[mikejm]

@benwilson512

I don’t want to downplay your struggle here but I do find it pretty confusing if I’m honest. I wonder if in part it’s because you’re picking this sort of “middle tier” between a complete from scratch solution and a completely off the shelf solution.

The stuff you are asking to do around tracking connections and sending messages is exactly what Phoenix channels and Phoenix pubsub accomplish, and there are endless tutorials in any format you could think of for how to use those tools to do these things. In under an hour you’ll have the whole thing.

Thanks. I think you are correct. I also appreciated your explanation of how the conn/Websock holds state without being a “process” or object. Ie. it is just looping on itself.

However, I would like to not use Phoenix channels or PubSub as I would like to understand how to actually communicate between these different things manually. I wish to create my own system for doing so for a variety of reasons.

I have been playing with WebSock and other things. I can understand now I believe how to communicate from a WebSock out in response to user input to any given Elixir process. Eg. One can create a GenServer per conn/Websock and store its PID into the state of that, then use Process.send to this PID as needed under handle_in. Presto. You have client → Any service in Elixir messaging.

However, I still don’t understand how to do the opposite. Ie. I don’t know how any given Elixir process can utilize a given active WebSock/conn and send the client a message on the Elixir process’s own initiative.

The Websock/conn is not a process and has no PID so can’t accept messages. It is not an object so no reference to it exists. But there is some process (Supervisor) running it, right? So is that where we need to go? Create and employ a custom supervisor for the Websocket/conn with custom message handling perhaps?

It appears that is what is happening in the timer example here where he says:

  defp schedule_alert, do: Process.send_after(self(), :alert, :timer.seconds(15))

What does self() reference here? As far as I can tell it is the supervisor that is running the Websock/conn, since the websock/conn itself has no PID to interface with processes.

I made a new thread here to more specifically ask that as my understanding is now a bit better.

Any help on this (here or there) would be very, very, very appreciated.

I think it’s the only major thing I still don’t know how to do in Elixir in order to build out my whole system. Obviously there is some way to do this, as Phoenix does it. So what is the basic trick?

Also sorry for venting my frustration. I am getting there in any case.