I was trying out a pattern I haven’t tried before: sending a message from a regular API controller to a LiveView process.

See code below for some of the relevant code. In a nutshell. One route for LiveView showing a registration form. One route for handling POST requests from that form. On form submit an AJAX POST request is made from the LiveView. In case there are any validation errors the form controller tries to send a message to the LiveView. At this point that message is just a non-sense test message. The LiveView does not receive the message, however.

# Router
    live "/form", FormLive
    post "/form", FormController, :create

# PageLive
      <script>
        function handleSubmit(event) {
          event.preventDefault()
          const form = event.srcElement
          const formdata = new FormData(form)
          const ajax = new XMLHttpRequest()
          ajax.open("POST", "/form", true)
          const crsfToken = document.querySelector('meta[name="csrf-token"]').getAttribute('content');
          ajax.setRequestHeader('x-csrf-token', crsfToken)
          ajax.send(formdata)
        }
      </script>

      def handle_info(:hello, socket) do
        IO.puts "RECEIVED" # Does not print after controller has sent the message
        {:noreply, socket}
      end

# RouteController
        # one or several validation errors
        %{"sender_pid" => sender_pid} = changeset.params
        IO.inspect sender_pid # "#PID<0.2900.0>" Note: String
        pid = String.slice(sender_pid, 5..-2)
        pid = pid(pid) |> IO.inspect # #PID<0.2900.0>
        send(pid, :hello)
        conn
        |> Plug.Conn.resp(406, "Not all form requirements have been met.")
        |> Plug.Conn.send_resp()

I hope this code provides sufficient context for my question: It seems I can’t send messages from my controller to the LiveView, why is that? I reckon I can use PubSub to get the job done, but I prefer to understand why the pattern I’m trying doesn’t work. I looked around in docs etc., but haven’t found a definite answer, yet.