I was recently experimenting with the possibility of retaining a channel instance’s state (assigns) between crashes.

In my testing application, I am causing the channel instance to crash and I noticed that the instance is not automatically restarted. It seems that channel instances are not supervised.

Why is it the case? Do we rely on the channel’s client to reestablish a connection thus creating a new channel instance on the server side?

DETAILS
Here is the code for the channel and the test that I am using:

defmodule ChanState.KablamChannel do
  use ChanState.Web, :channel

  def join("kablam", payload, socket) do
      {:ok, assign(socket, :ns, [])}
  end

  def handle_in("add", %{"n" => n}, socket) do
    ns = socket.assigns[:ns]
    {:noreply, assign(socket, :ns, ns ++ [n])}
  end

  def handle_in("get", _, socket) do
    ns = socket.assigns[:ns]
    {:reply, {:ok, %{"ns" => ns}}, socket}
  end

  def handle_in("oopsy", _, socket) do
    a = 1 / 0
    {:noreply, socket}
  end
  
end

TEST:

defmodule ChanState.KablamChannelTest do
  use ChanState.ChannelCase

  alias ChanState.KablamChannel

  setup do
    {:ok, _, socket} =
      socket()
      |> subscribe_and_join(KablamChannel, "kablam")

    {:ok, socket: socket}
  end

  test "main", %{socket: socket} do
    Process.unlink(socket.channel_pid)

    push socket, "add", %{"n" => 2149}
    push socket, "add", %{"n" => 1234}
    
    ref = push socket, "get", %{}
    assert_reply ref, :ok, %{"ns" => [2149, 1234]}
    
    push socket, "oopsy", %{}

    ref = push socket, "get", %{}
    

    ## The following returns undefined
    IO.inspect(:erlang.process_info(socket.channel_pid))
    assert_reply ref, :ok, %{"ns" => []}, 5000
  end
  
end