I am using something like this to to handle Websocket requests:

  def handle_in("new_msg", data, socket) do

    # do something with data that might result in exceptions/exits/errors raised

    {:reply, {:ok, output}, socket}
  end

And in JavaScript side, something like this

 channel.push("new_msg", data, 10000)
    .receive("ok", (output) => console.log("created message", output) )
    .receive("error", (reasons) => console.log("create failed", reasons) )
    .receive("timeout", () => console.log("Networking issue...") )

What happens is, when an exception is raised it seems the whole channel process (?) goes down, and the client which is waiting for a response gets no response and just times out.

What I would like instead is to be able to return an error immediately with maybe “unexpected error” reason kind of like a http 500 error.

I don’t want to leave the client hanging and it isn’t a “Networking issue” so timeout isn’t appropriate result.

After some trial and error, I now have the following, which seems to work nicely:

  def handle_in("new_msg", data, socket) do

    try do
        # do something with data that might result in exceptions/exits/errors raised
        {:reply, {:ok, output}, socket}
    catch
        :exit, error ->
            Logger.error(Exception.format_exit(reason))
            {:reply, {:error, %{reason: "Unexpected Error"}}, socket}
    end
  end

But I am a bit unsure, as

• I think for http requests Phoenix handles this and automatically responds with 500 code? But for websocket requests I have to handle this myself?
• And also the Elixir tutorial seems to say that you wouldn’t normally need to use try/catch
• And would I also need a rescue?

EDIT: I am now doing it like this as all my messages need replies:

 # try catch here
 def handle_in(event, params, socket) do
    try do
      {:reply, handle(event, params, socket), socket}
    catch
      :exit, reason ->
        Logger.info("responding with unexpected error")
        Logger.error(Exception.format_exit(reason))
        {:reply, {:error, %{reason: "Unexpected Error."}}, socket}
    end
  end

# handle each message type, no boilerplate
defp handle("new_msg", params, socket) do
  # do stuff
  {:ok, %{result: output}}
end

defp handle("another_msg", params, socket) do
  # do stuff
  {:ok, %{result: output}}
end