Improve UX when loading JS output fails or takes long time (#2975)

assets/js/hooks/js_view.js

@@ -56,8 +56,8 @@ import { initializeIframeSource } from "./js_view/iframe";
  *
  *   * `iframe-url` - an optional location to load the iframe from
  *
- *   * `timeout-message` - the message to show when the initial
- *     data does not load
+ *   * `unreachable-message` - the message to show when the initial
+ *     data fails to load
  *
  */
 const JSView = {
@@ -72,8 +72,6 @@ const JSView = {
     this.syncCallbackQueue = [];
     this.pongCallbackQueue = [];
 
-    this.initTimeout = setTimeout(() => this.handleInitTimeout(), 2_000);
-
     this.channel = getChannel(this.props.sessionToken);
 
     this.iframeActions = this.createIframe();
@@ -102,8 +100,13 @@ const JSView = {
     const initRef = this.channel.on(
       `init:${this.props.ref}:${this.id}`,
       (raw) => {
-        const [, payload] = transportDecode(raw);
-        this.handleServerInit(payload);
+        const [[ok], payload] = transportDecode(raw);
+        this.removeSkeleton();
+        if (ok) {
+          this.handleServerInit(payload);
+        } else {
+          this.handleInitUnreachable();
+        }
       },
     );
 
@@ -115,7 +118,10 @@ const JSView = {
     const errorRef = this.channel.on(
       `error:${this.props.ref}`,
       ({ message, init }) => {
-        this.handleServerError(message, init);
+        if (init) {
+          this.removeSkeleton();
+        }
+        this.handleServerError(message);
       },
     );
 
@@ -187,7 +193,7 @@ const JSView = {
       "connect-token",
       "iframe-port",
       "iframe-url",
-      "timeout-message",
+      "unreachable-message",
     ]);
   },
 
@@ -416,23 +422,14 @@ const JSView = {
     }
   },
 
-  handleInitTimeout() {
-    this.initTimeoutContainer = document.createElement("div");
-    this.initTimeoutContainer.classList.add("info-box");
-    this.el.prepend(this.initTimeoutContainer);
-    this.initTimeoutContainer.textContent = this.props.timeoutMessage;
-  },
-
-  clearInitTimeout() {
-    clearTimeout(this.initTimeout);
-
-    if (this.initTimeoutContainer) {
-      this.initTimeoutContainer.remove();
-    }
+  handleInitUnreachable() {
+    const container = document.createElement("div");
+    container.classList.add("info-box");
+    this.el.prepend(container);
+    container.textContent = this.props.unreachableMessage;
   },
 
   handleServerInit(payload) {
-    this.clearInitTimeout();
     this.initReceived = true;
 
     this.childReadyPromise.then(() => {
@@ -450,11 +447,7 @@ const JSView = {
     });
   },
 
-  handleServerError(message, init) {
-    if (init) {
-      this.clearInitTimeout();
-    }
-
+  handleServerError(message) {
     if (!this.errorContainer) {
       this.errorContainer = document.createElement("div");
       this.errorContainer.classList.add("error-box", "mb-4");
@@ -497,6 +490,11 @@ const JSView = {
       parentFocusableId === focusableId,
     );
   },
+
+  removeSkeleton() {
+    const skeletonEl = this.el.querySelector(`[data-el-skeleton]`);
+    skeletonEl.remove();
+  },
 };
 
 /**

lib/livebook_web/channels/js_view_channel.ex

@@ -28,8 +28,12 @@ defmodule LivebookWeb.JSViewChannel do
 
     socket =
       update_in(socket.assigns.ref_with_info[ref], fn
-        nil -> %{pid: pid, count: 1, connect_queue: [id]}
-        info -> %{info | count: info.count + 1, connect_queue: info.connect_queue ++ [id]}
+        nil ->
+          monitor_ref = Process.monitor(pid, tag: {:connect_down, ref})
+          %{pid: pid, monitor_ref: monitor_ref, count: 1, connect_queue: [id]}
+
+        info ->
+          %{info | count: info.count + 1, connect_queue: info.connect_queue ++ [id]}
       end)
 
     if socket.assigns.ref_with_info[ref].count == 1 do
@@ -66,13 +70,10 @@ defmodule LivebookWeb.JSViewChannel do
   def handle_in("disconnect", %{"ref" => ref}, socket) do
     socket =
       case socket.assigns.ref_with_info do
-        %{^ref => %{count: 1}} ->
-          Livebook.Session.unsubscribe_from_runtime_events(
-            socket.assigns.session_id,
-            "js_live",
-            ref
-          )
-
+        %{^ref => %{count: 1, monitor_ref: monitor_ref}} ->
+          Process.demonitor(monitor_ref, [:flush])
+          session_id = socket.assigns.session_id
+          Livebook.Session.unsubscribe_from_runtime_events(session_id, "js_live", ref)
           {_, socket} = pop_in(socket.assigns.ref_with_info[ref])
           socket
 
@@ -97,7 +98,7 @@ defmodule LivebookWeb.JSViewChannel do
         {id, queue}
       end)
 
-    with {:error, error} <- try_push(socket, "init:#{ref}:#{id}", nil, payload) do
+    with {:error, error} <- try_push(socket, "init:#{ref}:#{id}", [true], payload) do
       message = "Failed to serialize initial widget data, " <> error
       push(socket, "error:#{ref}", %{"message" => message, "init" => true})
     end
@@ -105,6 +106,17 @@ defmodule LivebookWeb.JSViewChannel do
     {:noreply, socket}
   end
 
+  def handle_info({{:connect_down, ref}, _ref, :process, _pid, _reason}, socket) do
+    Livebook.Session.unsubscribe_from_runtime_events(socket.assigns.session_id, "js_live", ref)
+    {%{connect_queue: ids}, socket} = pop_in(socket.assigns.ref_with_info[ref])
+
+    for id <- ids do
+      :ok = try_push(socket, "init:#{ref}:#{id}", [false], nil)
+    end
+
+    {:noreply, socket}
+  end
+
   def handle_info({:event, event, payload, %{ref: ref}}, socket) do
     with {:error, error} <- try_push(socket, "event:#{ref}", [event], payload) do
       message = "Failed to serialize widget data, " <> error

lib/livebook_web/live/js_view_component.ex

@@ -6,7 +6,7 @@ defmodule LivebookWeb.JSViewComponent do
     {:ok,
      socket
      |> assign(assigns)
-     |> assign_new(:timeout_message, fn -> "Not available" end)}
+     |> assign_new(:unreachable_message, fn -> "Not available" end)}
   end
 
   @impl true
@@ -26,8 +26,11 @@ defmodule LivebookWeb.JSViewComponent do
       data-p-connect-token={hook_prop(connect_token(@js_view.pid))}
       data-p-iframe-port={hook_prop(LivebookWeb.IframeEndpoint.port())}
       data-p-iframe-url={hook_prop(Livebook.Config.iframe_url())}
-      data-p-timeout-message={hook_prop(@timeout_message)}
+      data-p-unreachable-message={hook_prop(@unreachable_message)}
     >
+      <div class="delay-200 py-2" data-el-skeleton>
+        <.content_skeleton empty={false} />
+      </div>
     </div>
     """
   end

lib/livebook_web/live/output.ex

@@ -91,7 +91,7 @@ defmodule LivebookWeb.Output do
       js_view={@js_view}
       session_id={@session_id}
       client_id={@client_id}
-      timeout_message="Output data no longer available, please reevaluate this cell"
+      unreachable_message="Output data no longer available, please reevaluate this cell"
     />
     """
   end

test/livebook_web/channels/js_view_channel_test.exs

@@ -20,7 +20,7 @@ defmodule LivebookWeb.JSViewChannelTest do
     assert_receive {:connect, from, %{}}
     send(from, {:connect_reply, [1, 2, 3], %{ref: "1"}})
 
-    assert_push "init:1:id1", %{"root" => [nil, [1, 2, 3]]}
+    assert_push "init:1:id1", %{"root" => [[true], [1, 2, 3]]}
   end
 
   test "loads initial data for multiple connections separately", %{socket: socket} do
@@ -29,11 +29,31 @@ defmodule LivebookWeb.JSViewChannelTest do
 
     assert_receive {:connect, from, %{}}
     send(from, {:connect_reply, [1, 2, 3], %{ref: "1"}})
-    assert_push "init:1:id1", %{"root" => [nil, [1, 2, 3]]}
+    assert_push "init:1:id1", %{"root" => [[true], [1, 2, 3]]}
 
     assert_receive {:connect, from, %{}}
     send(from, {:connect_reply, [1, 2, 3], %{ref: "1"}})
-    assert_push "init:1:id2", %{"root" => [nil, [1, 2, 3]]}
+    assert_push "init:1:id2", %{"root" => [[true], [1, 2, 3]]}
+  end
+
+  test "sends init failure when the widget server terminates", %{socket: socket} do
+    widget_server_pid =
+      spawn(fn ->
+        # Respond only to the first one and terminate
+        receive do
+          {:connect, from, %{}} ->
+            send(from, {:connect_reply, [1, 2, 3], %{ref: "1"}})
+        end
+      end)
+
+    connect_token = connect_token(widget_server_pid)
+
+    push(socket, "connect", %{"connect_token" => connect_token, "ref" => "1", "id" => "id1"})
+    push(socket, "connect", %{"connect_token" => connect_token, "ref" => "1", "id" => "id2"})
+
+    assert_push "init:1:id1", %{"root" => [[true], [1, 2, 3]]}
+
+    assert_push "init:1:id2", %{"root" => [[false], nil]}
   end
 
   test "sends client events to the corresponding widget server", %{socket: socket} do
@@ -74,7 +94,7 @@ defmodule LivebookWeb.JSViewChannelTest do
       send(from, {:connect_reply, payload, %{ref: "1"}})
 
       assert_push "init:1:id1",
-                  {:binary, <<24::size(32), "[null,{\"message\":\"hey\"}]", 1, 2, 3>>}
+                  {:binary, <<26::size(32), "[[true],{\"message\":\"hey\"}]", 1, 2, 3>>}
     end
 
     test "form client to server", %{socket: socket} do
@@ -98,7 +118,7 @@ defmodule LivebookWeb.JSViewChannelTest do
     })
   end
 
-  defp connect_token() do
-    Phoenix.Token.sign(LivebookWeb.Endpoint, "js-view-connect", %{pid: self()})
+  defp connect_token(pid \\ self()) do
+    Phoenix.Token.sign(LivebookWeb.Endpoint, "js-view-connect", %{pid: pid})
   end
 end