Add LiveviewTelemetry

The liveview option in OpentelemetryPhoenix is not tracking enough,
causing no span to be present in some liveviews. It needs a custom
Telemetry module.

lib/tracing.ex

@@ -181,11 +181,9 @@ defmodule Tracing do
     Enum.each(elements, &(:ok = setup_element(&1)))
   end
 
-  def setup_element(:phoenix) do
-    OpentelemetryPhoenix.setup()
-  end
-
-  def setup_element(:oban), do: Tracing.ObanTelemetry.setup()
   def setup_element(:aws), do: Tracing.AWSTelemetry.setup()
   def setup_element(:chromic_pdf), do: Tracing.ChromicPDFTelemetry.setup()
+  def setup_element(:liveview), do: Tracing.LiveviewTelemetry.setup()
+  def setup_element(:oban), do: Tracing.ObanTelemetry.setup()
+  def setup_element(:phoenix), do: OpentelemetryPhoenix.setup()
 end

lib/tracing/liveview_telemetry.ex

@@ -0,0 +1,99 @@
+defmodule Tracing.LiveviewTelemetry do
+  require OpenTelemetry.Tracer
+  alias __MODULE__
+  alias OpenTelemetry.Span
+
+  @tracer_id LiveviewTelemetry
+
+  @event_names [
+    [:phoenix, :live_view, :mount, :start],
+    [:phoenix, :live_view, :mount, :stop],
+    [:phoenix, :live_view, :mount, :exception],
+    [:phoenix, :live_view, :handle_params, :start],
+    [:phoenix, :live_view, :handle_params, :stop],
+    [:phoenix, :live_view, :handle_params, :exception],
+    [:phoenix, :live_view, :handle_event, :start],
+    [:phoenix, :live_view, :handle_event, :stop],
+    [:phoenix, :live_view, :handle_event, :exception],
+    [:phoenix, :live_component, :handle_event, :start],
+    [:phoenix, :live_component, :handle_event, :stop],
+    [:phoenix, :live_component, :handle_event, :exception]
+  ]
+  def setup do
+    :telemetry.attach_many(
+      LiveviewTelemetry,
+      @event_names,
+      &LiveviewTelemetry.handle_event/4,
+      %{}
+    )
+  end
+
+  def handle_event([:phoenix, source, function, :start], _measurements, meta, _config)
+      when source in [:live_view, :live_component] do
+    %{socket: %{view: live_view}} = meta
+
+    OpentelemetryTelemetry.start_telemetry_span(
+      @tracer_id,
+      "#{inspect(live_view)}.#{function}",
+      meta,
+      %{kind: :internal}
+    )
+    |> Span.set_attributes(meta_based_attributes(meta, source, function))
+  end
+
+  def handle_event([:phoenix, source, _function, :stop], _measurements, meta, _config)
+      when source in [:live_view, :live_component] do
+    OpentelemetryTelemetry.end_telemetry_span(@tracer_id, meta)
+  end
+
+  def handle_event(
+        [:phoenix, source, _kind, :exception],
+        _measurements,
+        %{kind: kind, reason: reason, stacktrace: stacktrace} = meta,
+        _config
+      )
+      when source in [:live_view, :live_component] do
+    ctx = OpentelemetryTelemetry.set_current_telemetry_span(@tracer_id, meta)
+
+    exception = Exception.normalize(kind, reason, stacktrace)
+
+    Span.record_exception(ctx, exception, stacktrace, [])
+    Span.set_status(ctx, OpenTelemetry.status(:error, Exception.message(exception)))
+
+    OpentelemetryTelemetry.end_telemetry_span(@tracer_id, meta)
+  end
+
+  defp meta_based_attributes(meta, source, function) do
+    module =
+      case {source, meta} do
+        {:live_view, _} -> module_to_string(meta.socket.view)
+        {:live_component, %{component: component}} -> module_to_string(component)
+      end
+
+    attributes = [
+      "liveview.module": module,
+      "liveview.callback": Atom.to_string(function)
+    ]
+
+    Enum.reduce(meta, attributes, fn
+      {:uri, uri}, acc ->
+        Keyword.put(acc, :"liveview.uri", uri)
+
+      {:component, component}, acc ->
+        Keyword.put(acc, :"liveview.module", module_to_string(component))
+
+      {:event, event}, acc ->
+        Keyword.put(acc, :"liveview.event", event)
+
+      _, acc ->
+        acc
+    end)
+  end
+
+  defp module_to_string(module) when is_atom(module) do
+    case to_string(module) do
+      "Elixir." <> name -> name
+      erlang_module -> ":#{erlang_module}"
+    end
+  end
+end