Fix: Use topology name for message and exception tags

lib/prom_ex/plugins/broadway.ex

@@ -31,6 +31,8 @@ if Code.ensure_loaded?(Broadway) do
     end
     ```
 
+    ## GenStage Producer
+
     To correctly capture per-message metrics and error rate, add the following transform to your pipeline:
     ```
     defmodule WebApp.MyPipeline do
@@ -54,15 +56,25 @@ if Code.ensure_loaded?(Broadway) do
           acknowledger: {__MODULE__, :ack_id, :ack_data}
         }
       end
+
+      def ack(:ack_id, _successful_messages, _failed_messages) do
+        :ok
+      end
     end
     ```
+
+    ## BroadwayRabbitMQ.Producer
+
+    There's no need to configure an acknowledger on messages when using BroadwayRabbitMQ.
+
+    `BroadwayRabbitMQ.Producer` handles acking messages internally, which involves a unique `:delivery_tag` and `AMQP`.
     """
 
     use PromEx.Plugin
 
     require Logger
 
-    alias Broadway.{BatchInfo, Message, Options}
+    alias Broadway.{BatchInfo, Options}
     alias PromEx.Utils
 
     @millisecond_duration_buckets [10, 100, 500, 1_000, 10_000, 30_000, 60_000]
@@ -268,12 +280,7 @@ if Code.ensure_loaded?(Broadway) do
               buckets: @millisecond_duration_buckets
             ],
             tags: [:processor_key, :name],
-            tag_values: fn %{processor_key: processor_key, message: %Message{acknowledger: {acknowledger, _, _}}} ->
-              %{
-                processor_key: processor_key,
-                name: Utils.normalize_module_name(acknowledger)
-              }
-            end,
+            tag_values: &extract_message_tag_values/1,
             unit: {:native, :millisecond}
           ),
           distribution(
@@ -338,6 +345,13 @@ if Code.ensure_loaded?(Broadway) do
       )
     end
 
+    defp extract_message_tag_values(%{processor_key: processor_key, topology_name: name}) do
+      %{
+        processor_key: processor_key,
+        name: Utils.normalize_module_name(name)
+      }
+    end
+
     defp extract_batcher_tag_values(%{batch_info: batch_info = %BatchInfo{}, topology_name: name}) do
       %{
         name: Utils.normalize_module_name(name),
@@ -362,15 +376,15 @@ if Code.ensure_loaded?(Broadway) do
            kind: kind,
            reason: reason,
            stacktrace: stacktrace,
-           message: %Message{acknowledger: {acknowledger, _, _}}
+           topology_name: name
          }) do
       reason = Utils.normalize_exception(kind, reason, stacktrace)
 
       %{
         processor_key: processor_key,
         kind: kind,
         reason: reason,
-        name: Utils.normalize_module_name(acknowledger)
+        name: Utils.normalize_module_name(name)
       }
     end
   end

test/prom_ex/plugins/broadway_test.exs

@@ -1,8 +1,16 @@
 defmodule PromEx.Plugins.BroadwayTest do
   use ExUnit.Case, async: true
 
+  alias PromEx.MetricTypes.Event
   alias PromEx.Plugins.Broadway
   alias PromEx.Test.Support.{Events, Metrics}
+  alias Telemetry.Metrics.Distribution
+
+  @default_metadata %{
+    processor_key: :default,
+    topology_name: Elixir.SomeModule,
+    message: %Elixir.Broadway.Message{acknowledger: {Elixir.SomeAcker}, data: %{}}
+  }
 
   defmodule WebApp.PromEx do
     use PromEx, otp_app: :web_app
@@ -24,4 +32,28 @@ defmodule PromEx.Plugins.BroadwayTest do
 
     assert metrics == Metrics.read_expected(:broadway)
   end
+
+  describe "event_metrics/1" do
+    test "returns topology_name for message tags" do
+      metric = assert_event_metric(:broadway_message_event_metrics, [:broadway, :processor, :message, :stop])
+      assert %{name: "SomeModule", processor_key: :default} = metric.tag_values.(@default_metadata)
+    end
+
+    test "returns topology_name for message exception tags" do
+      metric = assert_event_metric(:broadway_message_event_metrics, [:broadway, :processor, :message, :exception])
+      exception_metadata = Map.merge(@default_metadata, %{kind: Error, reason: "notsure", stacktrace: []})
+      assert %{name: "SomeModule", processor_key: :default} = metric.tag_values.(exception_metadata)
+    end
+
+    defp assert_event_metric(metric_group, event) do
+      assert event_metrics = Broadway.event_metrics(otp_app: :web_app)
+
+      assert %Event{metrics: message_metrics} =
+               Enum.find(event_metrics, fn metrics -> metrics.group_name == metric_group end)
+
+      assert %Distribution{} = metric = Enum.find(message_metrics, fn dist -> dist.event_name == event end)
+
+      metric
+    end
+  end
 end