feat: allow converting otel trace ids to datadog values (#91)

* feat: allow converting otel trace ids to datadog values

* mix format

* update function for better performance

* add support for charlist values

Author: btkostner

lib/logger_json/formatters/datadog_logger.ex

@@ -29,7 +29,7 @@ defmodule LoggerJSON.Formatters.DatadogLogger do
   @behaviour LoggerJSON.Formatter
 
   @default_opts %{hostname: :system}
-  @processed_metadata_keys ~w[pid file line function module application span_id trace_id]a
+  @processed_metadata_keys ~w[pid file line function module application span_id trace_id otel_span_id otel_trace_id]a
 
   @impl true
   def init(formatter_opts \\ %{}) do
@@ -72,16 +72,46 @@ defmodule LoggerJSON.Formatters.DatadogLogger do
   # To connect logs and traces, span_id and trace_id keys are respectively dd.span_id and dd.trace_id
   # https://docs.datadoghq.com/tracing/faq/why-cant-i-see-my-correlated-logs-in-the-trace-id-panel/?tab=jsonlogs
   defp convert_tracing_keys(output, md) do
-    Enum.reduce([:trace_id, :span_id], output, fn key, acc ->
+    fields = %{
+      span_id: ["dd.span_id", & &1],
+      trace_id: ["dd.trace_id", & &1],
+      otel_span_id: ["dd.span_id", &convert_otel_field/1],
+      otel_trace_id: ["dd.trace_id", &convert_otel_field/1]
+    }
+
+    Enum.reduce(fields, output, fn {key, [new_key, transformer]}, acc ->
       if Keyword.has_key?(md, key) do
-        dd_key = "dd." <> Atom.to_string(key)
-        Map.merge(acc, %{dd_key => Keyword.get(md, key)})
+        new_value = apply(transformer, [Keyword.get(md, key)])
+        Map.merge(acc, %{new_key => new_value})
       else
         acc
       end
     end)
   end
 
+  # This converts native OpenTelemetry fields to the native Datadog format.
+  # This function is taken from the Datadog examples for converting. Mostly the Golang version
+  # https://docs.datadoghq.com/tracing/other_telemetry/connect_logs_and_traces/opentelemetry/?tab=go
+  # Tests were stolen from https://github.com/open-telemetry/opentelemetry-specification/issues/525
+  # and https://go.dev/play/p/pUBHcLdXJNy
+  defp convert_otel_field(<<value::binary-size(16)>>) do
+    {value, _} = Integer.parse(value, 16)
+    Integer.to_string(value, 10)
+  rescue
+    _ -> ""
+  end
+
+  defp convert_otel_field(value) when byte_size(value) < 16, do: ""
+
+  defp convert_otel_field(value) do
+    value = to_string(value)
+    len = byte_size(value) - 16
+    <<_front::binary-size(len), value::binary>> = value
+    convert_otel_field(value)
+  rescue
+    _ -> ""
+  end
+
   defp method_name(metadata) do
     function = Keyword.get(metadata, :function)
     module = Keyword.get(metadata, :module)

test/unit/logger_json_datadog_test.exs

@@ -223,6 +223,67 @@ defmodule LoggerJSONDatadogTest do
       assert Map.has_key?(log, "trace_id") == false
       assert Map.has_key?(log, "span_id") == false
     end
+
+    test "convert otel_trace_id/otel_span_id binary to expected datadog keys" do
+      Logger.configure_backend(LoggerJSON, metadata: :all)
+
+      Logger.metadata(
+        otel_trace_id:
+          <<98, 56, 49, 48, 100, 98, 97, 50, 57, 56, 48, 51, 101, 101, 54, 49, 101, 55, 99, 55, 49, 102, 102, 48, 99,
+            50, 99, 57, 53, 97, 57, 100>>
+      )
+
+      log =
+        fn -> Logger.debug("hello") end
+        |> capture_log()
+        |> Jason.decode!()
+
+      assert %{"dd.trace_id" => "16701352862047361693"} = log
+      assert Map.has_key?(log, "trace_id") == false
+      assert Map.has_key?(log, "span_id") == false
+    end
+
+    test "convert otel_trace_id/otel_span_id charlist to expected datadog keys" do
+      Logger.configure_backend(LoggerJSON, metadata: :all)
+      Logger.metadata(otel_trace_id: 'b810dba29803ee61e7c71ff0c2c95a9d')
+
+      log =
+        fn -> Logger.debug("hello") end
+        |> capture_log()
+        |> Jason.decode!()
+
+      assert %{"dd.trace_id" => "16701352862047361693"} = log
+      assert Map.has_key?(log, "trace_id") == false
+      assert Map.has_key?(log, "span_id") == false
+    end
+
+    test "convert otel_trace_id/otel_span_id string to expected datadog keys" do
+      Logger.configure_backend(LoggerJSON, metadata: :all)
+      Logger.metadata(otel_trace_id: "e7c71ff0c2c95a9d")
+
+      log =
+        fn -> Logger.debug("hello") end
+        |> capture_log()
+        |> Jason.decode!()
+
+      assert %{"dd.trace_id" => "16701352862047361693"} = log
+      assert Map.has_key?(log, "trace_id") == false
+      assert Map.has_key?(log, "span_id") == false
+    end
+
+    test "does not error on incorrect otel_trace_id/otel_span_id metadata" do
+      Logger.configure_backend(LoggerJSON, metadata: :all)
+      Logger.metadata(otel_trace_id: {:noop})
+
+      log =
+        fn -> Logger.debug("hello") end
+        |> capture_log()
+        |> Jason.decode!()
+
+      assert %{"dd.trace_id" => ""} = log
+      assert Map.has_key?(log, "trace_id") == false
+      assert Map.has_key?(log, "span_id") == false
+    end
   end
 
   describe "on_init/1 callback" do