feat(telemetry.serilog): TraceContextEnricher for trace<->log correlation

ZB.MOM.WW.Telemetry/src/ZB.MOM.WW.Telemetry.Serilog/TraceContextEnricher.cs

@@ -0,0 +1,43 @@
+using System.Diagnostics;
+using Serilog.Core;
+using Serilog.Events;
+
+namespace ZB.MOM.WW.Telemetry.Serilog;
+
+/// <summary>
+/// Stamps <c>trace_id</c> and <c>span_id</c> from <see cref="Activity.Current"/> onto every Serilog
+/// log event, enabling a log line to be correlated back to its originating trace in a backend.
+/// When <see cref="Activity.Current"/> is null (no active span — background services, startup,
+/// non-traced paths) the enricher emits nothing; it does NOT inject empty strings or zero values.
+/// </summary>
+public sealed class TraceContextEnricher : ILogEventEnricher
+{
+    /// <summary>Serilog property name carrying the W3C trace id.</summary>
+    public const string TraceIdPropertyName = "trace_id";
+
+    /// <summary>Serilog property name carrying the W3C span id.</summary>
+    public const string SpanIdPropertyName = "span_id";
+
+    /// <summary>
+    /// Adds <c>trace_id</c>/<c>span_id</c> properties from <see cref="Activity.Current"/> when an
+    /// activity is active; otherwise leaves the event untouched.
+    /// </summary>
+    /// <param name="logEvent">The log event to enrich.</param>
+    /// <param name="propertyFactory">Factory used to create the trace-context properties.</param>
+    public void Enrich(LogEvent logEvent, ILogEventPropertyFactory propertyFactory)
+    {
+        ArgumentNullException.ThrowIfNull(logEvent);
+        ArgumentNullException.ThrowIfNull(propertyFactory);
+
+        var activity = Activity.Current;
+        if (activity is null)
+        {
+            return;
+        }
+
+        logEvent.AddPropertyIfAbsent(
+            propertyFactory.CreateProperty(TraceIdPropertyName, activity.TraceId.ToString()));
+        logEvent.AddPropertyIfAbsent(
+            propertyFactory.CreateProperty(SpanIdPropertyName, activity.SpanId.ToString()));
+    }
+}

ZB.MOM.WW.Telemetry/src/ZB.MOM.WW.Telemetry.Serilog/ZbSerilogConfig.cs

@@ -64,6 +64,8 @@ public static class ZbSerilogConfig
 
         enrich.WithProperty(ZbLogEnricherNames.NodeHostname, Environment.MachineName);
 
+        enrich.With(new TraceContextEnricher());
+
         return loggerConfiguration;
     }
 }

ZB.MOM.WW.Telemetry/tests/ZB.MOM.WW.Telemetry.Serilog.Tests/TraceContextEnricherTests.cs

@@ -0,0 +1,66 @@
+using System.Diagnostics;
+using Serilog;
+using Serilog.Core;
+using Serilog.Events;
+using Serilog.Sinks.InMemory;
+using ZB.MOM.WW.Telemetry;
+using ZB.MOM.WW.Telemetry.Serilog;
+
+namespace ZB.MOM.WW.Telemetry.Serilog.Tests;
+
+public sealed class TraceContextEnricherTests
+{
+    private const string SourceName = "ZB.MOM.WW.Telemetry.Serilog.Tests.TraceContext";
+
+    private static Logger BuildLogger(InMemorySink sink) =>
+        new LoggerConfiguration()
+            .Enrich.With(new TraceContextEnricher())
+            .WriteTo.Sink(sink)
+            .CreateLogger();
+
+    private static string? ScalarOrNull(LogEvent logEvent, string propertyName) =>
+        logEvent.Properties.TryGetValue(propertyName, out var value) && value is ScalarValue scalar
+            ? scalar.Value?.ToString()
+            : null;
+
+    [Fact]
+    public void Active_activity_stamps_trace_id_and_span_id()
+    {
+        using var listener = new ActivityListener
+        {
+            ShouldListenTo = source => source.Name == SourceName,
+            Sample = (ref ActivityCreationOptions<ActivityContext> _) =>
+                ActivitySamplingResult.AllDataAndRecorded,
+        };
+        ActivitySource.AddActivityListener(listener);
+
+        using var activitySource = new ActivitySource(SourceName);
+        var sink = new InMemorySink();
+        using var logger = BuildLogger(sink);
+
+        using var activity = activitySource.StartActivity("unit-test");
+        Assert.NotNull(activity);
+        Assert.NotNull(Activity.Current);
+
+        logger.Information("traced");
+
+        var logEvent = Assert.Single(sink.LogEvents);
+        Assert.Equal(Activity.Current!.TraceId.ToString(), ScalarOrNull(logEvent, "trace_id"));
+        Assert.Equal(Activity.Current!.SpanId.ToString(), ScalarOrNull(logEvent, "span_id"));
+    }
+
+    [Fact]
+    public void No_active_activity_omits_trace_id_and_span_id()
+    {
+        Assert.Null(Activity.Current);
+
+        var sink = new InMemorySink();
+        using var logger = BuildLogger(sink);
+
+        logger.Information("untraced");
+
+        var logEvent = Assert.Single(sink.LogEvents);
+        Assert.False(logEvent.Properties.ContainsKey("trace_id"));
+        Assert.False(logEvent.Properties.ContainsKey("span_id"));
+    }
+}