Initialize Activity with parent ID (#41568)

Initialize Activity with parent ID in Hosting.

Author: adityamandaleeka

src/Hosting/Hosting/src/Internal/HostingApplicationDiagnostics.cs

@@ -310,17 +310,8 @@ private static void RecordRequestStartEventLog(HttpContext httpContext)
     [MethodImpl(MethodImplOptions.NoInlining)]
     private Activity? StartActivity(HttpContext httpContext, bool loggingEnabled, bool diagnosticListenerActivityCreationEnabled, out bool hasDiagnosticListener)
     {
-        var activity = _activitySource.CreateActivity(ActivityName, ActivityKind.Server);
-        if (activity is null && (loggingEnabled || diagnosticListenerActivityCreationEnabled))
-        {
-            activity = new Activity(ActivityName);
-        }
         hasDiagnosticListener = false;
 
-        if (activity is null)
-        {
-            return null;
-        }
         var headers = httpContext.Request.Headers;
         _propagator.ExtractTraceIdAndState(headers,
             static (object? carrier, string fieldName, out string? fieldValue, out IEnumerable<string>? fieldValues) =>
@@ -332,9 +323,44 @@ private static void RecordRequestStartEventLog(HttpContext httpContext)
             out var requestId,
             out var traceState);
 
+        Activity? activity = null;
+        if (_activitySource.HasListeners())
+        {
+            if (ActivityContext.TryParse(requestId, traceState, true, out ActivityContext context))
+            {
+                // The requestId used W3C ID format. Unfortunately the ActivitySource.CreateActivity overload that
+                // takes a string ID sets ActivityContext.IsRemote = false when it parses the string internally.
+                // We work around that by using the ActivityContext ID overload and setting ActivityContext.IsRemote
+                // to true after parsing it.
+                activity = _activitySource.CreateActivity(ActivityName, ActivityKind.Server, context);
+            }
+            else
+            {
+                // Pass in the ID we got from the headers if there was one.
+                activity = _activitySource.CreateActivity(ActivityName, ActivityKind.Server, string.IsNullOrEmpty(requestId) ? null! : requestId);
+            }
+        }
+
+        if (activity is null)
+        {
+            // CreateActivity didn't create an Activity (this is an optimization for the
+            // case when there are no listeners). Let's create it here if needed.
+            if (loggingEnabled || diagnosticListenerActivityCreationEnabled)
+            {
+                activity = new Activity(ActivityName);
+                if (!string.IsNullOrEmpty(requestId))
+                {
+                    activity.SetParentId(requestId);
+                }
+            }
+            else
+            {
+                return null;
+            }
+        }
+
         if (!string.IsNullOrEmpty(requestId))
         {
-            activity.SetParentId(requestId);
             if (!string.IsNullOrEmpty(traceState))
             {
                 activity.TraceStateString = traceState;

src/Hosting/Hosting/test/HostingApplicationDiagnosticsTests.cs

@@ -458,6 +458,50 @@ public void ActivityTraceParentAndTraceStateFromHeaders()
         Assert.Contains(Activity.Current.Baggage, pair => pair.Key == "Key2" && pair.Value == "value2");
     }
 
+    [Fact]
+    public void SamplersReceiveCorrectParentAndTraceIds()
+    {
+        var testSource = new ActivitySource(Path.GetRandomFileName());
+        var hostingApplication = CreateApplication(out var features, activitySource: testSource);
+        var parentId = "";
+        var parentSpanId = "";
+        var traceId = "";
+        using var listener = new ActivityListener
+        {
+            ShouldListenTo = activitySource => ReferenceEquals(activitySource, testSource),
+            Sample = (ref ActivityCreationOptions<ActivityContext> options) => ComputeActivitySamplingResult(ref options),
+            ActivityStarted = activity =>
+            {
+                parentId = activity.ParentId;
+                parentSpanId = activity.ParentSpanId.ToHexString();
+                traceId = activity.TraceId.ToHexString();
+            }
+        };
+
+        ActivitySource.AddActivityListener(listener);
+
+        features.Set<IHttpRequestFeature>(new HttpRequestFeature()
+        {
+            Headers = new HeaderDictionary()
+                {
+                    {"traceparent", "00-35aae61e3e99044eb5ea5007f2cd159b-40a8bd87c078cb4c-00"},
+                }
+        });
+
+        hostingApplication.CreateContext(features);
+        Assert.Equal("00-35aae61e3e99044eb5ea5007f2cd159b-40a8bd87c078cb4c-00", parentId);
+        Assert.Equal("40a8bd87c078cb4c", parentSpanId);
+        Assert.Equal("35aae61e3e99044eb5ea5007f2cd159b", traceId);
+
+        static ActivitySamplingResult ComputeActivitySamplingResult(ref ActivityCreationOptions<ActivityContext> options)
+        {
+            Assert.Equal("35aae61e3e99044eb5ea5007f2cd159b", options.TraceId.ToHexString());
+            Assert.Equal("40a8bd87c078cb4c", options.Parent.SpanId.ToHexString());
+
+            return ActivitySamplingResult.AllDataAndRecorded;
+        }
+    }
+
     [Fact]
     public void ActivityOnImportHookIsCalled()
     {