Add ActivityListener test

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

@@ -55,14 +55,14 @@ public void BeginRequest(HttpContext httpContext, HostingApplication.Context con
             // TODO: If loggingEnabled check to change to if ActivityPropogation options are enabled
             if (loggingEnabled || (diagnosticListenerEnabled && _diagnosticListener.IsEnabled(ActivityName, httpContext)))
             {
-                // Review: Force creation of Activity by creating dummy listener
                 _dummyListener = new ActivityListener()
                 {
                     ShouldListenTo = activitySource => activitySource.Name.Equals(ActivitySourceName),
                     Sample = (ref ActivityCreationOptions<ActivityContext> _) => ActivitySamplingResult.PropagationData
                 };
                 ActivitySource.AddActivityListener(_dummyListener);
             }
+
             context.Activity = StartActivity(httpContext, out var hasDiagnosticListener);
             context.HasDiagnosticListener = hasDiagnosticListener;
 
@@ -269,7 +269,12 @@ private static void RecordRequestStartEventLog(HttpContext httpContext)
                 hasDiagnosticListener = true;
             }
 
-            // TODO: Don't look at headers if there no listeners
+            // Short-circuit to avoid doing an expensive header lookup
+            if (!(hasDiagnosticListener || _activitySource.HasListeners()))
+            {
+                return null;
+            }
+
             var headers = httpContext.Request.Headers;
             if (!headers.TryGetValue(HeaderNames.TraceParent, out var requestId))
             {
@@ -307,6 +312,12 @@ private static void RecordRequestStartEventLog(HttpContext httpContext)
 
                 // Review: Breaking change: We will no longer fire OnActivityImport before Activity.Start()
                 _diagnosticListener.OnActivityImport(activity, httpContext);
+
+                if (hasDiagnosticListener)
+                {
+                    //Review: Do we need to explicity call this?
+                    _diagnosticListener.Write(ActivityStartKey, httpContext);
+                }
             }
             return activity;
         }
@@ -316,15 +327,20 @@ private void StopActivity(HttpContext httpContext, Activity activity, bool hasDi
         {
             if (hasDiagnosticListener)
             {
-                // Stop sets the end time if it was unset, but we want it set before we issue the write
-                // so we do it now.
-                if (activity.Duration == TimeSpan.Zero)
-                {
-                    activity.SetEndTime(DateTime.UtcNow);
-                }
-                _diagnosticListener.Write(ActivityStopKey, httpContext);
+                StopActivity(activity, httpContext);
+            }
+            activity.Stop();
+        }
+
+        private void StopActivity(Activity activity, HttpContext httpContext)
+        {
+            // Stop sets the end time if it was unset, but we want it set before we issue the write
+            // so we do it now.
+            if (activity.Duration == TimeSpan.Zero)
+            {
+                activity.SetEndTime(DateTime.UtcNow);
             }
-            activity.Dispose();
+            _diagnosticListener.Write(ActivityStopKey, httpContext);
         }
     }
 }

src/Hosting/Hosting/test/HostingApplicationDiagnosticsTests.cs

@@ -362,6 +362,7 @@ public void ActivityBaggagePrefersW3CBaggageHeaderName()
             Assert.Contains(Activity.Current.Baggage, pair => pair.Key == "Key2" && pair.Value == "value4");
         }
 
+
         [Fact]
         public void ActivityBaggagePreservesItemsOrder()
         {
@@ -494,6 +495,35 @@ public void ActivityOnImportHookIsCalled()
             Assert.True(Activity.Current.Recorded);
         }
 
+        [Fact]
+        public void ActivityListenersAreCalled()
+        {
+            var hostingApplication = CreateApplication(out var features);
+            using var listener = new ActivityListener
+            {
+                ShouldListenTo = activitySource => true,
+                Sample = (ref ActivityCreationOptions<ActivityContext> _) => ActivitySamplingResult.AllData,
+                ActivityStarted = activity =>
+                {
+                    Assert.Equal("0123456789abcdef", Activity.Current.ParentSpanId.ToHexString());
+                },
+                //ActivityStopped = activity => Assert..
+            };
+
+            ActivitySource.AddActivityListener(listener);
+
+            features.Set<IHttpRequestFeature>(new HttpRequestFeature()
+            {
+                Headers = new HeaderDictionary()
+                {
+                    {"traceparent", "00-0123456789abcdef0123456789abcdef-0123456789abcdef-01"},
+                    {"tracestate", "TraceState1"},
+                    {"baggage", "Key1=value1, Key2=value2"}
+                }
+            });
+            hostingApplication.CreateContext(features);
+        }
+
 
         private static void AssertProperty<T>(object o, string name)
         {