Add a new single-span diagnostic observer for ASP.NET Core

tracer/src/Datadog.Trace/ClrProfiler/Instrumentation.cs

@@ -490,7 +490,17 @@ private static void StartDiagnosticManager()
                 // Iast hasn't yet, but doing it now is fine
                 // span origins is _not_ initialized yet, and we can't guarantee it will be
                 // so just be lazy instead
-                observers.Add(new AspNetCoreDiagnosticObserver(Tracer.Instance, Security.Instance, Iast.Iast.Instance, spanCodeOrigin: null));
+#if NET6_0_OR_GREATER
+                if (Tracer.Instance.Settings.SingleSpanAspNetCoreEnabled)
+                {
+                    observers.Add(new SingleSpanAspNetCoreDiagnosticObserver(Tracer.Instance, Security.Instance, Iast.Iast.Instance, null));
+                }
+                else
+#endif
+                {
+                    observers.Add(new AspNetCoreDiagnosticObserver(Tracer.Instance, Security.Instance, Iast.Iast.Instance, spanCodeOrigin: null));
+                }
+
                 observers.Add(new QuartzDiagnosticObserver());
             }
 

tracer/src/Datadog.Trace/Configuration/TracerSettings.cs

@@ -378,9 +378,23 @@ not null when string.Equals(value, "otlp", StringComparison.OrdinalIgnoreCase) =
                                                .WithKeys(ConfigurationKeys.FeatureFlags.RouteTemplateResourceNamesEnabled)
                                                .AsBool(defaultValue: true);
 
+            SingleSpanAspNetCoreEnabled = config
+                                         .WithKeys(ConfigurationKeys.FeatureFlags.SingleSpanAspNetCoreEnabled)
+                                         .AsBool(defaultValue: false);
+#if !NET6_0_OR_GREATER
+            // single span aspnetcore is only supported in .NET 6+, so override for telemetry purposes
+            if (SingleSpanAspNetCoreEnabled)
+            {
+                SingleSpanAspNetCoreEnabled = false;
+                Log.Warning(
+                    $"{ConfigurationKeys.FeatureFlags.SingleSpanAspNetCoreEnabled} is set to true, but is only supported in .NET 6+. Using false instead.");
+                telemetry.Record(ConfigurationKeys.FeatureFlags.SingleSpanAspNetCoreEnabled, false, ConfigurationOrigins.Calculated);
+            }
+#endif
+
             ExpandRouteTemplatesEnabled = config
                                          .WithKeys(ConfigurationKeys.ExpandRouteTemplatesEnabled)
-                                         .AsBool(defaultValue: !RouteTemplateResourceNamesEnabled); // disabled by default if route template resource names enabled
+                                         .AsBool(defaultValue: !(RouteTemplateResourceNamesEnabled || SingleSpanAspNetCoreEnabled)); // disabled by default if route template resource names or single-span enabled
 
             AzureServiceBusBatchLinksEnabled = config
                                              .WithKeys(ConfigurationKeys.AzureServiceBusBatchLinksEnabled)
@@ -1089,10 +1103,16 @@ not null when string.Equals(value, "otlp", StringComparison.OrdinalIgnoreCase) =
 
         /// <summary>
         /// Gets a value indicating whether resource names for ASP.NET and ASP.NET Core spans should be expanded. Only applies
-        /// when <see cref="RouteTemplateResourceNamesEnabled"/> is <code>true</code>.
+        /// when <see cref="RouteTemplateResourceNamesEnabled"/> or <see cref="SingleSpanAspNetCoreEnabled"/> are <code>true</code>.
         /// </summary>
         internal bool ExpandRouteTemplatesEnabled { get; }
 
+        /// <summary>
+        /// Gets a value indicating whether single-span ASP.NET Core instrumentation should be used.
+        /// </summary>
+        /// <seealso cref="ConfigurationKeys.FeatureFlags.SingleSpanAspNetCoreEnabled"/>
+        internal bool SingleSpanAspNetCoreEnabled { get; }
+
         /// <summary>
         /// Gets the direct log submission settings.
         /// </summary>

tracer/src/Datadog.Trace/Configuration/configuration_keys_mapping.json

@@ -604,6 +604,10 @@
       "env_var": "DD_SITE",
       "const_name": "Site"
     },
+    {
+      "env_var": "DD_TRACE_SINGLE_SPAN_ASPNETCORE_ENABLED",
+      "const_name": "SingleSpanAspNetCoreEnabled"
+    },
     {
       "env_var": "DD_SPAN_SAMPLING_RULES",
       "const_name": "SpanSamplingRules"

tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml

@@ -1037,6 +1037,14 @@ DD_TRACE_SERVICE_MAPPING: |
   Configuration key for a map of services to rename.
   <seealso cref="Datadog.Trace.Configuration.MutableSettings.ServiceNameMappings"/>
 
+DD_TRACE_SINGLE_SPAN_ASPNETCORE_ENABLED: |
+  Feature Flag: Enables generating only a single span in the ASP.NET Core integration,
+  by only creating `aspnet_core.request` spans, without creating handler spans or tracking
+  specific route values. Defaults to <c>false</c>. Not compatible with
+  DD_TRACE_ROUTE_TEMPLATE_RESOURCE_NAMES_ENABLED (that value is ignored), but may be used
+  with DD_TRACE_EXPAND_ROUTE_TEMPLATES_ENABLED. Only supported on .NET 6+.
+  <seealso cref="Datadog.Trace.Configuration.TracerSettings.SingleSpanAspNetCoreEnabled"/>
+
 DD_TRACE_SPAN_ATTRIBUTE_SCHEMA: |
   Configuration key for setting the schema version for service naming and span attributes
   Accepted values are: "v1", "v0"

tracer/src/Datadog.Trace/Configuration/supported-configurations.json

@@ -1330,6 +1330,12 @@
         "A"
       ]
     },
+    "DD_TRACE_SINGLE_SPAN_ASPNETCORE_ENABLED": {
+      "version": [
+        "A"
+      ],
+      "product": "FeatureFlags"
+    },
     "DD_TRACE_SPAN_ATTRIBUTE_SCHEMA": {
       "version": [
         "A"

tracer/src/Datadog.Trace/DiagnosticListeners/AspNetCoreDiagnosticObserver.cs

@@ -645,7 +645,7 @@ private void OnMvcBeforeAction(object arg)
             }
         }
 
-        private bool TryGetTypeAndMethod(BeforeActionStruct beforeAction, out Type type, out MethodInfo method)
+        internal static bool TryGetTypeAndMethod(BeforeActionStruct beforeAction, [NotNullWhen(true)] out Type type, [NotNullWhen(true)] out MethodInfo method)
         {
             try
             {