[WCF] Fix exception when no endpoint action

src/OpenTelemetry.Instrumentation.Wcf/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+* Fixed `ArgumentNullException` thrown by `TelemetryEndpointBehavior` when an endpoint
+  operation has a `null` Action (e.g., when WCF service help pages are enabled).
+  ([#4026](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/4026))
+
 * Updated OpenTelemetry core component version(s) to `1.15.1`.
   ([#4020](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/4020))
 

src/OpenTelemetry.Instrumentation.Wcf/TelemetryEndpointBehavior.cs

@@ -81,6 +81,11 @@ internal static void ApplyClientBehaviorToClientRuntime(ClientRuntime clientRunt
 
         foreach (var clientOperation in clientRuntime.ClientOperations)
         {
+            if (clientOperation.Action == null)
+            {
+                continue;
+            }
+
             actionMappings[clientOperation.Action] = new ActionMetadata(
                 contractName: $"{clientRuntime.ContractNamespace}{clientRuntime.ContractName}",
                 operationName: clientOperation.Name);
@@ -96,6 +101,11 @@ internal static void ApplyDispatchBehaviorToEndpoint(EndpointDispatcher endpoint
 
         foreach (var dispatchOperation in endpointDispatcher.DispatchRuntime.Operations)
         {
+            if (dispatchOperation.Action == null)
+            {
+                continue;
+            }
+
             actionMappings[dispatchOperation.Action] = new ActionMetadata(
                 contractName: $"{endpointDispatcher.ContractNamespace}{endpointDispatcher.ContractName}",
                 operationName: dispatchOperation.Name);

test/OpenTelemetry.Instrumentation.Wcf.Tests/TelemetryEndpointBehaviorTests.cs

@@ -0,0 +1,60 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+using System.ServiceModel;
+using System.ServiceModel.Channels;
+using System.ServiceModel.Description;
+using System.ServiceModel.Dispatcher;
+using Xunit;
+
+namespace OpenTelemetry.Instrumentation.Wcf.Tests;
+
+public class TelemetryEndpointBehaviorTests
+{
+    [Fact]
+    public void ApplyClientBehaviorToClientRuntime_WithNullActionOperation_DoesNotThrow()
+    {
+        // Arrange
+        var contract = ContractDescription.GetContract(typeof(IServiceContract));
+        var endpoint = new ServiceEndpoint(contract, new BasicHttpBinding(), new EndpointAddress("http://localhost/dummy"));
+
+        endpoint.EndpointBehaviors.Add(new InjectNullActionOperationBehavior());
+        endpoint.EndpointBehaviors.Add(new TelemetryEndpointBehavior());
+
+        var factory = new ChannelFactory<IServiceContract>(endpoint);
+
+        try
+        {
+            var exception = Record.Exception(factory.Open);
+            Assert.Null(exception);
+        }
+        finally
+        {
+            factory.Abort();
+        }
+    }
+
+    private sealed class InjectNullActionOperationBehavior : IEndpointBehavior
+    {
+        public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
+        {
+            // No-op
+        }
+
+        public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
+        {
+            var nullActionOp = new ClientOperation(clientRuntime, "NullActionOperation", null);
+            clientRuntime.ClientOperations.Add(nullActionOp);
+        }
+
+        public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
+        {
+            // No-op
+        }
+
+        public void Validate(ServiceEndpoint endpoint)
+        {
+            // No-op
+        }
+    }
+}