Fix ConsoleExporter fails silently when exporting an ActivityLink without Tags.

src/OpenTelemetry.Exporter.Console/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+* Bug fix, ConsoleExporter fails silently when exporting an `ActivityLink`
+  without Tags.
+  ([#3932](https://github.com/open-telemetry/opentelemetry-dotnet/pull/3932))
+
 ## 1.4.0-beta.3
 
 Released 2022-Nov-07

src/OpenTelemetry.Exporter.Console/ConsoleActivityExporter.cs

@@ -116,11 +116,14 @@ public override ExportResult Export(in Batch<Activity> batch)
                     foreach (var activityLink in activity.Links)
                     {
                         this.WriteLine($"    {activityLink.Context.TraceId} {activityLink.Context.SpanId}");
-                        foreach (var attribute in activityLink.Tags)
+                        if (activityLink.Tags != null)
                         {
-                            if (ConsoleTagTransformer.Instance.TryTransformTag(attribute, out var result))
+                            foreach (var attribute in activityLink.Tags)
                             {
-                                this.WriteLine($"        {result}");
+                                if (ConsoleTagTransformer.Instance.TryTransformTag(attribute, out var result))
+                                {
+                                    this.WriteLine($"        {result}");
+                                }
                             }
                         }
                     }

test/OpenTelemetry.Tests/OpenTelemetry.Tests.csproj

@@ -10,6 +10,7 @@
   <ItemGroup>
     <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry\OpenTelemetry.csproj" />
     <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.InMemory\OpenTelemetry.Exporter.InMemory.csproj" />
+    <ProjectReference Include="$(RepoRoot)\src\OpenTelemetry.Exporter.Console\OpenTelemetry.Exporter.Console.csproj" />
   </ItemGroup>
 
   <ItemGroup>

test/OpenTelemetry.Tests/Shared/UnitTestEventListener.cs

@@ -0,0 +1,72 @@
+// <copyright file="UnitTestEventListener.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace OpenTelemetry.Tests.Shared
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Diagnostics.Tracing;
+
+    /// <summary>
+    /// This EventListener can be used to subscribe to a specific EventSourceName and EventLevel.
+    /// </summary>
+    public class UnitTestEventListener : EventListener
+    {
+        public List<EventWrittenEventArgs> CapturedEvents = new();
+
+        private readonly List<EventSource> subscribedEventSources = new();
+        private readonly Guid currentThreadActivityId = Guid.NewGuid();
+        private readonly string eventName;
+        private readonly EventLevel eventLevel;
+
+        public UnitTestEventListener(string eventSourceName, EventLevel eventLevel)
+        {
+            EventSource.SetCurrentThreadActivityId(this.currentThreadActivityId);
+            this.eventName = eventSourceName;
+            this.eventLevel = eventLevel;
+        }
+
+        public override void Dispose()
+        {
+            foreach (var eventSource in this.subscribedEventSources)
+            {
+                this.DisableEvents(eventSource);
+            }
+
+            base.Dispose();
+            GC.SuppressFinalize(this);
+        }
+
+        protected override void OnEventSourceCreated(EventSource eventSource)
+        {
+            if (eventSource?.Name == this.eventName)
+            {
+                this.subscribedEventSources.Add(eventSource);
+                this.EnableEvents(eventSource, this.eventLevel, EventKeywords.All);
+            }
+
+            base.OnEventSourceCreated(eventSource);
+        }
+
+        protected override void OnEventWritten(EventWrittenEventArgs eventData)
+        {
+            if (eventData.ActivityId == this.currentThreadActivityId)
+            {
+                this.CapturedEvents.Add(eventData);
+            }
+        }
+    }
+}

test/OpenTelemetry.Tests/Shared/VerifyNoEventSourceErrorsLoggedTestAttribute.cs

@@ -0,0 +1,47 @@
+// <copyright file="VerifyNoEventSourceErrorsLoggedTestAttribute.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace OpenTelemetry.Tests.Shared
+{
+    using System.Diagnostics.Tracing;
+    using System.Linq;
+    using System.Reflection;
+    using Xunit;
+    using Xunit.Sdk;
+
+    /// <summary>
+    /// Can be used to assert that no Errors were logged to EventSource during a unit test.
+    /// </summary>
+    internal class VerifyNoEventSourceErrorsLoggedTestAttribute : BeforeAfterTestAttribute
+    {
+        private readonly UnitTestEventListener myTestEventListener;
+
+        public VerifyNoEventSourceErrorsLoggedTestAttribute(string eventSourceName)
+        {
+            this.myTestEventListener = new UnitTestEventListener(eventSourceName, EventLevel.Error);
+        }
+
+        public override void After(MethodInfo methodUnderTest)
+        {
+            if (this.myTestEventListener.CapturedEvents.Any())
+            {
+                var eventNames = string.Join(",", this.myTestEventListener.CapturedEvents.Select(x => x.EventName));
+
+                Assert.Fail($"EventSource Exception captured during test run: {eventNames}");
+            }
+        }
+    }
+}

test/OpenTelemetry.Tests/Trace/ConsoleExporterTest.cs

@@ -0,0 +1,61 @@
+// <copyright file="ConsoleExporterTest.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace OpenTelemetry.Tests.Trace
+{
+    using System.Collections.Generic;
+    using System.Diagnostics;
+    using System.Linq;
+    using OpenTelemetry.Tests.Shared;
+    using OpenTelemetry.Trace;
+    using Xunit;
+
+    [VerifyNoEventSourceErrorsLoggedTest("OpenTelemetry-Sdk")]
+    public class ConsoleExporterTest
+    {
+        /// <summary>
+        /// Test case for https://github.com/open-telemetry/opentelemetry-dotnet/issues/3863.
+        /// </summary>
+        [Fact]
+        public void VerifyConsoleActivityExporterDoesntFailWithoutActivityLinkTags()
+        {
+            var exportedItems = new List<Activity>();
+
+            using var source = new ActivitySource("Testing");
+
+            using var tracerProvider = Sdk.CreateTracerProviderBuilder()
+                .AddSource("Testing")
+                .AddConsoleExporter()
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            ActivityContext context;
+            using (var first = source.StartActivity("first"))
+            {
+                context = first!.Context;
+            }
+
+            var links = new[] { new ActivityLink(context) };
+            using (var secondActivity = source.StartActivity(ActivityKind.Internal, links: links, name: "Second"))
+            {
+            }
+
+            // Assert that an Activity was exported where ActivityLink.Tags == null.
+            var activity = exportedItems.First(x => x.DisplayName == "Second");
+            Assert.Null(activity.Links.First().Tags);
+        }
+    }
+}