feat: Add helper methods to obtain ActivitySources

Google.Api.Gax.Tests/ActivitySourcesTest.cs

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2024 Google LLC All Rights Reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file or at
+ * https://developers.google.com/open-source/licenses/bsd
+ */
+
+using Xunit;
+
+namespace Google.Api.Gax.Tests;
+
+public class ActivitySourcesTest
+{
+    [Fact]
+    public void NameIsType()
+    {
+        var source = ActivitySources.FromType<ActivitySourcesTest>();
+        // Hard-coded to makeit obvious in the test what the value will actually look like.
+        Assert.Equal("Google.Api.Gax.Tests.ActivitySourcesTest", source.Name);
+    }
+
+    [Fact]
+    public void Caching()
+    {
+        var source1 = ActivitySources.FromType<ActivitySourcesTest>();
+        var source2 = ActivitySources.FromType<ActivitySourcesTest>();
+        var source3 = ActivitySources.FromType(typeof(ActivitySourcesTest));
+        var source4 = ActivitySources.FromType<PollingTest>();
+
+        Assert.Same(source1, source2);
+        Assert.Same(source1, source3);
+        Assert.NotSame(source1, source4);
+    }
+
+    [Fact]
+    public void Version_VersionedAssembly()
+    {
+        // Deliberately use a type in the main assembly, so that it's got a real version.
+        var source = ActivitySources.FromType<Expiration>();
+        Assert.NotEmpty(source.Version);
+        // We don't try to parse this as a System.Version, as that would fail for betas etc.
+        var majorVersion = int.Parse(source.Version.Split('.')[0]);
+        // This doesn't need to be changed when we bump the version of GAX - it's just checking
+        // that we've got a real version rather than a default of 1.0.
+        Assert.True(majorVersion >= 4);
+    }
+}

Google.Api.Gax/ActivitySources.cs

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2024 Google LLC All Rights Reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file or at
+ * https://developers.google.com/open-source/licenses/bsd
+ */
+
+using System.Collections.Concurrent;
+using System.Diagnostics;
+
+namespace Google.Api.Gax;
+
+// Note: currently internal until we're ready to roll out OpenTelemetry support "properly".
+
+/// <summary>
+/// Helper methods for obtaining <see cref="ActivitySource"/> values.
+/// Note that while some conventions suggest a single activity source per assembly, libraries for Google Cloud APIs
+/// use an activity source per client type, for simpler filtering. These can easily be obtained via the static
+/// properties on the client type itself, but this class allows a more generic approach where necessary.
+/// </summary>
+internal static class ActivitySources
+{
+    private static readonly ConcurrentDictionary<System.Type, ActivitySource> s_activitySources = new();
+
+    /// <summary>
+    /// Returns an <see cref="ActivitySource"/> named after the given type (typically an API client).
+    /// </summary>
+    /// <remarks>
+    /// Multiple calls to this method (or <see cref="FromType{T}()"/>) for the same
+    /// type will return the same cached activity source.
+    /// </remarks>
+    /// <param name="type">The client type to obtain an activity source for. Must not be null.</param>
+    /// <returns>An <see cref="ActivitySource"/> named after the given client type.</returns>
+    public static ActivitySource FromType(System.Type type)
+    {
+        GaxPreconditions.CheckNotNull(type, nameof(type));
+        return s_activitySources.GetOrAdd(type, CreateActivitySource);
+    }
+
+    /// <summary>
+    /// Returns an <see cref="ActivitySource"/> named after the given type (typically an API client).
+    /// </summary>
+    /// <remarks>
+    /// Multiple calls to this method (or <see cref="FromType(System.Type)"/>) for the same
+    /// type will return the same cached activity source.
+    /// </remarks>
+    /// <typeparam name="T">The type to obtain an activity source for.</typeparam>
+    /// <returns>An <see cref="ActivitySource"/> named after the given type.</returns>
+    public static ActivitySource FromType<T>() => FromType(typeof(T));
+
+    private static ActivitySource CreateActivitySource(System.Type type) =>
+        // TODO: Move FormatAssemblyVersion to a separate type? It's odd to call into VersionHeaderBuilder here.
+        new ActivitySource(type.FullName, VersionHeaderBuilder.FormatAssemblyVersion(type));
+}

Google.Api.Gax/VersionHeaderBuilder.cs

@@ -93,7 +93,10 @@ private static string GetEntryAssemblyVersionOrNull()
             }
         }
 
-        private static string FormatAssemblyVersion(System.Type type)
+        /// <summary>
+        /// Formats the version of the assembly containing the specified type, in a "generally informative" way.
+        /// </summary>
+        internal static string FormatAssemblyVersion(System.Type type)
         {
             // Prefer AssemblyInformationalVersion, then AssemblyFileVersion,
             // then AssemblyVersion.