feat: Support ActivitySource in ClientHelper

This wires everything up, but doesn't actually start any activities. The implementation will all be in ApiCallTracingExtensions, in another commit.

Google.Api.Gax.Grpc/ApiBidirectionalStreamingCall.cs

@@ -8,6 +8,7 @@
 using Grpc.Core;
 using Microsoft.Extensions.Logging;
 using System;
+using System.Diagnostics;
 
 namespace Google.Api.Gax.Grpc
 {
@@ -83,5 +84,9 @@ logger is null
                 ? this
                 : new ApiBidirectionalStreamingCall<TRequest, TResponse>(_methodName, _call.WithLogging(logger, _methodName), BaseCallSettings, StreamingSettings);
 
+        internal ApiBidirectionalStreamingCall<TRequest, TResponse> WithTracing(ActivitySource activitySource) =>
+            activitySource is null
+                ? this
+                : new ApiBidirectionalStreamingCall<TRequest, TResponse>(_methodName, _call.WithTracing(activitySource, _methodName), BaseCallSettings, StreamingSettings);
     }
 }

Google.Api.Gax.Grpc/ApiCall.cs

@@ -9,6 +9,7 @@
 using Grpc.Core;
 using Microsoft.Extensions.Logging;
 using System;
+using System.Diagnostics;
 using System.Threading.Tasks;
 
 namespace Google.Api.Gax.Grpc
@@ -173,6 +174,14 @@ logger is null
                     _syncCall.WithLogging(logger, _methodName),
                     BaseCallSettings);
 
+        internal ApiCall<TRequest, TResponse> WithTracing(ActivitySource activitySource) =>
+            activitySource is null
+                ? this
+                : new ApiCall<TRequest, TResponse>(
+                    _methodName, _asyncCall.WithTracing(activitySource, _methodName),
+                    _syncCall.WithTracing(activitySource, _methodName),
+                    BaseCallSettings);
+
         /// <summary>
         /// Constructs a new <see cref="ApiCall{TRequest, TResponse}"/> that applies an overlay to
         /// the underlying <see cref="CallSettings"/>. If a value exists in both the original and

Google.Api.Gax.Grpc/ApiCallTracingExtensions.cs

@@ -0,0 +1,51 @@
+/*  
+ * 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 Grpc.Core;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Google.Api.Gax.Grpc;
+
+/// <summary>
+/// Extension methods to provide tracing via <see cref="ActivitySource"/>.
+/// </summary>
+internal static class ApiCallTracingExtensions
+{
+    // Unary async
+    internal static Func<TRequest, CallSettings, Task<TResponse>> WithTracing<TRequest, TResponse>(
+        this Func<TRequest, CallSettings, Task<TResponse>> fn, ActivitySource activitySource, string methodName) =>
+        fn;
+
+    // Unary sync
+    internal static Func<TRequest, CallSettings, TResponse> WithTracing<TRequest, TResponse>(
+        this Func<TRequest, CallSettings, TResponse> fn, ActivitySource activitySource, string methodName) =>
+        fn;
+
+    // Server-streaming async
+    internal static Func<TRequest, CallSettings, Task<AsyncServerStreamingCall<TResponse>>> WithTracing<TRequest, TResponse>(
+        this Func<TRequest, CallSettings, Task<AsyncServerStreamingCall<TResponse>>> fn, ActivitySource activitySource, string methodName) =>
+        fn;
+
+    // Server-streaming sync
+    internal static Func<TRequest, CallSettings, AsyncServerStreamingCall<TResponse>> WithTracing<TRequest, TResponse>(
+        this Func<TRequest, CallSettings, AsyncServerStreamingCall<TResponse>> fn, ActivitySource activitySource, string methodName) =>
+        fn;
+
+    // Client-streaming
+    internal static Func<CallSettings, AsyncClientStreamingCall<TRequest, TResponse>> WithTracing<TRequest, TResponse>(
+        this Func<CallSettings, AsyncClientStreamingCall<TRequest, TResponse>> fn, ActivitySource activitySource, string methodName) =>
+        fn;
+
+    // Bidi-streaming
+    internal static Func<CallSettings, AsyncDuplexStreamingCall<TRequest, TResponse>> WithTracing<TRequest, TResponse>(
+        this Func<CallSettings, AsyncDuplexStreamingCall<TRequest, TResponse>> fn, ActivitySource activitySource, string methodName) =>
+        fn;
+}

Google.Api.Gax.Grpc/ApiClientStreamingCall.cs

@@ -8,6 +8,7 @@
 using Grpc.Core;
 using Microsoft.Extensions.Logging;
 using System;
+using System.Diagnostics;
 
 namespace Google.Api.Gax.Grpc
 {
@@ -80,5 +81,10 @@ internal ApiClientStreamingCall<TRequest, TResponse> WithLogging(ILogger logger)
             logger is null
                 ? this
                 : new ApiClientStreamingCall<TRequest, TResponse>(_methodName, _call.WithLogging(logger, _methodName), BaseCallSettings, StreamingSettings);
+
+        internal ApiClientStreamingCall<TRequest, TResponse> WithTracing(ActivitySource activitySource) =>
+            activitySource is null
+                ? this
+                : new ApiClientStreamingCall<TRequest, TResponse>(_methodName, _call.WithTracing(activitySource, _methodName), BaseCallSettings, StreamingSettings);
     }
 }

Google.Api.Gax.Grpc/ApiServerStreamingCall.cs

@@ -8,6 +8,7 @@
 using Grpc.Core;
 using Microsoft.Extensions.Logging;
 using System;
+using System.Diagnostics;
 using System.Threading.Tasks;
 
 namespace Google.Api.Gax.Grpc
@@ -144,5 +145,14 @@ logger is null
                     _asyncCall.WithLogging(logger, _methodName),
                     _syncCall.WithLogging(logger, _methodName),
                     BaseCallSettings);
+
+        internal ApiServerStreamingCall<TRequest, TResponse> WithTracing(ActivitySource activitySource) =>
+            activitySource is null
+                ? this
+                : new ApiServerStreamingCall<TRequest, TResponse>(
+                    _methodName,
+                    _asyncCall.WithTracing(activitySource, _methodName),
+                    _syncCall.WithTracing(activitySource, _methodName),
+                    BaseCallSettings);
     }
 }

Google.Api.Gax.Grpc/ClientHelper.cs

@@ -9,6 +9,7 @@
 using Grpc.Core;
 using Microsoft.Extensions.Logging;
 using System;
+using System.Diagnostics;
 
 namespace Google.Api.Gax.Grpc
 {
@@ -28,6 +29,8 @@ public class ClientHelper
         /// </summary>
         private readonly CallSettings _versionCallSettings;
 
+        private readonly ActivitySource _activitySource;
+
         /// <summary>
         /// Constructs a helper from the given settings.
         /// Behavior is undefined if settings are changed after construction.
@@ -61,6 +64,7 @@ public ClientHelper(Options options)
             {
                 _versionCallSettings = _versionCallSettings.WithHeader(ApiVersionHeaderName, options.ApiVersion);
             }
+            _activitySource = options.ActivitySource;
         }
 
         /// <summary>
@@ -105,6 +109,7 @@ public ApiCall<TRequest, TResponse> BuildApiCall<TRequest, TResponse>(
             // I.e. Version header is added first, then retry is performed.
             return ApiCall.Create(methodName, asyncGrpcCall, syncGrpcCall, baseCallSettings, Clock)
                 .WithLogging(Logger)
+                .WithTracing(_activitySource)
                 .WithRetry(Clock, Scheduler, Logger)
                 .WithMergedBaseCallSettings(_versionCallSettings);
         }
@@ -129,6 +134,7 @@ public ApiServerStreamingCall<TRequest, TResponse> BuildApiCall<TRequest, TRespo
             // I.e. Version header is added first, then retry is performed.
             return ApiServerStreamingCall.Create(methodName, grpcCall, baseCallSettings, Clock)
                 .WithLogging(Logger)
+                .WithTracing(_activitySource)
                 .WithMergedBaseCallSettings(_versionCallSettings);
         }
 
@@ -153,6 +159,7 @@ public ApiBidirectionalStreamingCall<TRequest, TResponse> BuildApiCall<TRequest,
             CallSettings baseCallSettings = _clientCallSettings.MergedWith(perMethodCallSettings);
             return ApiBidirectionalStreamingCall.Create(methodName, grpcCall, baseCallSettings, streamingSettings, Clock)
                 .WithLogging(Logger)
+                .WithTracing(_activitySource)
                 .WithMergedBaseCallSettings(_versionCallSettings);
         }
 
@@ -177,6 +184,7 @@ public ApiClientStreamingCall<TRequest, TResponse> BuildApiCall<TRequest, TRespo
             CallSettings baseCallSettings = _clientCallSettings.MergedWith(perMethodCallSettings);
             return ApiClientStreamingCall.Create(methodName, grpcCall, baseCallSettings, streamingSettings, Clock)
                 .WithLogging(Logger)
+                .WithTracing(_activitySource)
                 .WithMergedBaseCallSettings(_versionCallSettings);
         }
 
@@ -204,6 +212,12 @@ public sealed class Options
             /// The API version to send in the x-goog-api-version header, if any. This may be null.
             /// </summary>
             public string ApiVersion { get; set; }
+
+            /// <summary>
+            /// The activity source to use for tracing, if any. This may be null.
+            /// Note: currently internal until we're ready to roll out OpenTelemetry support "properly".
+            /// </summary>
+            internal ActivitySource ActivitySource { get; set; }
         }
     }
 }