[Extensions] Update BaggageActivityProcessor to use baggage key predicate

src/OpenTelemetry.Extensions/.publicApi/PublicAPI.Unshipped.txt

@@ -11,4 +11,4 @@ OpenTelemetry.Logs.LogToActivityEventConversionOptions.StateConverter.set -> voi
 OpenTelemetry.Trace.TracerProviderBuilderExtensions
 static Microsoft.Extensions.Logging.OpenTelemetryLoggingExtensions.AttachLogsToActivityEvent(this OpenTelemetry.Logs.OpenTelemetryLoggerOptions! loggerOptions, System.Action<OpenTelemetry.Logs.LogToActivityEventConversionOptions!>? configure = null) -> OpenTelemetry.Logs.OpenTelemetryLoggerOptions!
 static OpenTelemetry.Trace.TracerProviderBuilderExtensions.AddAutoFlushActivityProcessor(this OpenTelemetry.Trace.TracerProviderBuilder! builder, System.Func<System.Diagnostics.Activity!, bool>! predicate, int timeoutMilliseconds = 10000) -> OpenTelemetry.Trace.TracerProviderBuilder!
-static OpenTelemetry.Trace.TracerProviderBuilderExtensions.AddBaggageActivityProcessor(this OpenTelemetry.Trace.TracerProviderBuilder! builder) -> OpenTelemetry.Trace.TracerProviderBuilder!
+static OpenTelemetry.Trace.TracerProviderBuilderExtensions.AddBaggageActivityProcessor(this OpenTelemetry.Trace.TracerProviderBuilder! builder, System.Predicate<string!>! baggageKeyPredicate) -> OpenTelemetry.Trace.TracerProviderBuilder!

src/OpenTelemetry.Extensions/CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+* Update BaggageActivityProcessor to use baggage key predicate.
+  ([#1816](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/1816))
+
 ## 1.0.0-beta.5
 
 Released 2024-May-08

src/OpenTelemetry.Extensions/README.md

@@ -45,10 +45,19 @@ and adds the baggage keys and values to the `Activity` as tags (attributes) on s
 
 Add this activity processor to a tracer provider.
 
-Example of adding BaggageActivityProcessor to `TracerProvider`:
+For example, to add all baggage entries to new activities:
 
 ```cs
 var tracerProvider = Sdk.CreateTracerProviderBuilder()
-    .AddBaggageActivityProcessor()
+    .AddBaggageActivityProcessor(BaggageActivityProcessor.AllowAllBaggageKeys)
     .Build();
 ```
+
+Alternatively, you can provide a custom baggage key predicate to select which
+baggage keys you want to copy.
+
+For example, to only copy baggage entries that start with `my-key`:
+
+```cs
+new AddBaggageActivityProcessor(baggageKey => baggageKey.StartWith("my-key"))
+```

src/OpenTelemetry.Extensions/Trace/BaggageActivityProcessor.cs

@@ -1,21 +1,41 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using System;
 using System.Diagnostics;
 
 namespace OpenTelemetry.Trace;
 
 /// <summary>
-/// Activity processor that adds <see cref="Baggage"/> fields to every new span.
+/// Activity processor that adds <see cref="Baggage"/> fields to every new activity.
 /// </summary>
 internal sealed class BaggageActivityProcessor : BaseProcessor<Activity>
 {
+    /// <summary>
+    /// A predicate that allows all baggage keys.
+    /// </summary>
+    public static readonly Predicate<string> AllowAllBaggageKeys = _ => true;
+
+    private readonly Predicate<string> baggageKeyPredicate;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="BaggageActivityProcessor"/> class.
+    /// </summary>
+    /// <param name="baggageKeyPredicate">Predicate to determine which baggage keys should be added to the activity.</param>
+    public BaggageActivityProcessor(Predicate<string> baggageKeyPredicate)
+    {
+        this.baggageKeyPredicate = baggageKeyPredicate ?? throw new ArgumentNullException(nameof(baggageKeyPredicate));
+    }
+
     /// <inheritdoc />
     public override void OnStart(Activity activity)
     {
         foreach (var entry in Baggage.Current)
         {
-            activity.SetTag(entry.Key, entry.Value);
+            if (this.baggageKeyPredicate(entry.Key))
+            {
+                activity.SetTag(entry.Key, entry.Value);
+            }
         }
     }
 }

src/OpenTelemetry.Extensions/TracerProviderBuilderExtensions.cs

@@ -53,14 +53,16 @@ public static class TracerProviderBuilderExtensions
     /// Adds the <see cref="BaggageActivityProcessor"/> to the <see cref="TracerProviderBuilder"/>.
     /// </summary>
     /// <param name="builder"><see cref="TracerProviderBuilder"/> to add the <see cref="BaggageActivityProcessor"/> to.</param>
+    /// <param name="baggageKeyPredicate">Predicate to determine which baggage keys should be added to the activity.</param>
     /// <returns>The instance of <see cref="TracerProviderBuilder"/> to chain the calls.</returns>
     public static TracerProviderBuilder AddBaggageActivityProcessor(
-        this TracerProviderBuilder builder)
+        this TracerProviderBuilder builder,
+        Predicate<string> baggageKeyPredicate)
     {
         Guard.ThrowIfNull(builder);
 
 #pragma warning disable CA2000 // Dispose objects before losing scope
-        return builder.AddProcessor(new BaggageActivityProcessor());
+        return builder.AddProcessor(new BaggageActivityProcessor(baggageKeyPredicate));
 #pragma warning restore CA2000 // Dispose objects before losing scope
     }
 }