robcarlan-datadog · Nov 2, 2026 · Nov 9, 2026 · Nov 9, 2026 · Nov 10, 2026 · Nov 10, 2026
@@ -80,7 +80,7 @@ public static void InjectTraceIntoData<TRecordRequest>(Tracer tracer, TRecordReq
                     // payload was parsed to json.
                     if (payloadSize != 0 && payloadSize > MaxDsmHeaderSize)
                     {
-                        dataStreamsManager.InjectPathwayContext(scope.Span.Context.PathwayContext, adapter);
+                        dataStreamsManager.InjectPathwayContextAsBase64String(scope.Span.Context.PathwayContext, adapter);
                     }
 
                     propagatedContext = adapter.GetDictionary();

@@ -5,7 +5,6 @@
 
 #nullable enable
 
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
@@ -14,7 +13,7 @@
 
 namespace Datadog.Trace.ClrProfiler.AutoInstrumentation.AWS.Kinesis
 {
-    internal struct KinesisContextAdapter : IHeadersCollection, IBinaryHeadersCollection
+    internal struct KinesisContextAdapter : IHeadersCollection
     {
         private Dictionary<string, List<string>> headers = new Dictionary<string, List<string>>();
 
@@ -59,20 +58,5 @@ public void Remove(string name)
         {
             headers.Remove(name);
         }
-
-        public byte[] TryGetLastBytes(string name)
-        {
-            if (headers.TryGetValue(name, out var value))
-            {
-                return Convert.FromBase64String(value[value.Count - 1]);
-            }
-
-            return [];
-        }
-
-        public void Add(string name, byte[] value)
-        {
-            Add(name, Convert.ToBase64String(value));
-        }
     }
 }
@@ -20,9 +20,9 @@ namespace Datadog.Trace.ClrProfiler.AutoInstrumentation.AWS.Shared;
 
 internal static class AwsMessageAttributesHeadersAdapters
 {
-    public static IBinaryHeadersCollection GetInjectionAdapter(StringBuilder carrier)
+    public static IBinaryHeadersCollection GetInjectionAdapter(StringBuilder carrier, bool legacyEncodingBehaviorEnabled)
     {
-        return new StringBuilderJsonAdapter(carrier);
+        return new StringBuilderJsonAdapter(carrier, legacyEncodingBehaviorEnabled);
     }
 
     public static IBinaryHeadersCollection GetExtractionAdapter(IDictionary? messageAttributes)
@@ -36,10 +36,12 @@ public static IBinaryHeadersCollection GetExtractionAdapter(IDictionary? message
     private readonly struct StringBuilderJsonAdapter : IBinaryHeadersCollection
     {
         private readonly StringBuilder _carrier;
+        private readonly bool _legacyEncodingBehaviorEnabled;
 
-        public StringBuilderJsonAdapter(StringBuilder carrier)
+        public StringBuilderJsonAdapter(StringBuilder carrier, bool legacyEncodingBehaviorEnabled)
         {
             _carrier = carrier;
+            _legacyEncodingBehaviorEnabled = legacyEncodingBehaviorEnabled;
         }
 
         public byte[] TryGetLastBytes(string name)
@@ -49,16 +51,18 @@ public byte[] TryGetLastBytes(string name)
 
         public void Add(string key, byte[] value)
         {
-            // FIXME BREAKING CHANGE:
-            // We are preserving the existing bug with the extra Base64 layer on the Base64 pathway header
-            // We will address this as a follow up
             _carrier
                .Append(value: '"')
                .Append(key)
                .Append("\":\"")
-               .Append(Convert.ToBase64String(value))
+               .Append(ToJsonSafeString(key, value))
                .Append("\",");
         }
+
+        private string ToJsonSafeString(string key, byte[] value)
+            => key == DataStreamsPropagationHeaders.PropagationKeyBase64 && !_legacyEncodingBehaviorEnabled
+                   ? Encoding.UTF8.GetString(value)
+                   : Convert.ToBase64String(value);
     }
 
     /// <summary>

@@ -27,7 +27,7 @@ private static void Inject(Tracer tracer, PropagationContext context, IDictionar
 
             if (context.SpanContext?.PathwayContext is { } pathwayContext)
             {
-                dataStreamsManager?.InjectPathwayContext(pathwayContext, AwsMessageAttributesHeadersAdapters.GetInjectionAdapter(sb));
+                dataStreamsManager?.InjectPathwayContext(pathwayContext, AwsMessageAttributesHeadersAdapters.GetInjectionAdapter(sb, tracer.Settings.IsDataStreamsLegacyEncodingBehaviorEnabled));
             }
 
             sb.Remove(startIndex: sb.Length - 1, length: 1); // Remove trailing comma

@@ -550,6 +550,10 @@ not null when string.Equals(value, "otlp", StringComparison.OrdinalIgnoreCase) =
                                                .WithKeys(ConfigurationKeys.DataStreamsMonitoring.LegacyHeadersEnabled)
                                                .AsBool(!IsDataStreamsMonitoringInDefaultState);
 
+            IsDataStreamsLegacyEncodingBehaviorEnabled = config
+                                                        .WithKeys(ConfigurationKeys.DataStreamsMonitoring.LegacyEncodingBehaviorEnabled)
+                                                        .AsBool(false);
+
             IsRareSamplerEnabled = config
                                   .WithKeys(ConfigurationKeys.RareSamplerEnabled)
                                   .AsBool(false);
@@ -1362,6 +1366,11 @@ bool DisableIfOtelSdkDisabled(bool enabled, string key)
         /// </summary>
         internal bool IsDataStreamsLegacyHeadersEnabled { get; }
 
+        /// <summary>
+        /// Gets a value indicating whether SQS and SNS producers double Base64 encode the Data Streams pathway context.
+        /// </summary>
+        internal bool IsDataStreamsLegacyEncodingBehaviorEnabled { get; }
+
         /// <summary>
         /// Gets a value indicating whether the rare sampler is enabled or not.
         /// </summary>

@@ -708,6 +708,17 @@ supportedConfigurations:
     documentation: |-
       Enables data streams monitoring support
       <see cref="Datadog.Trace.Configuration.TracerSettings.IsDataStreamsMonitoringEnabled"/>
+  DD_DATA_STREAMS_LEGACY_ENCODING_BEHAVIOR_ENABLED:
+  - implementation: A
+    scope: managed
+    type: boolean
+    default: 'false'
+    product: DataStreamsMonitoring
+    const_name: LegacyEncodingBehaviorEnabled
+    documentation: |-
+      Configuration key for restoring the legacy double Base64 encoding of the Data Streams pathway context in SQS and SNS messages.
+      Enable while consumers still run a tracer version older than 3.55.0.
+      <see cref="Datadog.Trace.Configuration.TracerSettings.IsDataStreamsLegacyEncodingBehaviorEnabled"/>
   DD_DATA_STREAMS_LEGACY_HEADERS:
   - implementation: A
     scope: managed

@@ -23,6 +23,13 @@ internal static class DataStreamsMonitoring
         /// </summary>
         public const string Enabled = "DD_DATA_STREAMS_ENABLED";
 
+        /// <summary>
+        /// Configuration key for restoring the legacy double Base64 encoding of the Data Streams pathway context in SQS and SNS messages.
+        /// Enable while consumers still run a tracer version older than 3.55.0.
+        /// <see cref="Datadog.Trace.Configuration.TracerSettings.IsDataStreamsLegacyEncodingBehaviorEnabled"/>
+        /// </summary>
+        public const string LegacyEncodingBehaviorEnabled = "DD_DATA_STREAMS_LEGACY_ENCODING_BEHAVIOR_ENABLED";
+
         /// <summary>
         /// Configuration key for enabling legacy binary headers in Data Streams Monitoring.
         /// false by default if DSM is in default state, true otherwise

@@ -23,6 +23,13 @@ internal static class DataStreamsMonitoring
         /// </summary>
         public const string Enabled = "DD_DATA_STREAMS_ENABLED";
 
+        /// <summary>
+        /// Configuration key for restoring the legacy double Base64 encoding of the Data Streams pathway context in SQS and SNS messages.
+        /// Enable while consumers still run a tracer version older than 3.55.0.
+        /// <see cref="Datadog.Trace.Configuration.TracerSettings.IsDataStreamsLegacyEncodingBehaviorEnabled"/>
+        /// </summary>
+        public const string LegacyEncodingBehaviorEnabled = "DD_DATA_STREAMS_LEGACY_ENCODING_BEHAVIOR_ENABLED";
+
         /// <summary>
         /// Configuration key for enabling legacy binary headers in Data Streams Monitoring.
         /// false by default if DSM is in default state, true otherwise

@@ -23,6 +23,13 @@ internal static class DataStreamsMonitoring
         /// </summary>
         public const string Enabled = "DD_DATA_STREAMS_ENABLED";
 
+        /// <summary>
+        /// Configuration key for restoring the legacy double Base64 encoding of the Data Streams pathway context in SQS and SNS messages.
+        /// Enable while consumers still run a tracer version older than 3.55.0.
+        /// <see cref="Datadog.Trace.Configuration.TracerSettings.IsDataStreamsLegacyEncodingBehaviorEnabled"/>
+        /// </summary>
+        public const string LegacyEncodingBehaviorEnabled = "DD_DATA_STREAMS_LEGACY_ENCODING_BEHAVIOR_ENABLED";
+
         /// <summary>
         /// Configuration key for enabling legacy binary headers in Data Streams Monitoring.
         /// false by default if DSM is in default state, true otherwise

@@ -23,6 +23,13 @@ internal static class DataStreamsMonitoring
         /// </summary>
         public const string Enabled = "DD_DATA_STREAMS_ENABLED";
 
+        /// <summary>
+        /// Configuration key for restoring the legacy double Base64 encoding of the Data Streams pathway context in SQS and SNS messages.
+        /// Enable while consumers still run a tracer version older than 3.55.0.
+        /// <see cref="Datadog.Trace.Configuration.TracerSettings.IsDataStreamsLegacyEncodingBehaviorEnabled"/>
+        /// </summary>
+        public const string LegacyEncodingBehaviorEnabled = "DD_DATA_STREAMS_LEGACY_ENCODING_BEHAVIOR_ENABLED";
+
         /// <summary>
         /// Configuration key for enabling legacy binary headers in Data Streams Monitoring.
         /// false by default if DSM is in default state, true otherwise

@@ -236,19 +236,18 @@ public void Extract_InvalidLegacyHeader_ReturnsNull(bool binaryAttribute)
 
     [Theory]
     [CombinatorialData]
-    public void Inject_PreservesExistingDotnetWireFormat(bool legacyHeadersEnabled)
+    public void Inject_EncodesPathwayOnceUnlessLegacyEncodingEnabled(bool legacyHeadersEnabled, bool legacyEncodingBehaviorEnabled)
     {
         var carrier = new StringBuilder("{");
-        var adapter = AwsMessageAttributesHeadersAdapters.GetInjectionAdapter(carrier);
+        var adapter = AwsMessageAttributesHeadersAdapters.GetInjectionAdapter(carrier, legacyEncodingBehaviorEnabled);
         var context = new PathwayContext(new PathwayHash(Hash), 1_700_000_000_000_000_000, 1_700_000_001_000_000_000);
 
         DataStreamsContextPropagator.Instance.Inject(context, adapter, legacyHeadersEnabled);
         carrier.Length--; // Remove the trailing comma written by the injection adapter.
         carrier.Append('}');
         var headers = JsonConvert.DeserializeObject<Dictionary<string, string>>(carrier.ToString());
 
-        // Existing .NET consumers expect two Base64 layers for this header.
-        headers[DataStreamsPropagationHeaders.PropagationKeyBase64].Should().Be(EncodeAgain(Pathway));
+        headers[DataStreamsPropagationHeaders.PropagationKeyBase64].Should().Be(legacyEncodingBehaviorEnabled ? EncodeAgain(Pathway) : Pathway);
         if (legacyHeadersEnabled)
         {
             headers[DataStreamsPropagationHeaders.PropagationKey].Should().Be(Pathway);

@@ -12,6 +12,7 @@
 using Datadog.Trace.Agent;
 using Datadog.Trace.ClrProfiler.AutoInstrumentation.AWS.Kinesis;
 using Datadog.Trace.Configuration;
+using Datadog.Trace.DataStreamsMonitoring;
 using Datadog.Trace.DuckTyping;
 using Datadog.Trace.Sampling;
 using Datadog.Trace.TestHelpers.TestTracer;
@@ -202,6 +203,11 @@ public async Task InjectTraceIntoData_WithJsonString_AddsTraceContext()
         extractedTraceContext["x-datadog-parent-id"].Should().Be(scope?.Span.SpanId.ToString());
         extractedTraceContext["x-datadog-trace-id"].Should().Be(scope?.Span.TraceId.ToString());
         extractedTraceContext["dd-pathway-ctx-base64"].As<Newtonsoft.Json.Linq.JArray>().Should().HaveCount(1);
+
+        var pathway = extractedTraceContext["dd-pathway-ctx-base64"].As<Newtonsoft.Json.Linq.JArray>()[0].ToString();
+        var decoded = PathwayContextEncoder.Decode(Convert.FromBase64String(pathway));
+        decoded.Should().NotBeNull();
+        decoded!.Value.Hash.Should().Be(scope!.Span.Context.PathwayContext!.Value.Hash);
     }
 
     [Fact]

@@ -974,6 +974,16 @@ public void IsDataStreamsLegacyHeadersEnabled(string value, bool expected)
             settings.IsDataStreamsLegacyHeadersEnabled.Should().Be(expected);
         }
 
+        [Theory]
+        [MemberData(nameof(BooleanTestCases), false)]
+        public void IsDataStreamsLegacyEncodingBehaviorEnabled(string value, bool expected)
+        {
+            var source = CreateConfigurationSource((ConfigurationKeys.DataStreamsMonitoring.LegacyEncodingBehaviorEnabled, value));
+            var settings = new TracerSettings(source);
+
+            settings.IsDataStreamsLegacyEncodingBehaviorEnabled.Should().Be(expected);
+        }
+
         [Theory]
         [InlineData("1", true)]
         [InlineData("0", false)]