fix: Accept inbound tracing headers in Kafka consume method instrumentation (#2488)

* Process inbound tracing headers on Kafka consumer side

* Assert on tracing supportability metrics in Kafka integration test

* Remove stray comment

Author: nr-ahemsath

src/Agent/NewRelic/Agent/Extensions/Providers/Wrapper/Kafka/KafkaConsumerWrapper.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.Text;
 using Confluent.Kafka;
 using NewRelic.Agent.Api;
@@ -65,15 +66,15 @@ public AfterWrappedMethodDelegate BeforeWrappedMethod(InstrumentedMethodCall ins
                     segment.SetMessageBrokerDestination(topic);
                     transaction.SetKafkaMessageBrokerTransactionName(MessageBrokerDestinationType.Topic, BrokerVendorName, topic);
 
-                    // get the Message.Headers property and add distributed trace headers
+                    // get the Message.Headers property and process distributed trace headers
                     var messageAccessor = MessageAccessorDictionary.GetOrAdd(type, GetMessageAccessorFunc);
                     var messageAsObject = messageAccessor(resultAsObject);
 
                     var headersSize = 0L;
                     if (messageAsObject is MessageMetadata messageMetaData)
                     {
                         headersSize = GetHeadersSize(messageMetaData.Headers);
-                        transaction.InsertDistributedTraceHeaders(messageMetaData, DistributedTraceHeadersSetter);
+                        transaction.AcceptDistributedTraceHeaders(messageMetaData, DistributedTraceHeadersGetter, TransportType.Kafka);
                     }
 
                     ReportSizeMetrics(agent, transaction, topic, headersSize, messageAsObject);
@@ -133,14 +134,22 @@ private static Func<object, object> GetKeyAccessorFunc(Type t) =>
         private static Func<object, object> GetValueAccessorFunc(Type t) =>
             VisibilityBypasser.Instance.GeneratePropertyAccessor<object>(t, "Value");
 
-        private static void DistributedTraceHeadersSetter(MessageMetadata carrier, string key, string value)
+        private static IEnumerable<string> DistributedTraceHeadersGetter(MessageMetadata carrier, string key)
         {
-            carrier.Headers ??= new Headers();
-            if (!string.IsNullOrEmpty(key))
+            if (carrier.Headers != null)
             {
-                carrier.Headers.Remove(key);
-                carrier.Headers.Add(key, Encoding.ASCII.GetBytes(value));
+                var headerValues = new List<string>();
+                foreach (var item in carrier.Headers)
+                {
+                    if (item.Key.Equals(key, StringComparison.OrdinalIgnoreCase))
+                    {
+                        var decodedHeaderValue = Encoding.UTF8.GetString(item.GetValueBytes());
+                        headerValues.Add(decodedHeaderValue);
+                    }
+                }
+                return headerValues;
             }
+            return null;
         }
 
         private static long TryGetSize(object obj)

tests/Agent/IntegrationTests/ContainerIntegrationTests/Tests/KafkaTests.cs

@@ -83,6 +83,8 @@ public void Test()
             new Assertions.ExpectedMetric { metricName = consumeTransactionName, callCount = 2 },
             new Assertions.ExpectedMetric { metricName = messageBrokerConsume, callCount = 2 },
             new Assertions.ExpectedMetric { metricName = messageBrokerConsume, metricScope = consumeTransactionName, callCount = 2 },
+            new Assertions.ExpectedMetric { metricName = "Supportability/TraceContext/Create/Success", callCount = 2 },
+            new Assertions.ExpectedMetric { metricName = "Supportability/TraceContext/Accept/Success", callCount = 2 },
         };
 
         NrAssert.Multiple(
@@ -93,7 +95,7 @@ public void Test()
             () => Assert.True(consumeTxnSpan.UserAttributes.ContainsKey("kafka.consume.byteCount")),
             () => Assert.InRange((long)consumeTxnSpan.UserAttributes["kafka.consume.byteCount"], 450, 470), // includes headers
             () => Assert.True(consumeTxnSpan.IntrinsicAttributes.ContainsKey("traceId")),
-            () => Assert.False(consumeTxnSpan.IntrinsicAttributes.ContainsKey("parentId"))
+            () => Assert.True(consumeTxnSpan.IntrinsicAttributes.ContainsKey("parentId"))
         );
     }