Kafka: avoid registering duplicate metrics reporter

instrumentation/kafka/kafka-clients/kafka-clients-0.11/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/kafkaclients/v0_11/KafkaSingletons.java

@@ -17,6 +17,7 @@
 import io.opentelemetry.javaagent.bootstrap.internal.ExperimentalConfig;
 import io.opentelemetry.javaagent.bootstrap.internal.InstrumentationConfig;
 import java.util.Map;
+import java.util.regex.Pattern;
 import org.apache.kafka.clients.CommonClientConfigs;
 import org.apache.kafka.clients.producer.RecordMetadata;
 
@@ -33,6 +34,10 @@ public final class KafkaSingletons {
       InstrumentationConfig.get()
           .getBoolean("otel.instrumentation.kafka.metric-reporter.enabled", true);
 
+  private static final Pattern METRIC_REPORTER_PRESENT_PATTERN =
+      Pattern.compile(
+          "(^|,)" + Pattern.quote(OpenTelemetryMetricsReporter.class.getName()) + "($|,)");
+
   private static final Instrumenter<KafkaProducerRequest, RecordMetadata> PRODUCER_INSTRUMENTER;
   private static final Instrumenter<KafkaReceiveRequest, Void> CONSUMER_RECEIVE_INSTRUMENTER;
   private static final Instrumenter<KafkaProcessRequest, Void> CONSUMER_PROCESS_INSTRUMENTER;
@@ -74,7 +79,13 @@ public static void enhanceConfig(Map<? super String, Object> config) {
     config.merge(
         CommonClientConfigs.METRIC_REPORTER_CLASSES_CONFIG,
         OpenTelemetryMetricsReporter.class.getName(),
-        (class1, class2) -> class1 + "," + class2);
+        (class1, class2) -> {
+          if (class1 instanceof String
+              && METRIC_REPORTER_PRESENT_PATTERN.matcher((String) class1).find()) {
+            return class1;
+          }
+          return class1 + "," + class2;
+        });
     config.put(
         OpenTelemetryMetricsReporter.CONFIG_KEY_OPENTELEMETRY_SUPPLIER,
         new OpenTelemetrySupplier(GlobalOpenTelemetry.get()));

instrumentation/kafka/kafka-clients/kafka-clients-0.11/testing/src/main/java/io/opentelemetry/instrumentation/kafka/internal/AbstractOpenTelemetryMetricsReporterTest.java

@@ -33,7 +33,9 @@
 import org.apache.kafka.clients.CommonClientConfigs;
 import org.apache.kafka.clients.consumer.ConsumerConfig;
 import org.apache.kafka.clients.consumer.KafkaConsumer;
+import org.apache.kafka.clients.consumer.KafkaConsumerAccess;
 import org.apache.kafka.clients.producer.KafkaProducer;
+import org.apache.kafka.clients.producer.KafkaProducerAccess;
 import org.apache.kafka.clients.producer.ProducerConfig;
 import org.apache.kafka.clients.producer.ProducerRecord;
 import org.apache.kafka.common.MetricName;
@@ -135,6 +137,22 @@ protected Map<String, Object> consumerConfig() {
     return consumerConfig;
   }
 
+  @Test
+  void noDuplicateMetricsReporter() {
+    List<MetricsReporter> producerMetricsReporters =
+        KafkaProducerAccess.getMetricsReporters(producer);
+    assertThat(countOpenTelemetryMetricsReporters(producerMetricsReporters)).isEqualTo(1);
+    List<MetricsReporter> consumerMetricsReporters =
+        KafkaConsumerAccess.getMetricsReporters(consumer);
+    assertThat(countOpenTelemetryMetricsReporters(consumerMetricsReporters)).isEqualTo(1);
+  }
+
+  private static long countOpenTelemetryMetricsReporters(List<MetricsReporter> metricsReporters) {
+    return metricsReporters.stream()
+        .filter(reporter -> reporter.getClass().getName().endsWith("OpenTelemetryMetricsReporter"))
+        .count();
+  }
+
   @Test
   void observeMetrics() {
     produceRecords();

instrumentation/kafka/kafka-clients/kafka-clients-0.11/testing/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumerAccess.java

@@ -0,0 +1,18 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.apache.kafka.clients.consumer;
+
+import java.util.List;
+import org.apache.kafka.common.metrics.MetricsReporter;
+
+public class KafkaConsumerAccess {
+
+  private KafkaConsumerAccess() {}
+
+  public static List<MetricsReporter> getMetricsReporters(KafkaConsumer<?, ?> consumer) {
+    return consumer.metrics.reporters();
+  }
+}

instrumentation/kafka/kafka-clients/kafka-clients-0.11/testing/src/main/java/org/apache/kafka/clients/producer/KafkaProducerAccess.java

@@ -0,0 +1,18 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.apache.kafka.clients.producer;
+
+import java.util.List;
+import org.apache.kafka.common.metrics.MetricsReporter;
+
+public class KafkaProducerAccess {
+
+  private KafkaProducerAccess() {}
+
+  public static List<MetricsReporter> getMetricsReporters(KafkaProducer<?, ?> producer) {
+    return producer.metrics.reporters();
+  }
+}