Add check to prevent injection of repeated GRPC headers

dd-java-agent/instrumentation/armeria/armeria-grpc-0.84/src/main/java/datadog/trace/instrumentation/armeria/grpc/client/GrpcInjectAdapter.java

@@ -11,6 +11,11 @@ public final class GrpcInjectAdapter implements CarrierSetter<Metadata> {
 
   @Override
   public void set(final Metadata carrier, final String key, final String value) {
-    carrier.put(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER), value);
+    Metadata.Key<String> metadataKey = Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER);
+    if (carrier.containsKey(metadataKey)) {
+      carrier.removeAll(
+          metadataKey); // Remove existing to ensure identical behavior with other carriers
+    }
+    carrier.put(metadataKey, value);
   }
 }

dd-java-agent/instrumentation/armeria/armeria-grpc-0.84/src/test/groovy/GrpcInjectAdapterTest.groovy

@@ -0,0 +1,47 @@
+import datadog.trace.agent.test.naming.VersionedNamingTestBase
+import io.grpc.Metadata
+import static datadog.trace.instrumentation.grpc.client.GrpcInjectAdapter.SETTER
+
+class GrpcInjectAdapterTest extends VersionedNamingTestBase {
+  def "carrier overrides values for duplicate keys"() {
+    setup:
+    def carrier = new Metadata()
+
+    def baggage = [
+      ["ot-baggage-foo", "v1"],
+      ["ot-baggage-foo", "v2"],
+      ["ot-baggage-bar", "v3"]
+    ]
+
+    when:
+    baggage.each { pair ->
+      def (key, value) = pair
+      SETTER.set(carrier, key, value)
+    }
+
+    then:
+    carrier.headerCount() == 2
+    carrier.get(getKey("ot-baggage-foo")) == "v2" // overridden value wins
+    carrier.get(getKey("ot-baggage-bar")) == "v3"
+  }
+
+  Metadata.Key<String> getKey(String key){
+    Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER)
+  }
+
+
+  @Override
+  int version() {
+    return 0
+  }
+
+  @Override
+  String service() {
+    return null
+  }
+
+  @Override
+  String operation() {
+    return null
+  }
+}

dd-java-agent/instrumentation/grpc-1.5/src/main/java/datadog/trace/instrumentation/grpc/client/GrpcInjectAdapter.java

@@ -10,6 +10,11 @@ public final class GrpcInjectAdapter implements CarrierSetter<Metadata> {
 
   @Override
   public void set(final Metadata carrier, final String key, final String value) {
-    carrier.put(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER), value);
+    Metadata.Key<String> metadataKey = Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER);
+    if (carrier.containsKey(metadataKey)) {
+      carrier.removeAll(
+          metadataKey); // Remove existing to ensure identical behavior with other carriers
+    }
+    carrier.put(metadataKey, value);
   }
 }

dd-java-agent/instrumentation/grpc-1.5/src/test/groovy/GrpcInjectAdapterTest.groovy

@@ -0,0 +1,47 @@
+import datadog.trace.agent.test.naming.VersionedNamingTestBase
+import io.grpc.Metadata
+import static datadog.trace.instrumentation.grpc.client.GrpcInjectAdapter.SETTER
+
+class GrpcInjectAdapterTest extends VersionedNamingTestBase {
+  def "carrier overrides values for duplicate keys"() {
+    setup:
+    def carrier = new Metadata()
+
+    def baggage = [
+      ["ot-baggage-foo", "v1"],
+      ["ot-baggage-foo", "v2"],
+      ["ot-baggage-bar", "v3"]
+    ]
+
+    when:
+    baggage.each { pair ->
+      def (key, value) = pair
+      SETTER.set(carrier, key, value)
+    }
+
+    then:
+    carrier.headerCount() == 2
+    carrier.get(getKey("ot-baggage-foo")) == "v2" // overridden value wins
+    carrier.get(getKey("ot-baggage-bar")) == "v3"
+  }
+
+  Metadata.Key<String> getKey(String key){
+    Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER)
+  }
+
+
+  @Override
+  int version() {
+    return 0
+  }
+
+  @Override
+  String service() {
+    return null
+  }
+
+  @Override
+  String operation() {
+    return null
+  }
+}