Implementing ExtendedTextMapGetter in grpc-1.6 instrumentation (#13011)

Signed-off-by: xiepuhuan <[email protected]>

Author: xiepuhuan

instrumentation/grpc-1.6/library/src/main/java/io/opentelemetry/instrumentation/grpc/v1_6/GrpcRequestGetter.java

@@ -5,11 +5,14 @@
 
 package io.opentelemetry.instrumentation.grpc.v1_6;
 
+import static java.util.Collections.emptyIterator;
+
 import io.grpc.Metadata;
-import io.opentelemetry.context.propagation.TextMapGetter;
+import io.opentelemetry.context.propagation.internal.ExtendedTextMapGetter;
+import java.util.Iterator;
 import javax.annotation.Nullable;
 
-enum GrpcRequestGetter implements TextMapGetter<GrpcRequest> {
+enum GrpcRequestGetter implements ExtendedTextMapGetter<GrpcRequest> {
   INSTANCE;
 
   @Override
@@ -25,4 +28,19 @@ public String get(@Nullable GrpcRequest request, String key) {
     }
     return request.getMetadata().get(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER));
   }
+
+  @Override
+  public Iterator<String> getAll(@Nullable GrpcRequest request, String key) {
+    if (request == null) {
+      return emptyIterator();
+    }
+
+    Iterable<String> values =
+        request.getMetadata().getAll(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER));
+
+    if (values == null) {
+      return emptyIterator();
+    }
+    return values.iterator();
+  }
 }