[GRPC] Optimize source conversion in gRPC search hits using zero-copy BytesRef

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

Author: karenx

modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/proto/response/search/SearchHitProtoUtils.java

@@ -8,7 +8,10 @@
 package org.opensearch.transport.grpc.proto.response.search;
 
 import com.google.protobuf.ByteString;
+import com.google.protobuf.UnsafeByteOperations;
 import org.apache.lucene.search.Explanation;
+import org.apache.lucene.util.BytesRef;
+import org.opensearch.common.bytes.BytesArray;
 import org.opensearch.common.document.DocumentField;
 import org.opensearch.core.common.bytes.BytesReference;
 import org.opensearch.core.xcontent.ToXContent;
@@ -194,7 +197,20 @@ private static void processMetadataFields(SearchHit hit, org.opensearch.protobuf
      */
     private static void processSource(SearchHit hit, org.opensearch.protobufs.Hit.Builder hitBuilder) {
         if (hit.getSourceRef() != null) {
-            hitBuilder.setSource(ByteString.copyFrom(BytesReference.toBytes(hit.getSourceRef())));
+            BytesReference sourceRef = hit.getSourceRef();
+            BytesRef bytesRef = sourceRef.toBytesRef();
+
+            if (sourceRef instanceof BytesArray) {
+                if (bytesRef.offset == 0 && bytesRef.length == bytesRef.bytes.length) {
+                    hitBuilder.setSource(UnsafeByteOperations.unsafeWrap(bytesRef.bytes));
+                } else {
+                    hitBuilder.setSource(UnsafeByteOperations.unsafeWrap(
+                        bytesRef.bytes, bytesRef.offset, bytesRef.length));
+                }
+            } else {
+                hitBuilder.setSource(ByteString.copyFrom(
+                    bytesRef.bytes, bytesRef.offset, bytesRef.length));
+            }
         }
     }