added binary doc values fetcher

Signed-off-by: Anthony Leong <aj.leong623@gmail.com>

Author: ajleong623

server/src/main/java/org/opensearch/index/mapper/BinaryDocValuesFetcher.java

@@ -0,0 +1,39 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.mapper;
+
+import org.apache.lucene.index.BinaryDocValues;
+import org.apache.lucene.index.LeafReader;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+public class BinaryDocValuesFetcher extends FieldValueFetcher {
+
+    public BinaryDocValuesFetcher(MappedFieldType mappedFieldType, String simpleName) {
+        super(simpleName);
+        this.mappedFieldType = mappedFieldType;
+    }
+
+    @Override
+    public List<Object> fetch(LeafReader reader, int docId) throws IOException {
+        List<Object> values = new ArrayList<>();
+        try {
+            final BinaryDocValues binaryDocValues = reader.getBinaryDocValues(mappedFieldType.name());
+            if (binaryDocValues == null || !binaryDocValues.advanceExact(docId)) {
+                return values;
+            }
+            values.add(binaryDocValues.binaryValue());
+        } catch (IOException e) {
+            throw new IOException("Failed to read doc values for document " + docId + " in field " + mappedFieldType.name(), e);
+        }
+        return values;
+    }
+}

server/src/main/java/org/opensearch/index/mapper/WildcardFieldMapper.java

@@ -930,7 +930,7 @@ protected void canDeriveSourceInternal() {
      */
     @Override
     protected DerivedFieldGenerator derivedFieldGenerator() {
-        return new DerivedFieldGenerator(mappedFieldType, new SortedSetDocValuesFetcher(mappedFieldType, simpleName()) {
+        return new DerivedFieldGenerator(mappedFieldType, new BinaryDocValuesFetcher(mappedFieldType, simpleName()) {
             @Override
             public Object convert(Object value) {
                 if (value == null) {