From 246423728c3e6b3211511f85925efdf11e89b8b5 Mon Sep 17 00:00:00 2001
From: Gao Binlong <gbinlong@amazon.com>
Date: Fri, 10 May 2024 22:16:02 +0800
Subject: [PATCH] Add comment and remove unit test

Signed-off-by: Gao Binlong <gbinlong@amazon.com>
---
 .../mapping/get/GetFieldMappingsResponse.java |  1 +
 .../get/GetFieldMappingsResponseTests.java    | 47 -------------------
 2 files changed, 1 insertion(+), 47 deletions(-)

diff --git a/server/src/main/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java b/server/src/main/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
index 0e2a64061ef9b..7edba143a72f0 100644
--- a/server/src/main/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
+++ b/server/src/main/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
@@ -117,6 +117,7 @@ public class GetFieldMappingsResponse extends ActionResponse implements ToXConte
             String index = in.readString();
             if (in.getVersion().before(Version.V_2_0_0)) {
                 int typesSize = in.readVInt();
+                // if the requested field doesn't exist, type size in the received response from 1.x node is 0
                 if (typesSize == 0) {
                     indexMapBuilder.put(index, Collections.emptyMap());
                     continue;
diff --git a/server/src/test/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponseTests.java b/server/src/test/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponseTests.java
index 53b4626b17e95..23cf0ce14a8bd 100644
--- a/server/src/test/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponseTests.java
+++ b/server/src/test/java/org/opensearch/action/admin/indices/mapping/get/GetFieldMappingsResponseTests.java
@@ -32,7 +32,6 @@
 
 package org.opensearch.action.admin.indices.mapping.get;
 
-import org.opensearch.Version;
 import org.opensearch.action.admin.indices.mapping.get.GetFieldMappingsResponse.FieldMappingMetadata;
 import org.opensearch.common.io.stream.BytesStreamOutput;
 import org.opensearch.core.common.Strings;
@@ -41,7 +40,6 @@
 import org.opensearch.core.common.io.stream.Writeable;
 import org.opensearch.core.xcontent.MediaTypeRegistry;
 import org.opensearch.test.AbstractWireSerializingTestCase;
-import org.opensearch.test.VersionUtils;
 
 import java.io.IOException;
 import java.util.Collections;
@@ -74,51 +72,6 @@ public void testNullFieldMappingToXContent() {
         assertEquals("{\"index\":{\"mappings\":{}}}", Strings.toString(MediaTypeRegistry.JSON, response));
     }
 
-    public void testBwcSerializationWithNullField() throws Exception {
-        {
-            Map<String, Map<String, FieldMappingMetadata>> mappings = new HashMap<>();
-            mappings.put("index", Collections.emptyMap());
-            final GetFieldMappingsResponse getFieldMappingsResponse = new GetFieldMappingsResponse(mappings);
-
-            final Version version = VersionUtils.randomCompatibleVersion(random(), Version.CURRENT);
-            try (BytesStreamOutput out = new BytesStreamOutput()) {
-                out.setVersion(version);
-                getFieldMappingsResponse.writeTo(out);
-
-                try (StreamInput in = out.bytes().streamInput()) {
-                    in.setVersion(version);
-                    int indexSize = in.readVInt();
-                    String indexName = in.readString();
-                    int typeSize = in.readVInt();
-                    assertEquals(indexSize, 1);
-                    assertEquals(indexName, "index");
-                    assertEquals(typeSize, 0);
-                }
-            }
-        }
-
-        {
-            Map<String, Map<String, FieldMappingMetadata>> mappings = new HashMap<>();
-            String indexName = "index";
-            mappings.put(indexName, Collections.emptyMap());
-
-            final Version version = VersionUtils.randomCompatibleVersion(random(), Version.CURRENT);
-            try (BytesStreamOutput out = new BytesStreamOutput()) {
-                out.setVersion(version);
-                out.writeVInt(mappings.size());
-                out.writeString(indexName);
-                out.writeVInt(mappings.get(indexName).size());
-
-                try (StreamInput in = out.bytes().streamInput()) {
-                    in.setVersion(version);
-                    final GetFieldMappingsResponse fieldMappingsResponse = new GetFieldMappingsResponse(in);
-                    assertEquals(fieldMappingsResponse.mappings().size(), 1);
-                    assertEquals("{\"index\":{\"mappings\":{}}}", Strings.toString(MediaTypeRegistry.JSON, fieldMappingsResponse));
-                }
-            }
-        }
-    }
-
     @Override
     protected GetFieldMappingsResponse createTestInstance() {
         return new GetFieldMappingsResponse(randomMapping());