Fix for deserilization bug in weighted round robin metadata

CHANGELOG.md

@@ -205,6 +205,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix remote shards balancer and remove unused variables ([#11167](https://github.com/opensearch-project/OpenSearch/pull/11167))
 - Fix parsing of flat object fields with dots in keys ([#11425](https://github.com/opensearch-project/OpenSearch/pull/11425))
 - Fix bug where replication lag grows post primary relocation ([#11238](https://github.com/opensearch-project/OpenSearch/pull/11238))
+- Fix for deserilization bug in weighted round-robin metadata ([#11679](https://github.com/opensearch-project/OpenSearch/pull/11679))
 - Fix for stuck update action in a bulk with `retry_on_conflict` property ([#11152](https://github.com/opensearch-project/OpenSearch/issues/11152))
 - Fix template setting override for replication type ([#11417](https://github.com/opensearch-project/OpenSearch/pull/11417))
 - Fix Automatic addition of protocol broken in #11512 ([#11609](https://github.com/opensearch-project/OpenSearch/pull/11609))

server/src/main/java/org/opensearch/cluster/metadata/WeightedRoutingMetadata.java

@@ -26,6 +26,7 @@
 import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Objects;
 
 /**
  * Contains metadata for weighted routing
@@ -99,7 +100,7 @@ public static NamedDiff<Metadata.Custom> readDiffFrom(StreamInput in) throws IOE
     public static WeightedRoutingMetadata fromXContent(XContentParser parser) throws IOException {
         String attrKey = null;
         Double attrValue;
-        String attributeName = null;
+        String attributeName = "";
         Map<String, Double> weights = new HashMap<>();
         WeightedRouting weightedRouting;
         XContentParser.Token token;
@@ -162,12 +163,12 @@ public boolean equals(Object o) {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
         WeightedRoutingMetadata that = (WeightedRoutingMetadata) o;
-        return weightedRouting.equals(that.weightedRouting);
+        return weightedRouting.equals(that.weightedRouting) && version == that.version;
     }
 
     @Override
     public int hashCode() {
-        return weightedRouting.hashCode();
+        return Objects.hash(weightedRouting.hashCode(), version);
     }
 
     @Override

server/src/main/java/org/opensearch/cluster/routing/WeightedRouting.java

@@ -54,7 +54,9 @@ public boolean isSet() {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeString(attributeName);
+        if (attributeName != null) {
+            out.writeString(attributeName);
+        }
         out.writeGenericValue(weights);
     }
 

server/src/test/java/org/opensearch/cluster/metadata/WeightedRoutingMetadataTests.java

@@ -8,29 +8,60 @@
 
 package org.opensearch.cluster.metadata;
 
+import org.opensearch.cluster.ClusterModule;
+import org.opensearch.cluster.Diff;
 import org.opensearch.cluster.routing.WeightedRouting;
+import org.opensearch.core.common.io.stream.NamedWriteableRegistry;
+import org.opensearch.core.common.io.stream.Writeable;
 import org.opensearch.core.xcontent.XContentParser;
-import org.opensearch.test.AbstractXContentTestCase;
+import org.opensearch.test.AbstractDiffableSerializationTestCase;
 
 import java.io.IOException;
+import java.util.HashMap;
 import java.util.Map;
 
-public class WeightedRoutingMetadataTests extends AbstractXContentTestCase<WeightedRoutingMetadata> {
+public class WeightedRoutingMetadataTests extends AbstractDiffableSerializationTestCase<Metadata.Custom> {
+
+    @Override
+    protected Writeable.Reader<Metadata.Custom> instanceReader() {
+        return WeightedRoutingMetadata::new;
+    }
+
     @Override
     protected WeightedRoutingMetadata createTestInstance() {
+        String attributeName = "zone";
         Map<String, Double> weights = Map.of("a", 1.0, "b", 1.0, "c", 0.0);
-        WeightedRouting weightedRouting = new WeightedRouting("zone", weights);
+        if (randomBoolean()) {
+            weights = new HashMap<>();
+            attributeName = "";
+        }
+        WeightedRouting weightedRouting = new WeightedRouting(attributeName, weights);
         WeightedRoutingMetadata weightedRoutingMetadata = new WeightedRoutingMetadata(weightedRouting, -1);
+
         return weightedRoutingMetadata;
     }
 
+    @Override
+    protected NamedWriteableRegistry getNamedWriteableRegistry() {
+        return new NamedWriteableRegistry(ClusterModule.getNamedWriteables());
+    }
+
     @Override
     protected WeightedRoutingMetadata doParseInstance(XContentParser parser) throws IOException {
         return WeightedRoutingMetadata.fromXContent(parser);
     }
 
     @Override
-    protected boolean supportsUnknownFields() {
-        return false;
+    protected Metadata.Custom makeTestChanges(Metadata.Custom testInstance) {
+
+        WeightedRouting weightedRouting = new WeightedRouting("", new HashMap<>());
+        WeightedRoutingMetadata weightedRoutingMetadata = new WeightedRoutingMetadata(weightedRouting, -1);
+        return weightedRoutingMetadata;
     }
+
+    @Override
+    protected Writeable.Reader<Diff<Metadata.Custom>> diffReader() {
+        return WeightedRoutingMetadata::readDiffFrom;
+    }
+
 }