Fixing the custom object serialization bug in diffable utils. (#39544)

While serializing custom objects, the length of the list is computed after
filtering out the unsupported objects but while writing objects the filter
is not applied thus resulting in writing unsupported objects which will fail
to deserialize by the receiever. Adding the condition to filter out unsupported
custom objects.

Author: backslasht

server/src/main/java/org/elasticsearch/cluster/DiffableUtils.java

@@ -474,8 +474,10 @@ public void writeTo(StreamOutput out) throws IOException {
             }
             out.writeVInt(upsertsCount);
             for (Map.Entry<K, T> entry : upserts.entrySet()) {
-                keySerializer.writeKey(entry.getKey(), out);
-                valueSerializer.write(entry.getValue(), out);
+                if(valueSerializer.supportsVersion(entry.getValue(), version)) {
+                    keySerializer.writeKey(entry.getKey(), out);
+                    valueSerializer.write(entry.getValue(), out);
+                }
             }
         }
     }

server/src/test/java/org/elasticsearch/cluster/serialization/ClusterSerializationTests.java

@@ -20,11 +20,14 @@
 package org.elasticsearch.cluster.serialization;
 
 import org.elasticsearch.Version;
+import org.elasticsearch.cluster.AbstractNamedDiffable;
 import org.elasticsearch.cluster.ClusterModule;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.ClusterState.Custom;
 import org.elasticsearch.cluster.Diff;
 import org.elasticsearch.cluster.ESAllocationTestCase;
+import org.elasticsearch.cluster.NamedDiff;
 import org.elasticsearch.cluster.RestoreInProgress;
 import org.elasticsearch.cluster.SnapshotDeletionsInProgress;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
@@ -39,14 +42,17 @@
 import org.elasticsearch.common.io.stream.NamedWriteableAwareStreamInput;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.snapshots.Snapshot;
 import org.elasticsearch.snapshots.SnapshotId;
 import org.elasticsearch.test.VersionUtils;
 
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.List;
 
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.notNullValue;
@@ -205,4 +211,142 @@ public void testObjectReuseWhenApplyingClusterStateDiff() throws Exception {
         assertSame("template", serializedClusterState2.metaData().templates().get("test-template"),
             serializedClusterState3.metaData().templates().get("test-template"));
     }
+
+    public static class TestCustomOne extends AbstractNamedDiffable<Custom> implements Custom {
+
+        public static final String TYPE = "test_custom_one";
+        private final String strObject;
+
+        public TestCustomOne(String strObject) {
+            this.strObject = strObject;
+        }
+
+        public TestCustomOne(StreamInput in) throws IOException {
+            this.strObject = in.readString();
+        }
+
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
+            out.writeString(strObject);
+        }
+
+        @Override
+        public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
+            builder.startObject();
+            {
+                builder.field("custom_string_object", strObject);
+            }
+            builder.endObject();
+            return builder;
+        }
+
+        @Override
+        public String getWriteableName() {
+            return TYPE;
+        }
+
+        public static NamedDiff<Custom> readDiffFrom(StreamInput in) throws IOException {
+            return readDiffFrom(Custom.class, TYPE, in);
+        }
+
+        @Override
+        public Version getMinimalSupportedVersion() {
+            return Version.CURRENT;
+        }
+
+    }
+
+    public static class TestCustomTwo extends AbstractNamedDiffable<Custom>  implements Custom {
+
+        public static final String TYPE = "test_custom_two";
+        private final Integer intObject;
+
+        public TestCustomTwo(Integer intObject) {
+            this.intObject = intObject;
+        }
+
+        public TestCustomTwo(StreamInput in) throws IOException {
+            this.intObject = in.readInt();
+        }
+
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
+            out.writeInt(intObject);
+        }
+
+        @Override
+        public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
+            builder.startObject();
+            {
+                builder.field("custom_integer_object", intObject);
+            }
+            builder.endObject();
+            return builder;
+        }
+
+        @Override
+        public String getWriteableName() {
+            return TYPE;
+        }
+
+        public static NamedDiff<Custom> readDiffFrom(StreamInput in) throws IOException {
+            return readDiffFrom(Custom.class, TYPE, in);
+        }
+
+        @Override
+        public Version getMinimalSupportedVersion() {
+            return Version.CURRENT.minimumCompatibilityVersion();
+        }
+
+    }
+
+    public void testCustomSerialization() throws Exception {
+        ClusterState.Builder builder = ClusterState.builder(ClusterState.EMPTY_STATE)
+            .putCustom(TestCustomOne.TYPE, new TestCustomOne("test_custom_one"))
+            .putCustom(TestCustomTwo.TYPE, new TestCustomTwo(10));
+
+        ClusterState clusterState = builder.incrementVersion().build();
+
+        Diff<ClusterState> diffs = clusterState.diff(ClusterState.EMPTY_STATE);
+
+        // Add the new customs to named writeables
+        final List<NamedWriteableRegistry.Entry> entries = ClusterModule.getNamedWriteables();
+        entries.add(new NamedWriteableRegistry.Entry(ClusterState.Custom.class, TestCustomOne.TYPE, TestCustomOne::new));
+        entries.add(new NamedWriteableRegistry.Entry(NamedDiff.class, TestCustomOne.TYPE, TestCustomOne::readDiffFrom));
+        entries.add(new NamedWriteableRegistry.Entry(ClusterState.Custom.class, TestCustomTwo.TYPE, TestCustomTwo::new));
+        entries.add(new NamedWriteableRegistry.Entry(NamedDiff.class, TestCustomTwo.TYPE, TestCustomTwo::readDiffFrom));
+
+        // serialize with current version
+        BytesStreamOutput outStream = new BytesStreamOutput();
+        Version version = Version.CURRENT;
+        outStream.setVersion(version);
+        diffs.writeTo(outStream);
+        StreamInput inStream = outStream.bytes().streamInput();
+
+        inStream = new NamedWriteableAwareStreamInput(inStream, new NamedWriteableRegistry(entries));
+        inStream.setVersion(version);
+        Diff<ClusterState> serializedDiffs = ClusterState.readDiffFrom(inStream, clusterState.nodes().getLocalNode());
+        ClusterState stateAfterDiffs = serializedDiffs.apply(ClusterState.EMPTY_STATE);
+
+        // Current version - Both the customs are non null
+        assertThat(stateAfterDiffs.custom(TestCustomOne.TYPE), notNullValue());
+        assertThat(stateAfterDiffs.custom(TestCustomTwo.TYPE), notNullValue());
+
+        // serialize with minimum compatibile version
+        outStream = new BytesStreamOutput();
+        version = Version.CURRENT.minimumCompatibilityVersion();
+        outStream.setVersion(version);
+        diffs.writeTo(outStream);
+        inStream = outStream.bytes().streamInput();
+
+        inStream = new NamedWriteableAwareStreamInput(inStream, new NamedWriteableRegistry(entries));
+        inStream.setVersion(version);
+        serializedDiffs = ClusterState.readDiffFrom(inStream, clusterState.nodes().getLocalNode());
+        stateAfterDiffs = serializedDiffs.apply(ClusterState.EMPTY_STATE);
+
+        // Old version - TestCustomOne is null and TestCustomTwo is not null
+        assertThat(stateAfterDiffs.custom(TestCustomOne.TYPE), nullValue());
+        assertThat(stateAfterDiffs.custom(TestCustomTwo.TYPE), notNullValue());
+    }
+
 }