Deserialize deprecated thread pools compatibly with V9 (#118492)

ThreadPoolType.DIRECT and ThreadPoolType.FIXED_AUTO_QUEUE_SIZE are deprecated in V8 and will be removed in V9, but the types might still be used in transport messages from earlier versions. This change ensures that V8.18 can receive messages from earlier versions while still being able to communicate with V9 nodes where the types have been removed

Author: alexey-ivanov-es

server/src/main/java/org/elasticsearch/threadpool/ThreadPool.java

@@ -941,7 +941,12 @@ public Info(String name, ThreadPoolType type, int min, int max, @Nullable TimeVa
 
         public Info(StreamInput in) throws IOException {
             name = in.readString();
-            type = ThreadPoolType.fromType(in.readString());
+            ThreadPoolType receivedType = ThreadPoolType.fromType(in.readString());
+            type = switch (receivedType) {
+                case DIRECT, FIXED_AUTO_QUEUE_SIZE -> ThreadPoolType.FIXED;
+                default -> receivedType;
+            };
+
             min = in.readInt();
             max = in.readInt();
             keepAlive = in.readOptionalTimeValue();

server/src/test/java/org/elasticsearch/nodesinfo/NodeInfoStreamingTests.java

@@ -138,7 +138,11 @@ private static NodeInfo createNodeInfo() {
             List<ThreadPool.Info> threadPoolInfos = new ArrayList<>(numThreadPools);
             for (int i = 0; i < numThreadPools; i++) {
                 threadPoolInfos.add(
-                    new ThreadPool.Info(randomAlphaOfLengthBetween(3, 10), randomFrom(ThreadPool.ThreadPoolType.values()), randomInt())
+                    new ThreadPool.Info(
+                        randomAlphaOfLengthBetween(3, 10),
+                        randomFrom(ThreadPool.ThreadPoolType.FIXED, ThreadPool.ThreadPoolType.SCALING),
+                        randomInt()
+                    )
                 );
             }
             threadPoolInfo = new ThreadPoolInfo(threadPoolInfos);

server/src/test/java/org/elasticsearch/threadpool/ThreadPoolSerializationTests.java

@@ -37,7 +37,7 @@ public class ThreadPoolSerializationTests extends ESTestCase {
     @Before
     public void setUp() throws Exception {
         super.setUp();
-        threadPoolType = randomFrom(ThreadPool.ThreadPoolType.values());
+        threadPoolType = randomFrom(ThreadPool.ThreadPoolType.FIXED, ThreadPool.ThreadPoolType.SCALING);
     }
 
     public void testThatQueueSizeSerializationWorks() throws Exception {
@@ -123,4 +123,15 @@ public void testThatThreadPoolTypeIsSerializedCorrectly() throws IOException {
 
         assertThat(newInfo.getThreadPoolType(), is(threadPoolType));
     }
+
+    public void testThatDeprecatedTypesDeserializedAsFixed() throws IOException {
+        ThreadPool.Info info = new ThreadPool.Info("foo", ThreadPool.ThreadPoolType.DIRECT);
+        output.setTransportVersion(TransportVersion.current());
+        info.writeTo(output);
+
+        StreamInput input = output.bytes().streamInput();
+        ThreadPool.Info newInfo = new ThreadPool.Info(input);
+
+        assertThat(newInfo.getThreadPoolType(), is(ThreadPool.ThreadPoolType.FIXED));
+    }
 }