SOLR-17764: retry CloudSolrClient requests failing with ClosedChannelException

changelog/unreleased/SOLR-17764-retry-closedchannel.yml

@@ -0,0 +1,9 @@
+title: >
+  CloudSolrClient now retries requests that fail with ClosedChannelException, treating a connection
+  dropped mid-request the same as other communication errors.
+type: fixed
+authors:
+  - name: Serhiy Bzhezytskyy
+links:
+  - name: SOLR-17764
+    url: https://issues.apache.org/jira/browse/SOLR-17764

solr/solrj/src/java/org/apache/solr/client/solrj/impl/CloudSolrClient.java

@@ -23,6 +23,7 @@
 import java.lang.invoke.MethodHandles;
 import java.net.SocketException;
 import java.net.UnknownHostException;
+import java.nio.channels.ClosedChannelException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -208,7 +209,9 @@ public ClusterState getClusterState() {
 
   /** Is this a communication error? We will retry if so. */
   protected boolean wasCommError(Throwable t) {
-    return t instanceof SocketException || t instanceof UnknownHostException;
+    return t instanceof SocketException
+        || t instanceof UnknownHostException
+        || t instanceof ClosedChannelException;
   }
 
   @Override

solr/solrj/src/test/org/apache/solr/client/solrj/impl/CloudSolrClientCommErrorTest.java

@@ -0,0 +1,64 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.client.solrj.impl;
+
+import java.io.IOException;
+import java.net.SocketException;
+import java.net.UnknownHostException;
+import java.nio.channels.ClosedChannelException;
+import org.apache.solr.SolrTestCaseJ4;
+
+/** Unit tests for {@link CloudSolrClient#wasCommError(Throwable)}, which drives request retries. */
+public class CloudSolrClientCommErrorTest extends SolrTestCaseJ4 {
+
+  public void testCommErrorClassification() throws Exception {
+    try (ProbeClient client = new ProbeClient()) {
+      // connection-level failures: the target node is gone, so retrying on a fresh node makes sense
+      assertTrue(client.wasCommError(new SocketException("connection reset")));
+      assertTrue(client.wasCommError(new UnknownHostException("no such host")));
+      // a connection dropped mid-request (e.g. an HTTP/2 GOAWAY on server shutdown) surfaces as a
+      // ClosedChannelException; it is the same "node went away" case and should be retried too
+      assertTrue(client.wasCommError(new ClosedChannelException()));
+
+      // not comm errors: these should not trigger a comm-error retry
+      assertFalse(client.wasCommError(new IOException("some other io problem")));
+      assertFalse(client.wasCommError(new RuntimeException("boom")));
+    }
+  }
+
+  /** Minimal concrete subclass so the protected wasCommError can be exercised in isolation. */
+  private static final class ProbeClient extends CloudSolrClient implements AutoCloseable {
+    ProbeClient() {
+      super(true, true, false);
+    }
+
+    @Override
+    protected LBSolrClient getLbClient() {
+      return null;
+    }
+
+    @Override
+    public ClusterStateProvider getClusterStateProvider() {
+      return null;
+    }
+
+    @Override
+    public HttpSolrClient getHttpClient() {
+      return null;
+    }
+  }
+}