Remote reindex failure parse fix (#42928)

A search request that partially fails with failures without an index
(index: null) in the failure would cause a parse error in reindex from
remote. This would hide the original exception, making it hard to debug
the root cause. This commit fixes this so that we can tolerate null
index entries in a search failure.

modules/reindex/src/main/java/org/elasticsearch/index/reindex/remote/RemoteResponseParsers.java

@@ -143,7 +143,7 @@ class Fields {
                 return new SearchFailure(reasonThrowable, index, shardId, nodeId);
             });
     static {
-        SEARCH_FAILURE_PARSER.declareString(optionalConstructorArg(), new ParseField("index"));
+        SEARCH_FAILURE_PARSER.declareStringOrNull(optionalConstructorArg(), new ParseField("index"));
         SEARCH_FAILURE_PARSER.declareInt(optionalConstructorArg(), new ParseField("shard"));
         SEARCH_FAILURE_PARSER.declareString(optionalConstructorArg(), new ParseField("node"));
         SEARCH_FAILURE_PARSER.declareField(constructorArg(), (p, c) -> {

modules/reindex/src/test/java/org/elasticsearch/index/reindex/remote/RemoteResponseParsersTests.java

@@ -0,0 +1,52 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch 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.elasticsearch.index.reindex.remote;
+
+import org.elasticsearch.action.search.ShardSearchFailure;
+import org.elasticsearch.common.util.concurrent.EsRejectedExecutionException;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.index.reindex.ScrollableHitSource;
+import org.elasticsearch.test.ESTestCase;
+import org.hamcrest.Matchers;
+
+import java.io.IOException;
+
+import static org.elasticsearch.common.xcontent.XContentFactory.jsonBuilder;
+
+public class RemoteResponseParsersTests extends ESTestCase {
+
+    /**
+     * Check that we can parse shard search failures without index information.
+     */
+    public void testFailureWithoutIndex() throws IOException {
+        ShardSearchFailure failure = new ShardSearchFailure(new EsRejectedExecutionException("exhausted"));
+        XContentBuilder builder = jsonBuilder();
+        failure.toXContent(builder, ToXContent.EMPTY_PARAMS);
+        try (XContentParser parser = createParser(builder)) {
+            ScrollableHitSource.SearchFailure parsed = RemoteResponseParsers.SEARCH_FAILURE_PARSER.parse(parser, XContentType.JSON);
+            assertNotNull(parsed.getReason());
+            assertThat(parsed.getReason().getMessage(), Matchers.containsString("exhausted"));
+            assertThat(parsed.getReason(), Matchers.instanceOf(EsRejectedExecutionException.class));
+        }
+    }
+}