Prevent NullPointerException in TransportRolloverAction (elastic#43353)

It's possible for the passed in `IndexMetaData` to be null (for
instance, cluster state passed in does not have the index in its
metadata) which in turn can cause a `NullPointerException` when
evaluating the conditions for an index. This commit adds null protection
and unit tests for this case.

Resolves elastic#43296

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/TransportRolloverAction.java

@@ -44,6 +44,7 @@
 import org.elasticsearch.cluster.metadata.MetaDataIndexAliasesService;
 import org.elasticsearch.cluster.metadata.MetaDataIndexTemplateService;
 import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.index.shard.DocsStats;
@@ -54,6 +55,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Optional;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
@@ -233,7 +235,11 @@ static String generateRolloverIndexName(String sourceIndexName, IndexNameExpress
     }
 
     static Map<String, Boolean> evaluateConditions(final Collection<Condition<?>> conditions,
-                                                   final DocsStats docsStats, final IndexMetaData metaData) {
+                                                   @Nullable final DocsStats docsStats,
+                                                   @Nullable final IndexMetaData metaData) {
+        if (metaData == null) {
+            return conditions.stream().collect(Collectors.toMap(Condition::toString, cond -> false));
+        }
         final long numDocs = docsStats == null ? 0 : docsStats.getCount();
         final long indexSize = docsStats == null ? 0 : docsStats.getTotalSizeInBytes();
         final Condition.Stats stats = new Condition.Stats(numDocs, metaData.getCreationDate(), new ByteSizeValue(indexSize));
@@ -242,9 +248,18 @@ static Map<String, Boolean> evaluateConditions(final Collection<Condition<?>> co
             .collect(Collectors.toMap(result -> result.condition.toString(), result -> result.matched));
     }
 
-    static Map<String, Boolean> evaluateConditions(final Collection<Condition<?>> conditions, final IndexMetaData metaData,
-                                                    final IndicesStatsResponse statsResponse) {
-        return evaluateConditions(conditions, statsResponse.getIndex(metaData.getIndex().getName()).getPrimaries().getDocs(), metaData);
+    static Map<String, Boolean> evaluateConditions(final Collection<Condition<?>> conditions,
+                                                   @Nullable final IndexMetaData metaData,
+                                                   @Nullable final IndicesStatsResponse statsResponse) {
+        if (metaData == null) {
+            return conditions.stream().collect(Collectors.toMap(Condition::toString, cond -> false));
+        } else {
+            final DocsStats docsStats = Optional.ofNullable(statsResponse)
+                .map(stats -> stats.getIndex(metaData.getIndex().getName()))
+                .map(indexStats -> indexStats.getPrimaries().getDocs())
+                .orElse(null);
+            return evaluateConditions(conditions, docsStats, metaData);
+        }
     }
 
     static void validate(MetaData metaData, RolloverRequest request) {

server/src/test/java/org/elasticsearch/action/admin/indices/rollover/TransportRolloverActionTests.java

@@ -51,6 +51,7 @@
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.index.shard.DocsStats;
+import org.elasticsearch.rest.action.cat.RestIndicesActionTests;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.transport.TransportService;
@@ -165,6 +166,35 @@ public void testEvaluateWithoutDocStats() {
         }
     }
 
+    public void testEvaluateWithoutMetaData() {
+        MaxDocsCondition maxDocsCondition = new MaxDocsCondition(100L);
+        MaxAgeCondition maxAgeCondition = new MaxAgeCondition(TimeValue.timeValueHours(2));
+        MaxSizeCondition maxSizeCondition = new MaxSizeCondition(new ByteSizeValue(randomIntBetween(10, 100), ByteSizeUnit.MB));
+
+        long matchMaxDocs = randomIntBetween(100, 1000);
+        final Set<Condition<?>> conditions = Sets.newHashSet(maxDocsCondition, maxAgeCondition, maxSizeCondition);
+        Map<String, Boolean> results = evaluateConditions(conditions,
+            new DocsStats(matchMaxDocs, 0L, ByteSizeUnit.MB.toBytes(120)), null);
+        assertThat(results.size(), equalTo(3));
+        results.forEach((k, v) -> assertFalse(v));
+
+        final Settings settings = Settings.builder()
+            .put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT)
+            .put(IndexMetaData.SETTING_INDEX_UUID, UUIDs.randomBase64UUID())
+            .put(IndexMetaData.SETTING_NUMBER_OF_SHARDS, randomIntBetween(1, 1000))
+            .put(IndexMetaData.SETTING_NUMBER_OF_REPLICAS, randomInt(10))
+            .build();
+
+        final IndexMetaData metaData = IndexMetaData.builder(randomAlphaOfLength(10))
+            .creationDate(System.currentTimeMillis() - TimeValue.timeValueHours(randomIntBetween(5, 10)).getMillis())
+            .settings(settings)
+            .build();
+        IndicesStatsResponse indicesStats = RestIndicesActionTests.randomIndicesStatsResponse(new IndexMetaData[]{metaData});
+        Map<String, Boolean> results2 = evaluateConditions(conditions, null, indicesStats);
+        assertThat(results2.size(), equalTo(3));
+        results2.forEach((k, v) -> assertFalse(v));
+    }
+
     public void testCreateUpdateAliasRequest() {
         String sourceAlias = randomAlphaOfLength(10);
         String sourceIndex = randomAlphaOfLength(10);

server/src/test/java/org/elasticsearch/rest/action/cat/RestIndicesActionTests.java

@@ -151,7 +151,7 @@ public void testBuildTable() {
         }
     }
 
-    private IndicesStatsResponse randomIndicesStatsResponse(final IndexMetaData[] indices) {
+    public static IndicesStatsResponse randomIndicesStatsResponse(final IndexMetaData[] indices) {
         List<ShardStats> shardStats = new ArrayList<>();
         for (final IndexMetaData index : indices) {
             int numShards = randomIntBetween(1, 3);