Fix Broken Numeric Shard Generations in RepositoryData (#57813) (#57824)

Fix broken numeric shard generations when reading them from the wire
or physically from the physical repository.
This should be the cheapest way to clean up broken shard generations
in a BwC and safe-to-backport manner for now. We can potentially
further optimize this by also not doing the checks on the generations
based on the versions we see in the `RepositoryData` but I don't think
it matters much since we will read `RepositoryData` from cache in almost
all cases.

Closes #57798

server/src/internalClusterTest/java/org/elasticsearch/snapshots/CorruptedBlobStoreRepositoryIT.java

@@ -52,6 +52,7 @@
 import java.nio.file.StandardOpenOption;
 import java.util.Collections;
 import java.util.Locale;
+import java.util.Map;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -379,7 +380,7 @@ public void testHandleSnapshotErrorWithBwCFormat() throws IOException {
                 NamedXContentRegistry.EMPTY,
                 DeprecationHandler.THROW_UNSUPPORTED_OPERATION,
                 Strings.toString(jsonBuilder).replace(Version.CURRENT.toString(), SnapshotsService.OLD_SNAPSHOT_FORMAT.toString())),
-                repositoryData.getGenId());
+                repositoryData.getGenId(), randomBoolean());
         Files.write(repoPath.resolve(BlobStoreRepository.INDEX_FILE_PREFIX + repositoryData.getGenId()),
                 BytesReference.toBytes(BytesReference.bytes(
                         downgradedRepoData.snapshotsToXContent(XContentFactory.jsonBuilder(), false))),
@@ -409,6 +410,75 @@ public void testHandleSnapshotErrorWithBwCFormat() throws IOException {
         assertCreateSnapshotSuccess(repoName, "snapshot-2");
     }
 
+    public void testRepairBrokenShardGenerations() throws IOException {
+        final String repoName = "test-repo";
+        final Path repoPath = randomRepoPath();
+        createRepository(repoName, "fs", repoPath);
+
+        // Workaround to simulate BwC situation: taking a snapshot without indices here so that we don't create any new version shard
+        // generations (the existence of which would short-circuit checks for the repo containing old version snapshots)
+        final String oldVersionSnapshot = "old-version-snapshot";
+        final CreateSnapshotResponse createSnapshotResponse = client().admin().cluster()
+                .prepareCreateSnapshot(repoName, oldVersionSnapshot).setIndices().setWaitForCompletion(true).get();
+        assertThat(createSnapshotResponse.getSnapshotInfo().totalShards(), is(0));
+
+        logger.info("--> writing downgraded RepositoryData");
+        final RepositoryData repositoryData = getRepositoryData(repoName);
+        final XContentBuilder jsonBuilder = JsonXContent.contentBuilder();
+        repositoryData.snapshotsToXContent(jsonBuilder, false);
+        final RepositoryData downgradedRepoData = RepositoryData.snapshotsFromXContent(JsonXContent.jsonXContent.createParser(
+                NamedXContentRegistry.EMPTY,
+                DeprecationHandler.THROW_UNSUPPORTED_OPERATION,
+                Strings.toString(jsonBuilder).replace(Version.CURRENT.toString(), SnapshotsService.OLD_SNAPSHOT_FORMAT.toString())),
+                repositoryData.getGenId(), randomBoolean());
+        Files.write(repoPath.resolve(BlobStoreRepository.INDEX_FILE_PREFIX + repositoryData.getGenId()),
+                BytesReference.toBytes(BytesReference.bytes(
+                        downgradedRepoData.snapshotsToXContent(XContentFactory.jsonBuilder(), false))),
+                StandardOpenOption.TRUNCATE_EXISTING);
+
+        logger.info("--> recreating repository to clear caches");
+        client().admin().cluster().prepareDeleteRepository(repoName).get();
+        createRepository(repoName, "fs", repoPath);
+
+        final String indexName = "test-index";
+        createIndex(indexName);
+
+        assertCreateSnapshotSuccess(repoName, "snapshot-1");
+
+        logger.info("--> delete old version snapshot");
+        client().admin().cluster().prepareDeleteSnapshot(repoName, oldVersionSnapshot).get();
+
+        logger.info("--> move shard level metadata to new generation and make RepositoryData point at an older generation");
+        final IndexId indexId = getRepositoryData(repoName).resolveIndexId(indexName);
+        final Path shardPath = repoPath.resolve("indices").resolve(indexId.getId()).resolve("0");
+        final Path initialShardMetaPath = shardPath.resolve(BlobStoreRepository.INDEX_FILE_PREFIX + "0");
+        assertFileExists(initialShardMetaPath);
+        Files.move(initialShardMetaPath, shardPath.resolve(BlobStoreRepository.INDEX_FILE_PREFIX + randomIntBetween(1, 1000)));
+
+        final RepositoryData repositoryData1 = getRepositoryData(repoName);
+        final Map<String, SnapshotId> snapshotIds =
+                repositoryData1.getSnapshotIds().stream().collect(Collectors.toMap(SnapshotId::getUUID, Function.identity()));
+        final RepositoryData brokenRepoData = new RepositoryData(
+                repositoryData1.getGenId(), snapshotIds, snapshotIds.values().stream().collect(
+                Collectors.toMap(SnapshotId::getUUID, repositoryData1::getSnapshotState)),
+                snapshotIds.values().stream().collect(
+                        Collectors.toMap(SnapshotId::getUUID, repositoryData1::getVersion)),
+                repositoryData1.getIndices().values().stream().collect(
+                        Collectors.toMap(Function.identity(), repositoryData1::getSnapshots)
+                ),  ShardGenerations.builder().putAll(repositoryData1.shardGenerations()).put(indexId, 0, "0").build()
+        );
+        Files.write(repoPath.resolve(BlobStoreRepository.INDEX_FILE_PREFIX + repositoryData1.getGenId()),
+                BytesReference.toBytes(BytesReference.bytes(
+                        brokenRepoData.snapshotsToXContent(XContentFactory.jsonBuilder(), true))),
+                StandardOpenOption.TRUNCATE_EXISTING);
+
+        logger.info("--> recreating repository to clear caches");
+        client().admin().cluster().prepareDeleteRepository(repoName).get();
+        createRepository(repoName, "fs", repoPath);
+
+        assertCreateSnapshotSuccess(repoName, "snapshot-2");
+    }
+
     private void assertCreateSnapshotSuccess(String repoName, String snapshotName) {
         logger.info("--> create another snapshot");
         final SnapshotInfo snapshotInfo = client().admin().cluster().prepareCreateSnapshot(repoName, snapshotName)

server/src/main/java/org/elasticsearch/repositories/RepositoryData.java

@@ -427,8 +427,12 @@ public XContentBuilder snapshotsToXContent(final XContentBuilder builder, final
 
     /**
      * Reads an instance of {@link RepositoryData} from x-content, loading the snapshots and indices metadata.
+     *
+     * @param fixBrokenShardGens set to {@code true} to filter out broken shard generations read from the {@code parser} via
+     *                           {@link ShardGenerations#fixShardGeneration}. Used to disable fixing broken generations when reading
+     *                           from cached bytes that we trust to not contain broken generations.
      */
-    public static RepositoryData snapshotsFromXContent(final XContentParser parser, long genId) throws IOException {
+    public static RepositoryData snapshotsFromXContent(XContentParser parser, long genId, boolean fixBrokenShardGens) throws IOException {
         final Map<String, SnapshotId> snapshots = new HashMap<>();
         final Map<String, SnapshotState> snapshotStates = new HashMap<>();
         final Map<String, Version> snapshotVersions = new HashMap<>();
@@ -532,7 +536,13 @@ public static RepositoryData snapshotsFromXContent(final XContentParser parser,
                         assert indexId != null;
                         indexSnapshots.put(indexId, Collections.unmodifiableList(snapshotIds));
                         for (int i = 0; i < gens.size(); i++) {
-                            shardGenerations.put(indexId, i, gens.get(i));
+                            String parsedGen = gens.get(i);
+                            if (fixBrokenShardGens) {
+                                parsedGen = ShardGenerations.fixShardGeneration(parsedGen);
+                            }
+                            if (parsedGen != null) {
+                                shardGenerations.put(indexId, i, parsedGen);
+                            }
                         }
                     }
                 } else if (MIN_VERSION.equals(field)) {

server/src/main/java/org/elasticsearch/repositories/ShardGenerations.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.repositories;
 
 import org.elasticsearch.common.Nullable;
+import org.elasticsearch.index.snapshots.IndexShardSnapshotStatus;
 
 import java.util.Arrays;
 import java.util.Collection;
@@ -30,6 +31,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
+import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
 public final class ShardGenerations {
@@ -54,6 +56,24 @@ private ShardGenerations(Map<IndexId, List<String>> shardGenerations) {
         this.shardGenerations = shardGenerations;
     }
 
+    private static final Pattern IS_NUMBER = Pattern.compile("^\\d+$");
+
+    /**
+     * Filters out unreliable numeric shard generations read from {@link RepositoryData} or {@link IndexShardSnapshotStatus}, returning
+     * {@code null} in their place.
+     * @see <a href="https://github.com/elastic/elasticsearch/issues/57798">Issue #57988</a>
+     *
+     * @param shardGeneration shard generation to fix
+     * @return given shard generation or {@code null} if it was filtered out or {@code null} was passed
+     */
+    @Nullable
+    public static String fixShardGeneration(@Nullable String shardGeneration) {
+        if (shardGeneration == null) {
+            return null;
+        }
+        return IS_NUMBER.matcher(shardGeneration).matches() ? null : shardGeneration;
+    }
+
     /**
      * Returns the total number of shards tracked by this instance.
      */

server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java

@@ -1285,7 +1285,7 @@ private RepositoryData repositoryDataFromCachedEntry(Tuple<Long, BytesReference>
         return RepositoryData.snapshotsFromXContent(
             XContentType.JSON.xContent().createParser(NamedXContentRegistry.EMPTY,
                 LoggingDeprecationHandler.INSTANCE,
-                CompressorFactory.COMPRESSOR.streamInput(cacheEntry.v2().streamInput())), cacheEntry.v1());
+                CompressorFactory.COMPRESSOR.streamInput(cacheEntry.v2().streamInput())), cacheEntry.v1(), false);
     }
 
     private RepositoryException corruptedStateException(@Nullable Exception cause) {
@@ -1350,7 +1350,7 @@ private RepositoryData getRepositoryData(long indexGen) {
             try (InputStream blob = blobContainer().readBlob(snapshotsIndexBlobName);
                  XContentParser parser = XContentType.JSON.xContent().createParser(NamedXContentRegistry.EMPTY,
                      LoggingDeprecationHandler.INSTANCE, blob)) {
-                return RepositoryData.snapshotsFromXContent(parser, indexGen);
+                return RepositoryData.snapshotsFromXContent(parser, indexGen, true);
             }
         } catch (IOException ioe) {
             if (bestEffortConsistency) {
@@ -1639,7 +1639,7 @@ public void snapshotShard(Store store, MapperService mapperService, SnapshotId s
         final ShardId shardId = store.shardId();
         final long startTime = threadPool.absoluteTimeInMillis();
         try {
-            final String generation = snapshotStatus.generation();
+            final String generation = ShardGenerations.fixShardGeneration(snapshotStatus.generation());
             logger.debug("[{}] [{}] snapshot to [{}] [{}] ...", shardId, snapshotId, metadata.name(), generation);
             final BlobContainer shardContainer = shardContainer(indexId, shardId);
             final Set<String> blobs;
@@ -2086,6 +2086,8 @@ public BlobStoreIndexShardSnapshot loadShardSnapshot(BlobContainer shardContaine
     private Tuple<BlobStoreIndexShardSnapshots, String> buildBlobStoreIndexShardSnapshots(Set<String> blobs,
                                                                                           BlobContainer shardContainer,
                                                                                           @Nullable String generation) throws IOException {
+        assert ShardGenerations.fixShardGeneration(generation) == generation
+                : "Generation must not be numeric but received [" + generation + "]";
         if (generation != null) {
             if (generation.equals(ShardGenerations.NEW_SHARD_GEN)) {
                 return new Tuple<>(BlobStoreIndexShardSnapshots.EMPTY, ShardGenerations.NEW_SHARD_GEN);

server/src/test/java/org/elasticsearch/repositories/RepositoryDataTests.java

@@ -77,7 +77,7 @@ public void testXContent() throws IOException {
         repositoryData.snapshotsToXContent(builder, true);
         try (XContentParser parser = createParser(JsonXContent.jsonXContent, BytesReference.bytes(builder))) {
             long gen = (long) randomIntBetween(0, 500);
-            RepositoryData fromXContent = RepositoryData.snapshotsFromXContent(parser, gen);
+            RepositoryData fromXContent = RepositoryData.snapshotsFromXContent(parser, gen, randomBoolean());
             assertEquals(repositoryData, fromXContent);
             assertEquals(gen, fromXContent.getGenId());
         }
@@ -97,14 +97,14 @@ public void testAddSnapshots() {
             IndexId indexId = new IndexId(randomAlphaOfLength(7), UUIDs.randomBase64UUID());
             newIndices.add(indexId);
             indices.add(indexId);
-            builder.put(indexId, 0, "1");
+            builder.put(indexId, 0, UUIDs.randomBase64UUID(random()));
         }
         int numOld = randomIntBetween(1, indexIdMap.size());
         List<String> indexNames = new ArrayList<>(indexIdMap.keySet());
         for (int i = 0; i < numOld; i++) {
             final IndexId indexId = indexIdMap.get(indexNames.get(i));
             indices.add(indexId);
-            builder.put(indexId, 0, "2");
+            builder.put(indexId, 0, UUIDs.randomBase64UUID(random()));
         }
         RepositoryData newRepoData = repositoryData.addSnapshot(newSnapshot,
             randomFrom(SnapshotState.SUCCESS, SnapshotState.PARTIAL, SnapshotState.FAILED),
@@ -187,7 +187,7 @@ public void testIndexThatReferencesAnUnknownSnapshot() throws IOException {
         repositoryData.snapshotsToXContent(builder, true);
         RepositoryData parsedRepositoryData;
         try (XContentParser xParser = createParser(builder)) {
-            parsedRepositoryData = RepositoryData.snapshotsFromXContent(xParser, repositoryData.getGenId());
+            parsedRepositoryData = RepositoryData.snapshotsFromXContent(xParser, repositoryData.getGenId(), randomBoolean());
         }
         assertEquals(repositoryData, parsedRepositoryData);
 
@@ -226,7 +226,7 @@ public void testIndexThatReferencesAnUnknownSnapshot() throws IOException {
 
         try (XContentParser xParser = createParser(corruptedBuilder)) {
             ElasticsearchParseException e = expectThrows(ElasticsearchParseException.class, () ->
-                RepositoryData.snapshotsFromXContent(xParser, corruptedRepositoryData.getGenId()));
+                RepositoryData.snapshotsFromXContent(xParser, corruptedRepositoryData.getGenId(), randomBoolean()));
             assertThat(e.getMessage(), equalTo("Detected a corrupted repository, index " + corruptedIndexId + " references an unknown " +
                 "snapshot uuid [_does_not_exist]"));
         }
@@ -263,7 +263,7 @@ public void testIndexThatReferenceANullSnapshot() throws IOException {
 
         try (XContentParser xParser = createParser(builder)) {
             ElasticsearchParseException e = expectThrows(ElasticsearchParseException.class, () ->
-                RepositoryData.snapshotsFromXContent(xParser, randomNonNegativeLong()));
+                RepositoryData.snapshotsFromXContent(xParser, randomNonNegativeLong(), randomBoolean()));
             assertThat(e.getMessage(), equalTo("Detected a corrupted repository, " +
                 "index [docs/_id] references an unknown snapshot uuid [null]"));
         }

test/framework/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreTestUtil.java

@@ -132,7 +132,7 @@ public static void assertConsistency(BlobStoreRepository repository, Executor ex
                 try (InputStream blob = blobContainer.readBlob("index-" + latestGen);
                      XContentParser parser = XContentType.JSON.xContent().createParser(NamedXContentRegistry.EMPTY,
                          LoggingDeprecationHandler.INSTANCE, blob)) {
-                    repositoryData = RepositoryData.snapshotsFromXContent(parser, latestGen);
+                    repositoryData = RepositoryData.snapshotsFromXContent(parser, latestGen, false);
                 }
                 assertIndexUUIDs(blobContainer, repositoryData);
                 assertSnapshotUUIDs(repository, repositoryData);

x-pack/snapshot-tool/src/main/java/org/elasticsearch/snapshots/AbstractRepository.java

@@ -75,7 +75,7 @@ private RepositoryData getRepositoryData(long indexFileGeneration) throws IOExce
             // EMPTY is safe here because RepositoryData#fromXContent calls namedObject
             try (XContentParser parser = XContentHelper.createParser(NamedXContentRegistry.EMPTY,
                     LoggingDeprecationHandler.INSTANCE, out.bytes(), XContentType.JSON)) {
-                return RepositoryData.snapshotsFromXContent(parser, indexFileGeneration);
+                return RepositoryData.snapshotsFromXContent(parser, indexFileGeneration, true);
             }
         } catch (IOException e) {
             terminal.println("Failed to read " + snapshotsIndexBlobName + " file");