Test get-snapshots API with missing details (#111903)

Extends the test added in #111786 to check that the API still works
correctly even in the BwC case that the details needed are not in the
`RepositoryData` and must be read from the individual `SnapshotInfo`
blobs.

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

@@ -8,8 +8,12 @@
 
 package org.elasticsearch.snapshots;
 
+import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.action.ActionFuture;
+import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.ActionRequestValidationException;
+import org.elasticsearch.action.admin.cluster.repositories.delete.DeleteRepositoryRequest;
+import org.elasticsearch.action.admin.cluster.repositories.delete.TransportDeleteRepositoryAction;
 import org.elasticsearch.action.admin.cluster.repositories.put.PutRepositoryRequest;
 import org.elasticsearch.action.admin.cluster.repositories.put.TransportPutRepositoryAction;
 import org.elasticsearch.action.admin.cluster.snapshots.create.CreateSnapshotRequest;
@@ -23,17 +27,30 @@
 import org.elasticsearch.action.admin.indices.create.CreateIndexRequest;
 import org.elasticsearch.action.admin.indices.create.TransportCreateIndexAction;
 import org.elasticsearch.action.support.RefCountingListener;
+import org.elasticsearch.action.support.SubscribableListener;
+import org.elasticsearch.action.support.master.AcknowledgedResponse;
 import org.elasticsearch.cluster.SnapshotsInProgress;
 import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.blobstore.fs.FsBlobStore;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
+import org.elasticsearch.common.util.concurrent.EsExecutors;
+import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.core.Predicates;
+import org.elasticsearch.repositories.RepositoriesService;
+import org.elasticsearch.repositories.RepositoryData;
 import org.elasticsearch.repositories.RepositoryMissingException;
+import org.elasticsearch.repositories.blobstore.BlobStoreRepository;
 import org.elasticsearch.repositories.fs.FsRepository;
 import org.elasticsearch.search.sort.SortOrder;
 import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.XContentTestUtils;
 import org.elasticsearch.test.hamcrest.ElasticsearchAssertions;
 import org.elasticsearch.threadpool.ThreadPool;
+import org.elasticsearch.xcontent.XContentType;
+import org.elasticsearch.xcontent.json.JsonXContent;
 
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -819,6 +836,17 @@ public void testAllFeatures() {
             }
         });
 
+        if (randomBoolean()) {
+            // Sometimes also simulate bwc repository contents where some details are missing from the root blob
+            safeAwait(l -> {
+                try (var listeners = new RefCountingListener(l.map(v -> null))) {
+                    for (final var repositoryName : randomSubsetOf(repositories)) {
+                        removeDetailsForRandomSnapshots(repositoryName, listeners.acquire());
+                    }
+                }
+            });
+        }
+
         Predicate<SnapshotInfo> snapshotInfoPredicate = Predicates.always();
 
         // {repository} path parameter
@@ -1000,4 +1028,102 @@ public void testAllFeatures() {
 
         assertEquals(0, remaining);
     }
+
+    /**
+     * Older versions of Elasticsearch don't record in {@link RepositoryData} all the details needed for the get-snapshots API to pick out
+     * the right snapshots, so in this case the API must fall back to reading those details from each candidate {@link SnapshotInfo} blob.
+     * Simulate this situation by manipulating the {@link RepositoryData} blob directly to remove all the optional details from some subset
+     * of its snapshots.
+     */
+    private static void removeDetailsForRandomSnapshots(String repositoryName, ActionListener<Void> listener) {
+        final Set<SnapshotId> snapshotsWithoutDetails = ConcurrentCollections.newConcurrentSet();
+        final var masterRepositoriesService = internalCluster().getCurrentMasterNodeInstance(RepositoriesService.class);
+        final var repository = asInstanceOf(FsRepository.class, masterRepositoriesService.repository(repositoryName));
+        final var repositoryMetadata = repository.getMetadata();
+        final var repositorySettings = repositoryMetadata.settings();
+        final var repositoryDataBlobPath = asInstanceOf(FsBlobStore.class, repository.blobStore()).path()
+            .resolve(BlobStoreRepository.INDEX_FILE_PREFIX + repositoryMetadata.generation());
+
+        SubscribableListener
+
+            // unregister the repository while we're mucking around with its internals
+            .<AcknowledgedResponse>newForked(
+                l -> client().execute(
+                    TransportDeleteRepositoryAction.TYPE,
+                    new DeleteRepositoryRequest(TEST_REQUEST_TIMEOUT, TEST_REQUEST_TIMEOUT, repositoryName),
+                    l
+                )
+            )
+            .andThenAccept(ElasticsearchAssertions::assertAcked)
+
+            // rewrite the RepositoryData blob with some details removed
+            .andThenAccept(ignored -> {
+                // load the existing RepositoryData JSON blob as raw maps/lists/etc.
+                final var repositoryDataBytes = Files.readAllBytes(repositoryDataBlobPath);
+                final var repositoryDataMap = XContentHelper.convertToMap(
+                    JsonXContent.jsonXContent,
+                    repositoryDataBytes,
+                    0,
+                    repositoryDataBytes.length,
+                    true
+                );
+
+                // modify the contents
+                final var snapshotsList = asInstanceOf(List.class, repositoryDataMap.get("snapshots"));
+                for (final var snapshotObj : snapshotsList) {
+                    if (randomBoolean()) {
+                        continue;
+                    }
+                    final var snapshotMap = asInstanceOf(Map.class, snapshotObj);
+                    snapshotsWithoutDetails.add(
+                        new SnapshotId(
+                            asInstanceOf(String.class, snapshotMap.get("name")),
+                            asInstanceOf(String.class, snapshotMap.get("uuid"))
+                        )
+                    );
+
+                    // remove the optional details fields
+                    assertNotNull(snapshotMap.remove("start_time_millis"));
+                    assertNotNull(snapshotMap.remove("end_time_millis"));
+                    assertNotNull(snapshotMap.remove("slm_policy"));
+                }
+
+                // overwrite the RepositoryData JSON blob with its new contents
+                final var updatedRepositoryDataBytes = XContentTestUtils.convertToXContent(repositoryDataMap, XContentType.JSON);
+                try (var outputStream = Files.newOutputStream(repositoryDataBlobPath)) {
+                    BytesRef bytesRef;
+                    final var iterator = updatedRepositoryDataBytes.iterator();
+                    while ((bytesRef = iterator.next()) != null) {
+                        outputStream.write(bytesRef.bytes, bytesRef.offset, bytesRef.length);
+                    }
+                }
+            })
+
+            // re-register the repository
+            .<AcknowledgedResponse>andThen(
+                l -> client().execute(
+                    TransportPutRepositoryAction.TYPE,
+                    new PutRepositoryRequest(TEST_REQUEST_TIMEOUT, TEST_REQUEST_TIMEOUT, repositoryName).type(FsRepository.TYPE)
+                        .settings(repositorySettings),
+                    l
+                )
+            )
+            .andThenAccept(ElasticsearchAssertions::assertAcked)
+
+            // verify that the details are indeed now missing
+            .<RepositoryData>andThen(
+                l -> masterRepositoriesService.repository(repositoryName).getRepositoryData(EsExecutors.DIRECT_EXECUTOR_SERVICE, l)
+            )
+            .andThenAccept(repositoryData -> {
+                for (SnapshotId snapshotId : repositoryData.getSnapshotIds()) {
+                    assertEquals(
+                        repositoryName + "/" + snapshotId.toString() + ": " + repositoryData.getSnapshotDetails(snapshotId),
+                        snapshotsWithoutDetails.contains(snapshotId),
+                        repositoryData.hasMissingDetails(snapshotId)
+                    );
+                }
+            })
+
+            .addListener(listener);
+    }
 }