Stricter failure handling in TransportGetSnapshotsAction (#107191)

Today if there's a failure during a multi-repo get-snapshots request
then we record a per-repository failure but allow the rest of the
request to proceed. This is trappy for clients, it means that they must
always remember to check the `failures` response field or else risk
missing some results. It's also a pain for the implementation because it
means we have to collect the per-repository results separately first
before adding them to the final results set just in case the last one
triggers a failure.

This commit drops this leniency and bubbles all failures straight up to
the top level.

docs/changelog/107191.yaml

@@ -0,0 +1,17 @@
+pr: 107191
+summary: Stricter failure handling in multi-repo get-snapshots request handling
+area: Snapshot/Restore
+type: bug
+issues: []
+highlight:
+  title: Stricter failure handling in multi-repo get-snapshots request handling
+  body: |
+    If a multi-repo get-snapshots request encounters a failure in one of the
+    targeted repositories then earlier versions of Elasticsearch would proceed
+    as if the faulty repository did not exist, except for a per-repository
+    failure report in a separate section of the response body. This makes it
+    impossible to paginate the results properly in the presence of failures. In
+    versions 8.15.0 and later this API's failure handling behaviour has been
+    made stricter, reporting an overall failure if any targeted repository's
+    contents cannot be listed.
+  notable: true

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

@@ -31,10 +31,8 @@
 
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.hamcrest.Matchers.empty;
-import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasSize;
 import static org.hamcrest.Matchers.in;
-import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
 
 public class GetSnapshotsIT extends AbstractSnapshotIntegTestCase {
@@ -314,6 +312,7 @@ public void testExcludePatterns() throws Exception {
         assertThat(
             clusterAdmin().prepareGetSnapshots(TEST_REQUEST_TIMEOUT, matchAllPattern())
                 .setSnapshots("non-existing*", otherPrefixSnapshot1, "-o*")
+                .setIgnoreUnavailable(true)
                 .get()
                 .getSnapshots(),
             empty()
@@ -586,12 +585,17 @@ public void testRetrievingSnapshotsWhenRepositoryIsMissing() throws Exception {
         final List<String> snapshotNames = createNSnapshots(repoName, randomIntBetween(1, 10));
         snapshotNames.sort(String::compareTo);
 
-        final GetSnapshotsResponse response = clusterAdmin().prepareGetSnapshots(TEST_REQUEST_TIMEOUT, repoName, missingRepoName)
+        final var oneRepoFuture = clusterAdmin().prepareGetSnapshots(TEST_REQUEST_TIMEOUT, repoName, missingRepoName)
             .setSort(SnapshotSortKey.NAME)
-            .get();
-        assertThat(response.getSnapshots().stream().map(info -> info.snapshotId().getName()).toList(), equalTo(snapshotNames));
-        assertTrue(response.getFailures().containsKey(missingRepoName));
-        assertThat(response.getFailures().get(missingRepoName), instanceOf(RepositoryMissingException.class));
+            .setIgnoreUnavailable(randomBoolean())
+            .execute();
+        expectThrows(RepositoryMissingException.class, oneRepoFuture::actionGet);
+
+        final var multiRepoFuture = clusterAdmin().prepareGetSnapshots(TEST_REQUEST_TIMEOUT, repoName, missingRepoName)
+            .setSort(SnapshotSortKey.NAME)
+            .setIgnoreUnavailable(randomBoolean())
+            .execute();
+        expectThrows(RepositoryMissingException.class, multiRepoFuture::actionGet);
     }
 
     // Create a snapshot that is guaranteed to have a unique start time and duration for tests around ordering by either.

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

@@ -52,7 +52,6 @@
 import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.hamcrest.Matchers.hasSize;
-import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.oneOf;
@@ -395,16 +394,13 @@ public void testGetSnapshotsMultipleRepos() throws Exception {
         }
 
         logger.info("--> specify all snapshot names with ignoreUnavailable=false");
-        GetSnapshotsResponse getSnapshotsResponse2 = client.admin()
+        final var failingFuture = client.admin()
             .cluster()
             .prepareGetSnapshots(TEST_REQUEST_TIMEOUT, randomFrom("_all", "repo*"))
             .setIgnoreUnavailable(false)
             .setSnapshots(snapshotList.toArray(new String[0]))
-            .get();
-
-        for (String repo : repoList) {
-            assertThat(getSnapshotsResponse2.getFailures().get(repo), instanceOf(SnapshotMissingException.class));
-        }
+            .execute();
+        expectThrows(SnapshotMissingException.class, failingFuture::actionGet);
 
         logger.info("--> specify all snapshot names with ignoreUnavailable=true");
         GetSnapshotsResponse getSnapshotsResponse3 = client.admin()

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/get/GetSnapshotsRequest.java

@@ -15,7 +15,6 @@
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.regex.Regex;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.search.sort.SortOrder;
@@ -220,13 +219,6 @@ public String[] policies() {
         return policies;
     }
 
-    public boolean isSingleRepositoryRequest() {
-        return repositories.length == 1
-            && repositories[0] != null
-            && "_all".equals(repositories[0]) == false
-            && Regex.isSimpleMatchPattern(repositories[0]) == false;
-    }
-
     /**
      * Returns the names of the snapshots.
      *

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/get/GetSnapshotsResponse.java

@@ -16,6 +16,7 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.core.Nullable;
+import org.elasticsearch.core.UpdateForV9;
 import org.elasticsearch.snapshots.SnapshotInfo;
 import org.elasticsearch.xcontent.ToXContent;
 
@@ -33,6 +34,7 @@ public class GetSnapshotsResponse extends ActionResponse implements ChunkedToXCo
 
     private final List<SnapshotInfo> snapshots;
 
+    @UpdateForV9 // always empty, can be dropped
     private final Map<String, ElasticsearchException> failures;
 
     @Nullable

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/get/TransportGetSnapshotsAction.java

@@ -8,7 +8,6 @@
 
 package org.elasticsearch.action.admin.cluster.snapshots.get;
 
-import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.ActionType;
 import org.elasticsearch.action.support.ActionFilters;
@@ -120,10 +119,14 @@ protected void masterOperation(
     ) {
         assert task instanceof CancellableTask : task + " not cancellable";
 
+        final var resolvedRepositories = ResolvedRepositories.resolve(state, request.repositories());
+        if (resolvedRepositories.hasMissingRepositories()) {
+            throw new RepositoryMissingException(String.join(", ", resolvedRepositories.missing()));
+        }
+
         new GetSnapshotsOperation(
             (CancellableTask) task,
-            ResolvedRepositories.resolve(state, request.repositories()),
-            request.isSingleRepositoryRequest() == false,
+            resolvedRepositories.repositoryMetadata(),
             request.snapshots(),
             request.ignoreUnavailable(),
             request.policies(),
@@ -151,7 +154,6 @@ private class GetSnapshotsOperation {
 
         // repositories
         private final List<RepositoryMetadata> repositories;
-        private final boolean isMultiRepoRequest;
 
         // snapshots selection
         private final SnapshotNamePredicate snapshotNamePredicate;
@@ -179,7 +181,6 @@ private class GetSnapshotsOperation {
         private final GetSnapshotInfoExecutor getSnapshotInfoExecutor;
 
         // results
-        private final Map<String, ElasticsearchException> failuresByRepository = ConcurrentCollections.newConcurrentMap();
         private final Queue<List<SnapshotInfo>> allSnapshotInfos = ConcurrentCollections.newQueue();
 
         /**
@@ -195,8 +196,7 @@ private class GetSnapshotsOperation {
 
         GetSnapshotsOperation(
             CancellableTask cancellableTask,
-            ResolvedRepositories resolvedRepositories,
-            boolean isMultiRepoRequest,
+            List<RepositoryMetadata> repositories,
             String[] snapshots,
             boolean ignoreUnavailable,
             String[] policies,
@@ -211,8 +211,7 @@ private class GetSnapshotsOperation {
             boolean indices
         ) {
             this.cancellableTask = cancellableTask;
-            this.repositories = resolvedRepositories.repositoryMetadata();
-            this.isMultiRepoRequest = isMultiRepoRequest;
+            this.repositories = repositories;
             this.ignoreUnavailable = ignoreUnavailable;
             this.sortBy = sortBy;
             this.order = order;
@@ -232,10 +231,6 @@ private class GetSnapshotsOperation {
                 threadPool.info(ThreadPool.Names.SNAPSHOT_META).getMax(),
                 cancellableTask::isCancelled
             );
-
-            for (final var missingRepo : resolvedRepositories.missing()) {
-                failuresByRepository.put(missingRepo, new RepositoryMissingException(missingRepo));
-            }
         }
 
         void getMultipleReposSnapshotInfo(ActionListener<GetSnapshotsResponse> listener) {
@@ -249,6 +244,10 @@ void getMultipleReposSnapshotInfo(ActionListener<GetSnapshotsResponse> listener)
                                 continue;
                             }
 
+                            if (listeners.isFailing()) {
+                                return;
+                            }
+
                             SubscribableListener
 
                                 .<RepositoryData>newForked(repositoryDataListener -> {
@@ -261,14 +260,7 @@ void getMultipleReposSnapshotInfo(ActionListener<GetSnapshotsResponse> listener)
 
                                 .<Void>andThen((l, repositoryData) -> loadSnapshotInfos(repoName, repositoryData, l))
 
-                                .addListener(listeners.acquire().delegateResponse((l, e) -> {
-                                    if (isMultiRepoRequest && e instanceof ElasticsearchException elasticsearchException) {
-                                        failuresByRepository.put(repoName, elasticsearchException);
-                                        l.onResponse(null);
-                                    } else {
-                                        l.onFailure(e);
-                                    }
-                                }));
+                                .addListener(listeners.acquire());
                         }
                     }
                 })
@@ -503,7 +495,7 @@ private GetSnapshotsResponse buildResponse() {
             }
             return new GetSnapshotsResponse(
                 snapshotInfos,
-                failuresByRepository,
+                null,
                 remaining > 0 ? sortBy.encodeAfterQueryParam(snapshotInfos.get(snapshotInfos.size() - 1)) : null,
                 totalCount.get(),
                 remaining