Fix fromXContent() bug, add @nullable, update description string

Author: JeremyDahlgren

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/status/SnapshotIndexShardStatus.java

@@ -13,6 +13,7 @@
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.core.Nullable;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.index.snapshots.IndexShardSnapshotStatus;
 import org.elasticsearch.xcontent.ToXContentFragment;
@@ -90,7 +91,7 @@ public SnapshotIndexShardStatus(StreamInput in) throws IOException {
         SnapshotStats stats,
         String nodeId,
         String failure,
-        String description
+        @Nullable String description
     ) {
         super(shardId);
         this.stage = stage;
@@ -146,6 +147,7 @@ public String getFailure() {
     /**
      * Returns the optional description of the data values contained in the {@code stats} field.
      */
+    @Nullable
     public String getDescription() {
         return description;
     }

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/status/SnapshotStats.java

@@ -250,10 +250,10 @@ public static SnapshotStats fromXContent(XContentParser parser) throws IOExcepti
         long time = 0;
         int incrementalFileCount = 0;
         int totalFileCount = 0;
-        int processedFileCount = 0;
+        int processedFileCount = Integer.MIN_VALUE;
         long incrementalSize = 0;
         long totalSize = 0;
-        long processedSize = 0;
+        long processedSize = Long.MIN_VALUE;
         while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
             XContentParserUtils.ensureExpectedToken(XContentParser.Token.FIELD_NAME, token, parser);
             String currentName = parser.currentName();
@@ -328,10 +328,11 @@ public static SnapshotStats fromXContent(XContentParser parser) throws IOExcepti
                 }
             }
         }
-        // For missing stats incrementalFileCount will be -1, and we expect processedFileCount and processedSize to be omitted (still zero).
-        if (incrementalFileCount == -1) {
-            assert processedFileCount == 0 && processedSize == 0L && incrementalSize == -1L && totalFileCount == -1 && totalSize == -1L;
-            return SnapshotStats.forMissingStats();
+        // Handle the case where the "processed" sub-object is omitted in toXContent() when processedFileCount == incrementalFileCount.
+        if (processedFileCount == Integer.MIN_VALUE) {
+            assert processedSize == Long.MIN_VALUE;
+            processedFileCount = incrementalFileCount;
+            processedSize = incrementalSize;
         }
         return new SnapshotStats(
             startTime,

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/status/TransportSnapshotsStatusAction.java

@@ -246,8 +246,8 @@ void buildResponse(
                         if (minTransportVersion.onOrAfter(TransportVersions.SNAPSHOT_INDEX_SHARD_STATUS_MISSING_STATS)) {
                             shardStatus = SnapshotIndexShardStatus.forDoneButMissingStats(shardId, """
                                 Snapshot shard stats missing from a currently running snapshot due to a node leaving the cluster after \
-                                completing the shard snapshot; use /_snapshot/<repository>/<snapshot>/_status to load from the repository \
-                                once the snapshot has completed.""");
+                                completing the shard snapshot; retry once the snapshot has completed to load all shard stats from the \
+                                repository.""");
                         } else {
                             // BWC behavior, load the stats directly from the repository.
                             shardStatus = new SnapshotIndexShardStatus(

server/src/test/java/org/elasticsearch/action/admin/cluster/snapshots/status/SnapshotStatsTests.java

@@ -55,6 +55,26 @@ protected boolean supportsUnknownFields() {
         return true;
     }
 
+    public void testXContentSerializationWhenProcessedFileCountEqualsIncrementalFileCount() throws IOException {
+        final var instance = createTestInstance();
+        final var incrementalSameAsProcessed = new SnapshotStats(
+            instance.getStartTime(),
+            instance.getTime(),
+            instance.getIncrementalFileCount(),
+            instance.getTotalFileCount(),
+            instance.getIncrementalFileCount(), // processedFileCount
+            instance.getIncrementalSize(),
+            instance.getTotalSize(),
+            instance.getIncrementalSize() // processedSize
+        );
+        // toXContent() omits the "processed" sub-object in this case, make sure the processed values are set as expected in fromXContent().
+        testFromXContent(() -> incrementalSameAsProcessed);
+    }
+
+    public void testXContentSerializationForEmptyStats() throws IOException {
+        testFromXContent(SnapshotStats::new);
+    }
+
     public void testMissingStats() throws IOException {
         final var populatedStats = createTestInstance();
         final var missingStats = SnapshotStats.forMissingStats();