Fix SnapshotStats toXContent()/fromXContent() round trip serialization

toXContent() has a check to omit the "processed" sub-object if the
processedFileCount equals the incrementalFileCount.  In the scenario
where they are equal and greater than zero, if you were to read the
JSON back in with fromXContent(), the SnapshotStats object would not
be the same as the original since processedFileCount is not parsed
and set.  This change adds a fix and a unit test for this scenario.

Author: JeremyDahlgren

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

@@ -204,10 +204,10 @@ 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();
@@ -282,6 +282,12 @@ public static SnapshotStats fromXContent(XContentParser parser) throws IOExcepti
                 }
             }
         }
+        // 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,
             time,

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

@@ -39,6 +39,26 @@ protected SnapshotStats createTestInstance() {
         );
     }
 
+    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);
+    }
+
     @Override
     protected SnapshotStats doParseInstance(XContentParser parser) throws IOException {
         return SnapshotStats.fromXContent(parser);

test/framework/src/main/java/org/elasticsearch/test/AbstractXContentTestCase.java

@@ -284,9 +284,16 @@ public static <T extends ToXContent> void testFromXContent(
      * both for equality and asserts equality on the two queries.
      */
     public final void testFromXContent() throws IOException {
+        testFromXContent(this::createTestInstance);
+    }
+
+    /**
+     * Generic test that creates a new instance using the given supplier and verifies XContent round trip serialization.
+     */
+    public final void testFromXContent(Supplier<T> testInstanceSupplier) throws IOException {
         testFromXContent(
             NUMBER_OF_TEST_RUNS,
-            this::createTestInstance,
+            testInstanceSupplier,
             supportsUnknownFields(),
             getShuffleFieldsExceptions(),
             getRandomFieldsExcludeFilter(),