test: Add unit tests for internal vs user ignore settings separation

Add tests to verify that internal ignore patterns can filter protected

settings while user ignore patterns respect protection. Also optimize

the predicate to use Set.contains() instead of iteration.

Signed-off-by: Piyush Kumar <piykumab@amazon.com>

Author: Piyush Kumar

server/src/main/java/org/opensearch/snapshots/RestoreService.java

@@ -173,6 +173,78 @@ public class RestoreService implements ClusterStateApplier {
         USER_UNREMOVABLE_SETTINGS = unmodifiableSet(unremovable);
     }
 
+    /**
+     * Creates a settings filter predicate that separates internal ignore patterns from user ignore patterns.
+     * Internal ignore patterns override protection and can filter any setting.
+     * User ignore patterns respect protected settings and cannot filter them.
+     *
+     * @param userIgnoreSettings array of user-provided settings to ignore
+     * @param internalIgnoreSettings array of internal settings to ignore (override protection)
+     * @param protectedSettings set of settings that user cannot remove
+     * @return a predicate that returns true if the setting should be kept, false if it should be filtered out
+     */
+    static Predicate<String> createSettingsFilterPredicate(
+        String[] userIgnoreSettings,
+        String[] internalIgnoreSettings,
+        Set<String> protectedSettings
+    ) {
+        Set<String> userKeyFilters = new HashSet<>();
+        List<String> userSimpleMatchPatterns = new ArrayList<>();
+        Set<String> internalKeyFilters = new HashSet<>();
+        List<String> internalSimpleMatchPatterns = new ArrayList<>();
+
+        // Process user ignore settings
+        for (String ignoredSetting : userIgnoreSettings) {
+            if (!Regex.isSimpleMatchPattern(ignoredSetting)) {
+                userKeyFilters.add(ignoredSetting);
+            } else {
+                userSimpleMatchPatterns.add(ignoredSetting);
+            }
+        }
+
+        // Process internal ignore settings
+        for (String ignoredSetting : internalIgnoreSettings) {
+            if (!Regex.isSimpleMatchPattern(ignoredSetting)) {
+                internalKeyFilters.add(ignoredSetting);
+            } else {
+                internalSimpleMatchPatterns.add(ignoredSetting);
+            }
+        }
+
+        return k -> {
+            // Check internal ignore patterns first (they override protection)
+            if (internalKeyFilters.contains(k)) {
+                return false;
+            }
+            for (String pattern : internalSimpleMatchPatterns) {
+                if (Regex.simpleMatch(pattern, k)) {
+                    return false;
+                }
+            }
+
+            // Check user ignore patterns only for non-protected settings
+            if (!protectedSettings.contains(k)) {
+                if (userKeyFilters.contains(k)) {
+                    return false;
+                }
+                for (String pattern : userSimpleMatchPatterns) {
+                    if (Regex.simpleMatch(pattern, k)) {
+                        return false;
+                    }
+                }
+            }
+            return true;
+        };
+    }
+
+    /**
+     * Returns the set of settings that users cannot remove during restore.
+     * Exposed for testing purposes.
+     */
+    static Set<String> getUserUnremovableSettings() {
+        return USER_UNREMOVABLE_SETTINGS;
+    }
+
     private final ClusterService clusterService;
 
     private final RepositoriesService repositoriesService;
@@ -818,10 +890,6 @@ private IndexMetadata updateIndexSettings(
                         }
                         IndexMetadata.Builder builder = IndexMetadata.builder(indexMetadata);
                         Settings settings = indexMetadata.getSettings();
-                        Set<String> keyFilters = new HashSet<>();
-                        List<String> simpleMatchPatterns = new ArrayList<>();
-                        Set<String> internalKeyFilters = new HashSet<>();
-                        List<String> internalSimpleMatchPatterns = new ArrayList<>();
 
                         for (String ignoredSetting : ignoreSettings) {
                             if (!Regex.isSimpleMatchPattern(ignoredSetting)) {
@@ -835,51 +903,24 @@ private IndexMetadata updateIndexSettings(
                                         snapshot,
                                         "cannot remove UnmodifiableOnRestore setting [" + ignoredSetting + "] on restore"
                                     );
-                                } else {
-                                    keyFilters.add(ignoredSetting);
                                 }
-                            } else {
-                                simpleMatchPatterns.add(ignoredSetting);
                             }
                         }
 
-                        // add internal settings to separate ignore lists
-                        for (String ignoredSetting : ignoreSettingsInternal) {
-                            if (!Regex.isSimpleMatchPattern(ignoredSetting)) {
-                                internalKeyFilters.add(ignoredSetting);
-                            } else {
-                                internalSimpleMatchPatterns.add(ignoredSetting);
+                        // Build combined protected settings set including dynamic unmodifiable settings
+                        Set<String> protectedSettings = new HashSet<>(USER_UNREMOVABLE_SETTINGS);
+                        for (String key : settings.keySet()) {
+                            if (indexScopedSettings.isUnmodifiableOnRestoreSetting(key)) {
+                                protectedSettings.add(key);
                             }
                         }
 
-                        Predicate<String> settingsFilter = k -> {
-                            // Check internal ignore patterns first (they override protection)
-                            for (String filterKey : internalKeyFilters) {
-                                if (k.equals(filterKey)) {
-                                    return false;
-                                }
-                            }
-                            for (String pattern : internalSimpleMatchPatterns) {
-                                if (Regex.simpleMatch(pattern, k)) {
-                                    return false;
-                                }
-                            }
+                        Predicate<String> settingsFilter = createSettingsFilterPredicate(
+                            ignoreSettings,
+                            ignoreSettingsInternal,
+                            protectedSettings
+                        );
 
-                            // Check user ignore patterns only for non-protected settings
-                            if (USER_UNREMOVABLE_SETTINGS.contains(k) == false && !indexScopedSettings.isUnmodifiableOnRestoreSetting(k)) {
-                                for (String filterKey : keyFilters) {
-                                    if (k.equals(filterKey)) {
-                                        return false;
-                                    }
-                                }
-                                for (String pattern : simpleMatchPatterns) {
-                                    if (Regex.simpleMatch(pattern, k)) {
-                                        return false;
-                                    }
-                                }
-                            }
-                            return true;
-                        };
                         Settings.Builder settingsBuilder = Settings.builder()
                             .put(settings.filter(settingsFilter))
                             .put(normalizedChangeSettings.filter(k -> {

server/src/test/java/org/opensearch/snapshots/RestoreServiceTests.java

@@ -159,4 +159,36 @@ public void testValidateReplicationTypeRestoreSettings_WhenSnapshotIsSegment_Res
             () -> RestoreService.validateReplicationTypeRestoreSettings(snapshot, ReplicationType.SEGMENT.toString(), indexMetadata)
         );
     }
+
+    // Tests for internal vs user ignore settings filter separation (PR #20494)
+
+    public void testInternalIgnoreOverridesProtection() {
+        var filter = RestoreService.createSettingsFilterPredicate(
+            new String[] {},
+            new String[] { "index.remote_store.*" },
+            RestoreService.getUserUnremovableSettings()
+        );
+        // Internal pattern can filter protected settings
+        assertFalse(filter.test("index.remote_store.enabled"));
+    }
+
+    public void testUserIgnoreRespectsProtection() {
+        var filter = RestoreService.createSettingsFilterPredicate(
+            new String[] { "index.number_of_replicas" },
+            new String[] {},
+            RestoreService.getUserUnremovableSettings()
+        );
+        // User cannot filter protected settings
+        assertTrue(filter.test("index.number_of_replicas"));
+    }
+
+    public void testUserIgnoreWorksForNonProtected() {
+        var filter = RestoreService.createSettingsFilterPredicate(
+            new String[] { "index.custom.*" },
+            new String[] {},
+            RestoreService.getUserUnremovableSettings()
+        );
+        // User can filter non-protected settings
+        assertFalse(filter.test("index.custom.setting"));
+    }
 }