Listen for changes in data files and automatically update

bukkit/src/main/java/me/lucko/luckperms/bukkit/LPBukkitPlugin.java

@@ -71,6 +71,7 @@ import me.lucko.luckperms.common.tasks.ExpireTemporaryTask;
 import me.lucko.luckperms.common.tasks.UpdateTask;
 import me.lucko.luckperms.common.treeview.PermissionVault;
 import me.lucko.luckperms.common.utils.BufferedRequest;
+import me.lucko.luckperms.common.utils.FileWatcher;
 import me.lucko.luckperms.common.utils.LoggerImpl;
 
 import org.bukkit.World;
@@ -106,6 +107,7 @@ public class LPBukkitPlugin extends JavaPlugin implements LuckPermsPlugin {
     private GroupManager groupManager;
     private TrackManager trackManager;
     private Storage storage;
+    private FileWatcher fileWatcher = null;
     private InternalMessagingService messagingService = null;
     private UuidCache uuidCache;
     private BukkitListener listener;
@@ -168,6 +170,11 @@ public class LPBukkitPlugin extends JavaPlugin implements LuckPermsPlugin {
         listener = new BukkitListener(this);
         pm.registerEvents(listener, this);
 
+        if (getConfiguration().get(ConfigKeys.WATCH_FILES)) {
+            fileWatcher = new FileWatcher(this);
+            getScheduler().doAsyncRepeating(fileWatcher, 30L);
+        }
+
         // initialise datastore
         storage = StorageFactory.getInstance(this, StorageType.H2);
 
@@ -336,6 +343,10 @@ public class LPBukkitPlugin extends JavaPlugin implements LuckPermsPlugin {
         getLog().info("Closing datastore...");
         storage.shutdown();
 
+        if (fileWatcher != null) {
+            fileWatcher.close();
+        }
+
         if (messagingService != null) {
             getLog().info("Closing messaging service...");
             messagingService.close();
@@ -363,6 +374,7 @@ public class LPBukkitPlugin extends JavaPlugin implements LuckPermsPlugin {
         groupManager = null;
         trackManager = null;
         storage = null;
+        fileWatcher = null;
         messagingService = null;
         uuidCache = null;
         listener = null;

bukkit/src/main/resources/config.yml

@@ -192,6 +192,12 @@ group-name-rewrite:
 # Fill out connection info below if you're using MySQL, PostgreSQL or MongoDB
 storage-method: h2
 
+# When using a file-based storage type, LuckPerms can monitor the data files for changes, and then schedule automatic
+# updates when changes are detected.
+#
+# If you don't want this to happen, set this option to false.
+watch-files: true
+
 # This block enables support for split datastores.
 split-storage:
   enabled: false
@@ -217,9 +223,14 @@ data:
   # This should *not* be set to "lp_" if you have previously ran LuckPerms v2.16.81 or earlier with this database.
   table_prefix: 'luckperms_'
 
-  # Set to -1 to disable. If this is the only instance accessing the datastore, you can disable syncing.
+  # This option controls how frequently LuckPerms will perform a sync task.
-  # e.g. if you're using sqlite or flatfile, this can be set to -1 to save resources.
+  # A sync task will refresh all data from the storage, and ensure that the most up-to-date data is being used by the plugin.
-  sync-minutes: 3
+  #
+  # This is disabled by default, as most users will not need it. However, if you're using a remote storage type
+  # without a messaging service setup, you may wish to set this value to something like 3.
+  #
+  # Set to -1 to disable the task completely.
+  sync-minutes: -1
 
 # Settings for the messaging service
 #

bungee/src/main/java/me/lucko/luckperms/bungee/LPBungeePlugin.java

@@ -64,6 +64,7 @@ import me.lucko.luckperms.common.tasks.ExpireTemporaryTask;
 import me.lucko.luckperms.common.tasks.UpdateTask;
 import me.lucko.luckperms.common.treeview.PermissionVault;
 import me.lucko.luckperms.common.utils.BufferedRequest;
+import me.lucko.luckperms.common.utils.FileWatcher;
 import me.lucko.luckperms.common.utils.LoggerImpl;
 
 import net.md_5.bungee.api.connection.ProxiedPlayer;
@@ -88,6 +89,7 @@ public class LPBungeePlugin extends Plugin implements LuckPermsPlugin {
     private GroupManager groupManager;
     private TrackManager trackManager;
     private Storage storage;
+    private FileWatcher fileWatcher = null;
     private InternalMessagingService messagingService = null;
     private UuidCache uuidCache;
     private ApiProvider apiProvider;
@@ -122,6 +124,11 @@ public class LPBungeePlugin extends Plugin implements LuckPermsPlugin {
         // register events
         getProxy().getPluginManager().registerListener(this, new BungeeListener(this));
 
+        if (getConfiguration().get(ConfigKeys.WATCH_FILES)) {
+            fileWatcher = new FileWatcher(this);
+            getScheduler().doAsyncRepeating(fileWatcher, 30L);
+        }
+
         // initialise datastore
         storage = StorageFactory.getInstance(this, StorageType.H2);
 
@@ -226,6 +233,10 @@ public class LPBungeePlugin extends Plugin implements LuckPermsPlugin {
         getLog().info("Closing datastore...");
         storage.shutdown();
 
+        if (fileWatcher != null) {
+            fileWatcher.close();
+        }
+
         if (messagingService != null) {
             getLog().info("Closing messaging service...");
             messagingService.close();

bungee/src/main/resources/config.yml

@@ -134,6 +134,12 @@ meta-formatting:
 # Fill out connection info below if you're using MySQL, PostgreSQL or MongoDB
 storage-method: h2
 
+# When using a file-based storage type, LuckPerms can monitor the data files for changes, and then schedule automatic
+# updates when changes are detected.
+#
+# If you don't want this to happen, set this option to false.
+watch-files: true
+
 # This block enables support for split datastores.
 split-storage:
   enabled: false
@@ -159,9 +165,14 @@ data:
   # This should *not* be set to "lp_" if you have previously ran LuckPerms v2.16.81 or earlier with this database.
   table_prefix: 'luckperms_'
 
-  # Set to -1 to disable. If this is the only instance accessing the datastore, you can disable syncing.
+  # This option controls how frequently LuckPerms will perform a sync task.
-  # e.g. if you're using sqlite or flatfile, this can be set to -1 to save resources.
+  # A sync task will refresh all data from the storage, and ensure that the most up-to-date data is being used by the plugin.
-  sync-minutes: 3
+  #
+  # This is disabled by default, as most users will not need it. However, if you're using a remote storage type
+  # without a messaging service setup, you may wish to set this value to something like 3.
+  #
+  # Set to -1 to disable the task completely.
+  sync-minutes: -1
 
 # Settings for the messaging service
 #

common/src/main/java/me/lucko/luckperms/common/config/ConfigKeys.java

@@ -51,7 +51,7 @@ import java.util.Map;
 public class ConfigKeys {
 
     public static final ConfigKey<String> SERVER = StringKey.of("server", "global");
-    public static final ConfigKey<Integer> SYNC_TIME = EnduringKey.wrap(IntegerKey.of("data.sync-minutes", 3));
+    public static final ConfigKey<Integer> SYNC_TIME = EnduringKey.wrap(IntegerKey.of("data.sync-minutes", -1));
     public static final ConfigKey<String> DEFAULT_GROUP_NODE = StaticKey.of("group.default"); // constant since 2.6
     public static final ConfigKey<String> DEFAULT_GROUP_NAME = StaticKey.of("default"); // constant since 2.6
     public static final ConfigKey<Boolean> INCLUDING_GLOBAL_PERMS = BooleanKey.of("include-global", true);
@@ -140,6 +140,7 @@ public class ConfigKeys {
     }));
     public static final ConfigKey<String> SQL_TABLE_PREFIX = EnduringKey.wrap(StringKey.of("data.table_prefix", "luckperms_"));
     public static final ConfigKey<String> STORAGE_METHOD = EnduringKey.wrap(StringKey.of("storage-method", "h2"));
+    public static final ConfigKey<Boolean> WATCH_FILES = BooleanKey.of("watch-files", true);
     public static final ConfigKey<Boolean> SPLIT_STORAGE = EnduringKey.wrap(BooleanKey.of("split-storage.enabled", false));
     public static final ConfigKey<Map<String, String>> SPLIT_STORAGE_OPTIONS = EnduringKey.wrap(AbstractKey.of(c -> {
         return ImmutableMap.<String, String>builder()

common/src/main/java/me/lucko/luckperms/common/plugin/LuckPermsPlugin.java

@@ -46,6 +46,7 @@ import me.lucko.luckperms.common.messaging.InternalMessagingService;
 import me.lucko.luckperms.common.storage.Storage;
 import me.lucko.luckperms.common.treeview.PermissionVault;
 import me.lucko.luckperms.common.utils.BufferedRequest;
+import me.lucko.luckperms.common.utils.FileWatcher;
 
 import java.io.File;
 import java.io.InputStream;
@@ -54,6 +55,7 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Set;
 import java.util.UUID;
+import java.util.function.Consumer;
 
 /**
  * Main internal interface for LuckPerms plugins, providing the base for abstraction throughout the project.
@@ -216,6 +218,20 @@ public interface LuckPermsPlugin {
      */
     String getServerVersion();
 
+    /**
+     * Gets the file watcher running on the platform, or null if it's not enabled.
+     *
+     * @return the file watcher, or null
+     */
+    FileWatcher getFileWatcher();
+
+    default void applyToFileWatcher(Consumer<FileWatcher> consumer) {
+        FileWatcher fw = getFileWatcher();
+        if (fw != null) {
+            consumer.accept(fw);
+        }
+    }
+
     /**
      * Gets the plugins main data storage directory
      *

common/src/main/java/me/lucko/luckperms/common/storage/backing/FlatfileBacking.java

@@ -23,7 +23,9 @@
 package me.lucko.luckperms.common.storage.backing;
 
 import me.lucko.luckperms.api.LogEntry;
+import me.lucko.luckperms.common.commands.utils.Util;
 import me.lucko.luckperms.common.constants.Constants;
+import me.lucko.luckperms.common.core.model.User;
 import me.lucko.luckperms.common.data.Log;
 import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
 
@@ -49,23 +51,27 @@ abstract class FlatfileBacking extends AbstractBacking {
     private static final String LOG_FORMAT = "%s(%s): [%s] %s(%s) --> %s";
 
     private final Logger actionLogger = Logger.getLogger("lp_actions");
+    private Map<String, String> uuidCache = new ConcurrentHashMap<>();
+
     private final File pluginDir;
+    private final String fileExtension;
+
+    private File uuidData;
+    private File actionLog;
     File usersDir;
     File groupsDir;
     File tracksDir;
-    private Map<String, String> uuidCache = new ConcurrentHashMap<>();
-    private File uuidData;
-    private File actionLog;
 
-    FlatfileBacking(LuckPermsPlugin plugin, String name, File pluginDir) {
+    FlatfileBacking(LuckPermsPlugin plugin, String name, File pluginDir, String fileExtension) {
         super(plugin, name);
         this.pluginDir = pluginDir;
+        this.fileExtension = fileExtension;
     }
 
     @Override
     public void init() {
         try {
-            makeFiles();
+            setupFiles();
         } catch (IOException e) {
             e.printStackTrace();
             return;
@@ -93,7 +99,7 @@ abstract class FlatfileBacking extends AbstractBacking {
         setAcceptingLogins(true);
     }
 
-    private void makeFiles() throws IOException {
+    private void setupFiles() throws IOException {
         File data = new File(pluginDir, "data");
         data.mkdirs();
 
@@ -111,6 +117,45 @@ abstract class FlatfileBacking extends AbstractBacking {
 
         actionLog = new File(data, "actions.log");
         actionLog.createNewFile();
+
+        // Listen for file changes.
+        plugin.applyToFileWatcher(watcher -> {
+            watcher.subscribe("users", usersDir.toPath(), s -> {
+                if (!s.endsWith(fileExtension)) {
+                    return;
+                }
+
+                String user = s.substring(0, s.length() - fileExtension.length());
+                UUID uuid = Util.parseUuid(user);
+                if (uuid == null) {
+                    return;
+                }
+
+                User u = plugin.getUserManager().get(uuid);
+                if (u != null) {
+                    plugin.getLog().info("[FileWatcher] Refreshing user " + u.getName());
+                    plugin.getStorage().loadUser(uuid, "null");
+                }
+            });
+            watcher.subscribe("groups", groupsDir.toPath(), s -> {
+                if (!s.endsWith(fileExtension)) {
+                    return;
+                }
+
+                String groupName = s.substring(0, s.length() - fileExtension.length());
+                plugin.getLog().info("[FileWatcher] Refreshing group " + groupName);
+                plugin.getUpdateTaskBuffer().request();
+            });
+            watcher.subscribe("tracks", tracksDir.toPath(), s -> {
+                if (!s.endsWith(fileExtension)) {
+                    return;
+                }
+
+                String trackName = s.substring(0, s.length() - fileExtension.length());
+                plugin.getLog().info("[FileWatcher] Refreshing track " + trackName);
+                plugin.getStorage().loadAllTracks();
+            });
+        });
     }
 
     @Override
@@ -118,6 +163,10 @@ abstract class FlatfileBacking extends AbstractBacking {
         saveUUIDCache(uuidCache);
     }
 
+    protected void registerFileAction(String type, File file) {
+        plugin.applyToFileWatcher(fileWatcher -> fileWatcher.registerChange(type, file.getName()));
+    }
+
     @Override
     public boolean logAction(LogEntry entry) {
         actionLogger.info(String.format(LOG_FORMAT,

common/src/main/java/me/lucko/luckperms/common/storage/backing/JSONBacking.java

@@ -70,7 +70,7 @@ public class JSONBacking extends FlatfileBacking {
     }
 
     public JSONBacking(LuckPermsPlugin plugin, File pluginDir) {
-        super(plugin, "JSON", pluginDir);
+        super(plugin, "JSON", pluginDir, ".json");
     }
 
     private boolean fileToWriter(File file, ThrowingFunction<JsonWriter, Boolean> writeOperation) {
@@ -108,6 +108,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File userFile = new File(usersDir, uuid.toString() + ".json");
+                registerFileAction("users", userFile);
+
                 if (userFile.exists()) {
                     return fileToReader(userFile, reader -> {
                         reader.beginObject();
@@ -178,6 +180,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File userFile = new File(usersDir, user.getUuid().toString() + ".json");
+                registerFileAction("users", userFile);
+
                 if (!GenericUserManager.shouldSave(user)) {
                     if (userFile.exists()) {
                         userFile.delete();
@@ -221,6 +225,8 @@ public class JSONBacking extends FlatfileBacking {
             if (files == null) return false;
 
             for (File file : files) {
+                registerFileAction("users", file);
+
                 Map<String, Boolean> nodes = new HashMap<>();
                 fileToReader(file, reader -> {
                     reader.beginObject();
@@ -277,6 +283,8 @@ public class JSONBacking extends FlatfileBacking {
             if (files == null) return false;
 
             for (File file : files) {
+                registerFileAction("users", file);
+
                 UUID holder = UUID.fromString(file.getName().substring(0, file.getName().length() - 5));
                 Map<String, Boolean> nodes = new HashMap<>();
                 fileToReader(file, reader -> {
@@ -321,6 +329,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, name + ".json");
+                registerFileAction("groups", groupFile);
+
                 if (groupFile.exists()) {
                     return fileToReader(groupFile, reader -> {
                         reader.beginObject();
@@ -374,6 +384,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, name + ".json");
+                registerFileAction("groups", groupFile);
+
                 return groupFile.exists() && fileToReader(groupFile, reader -> {
                     reader.beginObject();
                     reader.nextName(); // name record
@@ -420,6 +432,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, group.getName() + ".json");
+                registerFileAction("groups", groupFile);
+
                 if (!groupFile.exists()) {
                     try {
                         groupFile.createNewFile();
@@ -453,6 +467,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, group.getName() + ".json");
+                registerFileAction("groups", groupFile);
+
                 if (groupFile.exists()) {
                     groupFile.delete();
                 }
@@ -471,6 +487,8 @@ public class JSONBacking extends FlatfileBacking {
             if (files == null) return false;
 
             for (File file : files) {
+                registerFileAction("groups", file);
+
                 String holder = file.getName().substring(0, file.getName().length() - 5);
                 Map<String, Boolean> nodes = new HashMap<>();
                 fileToReader(file, reader -> {
@@ -511,6 +529,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, name + ".json");
+                registerFileAction("tracks", trackFile);
+
                 if (trackFile.exists()) {
                     return fileToReader(trackFile, reader -> {
                         reader.beginObject();
@@ -561,6 +581,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, name + ".json");
+                registerFileAction("tracks", trackFile);
+
                 return trackFile.exists() && fileToReader(trackFile, reader -> {
                     reader.beginObject();
                     reader.nextName(); // name record
@@ -606,6 +628,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, track.getName() + ".json");
+                registerFileAction("tracks", trackFile);
+
                 if (!trackFile.exists()) {
                     try {
                         trackFile.createNewFile();
@@ -639,6 +663,8 @@ public class JSONBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, track.getName() + ".json");
+                registerFileAction("tracks", trackFile);
+
                 if (trackFile.exists()) {
                     trackFile.delete();
                 }

common/src/main/java/me/lucko/luckperms/common/storage/backing/YAMLBacking.java

@@ -77,7 +77,7 @@ public class YAMLBacking extends FlatfileBacking {
     }
 
     public YAMLBacking(LuckPermsPlugin plugin, File pluginDir) {
-        super(plugin, "YAML", pluginDir);
+        super(plugin, "YAML", pluginDir, ".yml");
     }
 
     private boolean writeMapToFile(File file, Map<String, Object> values) {
@@ -110,6 +110,7 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File userFile = new File(usersDir, uuid.toString() + ".yml");
+                registerFileAction("users", userFile);
                 if (userFile.exists()) {
                     return readMapFromFile(userFile, values -> {
                         // User exists, let's load.
@@ -159,6 +160,7 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File userFile = new File(usersDir, user.getUuid().toString() + ".yml");
+                registerFileAction("users", userFile);
                 if (!GenericUserManager.shouldSave(user)) {
                     if (userFile.exists()) {
                         userFile.delete();
@@ -194,6 +196,7 @@ public class YAMLBacking extends FlatfileBacking {
             if (files == null) return false;
 
             for (File file : files) {
+                registerFileAction("users", file);
                 Map<String, Boolean> nodes = new HashMap<>();
                 readMapFromFile(file, values -> {
                     Map<String, Boolean> perms = (Map<String, Boolean>) values.get("perms");
@@ -235,6 +238,8 @@ public class YAMLBacking extends FlatfileBacking {
             if (files == null) return false;
 
             for (File file : files) {
+                registerFileAction("users", file);
+
                 UUID holder = UUID.fromString(file.getName().substring(0, file.getName().length() - 4));
                 Map<String, Boolean> nodes = new HashMap<>();
                 readMapFromFile(file, values -> {
@@ -264,6 +269,7 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, name + ".yml");
+                registerFileAction("groups", groupFile);
                 if (groupFile.exists()) {
                     return readMapFromFile(groupFile, values -> {
                         Map<String, Boolean> perms = (Map<String, Boolean>) values.get("perms");
@@ -296,6 +302,7 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, name + ".yml");
+                registerFileAction("groups", groupFile);
                 return groupFile.exists() && readMapFromFile(groupFile, values -> {
                     Map<String, Boolean> perms = (Map<String, Boolean>) values.get("perms");
                     group.setNodes(perms);
@@ -331,6 +338,7 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, group.getName() + ".yml");
+                registerFileAction("groups", groupFile);
                 if (!groupFile.exists()) {
                     try {
                         groupFile.createNewFile();
@@ -356,6 +364,7 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File groupFile = new File(groupsDir, group.getName() + ".yml");
+                registerFileAction("groups", groupFile);
                 if (groupFile.exists()) {
                     groupFile.delete();
                 }
@@ -374,6 +383,8 @@ public class YAMLBacking extends FlatfileBacking {
             if (files == null) return false;
 
             for (File file : files) {
+                registerFileAction("groups", file);
+
                 String holder = file.getName().substring(0, file.getName().length() - 4);
                 Map<String, Boolean> nodes = new HashMap<>();
                 readMapFromFile(file, values -> {
@@ -403,6 +414,8 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, name + ".yml");
+                registerFileAction("tracks", trackFile);
+
                 if (trackFile.exists()) {
                     return readMapFromFile(trackFile, values -> {
                         track.setGroups((List<String>) values.get("groups"));
@@ -435,6 +448,8 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, name + ".yml");
+                registerFileAction("tracks", trackFile);
+
                 return trackFile.exists() && readMapFromFile(trackFile, values -> {
                     track.setGroups((List<String>) values.get("groups"));
                     return true;
@@ -468,6 +483,8 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, track.getName() + ".yml");
+                registerFileAction("tracks", trackFile);
+
                 if (!trackFile.exists()) {
                     try {
                         trackFile.createNewFile();
@@ -493,6 +510,8 @@ public class YAMLBacking extends FlatfileBacking {
         try {
             return call(() -> {
                 File trackFile = new File(tracksDir, track.getName() + ".yml");
+                registerFileAction("tracks", trackFile);
+
                 if (trackFile.exists()) {
                     trackFile.delete();
                 }

common/src/main/java/me/lucko/luckperms/common/utils/FileWatcher.java

@@ -0,0 +1,151 @@
+/*
+ * Copyright (c) 2016 Lucko (Luck) <luck@lucko.me>
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining a copy
+ *  of this software and associated documentation files (the "Software"), to deal
+ *  in the Software without restriction, including without limitation the rights
+ *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *  copies of the Software, and to permit persons to whom the Software is
+ *  furnished to do so, subject to the following conditions:
+ *
+ *  The above copyright notice and this permission notice shall be included in all
+ *  copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ *  SOFTWARE.
+ */
+
+package me.lucko.luckperms.common.utils;
+
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.nio.file.StandardWatchEventKinds;
+import java.nio.file.WatchEvent;
+import java.nio.file.WatchKey;
+import java.nio.file.WatchService;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Consumer;
+
+public class FileWatcher implements Runnable {
+    private final LuckPermsPlugin plugin;
+
+    private final Map<String, WatchedLocation> keyMap;
+    private final Map<String, Long> internalChanges;
+    private WatchService watchService = null;
+
+    public FileWatcher(LuckPermsPlugin plugin) {
+        this.plugin = plugin;
+        this.keyMap = Collections.synchronizedMap(new HashMap<>());
+        this.internalChanges = Collections.synchronizedMap(new HashMap<>());
+        try {
+            this.watchService = plugin.getDataDirectory().toPath().getFileSystem().newWatchService();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public void subscribe(String id, Path path, Consumer<String> consumer) {
+        if (watchService == null) {
+            return;
+        }
+
+        // Register with a delay to ignore changes made at startup
+        plugin.getScheduler().doAsyncLater(() -> {
+            try {
+                // doesn't need to be atomic
+                if (keyMap.containsKey(id)) {
+                    throw new IllegalArgumentException("id already registered");
+                }
+
+                WatchKey key = path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);
+                keyMap.put(id, new WatchedLocation(path, key, consumer));
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        }, 40L);
+    }
+
+    public void registerChange(String id, String filename) {
+        internalChanges.put(id + "/" + filename, System.currentTimeMillis());
+    }
+
+    public void close() {
+        if (watchService == null) {
+            return;
+        }
+
+        try {
+            watchService.close();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    @Override
+    public void run() {
+        long expireTime = System.currentTimeMillis() - TimeUnit.SECONDS.toMillis(4);
+        // was either processed last time, or recently modified by the system.
+        internalChanges.values().removeIf(lastChange -> lastChange < expireTime);
+
+        List<String> expired = new ArrayList<>();
+
+        for (Map.Entry<String, WatchedLocation> ent : keyMap.entrySet()) {
+            String id = ent.getKey();
+            Path path = ent.getValue().getPath();
+            WatchKey key = ent.getValue().getKey();
+
+            List<WatchEvent<?>> watchEvents = key.pollEvents();
+
+            for (WatchEvent<?> event : watchEvents) {
+                Path name = (Path) event.context();
+                Path file = path.resolve(name);
+
+                String fileName = name.toString();
+
+                if (internalChanges.containsKey(id + "/" + fileName)) {
+                    // This file was modified by the system.
+                    continue;
+                }
+
+                registerChange(id, fileName);
+
+                plugin.getLog().info("[FileWatcher] Detected change in file: " + file.toString());
+
+                // Process the change
+                ent.getValue().getFileConsumer().accept(fileName);
+            }
+
+            boolean valid = key.reset();
+            if (!valid) {
+                new RuntimeException("WatchKey no longer valid: " + key.toString()).printStackTrace();
+                expired.add(id);
+            }
+        }
+
+        expired.forEach(keyMap::remove);
+    }
+
+    @Getter
+    @RequiredArgsConstructor
+    private static class WatchedLocation {
+        private final Path path;
+        private final WatchKey key;
+        private final Consumer<String> fileConsumer;
+    }
+
+}

sponge/src/main/java/me/lucko/luckperms/sponge/LPSpongePlugin.java

@@ -62,6 +62,7 @@ import me.lucko.luckperms.common.tasks.ExpireTemporaryTask;
 import me.lucko.luckperms.common.tasks.UpdateTask;
 import me.lucko.luckperms.common.treeview.PermissionVault;
 import me.lucko.luckperms.common.utils.BufferedRequest;
+import me.lucko.luckperms.common.utils.FileWatcher;
 import me.lucko.luckperms.common.utils.LoggerImpl;
 import me.lucko.luckperms.sponge.commands.SpongeMainCommand;
 import me.lucko.luckperms.sponge.contexts.WorldCalculator;
@@ -146,6 +147,7 @@ public class LPSpongePlugin implements LuckPermsPlugin {
     private SpongeGroupManager groupManager;
     private TrackManager trackManager;
     private Storage storage;
+    private FileWatcher fileWatcher = null;
     private InternalMessagingService messagingService = null;
     private UuidCache uuidCache;
     private ApiProvider apiProvider;
@@ -183,6 +185,11 @@ public class LPSpongePlugin implements LuckPermsPlugin {
         // register events
         game.getEventManager().registerListeners(this, new SpongeListener(this));
 
+        if (getConfiguration().get(ConfigKeys.WATCH_FILES)) {
+            fileWatcher = new FileWatcher(this);
+            getScheduler().doAsyncRepeating(fileWatcher, 30L);
+        }
+
         // initialise datastore
         storage = StorageFactory.getInstance(this, StorageType.H2);
 
@@ -309,6 +316,10 @@ public class LPSpongePlugin implements LuckPermsPlugin {
         getLog().info("Closing datastore...");
         storage.shutdown();
 
+        if (fileWatcher != null) {
+            fileWatcher.close();
+        }
+
         if (messagingService != null) {
             getLog().info("Closing messaging service...");
             messagingService.close();

sponge/src/main/resources/luckperms.conf

@@ -138,6 +138,12 @@ meta-formatting {
 # Fill out connection info below if you're using MySQL, PostgreSQL or MongoDB
 storage-method="h2"
 
+# When using a file-based storage type, LuckPerms can monitor the data files for changes, and then schedule automatic
+# updates when changes are detected.
+#
+# If you don't want this to happen, set this option to false.
+watch-files=true
+
 # This block enables support for split datastores.
 split-storage {
   enabled=false
@@ -165,9 +171,14 @@ data {
   # This should *not* be set to "lp_" if you have previously ran LuckPerms v2.16.81 or earlier with this database.
   table_prefix="luckperms_"
 
-  # Set to -1 to disable. If this is the only instance accessing the datastore, you can disable syncing.
+  # This option controls how frequently LuckPerms will perform a sync task.
-  # e.g. if you're using sqlite or flatfile, this can be set to -1 to save resources.
+  # A sync task will refresh all data from the storage, and ensure that the most up-to-date data is being used by the plugin.
-  sync-minutes=3
+  #
+  # This is disabled by default, as most users will not need it. However, if you're using a remote storage type
+  # without a messaging service setup, you may wish to set this value to something like 3.
+  #
+  # Set to -1 to disable the task completely.
+  sync-minutes=-1
 }
 
 # Settings for the messaging service