feat: improve data syncing with checkin petitions

This improves data fetching speed in cases where a user logs out during sync application; when they log back in, the server will petition the server they are checked out on to check them out.

We also now unlock users after saving sync on a server to accommodate this, and track user disconnection status to avoid inconsistencies with what platforms return for `isOnline`

bukkit/src/main/java/net/william278/husksync/BukkitHuskSync.java

@@ -99,6 +99,7 @@ public class BukkitHuskSync extends JavaPlugin implements HuskSync, BukkitTask.S
     private final Map<Integer, MapView> mapViews = Maps.newConcurrentMap();
     private final List<Migrator> availableMigrators = Lists.newArrayList();
     private final Set<UUID> lockedPlayers = Sets.newConcurrentHashSet();
+    private final Set<UUID> disconnectingPlayers = Sets.newConcurrentHashSet();
 
     private boolean disabling;
     private Gson gson;

bukkit/src/main/java/net/william278/husksync/data/BukkitUserDataHolder.java

@@ -31,7 +31,11 @@ public interface BukkitUserDataHolder extends UserDataHolder {
 
     @Override
     default Optional<? extends Data> getData(@NotNull Identifier id) {
-        if (!id.isCustom()) {
+        if (id.isCustom()) {
+            return Optional.ofNullable(getCustomDataStore().get(id));
+        }
+
+        try {
             return switch (id.getKeyValue()) {
                 case "inventory" -> getInventory();
                 case "ender_chest" -> getEnderChest();
@@ -48,8 +52,10 @@ public interface BukkitUserDataHolder extends UserDataHolder {
                 case "persistent_data" -> getPersistentData();
                 default -> throw new IllegalStateException(String.format("Unexpected data type: %s", id));
             };
+        } catch (Throwable e) {
+            getPlugin().debug("Failed to get data for key: " + id.asMinimalString(), e);
+            return Optional.empty();
         }
-        return Optional.ofNullable(getCustomDataStore().get(id));
     }
 
     @Override

bukkit/src/main/java/net/william278/husksync/listener/PaperEventListener.java

@@ -44,6 +44,7 @@ public class PaperEventListener extends BukkitEventListener {
     }
 
     @Override
+    @SuppressWarnings("RedundantMethodOverride")
     public void onEnable() {
         getPlugin().getServer().getPluginManager().registerEvents(this, getPlugin());
         lockedHandler.onEnable();

bukkit/src/main/java/net/william278/husksync/user/BukkitUser.java

@@ -57,8 +57,9 @@ public class BukkitUser extends OnlineUser implements BukkitUserDataHolder {
     }
 
     @Override
-    public boolean isOffline() {
+    public boolean hasDisconnected() {
-        return player == null || !player.isOnline();
+        return getPlugin().getDisconnectingPlayers().contains(getUuid())
+                || player == null || !player.isOnline();
     }
 
     @Override

common/src/main/java/net/william278/husksync/HuskSync.java

@@ -20,6 +20,7 @@
 package net.william278.husksync;
 
 import com.fatboyindustrial.gsonjavatime.Converters;
+import com.google.common.collect.Maps;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import net.kyori.adventure.audience.Audience;
@@ -140,7 +141,7 @@ public interface HuskSync extends Task.Supplier, EventDispatcher, ConfigProvider
         if (getPlayerCustomDataStore().containsKey(user.getUuid())) {
             return getPlayerCustomDataStore().get(user.getUuid());
         }
-        final Map<Identifier, Data> data = new HashMap<>();
+        final Map<Identifier, Data> data = Maps.newHashMap();
         getPlayerCustomDataStore().put(user.getUuid(), data);
         return data;
     }
@@ -315,6 +316,12 @@ public interface HuskSync extends Task.Supplier, EventDispatcher, ConfigProvider
     @NotNull
     Set<UUID> getLockedPlayers();
 
+    /**
+     * Get the set of UUIDs of players who are currently marked as disconnecting or disconnected
+     */
+    @NotNull
+    Set<UUID> getDisconnectingPlayers();
+
     default boolean isLocked(@NotNull UUID uuid) {
         return getLockedPlayers().contains(uuid);
     }

common/src/main/java/net/william278/husksync/data/Identifier.java

@@ -22,6 +22,7 @@ package net.william278.husksync.data;
 import lombok.*;
 import net.kyori.adventure.key.InvalidKeyException;
 import net.kyori.adventure.key.Key;
+import net.kyori.adventure.key.KeyPattern;
 import org.intellij.lang.annotations.Subst;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
@@ -39,6 +40,9 @@ import java.util.stream.Stream;
 @Getter
 public class Identifier {
 
+    // Namespace for built-in identifiers
+    private static final @KeyPattern String DEFAULT_NAMESPACE = "husksync";
+
     // Built-in identifiers
     public static final Identifier PERSISTENT_DATA = huskSync("persistent_data", true);
     public static final Identifier INVENTORY = huskSync("inventory", true);
@@ -93,8 +97,8 @@ public class Identifier {
      */
     @NotNull
     public static Identifier from(@NotNull Key key, @NotNull Set<Dependency> dependencies) {
-        if (key.namespace().equals("husksync")) {
+        if (key.namespace().equals(DEFAULT_NAMESPACE)) {
-            throw new IllegalArgumentException("You cannot register a key with \"husksync\" as the namespace!");
+            throw new IllegalArgumentException("Cannot register with %s as key namespace!".formatted(key.namespace()));
         }
         return new Identifier(key, true, dependencies);
     }
@@ -143,7 +147,7 @@ public class Identifier {
     @NotNull
     private static Identifier huskSync(@Subst("null") @NotNull String name,
                                        boolean configDefault) throws InvalidKeyException {
-        return new Identifier(Key.key("husksync", name), configDefault, Collections.emptySet());
+        return new Identifier(Key.key(DEFAULT_NAMESPACE, name), configDefault, Collections.emptySet());
     }
 
     // Return an identifier with a HuskSync namespace
@@ -151,7 +155,7 @@ public class Identifier {
     private static Identifier huskSync(@Subst("null") @NotNull String name,
                                        @SuppressWarnings("SameParameterValue") boolean configDefault,
                                        @NotNull Dependency... dependents) throws InvalidKeyException {
-        return new Identifier(Key.key("husksync", name), configDefault, Set.of(dependents));
+        return new Identifier(Key.key(DEFAULT_NAMESPACE, name), configDefault, Set.of(dependents));
     }
 
     /**
@@ -209,13 +213,30 @@ public class Identifier {
      * @return {@code false} if {@link #getKeyNamespace()} returns "husksync"; {@code true} otherwise
      */
     public boolean isCustom() {
-        return !getKeyNamespace().equals("husksync");
+        return !getKeyNamespace().equals(DEFAULT_NAMESPACE);
+    }
+
+    /**
+     * Get the minimal string representation of this key.
+     * <p>
+     * If the namespace of the key is {@link #DEFAULT_NAMESPACE}, only the key value will be returned.
+     *
+     * @return the minimal string key representation
+     * @since 3.8
+     */
+    @NotNull
+    public String asMinimalString() {
+        if (getKey().namespace().equals(DEFAULT_NAMESPACE)) {
+            return getKey().value();
+        }
+        return getKey().asString();
     }
 
     /**
      * Returns the identifier as a string (the key)
      *
      * @return the identifier as a string
+     * @since 3.0
      */
     @NotNull
     @Override
@@ -224,19 +245,29 @@ public class Identifier {
     }
 
     /**
-     * Returns {@code true} if the given object is an identifier with the same key as this identifier
+     * Return whether this Identifier is equal to another Identifier
      *
-     * @param obj the object to compare
+     * @param obj another object
-     * @return {@code true} if the given object is an identifier with the same key as this identifier
+     * @return {@code true} if this identifier matches the identifier of {@code obj}
+     * @since 3.8
      */
     @Override
     public boolean equals(@Nullable Object obj) {
-        return obj instanceof Identifier other ? toString().equals(other.toString()) : super.equals(obj);
+        if (obj instanceof Identifier other) {
+            return asMinimalString().equals(other.asMinimalString());
+        }
+        return false;
     }
 
+    /**
+     * Get the hash code of the Identifier (equivalent to {@link #asMinimalString()}->{@code #hashCode()}
+     *
+     * @return the hash code
+     * @since 3.8
+     */
     @Override
     public int hashCode() {
-        return key.toString().hashCode();
+        return asMinimalString().hashCode();
     }
 
     // Get the config entry for the identifier

common/src/main/java/net/william278/husksync/data/UserDataHolder.java

@@ -75,6 +75,15 @@ public interface UserDataHolder extends DataHolder {
         return DataSnapshot.builder(getPlugin()).data(this.getData()).saveCause(saveCause).buildAndPack();
     }
 
+    /**
+     * Returns whether data can be applied to the holder at this time
+     *
+     * @return {@code true} if data can be applied, otherwise false
+     */
+    default boolean cannotApplySnapshot() {
+        return false;
+    }
+
     /**
      * Deserialize and apply a data snapshot to this data owner
      * <p>
@@ -90,9 +99,12 @@ public interface UserDataHolder extends DataHolder {
      * @since 3.0
      */
     default void applySnapshot(@NotNull DataSnapshot.Packed snapshot, @NotNull ThrowingConsumer<Boolean> runAfter) {
-        final HuskSync plugin = getPlugin();
+        if (cannotApplySnapshot()) {
+            return;
+        }
 
         // Unpack the snapshot
+        final HuskSync plugin = getPlugin();
         final DataSnapshot.Unpacked unpacked;
         try {
             unpacked = snapshot.unpack(plugin);
@@ -104,6 +116,10 @@ public interface UserDataHolder extends DataHolder {
 
         // Synchronously attempt to apply the snapshot
         plugin.runSync(() -> {
+            if (cannotApplySnapshot()) {
+                return;
+            }
+
             try {
                 for (Map.Entry<Identifier, Data> entry : unpacked.getData().entrySet()) {
                     final Identifier identifier = entry.getKey();

common/src/main/java/net/william278/husksync/listener/EventListener.java

@@ -25,9 +25,7 @@ import net.william278.husksync.data.DataSnapshot;
 import net.william278.husksync.user.OnlineUser;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.Arrays;
+import java.util.*;
-import java.util.List;
-import java.util.Map;
 
 import static net.william278.husksync.config.Settings.SynchronizationSettings.SaveOnDeathSettings;
 
@@ -49,6 +47,7 @@ public abstract class EventListener {
      * @param user The {@link OnlineUser} to handle
      */
     protected final void handlePlayerJoin(@NotNull OnlineUser user) {
+        plugin.getDisconnectingPlayers().remove(user.getUuid());
         if (user.isNpc()) {
             return;
         }
@@ -62,12 +61,18 @@ public abstract class EventListener {
      * @param user The {@link OnlineUser} to handle
      */
     protected final void handlePlayerQuit(@NotNull OnlineUser user) {
-        if (user.isNpc() || plugin.isDisabling() || plugin.isLocked(user.getUuid())) {
+        // Check the user is a user, the plugin isn't disabling, then mark as disconnecting
+        if (user.isNpc() || plugin.isDisabling()) {
             return;
         }
+        plugin.getDisconnectingPlayers().add(user.getUuid());
+
+        // Lock, then save their data if the user is unlocked
+        if (!plugin.isLocked(user.getUuid())) {
             plugin.lockPlayer(user.getUuid());
             plugin.getDataSyncer().syncSaveUserData(user);
         }
+    }
 
     /**
      * Handles the saving of data when the world save event is fired
@@ -79,7 +84,7 @@ public abstract class EventListener {
             return;
         }
         usersInWorld.stream()
-                .filter(user -> !plugin.isLocked(user.getUuid()) && !user.isNpc())
+                .filter(user -> !user.isNpc() && !user.hasDisconnected() && !plugin.isLocked(user.getUuid()))
                 .forEach(user -> plugin.getDataSyncer().saveCurrentUserData(
                         user, DataSnapshot.SaveCause.WORLD_SAVE
                 ));

common/src/main/java/net/william278/husksync/redis/RedisManager.java

@@ -158,7 +158,7 @@ public class RedisManager extends JedisPubSub {
 
         final RedisMessage redisMessage = RedisMessage.fromJson(plugin, message);
         switch (messageType) {
-            case UPDATE_USER_DATA -> plugin.getOnlineUser(redisMessage.getTargetUuid()).ifPresent(
+            case UPDATE_USER_DATA -> redisMessage.getTargetUser(plugin).ifPresent(
                     user -> {
                         plugin.lockPlayer(user.getUuid());
                         try {
@@ -170,16 +170,30 @@ public class RedisManager extends JedisPubSub {
                         }
                     }
             );
-            case REQUEST_USER_DATA -> plugin.getOnlineUser(redisMessage.getTargetUuid()).ifPresent(
+            case REQUEST_USER_DATA -> redisMessage.getTargetUser(plugin).ifPresent(
                     user -> RedisMessage.create(
                             UUID.fromString(new String(redisMessage.getPayload(), StandardCharsets.UTF_8)),
                             user.createSnapshot(DataSnapshot.SaveCause.INVENTORY_COMMAND).asBytes(plugin)
                     ).dispatch(plugin, RedisMessage.Type.RETURN_USER_DATA)
             );
+            case CHECK_IN_PETITION -> {
+                if (!redisMessage.isTargetServer(plugin)) {
+                    return;
+                }
+                final String payload = new String(redisMessage.getPayload(), StandardCharsets.UTF_8);
+                final User user = new User(UUID.fromString(payload.split("/")[0]), payload.split("/")[1]);
+                boolean online = plugin.getDisconnectingPlayers().contains(user.getUuid())
+                        || plugin.getOnlineUser(user.getUuid()).isEmpty();
+                if (!online && !plugin.isLocked(user.getUuid())) {
+                    plugin.debug("[%s] Received check-in petition for online/unlocked user, ignoring".formatted(user.getName()));
+                    return;
+                }
+                plugin.getRedisManager().setUserCheckedOut(user, false);
+                plugin.debug("[%s] Received petition for offline user, checking them in".formatted(user.getName()));
+            }
             case RETURN_USER_DATA -> {
-                final CompletableFuture<Optional<DataSnapshot.Packed>> future = pendingRequests.get(
+                final UUID target = redisMessage.getTargetUuid().orElse(null);
-                        redisMessage.getTargetUuid()
+                final CompletableFuture<Optional<DataSnapshot.Packed>> future = pendingRequests.get(target);
-                );
                 if (future != null) {
                     try {
                         final DataSnapshot.Packed data = DataSnapshot.deserialize(plugin, redisMessage.getPayload());
@@ -188,7 +202,7 @@ public class RedisManager extends JedisPubSub {
                         plugin.log(Level.SEVERE, "An exception occurred returning user data from Redis", e);
                         future.complete(Optional.empty());
                     }
-                    pendingRequests.remove(redisMessage.getTargetUuid());
+                    pendingRequests.remove(target);
                 }
             }
         }
@@ -211,11 +225,17 @@ public class RedisManager extends JedisPubSub {
         }
     }
 
+    @Blocking
     public void sendUserDataUpdate(@NotNull User user, @NotNull DataSnapshot.Packed data) {
-        plugin.runAsync(() -> {
         final RedisMessage redisMessage = RedisMessage.create(user.getUuid(), data.asBytes(plugin));
         redisMessage.dispatch(plugin, RedisMessage.Type.UPDATE_USER_DATA);
-        });
+    }
+
+    @Blocking
+    public void petitionServerCheckin(@NotNull String server, @NotNull User user) {
+        final RedisMessage redisMessage = RedisMessage.create(
+                server, "%s/%s".formatted(user.getUuid(), user.getName()).getBytes(StandardCharsets.UTF_8));
+        redisMessage.dispatch(plugin, RedisMessage.Type.CHECK_IN_PETITION);
     }
 
     public CompletableFuture<Optional<DataSnapshot.Packed>> getOnlineUserData(@NotNull UUID requestId, @NotNull User user,
@@ -421,7 +441,7 @@ public class RedisManager extends JedisPubSub {
         final long startTime = System.currentTimeMillis();
         try (Jedis jedis = jedisPool.getResource()) {
             jedis.ping();
-            return startTime - System.currentTimeMillis();
+            return System.currentTimeMillis() - startTime;
         }
     }
 

common/src/main/java/net/william278/husksync/redis/RedisMessage.java

@@ -25,25 +25,38 @@ import lombok.Getter;
 import lombok.Setter;
 import net.william278.husksync.HuskSync;
 import net.william278.husksync.adapter.Adaptable;
+import net.william278.husksync.user.OnlineUser;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Arrays;
 import java.util.Locale;
 import java.util.Optional;
 import java.util.UUID;
 
+@Setter
 public class RedisMessage implements Adaptable {
 
+    private @Nullable String targetServer;
     @SerializedName("target_uuid")
-    private UUID targetUuid;
+    private @Nullable UUID targetUuid;
     @Getter
     @Setter
     @SerializedName("payload")
     private byte[] payload;
 
+    private RedisMessage(byte[] payload) {
+        setPayload(payload);
+    }
+
     private RedisMessage(@NotNull UUID targetUuid, byte[] message) {
+        this(message);
         this.setTargetUuid(targetUuid);
-        this.setPayload(message);
+    }
+
+    private RedisMessage(@NotNull String targetServer, byte[] message) {
+        this(message);
+        this.setTargetServer(targetServer);
     }
 
     @SuppressWarnings("unused")
@@ -55,6 +68,11 @@ public class RedisMessage implements Adaptable {
         return new RedisMessage(targetUuid, message);
     }
 
+    @NotNull
+    public static RedisMessage create(@NotNull String targetServer, byte[] message) {
+        return new RedisMessage(targetServer, message);
+    }
+
     @NotNull
     public static RedisMessage fromJson(@NotNull HuskSync plugin, @NotNull String json) throws JsonSyntaxException {
         return plugin.getGson().fromJson(json, RedisMessage.class);
@@ -67,20 +85,23 @@ public class RedisMessage implements Adaptable {
         ));
     }
 
-    @NotNull
+    public Optional<UUID> getTargetUuid() {
-    public UUID getTargetUuid() {
+        return Optional.ofNullable(targetUuid);
-        return targetUuid;
     }
 
-    public void setTargetUuid(@NotNull UUID targetUuid) {
+    public Optional<OnlineUser> getTargetUser(@NotNull HuskSync plugin) {
-        this.targetUuid = targetUuid;
+        return getTargetUuid().flatMap(plugin::getOnlineUser);
+    }
+
+    public boolean isTargetServer(@NotNull HuskSync plugin) {
+        return targetServer != null && targetServer.equals(plugin.getServerName());
     }
 
     public enum Type {
-
         UPDATE_USER_DATA,
         REQUEST_USER_DATA,
-        RETURN_USER_DATA;
+        RETURN_USER_DATA,
+        CHECK_IN_PETITION;
 
         @NotNull
         public String getMessageChannel(@NotNull String clusterId) {

common/src/main/java/net/william278/husksync/sync/DataSyncer.java

@@ -185,7 +185,7 @@ public abstract class DataSyncer {
         final AtomicReference<Task.Repeating> task = new AtomicReference<>();
         final AtomicBoolean processing = new AtomicBoolean(false);
         final Runnable runnable = () -> {
-            if (user.isOffline()) {
+            if (user.cannotApplySnapshot()) {
                 task.get().cancel();
                 return;
             }

common/src/main/java/net/william278/husksync/sync/DelayDataSyncer.java

@@ -62,7 +62,10 @@ public class DelayDataSyncer extends DataSyncer {
             getRedis().setUserServerSwitch(onlineUser);
             saveData(
                     onlineUser, onlineUser.createSnapshot(DataSnapshot.SaveCause.DISCONNECT),
-                    (user, data) -> getRedis().setUserData(user, data)
+                    (user, data) -> {
+                        getRedis().setUserData(user, data);
+                        plugin.unlockPlayer(user.getUuid());
+                    }
             );
         });
     }

common/src/main/java/net/william278/husksync/sync/LockstepDataSyncer.java

@@ -24,6 +24,8 @@ import net.william278.husksync.data.DataSnapshot;
 import net.william278.husksync.user.OnlineUser;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.Optional;
+
 public class LockstepDataSyncer extends DataSyncer {
 
     public LockstepDataSyncer(@NotNull HuskSync plugin) {
@@ -44,13 +46,19 @@ public class LockstepDataSyncer extends DataSyncer {
     @Override
     public void syncApplyUserData(@NotNull OnlineUser user) {
         this.listenForRedisData(user, () -> {
-            if (user.isOffline()) {
+            if (user.cannotApplySnapshot()) {
-                plugin.debug("Not applying data for offline user %s".formatted(user.getName()));
+                plugin.debug("Not checking data state for user who has gone offline: %s".formatted(user.getName()));
                 return false;
             }
-            if (getRedis().getUserCheckedOut(user).isPresent()) {
+
+            // If they are checked out, ask the server to check them back in and return false
+            final Optional<String> server = getRedis().getUserCheckedOut(user);
+            if (server.isPresent() && !server.get().equals(plugin.getServerName())) {
+//                getRedis().petitionServerCheckin(server.get(), user);
                 return false;
             }
+
+            // If they are checked in - or checked out on *this* server - we can apply their latest data
             getRedis().setUserCheckedOut(user, true);
             getRedis().getUserData(user).ifPresentOrElse(
                     data -> user.applySnapshot(data, DataSnapshot.UpdateCause.SYNCHRONIZED),
@@ -67,6 +75,7 @@ public class LockstepDataSyncer extends DataSyncer {
                 (user, data) -> {
                     getRedis().setUserData(user, data);
                     getRedis().setUserCheckedOut(user, false);
+                    plugin.unlockPlayer(user.getUuid());
                 }
         ));
     }

common/src/main/java/net/william278/husksync/user/OnlineUser.java

@@ -43,11 +43,27 @@ public abstract class OnlineUser extends User implements CommandUser, UserDataHo
     }
 
     /**
-     * Indicates if the player has gone offline
+     * Indicates if the player is offline
      *
      * @return {@code true} if the player has left the server; {@code false} otherwise
+     * @deprecated use {@code hasDisconnected} instead
      */
-    public abstract boolean isOffline();
+    @Deprecated(since = "3.8")
+    public boolean isOffline() {
+        return hasDisconnected();
+    }
+
+    public abstract boolean hasDisconnected();
+
+    // Users cannot have snapshots applied if they have disconnected!
+    @Override
+    public boolean cannotApplySnapshot() {
+        if (hasDisconnected()) {
+            getPlugin().debug("[%s] Cannot apply snapshot as user is offline!".formatted(getName()));
+            return true;
+        }
+        return false;
+    }
 
     @NotNull
     @Override
@@ -117,7 +133,7 @@ public abstract class OnlineUser extends User implements CommandUser, UserDataHo
 
 
     /**
-     * Set a player's status from a {@link DataSnapshot}
+     * Apply a {@link DataSnapshot} to a player, updating their data
      *
      * @param snapshot The {@link DataSnapshot} to set the player's status from
      * @param cause    The {@link DataSnapshot.UpdateCause} of the snapshot
@@ -125,14 +141,12 @@ public abstract class OnlineUser extends User implements CommandUser, UserDataHo
      */
     public void applySnapshot(@NotNull DataSnapshot.Packed snapshot, @NotNull DataSnapshot.UpdateCause cause) {
         getPlugin().fireEvent(getPlugin().getPreSyncEvent(this, snapshot), (event) -> {
-            if (!isOffline()) {
+            getPlugin().debug(String.format("Attempting to apply snapshot (%s) to %s (cause: %s)",
-                getPlugin().debug(String.format("Applying snapshot (%s) to %s (cause: %s)",
                     snapshot.getShortId(), getName(), cause.getDisplayName()
             ));
             UserDataHolder.super.applySnapshot(
                     event.getData(), (succeeded) -> completeSync(succeeded, cause, getPlugin())
             );
-            }
         });
     }
 

fabric/src/main/java/net/william278/husksync/FabricHuskSync.java

@@ -54,7 +54,6 @@ import net.william278.husksync.database.PostgresDatabase;
 import net.william278.husksync.event.FabricEventDispatcher;
 import net.william278.husksync.event.ModLoadedCallback;
 import net.william278.husksync.hook.PlanHook;
-import net.william278.husksync.listener.EventListener;
 import net.william278.husksync.listener.FabricEventListener;
 import net.william278.husksync.listener.LockedHandler;
 import net.william278.husksync.migrator.Migrator;
@@ -109,6 +108,7 @@ public class FabricHuskSync implements DedicatedServerModInitializer, HuskSync,
     private final Map<String, Boolean> permissions = Maps.newHashMap();
     private final List<Migrator> availableMigrators = Lists.newArrayList();
     private final Set<UUID> lockedPlayers = Sets.newConcurrentHashSet();
+    private final Set<UUID> disconnectingPlayers = Sets.newConcurrentHashSet();
     private final Map<UUID, FabricUser> playerMap = Maps.newConcurrentMap();
 
     private Logger logger;

fabric/src/main/java/net/william278/husksync/data/FabricUserDataHolder.java

@@ -34,7 +34,10 @@ public interface FabricUserDataHolder extends UserDataHolder {
 
     @Override
     default Optional<? extends Data> getData(@NotNull Identifier id) {
-        if (!id.isCustom()) {
+        if (id.isCustom()) {
+            return Optional.ofNullable(getCustomDataStore().get(id));
+        }
+
         try {
             return switch (id.getKeyValue()) {
                 case "inventory" -> getInventory();
@@ -53,11 +56,10 @@ public interface FabricUserDataHolder extends UserDataHolder {
                 default -> throw new IllegalStateException(String.format("Unexpected data type: %s", id));
             };
         } catch (Throwable e) {
-                getPlugin().debug("Failed to get data for key: " + id.getKeyValue(), e);
+            getPlugin().debug("Failed to get data for key: " + id.asMinimalString(), e);
+            return Optional.empty();
         }
     }
-        return Optional.ofNullable(getCustomDataStore().get(id));
-    }
 
     @Override
     default void setData(@NotNull Identifier id, @NotNull Data data) {

fabric/src/main/java/net/william278/husksync/user/FabricUser.java

@@ -64,8 +64,9 @@ public class FabricUser extends OnlineUser implements FabricUserDataHolder {
     }
 
     @Override
-    public boolean isOffline() {
+    public boolean hasDisconnected() {
-        return player == null || player.isDisconnected();
+        return getPlugin().getDisconnectingPlayers().contains(getUuid())
+                || player == null || player.isDisconnected();
     }
 
     @NotNull