feat(stealth): mask identities and notify admins on login

src/main/java/games/dmg/spigotstealth/BukkitIdentityPresentation.java

@@ -18,6 +18,18 @@ public final class BukkitIdentityPresentation implements IdentityPresentation {
     private final Supplier<SleepCountPolicy> sleepCountPolicy;
     private final Map<UUID, Player> concealedPlayers = new LinkedHashMap<>();
     private final Map<UUID, Boolean> previousSleepingIgnored = new LinkedHashMap<>();
+    private final Map<UUID, String> previousDisplayNames = new LinkedHashMap<>();
+    private volatile java.util.Set<String> concealedNames = java.util.Set.of();
+
+    /** Immutable snapshot safe to read from outgoing packet threads. */
+    public java.util.Set<String> concealedNames() {
+        return concealedNames;
+    }
+
+    private void publishNames() {
+        concealedNames = concealedPlayers.values().stream().map(Player::getName)
+                .collect(java.util.stream.Collectors.toUnmodifiableSet());
+    }
 
     public BukkitIdentityPresentation(
             Supplier<? extends Collection<? extends Player>> onlinePlayers,
@@ -40,12 +52,17 @@ public final class BukkitIdentityPresentation implements IdentityPresentation {
     @Override
     public void conceal(Player player) {
         concealedPlayers.put(player.getUniqueId(), player);
+        publishNames();
+        previousDisplayNames.putIfAbsent(player.getUniqueId(), player.getDisplayName());
+        player.setDisplayName("§kAnonymous§r");
         applySleepCountPolicy(player);
         Team team = scoreboard.getTeam(teamName(player.getUniqueId()));
         if (team == null) {
             team = scoreboard.registerNewTeam(teamName(player.getUniqueId()));
         }
-        team.setOption(Team.Option.NAME_TAG_VISIBILITY, Team.OptionStatus.NEVER);
+        team.setOption(Team.Option.NAME_TAG_VISIBILITY, Team.OptionStatus.ALWAYS);
+        team.setPrefix("§k");
+        team.setSuffix("§r");
         team.addEntry(player.getName());
         for (Player observer : onlinePlayers.get()) {
             if (!observer.getUniqueId().equals(player.getUniqueId())) {
@@ -57,6 +74,10 @@ public final class BukkitIdentityPresentation implements IdentityPresentation {
     @Override
     public void reveal(Player player) {
         boolean wasConcealed = concealedPlayers.remove(player.getUniqueId()) != null;
+        publishNames();
+        if (previousDisplayNames.containsKey(player.getUniqueId())) {
+            player.setDisplayName(previousDisplayNames.remove(player.getUniqueId()));
+        }
         restoreSleepingIgnored(player);
         Team team = scoreboard.getTeam(teamName(player.getUniqueId()));
         if (team != null) {

src/main/java/games/dmg/spigotstealth/IdentityPacketFields.java

@@ -0,0 +1,46 @@
+package games.dmg.spigotstealth;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+import java.lang.reflect.RecordComponent;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.function.UnaryOperator;
+
+/** Small reflective bridge: avoids a compile/runtime dependency on a specific NMS or Brigadier version. */
+final class IdentityPacketFields {
+    private IdentityPacketFields() { }
+
+    static List<?> filterEntries(List<?> entries, StealthChatMasker masker) throws ReflectiveOperationException {
+        List<Object> filtered = new ArrayList<>();
+        for (Object entry : entries) {
+            Method text;
+            try {
+                text = entry.getClass().getMethod("text");
+            } catch (NoSuchMethodException exception) {
+                text = entry.getClass().getMethod("getText");
+            }
+            if (!masker.isConcealedName((String) text.invoke(entry))) {
+                filtered.add(entry);
+            }
+        }
+        return List.copyOf(filtered);
+    }
+
+    static Object mapRecord(Object record, UnaryOperator<Object> mapper) throws ReflectiveOperationException {
+        RecordComponent[] components = record.getClass().getRecordComponents();
+        if (components == null) {
+            throw new IllegalArgumentException("Unsupported non-record chat binding");
+        }
+        Class<?>[] types = new Class<?>[components.length];
+        Object[] values = new Object[components.length];
+        for (int i = 0; i < components.length; i++) {
+            types[i] = components[i].getType();
+            Object value = components[i].getAccessor().invoke(record);
+            values[i] = value instanceof Optional<?> optional ? optional.map(mapper) : mapper.apply(value);
+        }
+        Constructor<?> constructor = record.getClass().getDeclaredConstructor(types);
+        return constructor.newInstance(values);
+    }
+}

src/main/java/games/dmg/spigotstealth/ProtocolLibIdentityMaskingListener.java

@@ -0,0 +1,136 @@
+package games.dmg.spigotstealth;
+
+import com.comphenix.protocol.PacketType;
+import com.comphenix.protocol.events.ListenerPriority;
+import com.comphenix.protocol.events.PacketAdapter;
+import com.comphenix.protocol.events.PacketContainer;
+import com.comphenix.protocol.events.PacketEvent;
+import com.comphenix.protocol.reflect.StructureModifier;
+import com.comphenix.protocol.utility.MinecraftReflection;
+import com.comphenix.protocol.wrappers.WrappedChatComponent;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import org.bukkit.plugin.Plugin;
+
+/**
+ * Outgoing identity-only masking. Registration is deliberately left to the plugin.
+ * The supplier must return an immutable, safely published snapshot (for example AtomicReference::get).
+ * It must not inspect Bukkit players or mutable session collections on the packet thread.
+ */
+public final class ProtocolLibIdentityMaskingListener extends PacketAdapter {
+    private final Supplier<Set<String>> concealedNames;
+    private final Consumer<String> warningLog;
+    private final Set<PacketType> warned = ConcurrentHashMap.newKeySet();
+
+    public ProtocolLibIdentityMaskingListener(
+            Plugin plugin, Supplier<Set<String>> concealedNames, Consumer<String> warningLog) {
+        // ProtocolLib calls the vanilla PLAYER_CHAT packet CHAT.
+        super(plugin, ListenerPriority.HIGHEST, PacketType.Play.Server.TAB_COMPLETE,
+                PacketType.Play.Server.SYSTEM_CHAT, PacketType.Play.Server.CHAT,
+                PacketType.Play.Server.DISGUISED_CHAT);
+        this.concealedNames = Objects.requireNonNull(concealedNames, "concealedNames");
+        this.warningLog = Objects.requireNonNull(warningLog, "warningLog");
+    }
+
+    @Override
+    public void onPacketSending(PacketEvent event) {
+        if (event.isCancelled()) {
+            return;
+        }
+        try {
+            Set<String> snapshot = concealedNames.get();
+            if (snapshot.isEmpty()) {
+                return;
+            }
+            StealthChatMasker masker = new StealthChatMasker(snapshot);
+            PacketContainer packet = event.getPacket().shallowClone();
+            if (event.getPacketType().equals(PacketType.Play.Server.TAB_COMPLETE)) {
+                filterSuggestions(packet, masker);
+            } else if (event.getPacketType().equals(PacketType.Play.Server.SYSTEM_CHAT)) {
+                maskSystemChat(packet, masker);
+            } else {
+                maskBoundNames(packet, masker);
+            }
+            event.setPacket(packet);
+        } catch (ReflectiveOperationException | RuntimeException exception) {
+            // Keep delivery usable; do not cancel signed chat and break the acknowledgement chain.
+            if (warned.add(event.getPacketType())) {
+                warningLog.accept("Stealth identity masking unavailable for " + event.getPacketType()
+                        + "; original packet retained. Failure: " + exception.getClass().getSimpleName());
+            }
+        }
+    }
+
+    private static void filterSuggestions(PacketContainer packet, StealthChatMasker masker)
+            throws ReflectiveOperationException {
+        StructureModifier<Object> fields = packet.getModifier();
+        for (int i = 0; i < fields.size(); i++) {
+            Object value = fields.read(i);
+            if (value instanceof List<?> entries) {
+                // Modern ClientboundCommandSuggestionsPacket stores its Entry list directly.
+                fields.write(i, IdentityPacketFields.filterEntries(entries, masker));
+                return;
+            }
+            if (value != null && value.getClass().getName().equals("com.mojang.brigadier.suggestion.Suggestions")) {
+                Object range = value.getClass().getMethod("getRange").invoke(value);
+                List<?> entries = (List<?>) value.getClass().getMethod("getList").invoke(value);
+                List<?> filtered = IdentityPacketFields.filterEntries(entries, masker);
+                fields.write(i, value.getClass().getConstructor(range.getClass(), List.class).newInstance(range, filtered));
+                return;
+            }
+        }
+        // Pre-Brigadier protocol compatibility.
+        StructureModifier<String[]> arrays = packet.getStringArrays();
+        if (arrays.size() > 0) {
+            arrays.write(0, java.util.Arrays.stream(arrays.read(0))
+                    .filter(name -> !masker.isConcealedName(name)).toArray(String[]::new));
+            return;
+        }
+        throw new IllegalStateException("Unsupported command suggestions layout");
+    }
+
+    private static void maskSystemChat(PacketContainer packet, StealthChatMasker masker) {
+        StructureModifier<WrappedChatComponent> components = packet.getChatComponents();
+        if (components.size() > 0) {
+            WrappedChatComponent original = components.read(0);
+            String json = original.getJson();
+            String masked = masker.maskAnnouncement(json);
+            if (!json.equals(masked)) {
+                components.write(0, WrappedChatComponent.fromJson(masked));
+            }
+        } else if (packet.getStrings().size() > 0) {
+            // Older SYSTEM_CHAT represents its component as JSON text.
+            String json = packet.getStrings().read(0);
+            packet.getStrings().write(0, masker.maskAnnouncement(json));
+        } else {
+            throw new IllegalStateException("Unsupported system chat layout");
+        }
+    }
+
+    private static void maskBoundNames(PacketContainer packet, StealthChatMasker masker)
+            throws ReflectiveOperationException {
+        StructureModifier<Object> fields = packet.getModifier();
+        for (int i = 0; i < fields.size(); i++) {
+            Object value = fields.read(i);
+            if (value != null && (value.getClass().getName().endsWith("ChatType$BoundNetwork")
+                    || value.getClass().getName().endsWith("ChatType$Bound"))) {
+                Object masked = IdentityPacketFields.mapRecord(value, field -> {
+                    if (field != null && MinecraftReflection.getIChatBaseComponentClass().isInstance(field)) {
+                        String json = WrappedChatComponent.fromHandle(field).getJson();
+                        String replacement = masker.maskDisplayName(json);
+                        return json.equals(replacement) ? field : WrappedChatComponent.fromJson(replacement).getHandle();
+                    }
+                    return field;
+                });
+                fields.write(i, masked);
+                return;
+            }
+        }
+        // Intentionally never touch signed body, unsigned body, UUID, signature, or filter mask.
+        throw new IllegalStateException("Unsupported player chat display-name layout");
+    }
+}

src/main/java/games/dmg/spigotstealth/SpigotStealthPlugin.java

@@ -77,11 +77,14 @@ public final class SpigotStealthPlugin extends JavaPlugin {
                 manager, settings.unlockThreshold(), System::nanoTime, notifier);
         sessions = new StealthSessionService(manager, progression);
         protocolManager = ProtocolLibrary.getProtocolManager();
-        identityPresentation = new BukkitIdentityPresentation(
+        BukkitIdentityPresentation bukkitPresentation = new BukkitIdentityPresentation(
                 getServer()::getOnlinePlayers,
                 Objects.requireNonNull(getServer().getScoreboardManager(), "scoreboard manager").getMainScoreboard(),
                 new ProtocolLibTabListController(protocolManager),
                 () -> manager.snapshot().sleepCountPolicy());
+        identityPresentation = bukkitPresentation;
+        protocolManager.addPacketListener(new ProtocolLibIdentityMaskingListener(
+                this, bukkitPresentation::concealedNames, getLogger()::warning));
         protocolManager.addPacketListener(new ProtocolLibServerListPingListener(
                 this, sessions::concealedPlayerIds, getLogger()::warning));
         getServer().getPluginManager().registerEvents(
@@ -90,6 +93,8 @@ public final class SpigotStealthPlugin extends JavaPlugin {
                 new InvisibilityEffectListener(progression, Clock.systemUTC()), this);
         getServer().getPluginManager().registerEvents(
                 new StealthSessionListener(sessions, identityPresentation, settings.concealedMessage()), this);
+        getServer().getPluginManager().registerEvents(
+                new StealthAdminJoinListener(sessions, getServer()::getOnlinePlayers), this);
         org.bukkit.command.PluginCommand stealthPluginCommand =
                 Objects.requireNonNull(getCommand("stealth"), "stealth command");
         StealthCommand stealthCommand = new StealthCommand(manager, progression, settings);

src/main/java/games/dmg/spigotstealth/StealthAdminJoinListener.java

@@ -0,0 +1,49 @@
+package games.dmg.spigotstealth;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+import java.util.function.Supplier;
+import org.bukkit.entity.Player;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.EventPriority;
+import org.bukkit.event.Listener;
+import org.bukkit.event.player.PlayerJoinEvent;
+
+/** Private administrative notices after the HIGHEST-priority session transition. */
+public final class StealthAdminJoinListener implements Listener {
+    private static final String PERMISSION = "spigotstealth.admin";
+    private static final String HINT = " Use /stealthadmin list to see who.";
+    private final StealthSessionService sessions;
+    private final Supplier<? extends Collection<? extends Player>> onlinePlayers;
+
+    public StealthAdminJoinListener(
+            StealthSessionService sessions,
+            Supplier<? extends Collection<? extends Player>> onlinePlayers) {
+        this.sessions = Objects.requireNonNull(sessions, "sessions");
+        this.onlinePlayers = Objects.requireNonNull(onlinePlayers, "onlinePlayers");
+    }
+
+    @EventHandler(priority = EventPriority.MONITOR)
+    public void onJoin(PlayerJoinEvent event) {
+        Player joining = event.getPlayer();
+        Set<UUID> concealed = sessions.concealedPlayerIds();
+        int count = concealed.size();
+        if (count == 0) {
+            return;
+        }
+        String quantity = count + (count == 1 ? " player is" : " players are");
+        if (joining.hasPermission(PERMISSION)) {
+            joining.sendMessage("[Stealth] " + quantity + " invisible." + HINT);
+        }
+        if (concealed.contains(joining.getUniqueId())) {
+            String notice = "[Stealth] An invisible player joined. " + quantity + " now invisible." + HINT;
+            for (Player observer : onlinePlayers.get()) {
+                if (!observer.getUniqueId().equals(joining.getUniqueId()) && observer.hasPermission(PERMISSION)) {
+                    observer.sendMessage(notice);
+                }
+            }
+        }
+    }
+}

src/main/java/games/dmg/spigotstealth/StealthChatMasker.java

@@ -0,0 +1,117 @@
+package games.dmg.spigotstealth;
+
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonParser;
+import java.util.Locale;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/** Masks semantic name slots, never searching/replacing user-authored message text. */
+public final class StealthChatMasker {
+    private static final Set<String> NAME_FIRST_TRANSLATIONS = Set.of(
+            "chat.type.text", "chat.type.announcement", "chat.type.emote",
+            "commands.message.display.incoming", "commands.message.display.outgoing",
+            "chat.type.advancement.task", "chat.type.advancement.goal", "chat.type.advancement.challenge");
+    private final Set<String> names;
+
+    public StealthChatMasker(Set<String> concealedNames) {
+        names = concealedNames.stream().map(name -> name.toLowerCase(Locale.ROOT)).collect(Collectors.toUnmodifiableSet());
+    }
+
+    public boolean isConcealedName(String text) {
+        return names.contains(text.toLowerCase(Locale.ROOT));
+    }
+
+    public String maskAnnouncement(String json) {
+        try {
+            JsonElement component = JsonParser.parseString(json);
+            return maskAnnouncement(component) ? component.toString() : json;
+        } catch (JsonParseException | IllegalStateException exception) {
+            return json;
+        }
+    }
+
+    public String maskDisplayName(String json) {
+        try {
+            return isConcealedName(plainName(JsonParser.parseString(json))) ? anonymous().toString() : json;
+        } catch (JsonParseException | IllegalStateException exception) {
+            return json;
+        }
+    }
+
+    private boolean maskAnnouncement(JsonElement component) {
+        boolean changed = false;
+        if (component.isJsonArray()) {
+            for (JsonElement child : component.getAsJsonArray()) {
+                changed |= maskAnnouncement(child);
+            }
+            if (changed && !component.getAsJsonArray().isEmpty()) {
+                clearInheritedActions(component.getAsJsonArray().get(0));
+            }
+        } else if (component.isJsonObject()) {
+            JsonObject object = component.getAsJsonObject();
+            // Translation arguments other than the explicitly known name slot are message content.
+            if (object.has("translate") && object.get("translate").isJsonPrimitive()
+                    && NAME_FIRST_TRANSLATIONS.contains(object.get("translate").getAsString())
+                    && object.has("with") && object.get("with").isJsonArray()) {
+                JsonArray arguments = object.getAsJsonArray("with");
+                if (!arguments.isEmpty() && isConcealedName(plainName(arguments.get(0)))) {
+                    arguments.set(0, anonymous());
+                    changed = true;
+                }
+            }
+            if (object.has("extra")) {
+                changed |= maskAnnouncement(object.get("extra"));
+            }
+            // Prevent masked descendants from inheriting an identifying action from their parent.
+            if (changed) {
+                clearInheritedActions(object);
+            }
+        }
+        return changed;
+    }
+
+    private static void clearInheritedActions(JsonElement component) {
+        if (component.isJsonObject()) {
+            for (String key : Set.of("hoverEvent", "clickEvent", "hover_event", "click_event", "insertion")) {
+                component.getAsJsonObject().remove(key);
+            }
+        } else if (component.isJsonArray() && !component.getAsJsonArray().isEmpty()) {
+            clearInheritedActions(component.getAsJsonArray().get(0));
+        }
+    }
+
+    private static String plainName(JsonElement component) {
+        if (component.isJsonPrimitive()) {
+            return component.getAsString();
+        }
+        StringBuilder text = new StringBuilder();
+        if (component.isJsonArray()) {
+            for (JsonElement child : component.getAsJsonArray()) {
+                text.append(plainName(child));
+            }
+        } else if (component.isJsonObject()) {
+            JsonObject object = component.getAsJsonObject();
+            if (object.has("text") && object.get("text").isJsonPrimitive()) {
+                text.append(object.get("text").getAsString());
+            }
+            if (object.has("extra")) {
+                text.append(plainName(object.get("extra")));
+            }
+        }
+        return text.toString();
+    }
+
+    private static JsonObject anonymous() {
+        JsonObject alias = new JsonObject();
+        alias.addProperty("text", "Anonymous");
+        alias.addProperty("obfuscated", true);
+        alias.add("hoverEvent", com.google.gson.JsonNull.INSTANCE);
+        alias.add("clickEvent", com.google.gson.JsonNull.INSTANCE);
+        alias.addProperty("insertion", "");
+        return alias;
+    }
+}