fix(stealth): hide concealed players from server ping

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

@@ -0,0 +1,44 @@
+package games.dmg.spigotstealth;
+
+import com.comphenix.protocol.PacketType;
+import com.comphenix.protocol.events.PacketAdapter;
+import com.comphenix.protocol.events.PacketEvent;
+import com.comphenix.protocol.wrappers.WrappedGameProfile;
+import com.comphenix.protocol.wrappers.WrappedServerPing;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+import java.util.function.Supplier;
+import org.bukkit.plugin.Plugin;
+
+/** Rewrites outgoing server-list responses without changing actual online-player state. */
+public final class ProtocolLibServerListPingListener extends PacketAdapter {
+    private final Supplier<Set<UUID>> concealedPlayerIds;
+
+    public ProtocolLibServerListPingListener(Plugin plugin, Supplier<Set<UUID>> concealedPlayerIds) {
+        super(plugin, PacketType.Status.Server.SERVER_INFO);
+        this.concealedPlayerIds = Objects.requireNonNull(concealedPlayerIds, "concealedPlayerIds");
+    }
+
+    @Override
+    public void onPacketSending(PacketEvent event) {
+        WrappedServerPing visiblePing = event.getPacket().getServerPings().read(0).deepClone();
+        boolean sampleVisible = visiblePing.isPlayersVisible();
+        List<WrappedGameProfile> sample = sampleVisible ? visiblePing.getPlayers() : List.of();
+        Set<UUID> concealed = concealedPlayerIds.get();
+        ServerListPingVisibility.Snapshot visible = ServerListPingVisibility.adjust(
+                visiblePing.getPlayersOnline(),
+                visiblePing.getPlayersMaximum(),
+                sample.stream().map(WrappedGameProfile::getUUID).toList(),
+                concealed);
+        Set<UUID> visibleSampleIds = Set.copyOf(visible.samplePlayerIds());
+        visiblePing.setPlayersOnline(visible.playersOnline());
+        if (sampleVisible) {
+            visiblePing.setPlayers(sample.stream()
+                    .filter(profile -> visibleSampleIds.contains(profile.getUUID()))
+                    .toList());
+        }
+        event.getPacket().getServerPings().write(0, visiblePing);
+    }
+}

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

@@ -0,0 +1,33 @@
+package games.dmg.spigotstealth;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+/** Computes the public multiplayer server-list view for concealed sessions. */
+public final class ServerListPingVisibility {
+    private ServerListPingVisibility() { }
+
+    public static Snapshot adjust(
+            int playersOnline,
+            int playersMaximum,
+            List<UUID> samplePlayerIds,
+            Set<UUID> concealedPlayerIds) {
+        Objects.requireNonNull(samplePlayerIds, "samplePlayerIds");
+        Objects.requireNonNull(concealedPlayerIds, "concealedPlayerIds");
+        List<UUID> visibleSample = samplePlayerIds.stream()
+                .filter(playerId -> !concealedPlayerIds.contains(playerId))
+                .toList();
+        return new Snapshot(
+                Math.max(0, playersOnline - concealedPlayerIds.size()),
+                playersMaximum,
+                visibleSample);
+    }
+
+    public record Snapshot(int playersOnline, int playersMaximum, List<UUID> samplePlayerIds) {
+        public Snapshot {
+            samplePlayerIds = List.copyOf(samplePlayerIds);
+        }
+    }
+}

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

@@ -1,6 +1,7 @@
 package games.dmg.spigotstealth;
 
 import com.comphenix.protocol.ProtocolLibrary;
+import com.comphenix.protocol.ProtocolManager;
 import java.nio.file.Path;
 import java.time.Clock;
 import java.util.Objects;
@@ -15,6 +16,7 @@ public final class SpigotStealthPlugin extends JavaPlugin {
     private QualifyingInvisibilityService progression;
     private StealthSessionService sessions;
     private IdentityPresentation identityPresentation;
+    private ProtocolManager protocolManager;
 
     @Override
     public void onEnable() {
@@ -41,6 +43,9 @@ public final class SpigotStealthPlugin extends JavaPlugin {
 
     @Override
     public void onDisable() {
+        if (protocolManager != null) {
+            protocolManager.removePacketListeners(this);
+        }
         if (identityPresentation != null && sessions != null) {
             for (org.bukkit.entity.Player player : getServer().getOnlinePlayers()) {
                 if (sessions.isConcealed(player.getUniqueId())) {
@@ -71,10 +76,13 @@ public final class SpigotStealthPlugin extends JavaPlugin {
         progression = new QualifyingInvisibilityService(
                 manager, settings.unlockThreshold(), System::nanoTime, notifier);
         sessions = new StealthSessionService(manager, progression);
+        protocolManager = ProtocolLibrary.getProtocolManager();
         identityPresentation = new BukkitIdentityPresentation(
                 getServer()::getOnlinePlayers,
                 Objects.requireNonNull(getServer().getScoreboardManager(), "scoreboard manager").getMainScoreboard(),
-                new ProtocolLibTabListController(ProtocolLibrary.getProtocolManager()));
+                new ProtocolLibTabListController(protocolManager));
+        protocolManager.addPacketListener(
+                new ProtocolLibServerListPingListener(this, sessions::concealedPlayerIds));
         getServer().getPluginManager().registerEvents(
                 new InvisibilityEffectListener(progression, Clock.systemUTC()), this);
         getServer().getPluginManager().registerEvents(

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

@@ -1,7 +1,9 @@
 package games.dmg.spigotstealth;
 
 import java.util.Objects;
+import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -9,6 +11,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 public final class StealthSessionService {
     private final StealthStateManager stateManager;
     private final QualifyingInvisibilityService progression;
+    private final Set<UUID> concealedOnlinePlayerIds = ConcurrentHashMap.newKeySet();
 
     public StealthSessionService(
             StealthStateManager stateManager,
@@ -18,6 +21,7 @@ public final class StealthSessionService {
     }
 
     public CompletableFuture<Void> disconnect(UUID playerId) {
+        concealedOnlinePlayerIds.remove(playerId);
         boolean qualifyingAtDisconnect = progression.isQualifying(playerId);
         return progression.stop(playerId).thenCompose(ignored -> stateManager.update(state -> {
             PlayerStealthState player = state.player(playerId);
@@ -34,10 +38,16 @@ public final class StealthSessionService {
             concealed.set(conceal);
             return state.withPlayer(player.withSession(false, conceal).withQualifyingSince(null));
         });
+        if (concealed.get()) {
+            concealedOnlinePlayerIds.add(playerId);
+        } else {
+            concealedOnlinePlayerIds.remove(playerId);
+        }
         return new LoginTransition(concealed.get(), saved);
     }
 
     public CompletableFuture<Void> endConcealment(UUID playerId) {
+        concealedOnlinePlayerIds.remove(playerId);
         return stateManager.update(state -> {
             PlayerStealthState player = state.player(playerId);
             return state.withPlayer(player.withSession(player.preparedLogin(), false));
@@ -48,5 +58,9 @@ public final class StealthSessionService {
         return stateManager.snapshot().player(playerId).concealed();
     }
 
+    public Set<UUID> concealedPlayerIds() {
+        return Set.copyOf(concealedOnlinePlayerIds);
+    }
+
     public record LoginTransition(boolean concealed, CompletableFuture<Void> saved) { }
 }