feat: Add event to modify and/or block backend updates to the tablist

api/src/main/java/com/velocitypowered/api/event/player/ServerUpdateTabListEvent.java

@@ -0,0 +1,194 @@
+/*
+ * Copyright (C) 2019-2024 Velocity Contributors
+ *
+ * The Velocity API is licensed under the terms of the MIT License. For more details,
+ * reference the LICENSE file in the api top-level directory.
+ */
+
+package com.velocitypowered.api.event.player;
+
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.event.ResultedEvent;
+import com.velocitypowered.api.event.annotation.AwaitingEvent;
+import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.api.proxy.player.TabListEntry;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * This event is fired, when a {@link com.velocitypowered.api.proxy.player.TabList Tablist} is updated
+ * by a {@link com.velocitypowered.api.proxy.ServerConnection server}.
+ * It can be used to override or cancel updates for {@link TabListEntry}s.
+ * Velocity will wait for this event to finish firing before forwarding it to the server.
+ *
+ * <p>Note: If the {@code actions} contain {@link Action#REMOVE_PLAYER Action.REMOVE_PLAYER}, that may be the only action.
+ *
+ * <p><b>Version-specific behavior:</b>
+ *   <li>For versions below 1.19.3, {@code actions} may only contain one action, and if that action
+ *   is {@link Action#ADD_PLAYER Action.ADD_PLAYER}, the values normally set by other actions
+ *       (e.g., {@link Action#UPDATE_GAME_MODE Action.UPDATE_GAME_MODE}) may still be set.
+ *   <li>For versions below 1.8, {@code actions} may only contain {@link Action#ADD_PLAYER Action.ADD_PLAYER}
+ *       or {@link Action#REMOVE_PLAYER Action.REMOVE_PLAYER}. {@link Action#ADD_PLAYER Action.ADD_PLAYER} may also act as a replacement
+ *       for actions like {@link Action#UPDATE_LATENCY Action.UPDATE_LATENCY}}.
+ */
+@AwaitingEvent
+public class ServerUpdateTabListEvent implements ResultedEvent<ServerUpdateTabListEvent.TabListUpdateResult> {
+
+  private final Player player;
+  private final Set<Action> actions;
+  private final List<TabListEntry> entries;
+  private TabListUpdateResult result;
+
+  /**
+   * Constructs a {@link ServerUpdateTabListEvent} instance.
+   *
+   * @param player the player for whom the tab list is being updated
+   * @param actions the {@link Action Action}s from the server for this tab list update
+   * @param entries the {@link TabListEntry}s in their updated form
+   */
+  public ServerUpdateTabListEvent(Player player, Set<Action> actions, List<TabListEntry> entries) {
+    this.player = Preconditions.checkNotNull(player, "player");
+    this.actions = Preconditions.checkNotNull(actions, "actions");
+    this.entries = Preconditions.checkNotNull(entries, "entries");
+    this.result = TabListUpdateResult.allowed();
+  }
+
+  public Player getPlayer() {
+    return player;
+  }
+
+  public Set<Action> getActions() {
+    return actions;
+  }
+
+  /**
+   * The updated {@link TabListEntry}s that will be applied to the {@link com.velocitypowered.api.proxy.player.TabList Tablist}
+   * of the {@code player} (or in the case of {@link Action#REMOVE_PLAYER Action.REMOVE_PLAYER} removed).
+   *
+   * @return the updated entries, normally immutable
+   */
+  public List<TabListEntry> getEntries() {
+    return entries;
+  }
+
+  @Override
+  public TabListUpdateResult getResult() {
+    return result;
+  }
+
+  @Override
+  public void setResult(TabListUpdateResult result) {
+    this.result = Preconditions.checkNotNull(result, "result");
+  }
+
+  @Override
+  public String toString() {
+    return "ServerUpdateTabListEvent{"
+        + "player=" + player
+        + ", actions=" + actions
+        + ", entries=" + entries
+        + '}';
+  }
+
+  /**
+   * Represents an action of the {@link ServerUpdateTabListEvent}.
+   */
+  public enum Action {
+    /**
+     * Add new players to the player list.
+     */
+    ADD_PLAYER,
+    /**
+     * Initialize the chat session for the entries.
+     */
+    INITIALIZE_CHAT,
+    /**
+     * Update the gamemode for the entries.
+     */
+    UPDATE_GAME_MODE,
+    /**
+     * Update the latency for the entries.
+     */
+    UPDATE_LISTED,
+    /**
+     * Update the latency for the entries.
+     */
+    UPDATE_LATENCY,
+    /**
+     * Update the display name for the specific entries.
+     */
+    UPDATE_DISPLAY_NAME,
+    /**
+     * Remove players from the player list.
+     */
+    REMOVE_PLAYER
+  }
+
+  /**
+   * Represents the result of the {@link ServerUpdateTabListEvent}.
+   */
+  public static final class TabListUpdateResult implements ResultedEvent.Result {
+
+    private static final TabListUpdateResult ALLOWED = new TabListUpdateResult(true);
+    private static final TabListUpdateResult DENIED = new TabListUpdateResult(false);
+
+    private final boolean status;
+    private final Set<UUID> ids;
+
+    public TabListUpdateResult(boolean status) {
+      this.status = status;
+      ids = Collections.emptySet();
+    }
+
+    public TabListUpdateResult(boolean status, Set<UUID> ids) {
+      this.status = status;
+      this.ids = ids;
+    }
+
+    @Override
+    public boolean isAllowed() {
+      return status;
+    }
+
+    public Set<UUID> getIds() {
+      return ids;
+    }
+
+    /**
+     * Allows the {@link TabListEntry}s to be updated, with or without modification.
+     *
+     * @return the allowed result
+     */
+    public static TabListUpdateResult allowed() {
+      return ALLOWED;
+    }
+
+    /**
+     * Prevents the {@link TabListEntry}s from being updated.
+     *
+     * @return the denied result
+     */
+    public static TabListUpdateResult denied() {
+      return DENIED;
+    }
+
+    /**
+     * Only allows specific {@link TabListEntry}s to be updated.
+     * The updates for the remaining entries will be dropped.
+     *
+     * <p>Note: You can get the id of an entry with {@link TabListEntry#getProfile()}{@link com.velocitypowered.api.util.GameProfile#getId() .getId()}
+     *
+     * @param allowedOnly A non-empty set of ids of the entries that should be updated
+     * @return a result with the specified entries to be updated
+     */
+    public static TabListUpdateResult allowedSpecific(final Set<UUID> allowedOnly) {
+      Preconditions.checkNotNull(allowedOnly, "allowedOnly");
+      Preconditions.checkArgument(!allowedOnly.isEmpty(), "allowedOnly empty");
+      return new TabListUpdateResult(true, allowedOnly);
+    }
+
+  }
+
+}

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -334,20 +334,20 @@ public boolean handle(TabCompleteResponsePacket packet) {
 
   @Override
   public boolean handle(LegacyPlayerListItemPacket packet) {
-    serverConn.getPlayer().getTabList().processLegacy(packet);
-    return false;
+    serverConn.getPlayer().getTabList().processLegacyUpdate(packet);
+    return true;
   }
 
   @Override
   public boolean handle(UpsertPlayerInfoPacket packet) {
     serverConn.getPlayer().getTabList().processUpdate(packet);
-    return false;
+    return true;
   }
 
   @Override
   public boolean handle(RemovePlayerInfoPacket packet) {
     serverConn.getPlayer().getTabList().processRemove(packet);
-    return false;
+    return true;
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -202,7 +202,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
     this.onlineMode = onlineMode;
 
     if (connection.getProtocolVersion().noLessThan(ProtocolVersion.MINECRAFT_1_19_3)) {
-      this.tabList = new VelocityTabList(this);
+      this.tabList = new VelocityTabList(this, server);
     } else if (connection.getProtocolVersion().noLessThan(ProtocolVersion.MINECRAFT_1_8)) {
       this.tabList = new KeyedVelocityTabList(this, server);
     } else {

proxy/src/main/java/com/velocitypowered/proxy/tablist/InternalTabList.java

@@ -30,7 +30,7 @@ public interface InternalTabList extends TabList {
 
   Player getPlayer();
 
-  default void processLegacy(LegacyPlayerListItemPacket packet) {
+  default void processLegacyUpdate(LegacyPlayerListItemPacket packet) {
   }
 
   default void processUpdate(UpsertPlayerInfoPacket infoPacket) {