add event to modify and/or block specific updates to the tablist of a player

Inspired by https://github.com/PaperMC/Velocity/pull/874

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

@@ -0,0 +1,193 @@
+/*
+ * 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.
+ * 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 class BackendPlaySessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(LegacyPlayerListItemPacket packet) {
-    serverConn.getPlayer().getTabList().processLegacy(packet);
+    serverConn.getPlayer().getTabList().processLegacyUpdate(packet);
-    return false;
+    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) {

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

@@ -18,6 +18,7 @@
 package com.velocitypowered.proxy.tablist;
 
 import com.google.common.base.Preconditions;
+import com.velocitypowered.api.event.player.ServerUpdateTabListEvent;
 import com.velocitypowered.api.proxy.Player;
 import com.velocitypowered.api.proxy.ProxyServer;
 import com.velocitypowered.api.proxy.crypto.IdentifiedKey;
@@ -35,6 +36,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
 import net.kyori.adventure.text.Component;
@@ -78,20 +80,27 @@ public class KeyedVelocityTabList implements InternalTabList {
   }
 
   @Override
-  public void addEntry(TabListEntry entry) {
+  public void addEntry(TabListEntry entry1) {
+    KeyedVelocityTabListEntry entry;
+    if (entry1 instanceof KeyedVelocityTabListEntry) {
+      entry = (KeyedVelocityTabListEntry) entry1;
+    } else {
+      entry = new KeyedVelocityTabListEntry(this, entry1.getProfile(),
+          entry1.getDisplayNameComponent().orElse(null),
+          entry1.getLatency(), entry1.getGameMode(), entry1.getIdentifiedKey());
+    }
+
     Preconditions.checkNotNull(entry, "entry");
     Preconditions.checkArgument(entry.getTabList().equals(this),
         "The provided entry was not created by this tab list");
     Preconditions.checkArgument(!entries.containsKey(entry.getProfile().getId()),
         "this TabList already contains an entry with the same uuid");
-    Preconditions.checkArgument(entry instanceof KeyedVelocityTabListEntry,
-        "Not a Velocity tab list entry");
 
     LegacyPlayerListItemPacket.Item packetItem = LegacyPlayerListItemPacket.Item.from(entry);
     connection.write(
         new LegacyPlayerListItemPacket(LegacyPlayerListItemPacket.ADD_PLAYER,
             Collections.singletonList(packetItem)));
-    entries.put(entry.getProfile().getId(), (KeyedVelocityTabListEntry) entry);
+    entries.put(entry.getProfile().getId(), entry);
   }
 
   @Override
@@ -166,20 +175,178 @@ public class KeyedVelocityTabList implements InternalTabList {
   }
 
   @Override
-  public void processLegacy(LegacyPlayerListItemPacket packet) {
+  public void processLegacyUpdate(LegacyPlayerListItemPacket packet) {
-    // Packets are already forwarded on, so no need to do that here
+    ServerUpdateTabListEvent.Action action = mapToEventAction(packet.getAction());
-    for (LegacyPlayerListItemPacket.Item item : packet.getItems()) {
+    Preconditions.checkNotNull(action, "action");
-      UUID uuid = item.getUuid();
-      assert uuid != null : "1.7 tab list entry given to modern tab list handler!";
 
-      if (packet.getAction() != LegacyPlayerListItemPacket.ADD_PLAYER
+    List<UpdateEventTabListEntry> entries = mapToEventEntries(packet.getAction(), packet.getItems());
-              && !entries.containsKey(uuid)) {
+
+    proxyServer.getEventManager().fire(
+        new ServerUpdateTabListEvent(
+            player,
+            Set.of(action),
+            Collections.unmodifiableList(entries)
+        )
+    ).thenAcceptAsync(event -> {
+      if (event.getResult().isAllowed()) {
+        if (event.getResult().getIds().isEmpty()) {
+          boolean rewrite = false;
+          for (UpdateEventTabListEntry entry : entries) {
+            if (entry.isRewrite()) {
+              rewrite = true;
+              break;
+            }
+          }
+
+          if (rewrite) {
+            //listeners have modified entries, requires manual processing
+            if (action != ServerUpdateTabListEvent.Action.REMOVE_PLAYER) {
+              for (UpdateEventTabListEntry entry : entries) {
+                if (this.entries.containsKey(entry.getProfile().getId())) {
+                  removeEntry(entry.getProfile().getId());
+                }
+
+                addEntry(entry);
+              }
+            } else {
+              for (UpdateEventTabListEntry entry : entries) {
+                removeEntry(entry.getProfile().getId());
+              }
+            }
+          } else {
+            //listeners haven't modified entries
+            for (LegacyPlayerListItemPacket.Item item : packet.getItems()) {
+              processLegacy(packet.getAction(), item);
+            }
+
+            connection.write(packet);
+          }
+        } else {
+          //listeners have denied entries (and may have modified others), requires manual processing
+          if (action != ServerUpdateTabListEvent.Action.REMOVE_PLAYER) {
+            for (UpdateEventTabListEntry entry : entries) {
+              if (event.getResult().getIds().contains(entry.getProfile().getId())) {
+                if (this.entries.containsKey(entry.getProfile().getId())) {
+                  removeEntry(entry.getProfile().getId());
+                }
+
+                addEntry(entry);
+              }
+            }
+          } else {
+            for (UpdateEventTabListEntry entry : entries) {
+              if (event.getResult().getIds().contains(entry.getProfile().getId())) {
+                removeEntry(entry.getProfile().getId());
+              }
+            }
+          }
+        }
+      }
+    });
+  }
+
+  protected ServerUpdateTabListEvent.@Nullable Action mapToEventAction(int action) {
+    return switch (action) {
+      case LegacyPlayerListItemPacket.ADD_PLAYER -> ServerUpdateTabListEvent.Action.ADD_PLAYER;
+      case LegacyPlayerListItemPacket.REMOVE_PLAYER -> ServerUpdateTabListEvent.Action.REMOVE_PLAYER;
+      case LegacyPlayerListItemPacket.UPDATE_GAMEMODE -> ServerUpdateTabListEvent.Action.UPDATE_GAME_MODE;
+      case LegacyPlayerListItemPacket.UPDATE_LATENCY -> ServerUpdateTabListEvent.Action.UPDATE_LATENCY;
+      case LegacyPlayerListItemPacket.UPDATE_DISPLAY_NAME -> ServerUpdateTabListEvent.Action.UPDATE_DISPLAY_NAME;
+      default -> null;
+    };
+  }
+
+  private List<UpdateEventTabListEntry> mapToEventEntries(int action, List<LegacyPlayerListItemPacket.Item> packetItems) {
+    List<UpdateEventTabListEntry> entries = new ArrayList<>(packetItems.size());
+
+    for (LegacyPlayerListItemPacket.Item item : packetItems) {
+      UUID uuid = item.getUuid();
+      Preconditions.checkNotNull(uuid, "1.7 tab list entry given to modern tab list handler!");
+
+      if (action != LegacyPlayerListItemPacket.ADD_PLAYER
+          && !this.entries.containsKey(uuid)) {
         // Sometimes UPDATE_GAMEMODE is sent before ADD_PLAYER so don't want to warn here
         continue;
       }
 
-      switch (packet.getAction()) {
+      UpdateEventTabListEntry currentEntry = null;
-        case LegacyPlayerListItemPacket.ADD_PLAYER: {
+      KeyedVelocityTabListEntry oldCurrentEntry = this.entries.get(uuid);
+
+      if (oldCurrentEntry != null) {
+        currentEntry = new UpdateEventTabListEntry(
+            this,
+            oldCurrentEntry.getProfile(),
+            oldCurrentEntry.getDisplayNameComponent().orElse(null),
+            oldCurrentEntry.getLatency(),
+            oldCurrentEntry.getGameMode(),
+            oldCurrentEntry.getChatSession(),
+            oldCurrentEntry.isListed()
+        );
+      }
+
+      switch (action) {
+        case LegacyPlayerListItemPacket.ADD_PLAYER -> {
+          // ensure that name and properties are available
+          String name = item.getName();
+          List<GameProfile.Property> properties = item.getProperties();
+          if (name == null || properties == null) {
+            throw new IllegalStateException("Got null game profile for ADD_PLAYER");
+          }
+
+          currentEntry = new UpdateEventTabListEntry(
+              this,
+              new GameProfile(uuid, name, properties),
+              item.getDisplayName(),
+              item.getLatency(),
+              item.getGameMode(),
+              new RemoteChatSession(null, item.getPlayerKey()),
+              true
+          );
+        }
+        case LegacyPlayerListItemPacket.REMOVE_PLAYER -> {
+          //Nothing should be done here, as all entries which are not allowed are removed
+          // if the action is ServerUpdateTabListEvent.Action.REMOVE_PLAYER
+        }
+        case LegacyPlayerListItemPacket.UPDATE_DISPLAY_NAME -> {
+          if (currentEntry != null) {
+            currentEntry.setDisplayNameWithoutRewrite(item.getDisplayName());
+          }
+        }
+        case LegacyPlayerListItemPacket.UPDATE_LATENCY -> {
+          if (currentEntry != null) {
+            currentEntry.setLatencyWithoutRewrite(item.getLatency());
+          }
+        }
+        case LegacyPlayerListItemPacket.UPDATE_GAMEMODE -> {
+          if (currentEntry != null) {
+            currentEntry.setGameModeWithoutRewrite(item.getGameMode());
+          }
+        }
+        default -> {
+          // Nothing we can do here
+        }
+      }
+
+      if (currentEntry != null) {
+        entries.add(currentEntry);
+      }
+    }
+
+    return entries;
+  }
+
+  private void processLegacy(int action, LegacyPlayerListItemPacket.Item item) {
+    UUID uuid = item.getUuid();
+    assert uuid != null : "1.7 tab list entry given to modern tab list handler!";
+
+    if (action != LegacyPlayerListItemPacket.ADD_PLAYER
+        && !entries.containsKey(uuid)) {
+      // Sometimes UPDATE_GAMEMODE is sent before ADD_PLAYER so don't want to warn here
+      return;
+    }
+
+    switch (action) {
+      case LegacyPlayerListItemPacket.ADD_PLAYER -> {
         // ensure that name and properties are available
         String name = item.getName();
         List<GameProfile.Property> properties = item.getProperties();
@@ -195,35 +362,28 @@ public class KeyedVelocityTabList implements InternalTabList {
             .chatSession(new RemoteChatSession(null, item.getPlayerKey()))
             .gameMode(item.getGameMode())
             .build());
-          break;
       }
-        case LegacyPlayerListItemPacket.REMOVE_PLAYER:
+      case LegacyPlayerListItemPacket.REMOVE_PLAYER -> entries.remove(uuid);
-          entries.remove(uuid);
+      case LegacyPlayerListItemPacket.UPDATE_DISPLAY_NAME -> {
-          break;
-        case LegacyPlayerListItemPacket.UPDATE_DISPLAY_NAME: {
         KeyedVelocityTabListEntry entry = entries.get(uuid);
         if (entry != null) {
           entry.setDisplayNameInternal(item.getDisplayName());
         }
-          break;
       }
-        case LegacyPlayerListItemPacket.UPDATE_LATENCY: {
+      case LegacyPlayerListItemPacket.UPDATE_LATENCY -> {
         KeyedVelocityTabListEntry entry = entries.get(uuid);
         if (entry != null) {
           entry.setLatencyInternal(item.getLatency());
         }
-          break;
       }
-        case LegacyPlayerListItemPacket.UPDATE_GAMEMODE: {
+      case LegacyPlayerListItemPacket.UPDATE_GAMEMODE -> {
         KeyedVelocityTabListEntry entry = entries.get(uuid);
         if (entry != null) {
           entry.setGameModeInternal(item.getGameMode());
         }
-          break;
       }
-        default:
+      default -> {
         // Nothing we can do here
-          break;
       }
     }
   }

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

@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2018-2024 Velocity Contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.velocitypowered.proxy.tablist;
+
+import com.velocitypowered.api.event.player.ServerUpdateTabListEvent;
+import com.velocitypowered.api.proxy.player.ChatSession;
+import com.velocitypowered.api.proxy.player.TabList;
+import com.velocitypowered.api.proxy.player.TabListEntry;
+import com.velocitypowered.api.util.GameProfile;
+import java.util.Optional;
+import net.kyori.adventure.text.Component;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * Represents a {@link TabListEntry} of the {@link ServerUpdateTabListEvent}.
+ */
+public class UpdateEventTabListEntry implements TabListEntry {
+
+  private final TabList tabList;
+  private final GameProfile profile;
+  private @Nullable Component displayName;
+  private int latency;
+  private int gameMode;
+  private boolean listed;
+  private @Nullable ChatSession session;
+  private boolean rewrite = false;
+
+  /**
+   * Constructs an instance.
+   */
+  public UpdateEventTabListEntry(TabList tabList, GameProfile profile, @Nullable Component displayName,
+                                 int latency,
+                                 int gameMode, @Nullable ChatSession session, boolean listed) {
+    this.tabList = tabList;
+    this.profile = profile;
+    this.displayName = displayName;
+    this.latency = latency;
+    this.gameMode = gameMode;
+    this.session = session;
+    this.listed = listed;
+  }
+
+  @Override
+  public @Nullable ChatSession getChatSession() {
+    return this.session;
+  }
+
+  @Override
+  public TabList getTabList() {
+    return this.tabList;
+  }
+
+  @Override
+  public GameProfile getProfile() {
+    return this.profile;
+  }
+
+  @Override
+  public Optional<Component> getDisplayNameComponent() {
+    return Optional.ofNullable(displayName);
+  }
+
+  @Override
+  public TabListEntry setDisplayName(@Nullable Component displayName) {
+    this.displayName = displayName;
+    rewrite = true;
+    return this;
+  }
+
+  void setDisplayNameWithoutRewrite(@Nullable Component displayName) {
+    this.displayName = displayName;
+  }
+
+  @Override
+  public int getLatency() {
+    return this.latency;
+  }
+
+  @Override
+  public TabListEntry setLatency(int latency) {
+    this.latency = latency;
+    rewrite = true;
+    return this;
+  }
+
+  void setLatencyWithoutRewrite(int latency) {
+    this.latency = latency;
+  }
+
+  @Override
+  public int getGameMode() {
+    return this.gameMode;
+  }
+
+  @Override
+  public TabListEntry setGameMode(int gameMode) {
+    this.gameMode = gameMode;
+    rewrite = true;
+    return this;
+  }
+
+  void setGameModeWithoutRewrite(int gameMode) {
+    this.gameMode = gameMode;
+  }
+
+  void setChatSessionWithoutRewrite(@Nullable ChatSession session) {
+    this.session = session;
+  }
+
+  @Override
+  public boolean isListed() {
+    return listed;
+  }
+
+  @Override
+  public TabListEntry setListed(boolean listed) {
+    this.listed = listed;
+    rewrite = true;
+    return this;
+  }
+
+  void setListedWithoutRewrite(boolean listed) {
+    this.listed = listed;
+  }
+
+  boolean isRewrite() {
+    return rewrite;
+  }
+
+}

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

@@ -19,7 +19,9 @@ package com.velocitypowered.proxy.tablist;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Maps;
+import com.velocitypowered.api.event.player.ServerUpdateTabListEvent;
 import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.api.proxy.ProxyServer;
 import com.velocitypowered.api.proxy.player.ChatSession;
 import com.velocitypowered.api.proxy.player.TabListEntry;
 import com.velocitypowered.api.util.GameProfile;
@@ -32,11 +34,13 @@ import com.velocitypowered.proxy.protocol.packet.chat.ComponentHolder;
 import com.velocitypowered.proxy.protocol.packet.chat.RemoteChatSession;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.EnumSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.Set;
 import java.util.UUID;
 import net.kyori.adventure.text.Component;
 import org.apache.logging.log4j.LogManager;
@@ -51,6 +55,7 @@ public class VelocityTabList implements InternalTabList {
   private static final Logger logger = LogManager.getLogger(VelocityConsole.class);
   private final ConnectedPlayer player;
   private final MinecraftConnection connection;
+  protected final ProxyServer proxyServer;
   private final Map<UUID, VelocityTabListEntry> entries;
 
   /**
@@ -58,8 +63,9 @@ public class VelocityTabList implements InternalTabList {
    *
    * @param player player associated with this tab list
    */
-  public VelocityTabList(ConnectedPlayer player) {
+  public VelocityTabList(ConnectedPlayer player, final ProxyServer proxyServer) {
     this.player = player;
+    this.proxyServer = proxyServer;
     this.connection = player.getConnection();
     this.entries = Maps.newConcurrentMap();
   }
@@ -214,9 +220,45 @@ public class VelocityTabList implements InternalTabList {
 
   @Override
   public void processUpdate(UpsertPlayerInfoPacket infoPacket) {
+    List<UpdateEventTabListEntry> entries = mapToEventEntries(infoPacket.getActions(), infoPacket.getEntries());
+
+    proxyServer.getEventManager().fire(new ServerUpdateTabListEvent(player,
+        Collections.unmodifiableSet(mapToEventActions(infoPacket.getActions())),
+        Collections.unmodifiableList(entries))
+    ).thenAcceptAsync(event -> {
+      if (event.getResult().isAllowed()) {
+        if (event.getResult().getIds().isEmpty()) {
+          boolean rewrite = false;
+          for (UpdateEventTabListEntry entry : entries) {
+            if (entry.isRewrite()) {
+              rewrite = true;
+              break;
+            }
+          }
+
+          if (rewrite) {
+            //listeners have modified entries, requires manual processing
+            for (UpdateEventTabListEntry entry : entries) {
+              addEntry(entry);
+            }
+          } else {
+            //listeners haven't modified entries
             for (UpsertPlayerInfoPacket.Entry entry : infoPacket.getEntries()) {
               processUpsert(infoPacket.getActions(), entry);
             }
+
+            connection.write(infoPacket);
+          }
+        } else {
+          //listeners have denied entries (and may have modified others), requires manual processing
+          for (UpdateEventTabListEntry entry : entries) {
+            if (event.getResult().getIds().contains(entry.getProfile().getId())) {
+              addEntry(entry);
+            }
+          }
+        }
+      }
+    });
   }
 
   protected UpsertPlayerInfoPacket.Entry createRawEntry(VelocityTabListEntry entry) {
@@ -231,6 +273,134 @@ public class VelocityTabList implements InternalTabList {
     this.connection.write(new UpsertPlayerInfoPacket(EnumSet.of(action), List.of(entry)));
   }
 
+  private EnumSet<ServerUpdateTabListEvent.Action> mapToEventActions(EnumSet<UpsertPlayerInfoPacket.Action> packetActions) {
+    EnumSet<ServerUpdateTabListEvent.Action> actions = EnumSet.noneOf(ServerUpdateTabListEvent.Action.class);
+
+    for (UpsertPlayerInfoPacket.Action packetAction : packetActions) {
+      switch (packetAction) {
+        case ADD_PLAYER -> {
+          actions.add(ServerUpdateTabListEvent.Action.ADD_PLAYER);
+        }
+        case INITIALIZE_CHAT -> {
+          actions.add(ServerUpdateTabListEvent.Action.INITIALIZE_CHAT);
+        }
+        case UPDATE_GAME_MODE -> {
+          actions.add(ServerUpdateTabListEvent.Action.UPDATE_GAME_MODE);
+        }
+        case UPDATE_LISTED -> {
+          actions.add(ServerUpdateTabListEvent.Action.UPDATE_LISTED);
+        }
+        case UPDATE_LATENCY -> {
+          actions.add(ServerUpdateTabListEvent.Action.UPDATE_LATENCY);
+        }
+        case UPDATE_DISPLAY_NAME -> {
+          actions.add(ServerUpdateTabListEvent.Action.UPDATE_DISPLAY_NAME);
+        }
+        default -> {
+          // Nothing we can do here
+        }
+      }
+    }
+
+    return actions;
+  }
+
+  private List<UpdateEventTabListEntry> mapToEventEntries(EnumSet<UpsertPlayerInfoPacket.Action> actions,
+                                                          List<UpsertPlayerInfoPacket.Entry> packetEntries) {
+    List<UpdateEventTabListEntry> entries = new ArrayList<>(packetEntries.size());
+
+    for (UpsertPlayerInfoPacket.Entry rawEntry : packetEntries) {
+      Preconditions.checkNotNull(rawEntry.getProfileId(), "Profile ID cannot be null");
+      UUID profileId = rawEntry.getProfileId();
+      UpdateEventTabListEntry currentEntry = null;
+      VelocityTabListEntry oldCurrentEntry = this.entries.get(profileId);
+
+      if (oldCurrentEntry != null) {
+        currentEntry = new UpdateEventTabListEntry(
+            this,
+            oldCurrentEntry.getProfile(),
+            oldCurrentEntry.getDisplayNameComponent().orElse(null),
+            oldCurrentEntry.getLatency(),
+            oldCurrentEntry.getGameMode(),
+            oldCurrentEntry.getChatSession(),
+            oldCurrentEntry.isListed()
+        );
+      }
+
+      if (actions.contains(UpsertPlayerInfoPacket.Action.ADD_PLAYER)) {
+        if (currentEntry == null) {
+          currentEntry = new UpdateEventTabListEntry(
+              this,
+              rawEntry.getProfile(),
+              null,
+              0,
+              -1,
+              null,
+              false
+          );
+        } else {
+          logger.debug("Received an add player packet for an existing entry; this does nothing.");
+        }
+      } else if (currentEntry == null) {
+        logger.debug(
+            "Received a partial player before an ADD_PLAYER action; profile could not be built. {}",
+            rawEntry);
+        continue;
+      } else {
+        currentEntry = new UpdateEventTabListEntry(
+            this,
+            currentEntry.getProfile(),
+            currentEntry.getDisplayNameComponent().orElse(null),
+            currentEntry.getLatency(),
+            currentEntry.getGameMode(),
+            currentEntry.getChatSession(),
+            currentEntry.isListed()
+        );
+      }
+      if (actions.contains(UpsertPlayerInfoPacket.Action.UPDATE_GAME_MODE)) {
+        currentEntry.setGameModeWithoutRewrite(rawEntry.getGameMode());
+      }
+      if (actions.contains(UpsertPlayerInfoPacket.Action.UPDATE_LATENCY)) {
+        currentEntry.setLatencyWithoutRewrite(rawEntry.getLatency());
+      }
+      if (actions.contains(UpsertPlayerInfoPacket.Action.UPDATE_DISPLAY_NAME)) {
+        currentEntry.setDisplayNameWithoutRewrite(rawEntry.getDisplayName() != null
+            ? rawEntry.getDisplayName().getComponent() : null);
+      }
+      if (actions.contains(UpsertPlayerInfoPacket.Action.INITIALIZE_CHAT)) {
+        currentEntry.setChatSessionWithoutRewrite(rawEntry.getChatSession());
+      }
+      if (actions.contains(UpsertPlayerInfoPacket.Action.UPDATE_LISTED)) {
+        currentEntry.setListedWithoutRewrite(rawEntry.isListed());
+      }
+      entries.add(currentEntry);
+    }
+
+    return entries;
+  }
+
+  private List<UpdateEventTabListEntry> mapToEventEntries(Collection<UUID> uuids) {
+    List<UpdateEventTabListEntry> entries = new ArrayList<>();
+
+    for (Map.Entry<UUID, VelocityTabListEntry> entry : this.entries.entrySet()) {
+      if (uuids.contains(entry.getKey())) {
+        entries.add(
+            new UpdateEventTabListEntry(
+                this,
+                entry.getValue().getProfile(),
+                entry.getValue().getDisplayNameComponent().orElse(null),
+                entry.getValue().getLatency(),
+                entry.getValue().getGameMode(),
+                entry.getValue().getChatSession(),
+                entry.getValue().isListed()
+            )
+        );
+      }
+    }
+
+    return entries;
+  }
+
   private void processUpsert(EnumSet<UpsertPlayerInfoPacket.Action> actions,
       UpsertPlayerInfoPacket.Entry entry) {
     Preconditions.checkNotNull(entry.getProfileId(), "Profile ID cannot be null");
@@ -278,8 +448,34 @@ public class VelocityTabList implements InternalTabList {
 
   @Override
   public void processRemove(RemovePlayerInfoPacket infoPacket) {
+    List<UpdateEventTabListEntry> entries = mapToEventEntries(infoPacket.getProfilesToRemove());
+
+    proxyServer.getEventManager().fire(
+        new ServerUpdateTabListEvent(
+            player,
+            Set.of(ServerUpdateTabListEvent.Action.REMOVE_PLAYER),
+            Collections.unmodifiableList(entries)
+        )
+    ).thenAcceptAsync(event -> { //not sure what should be used here!
+      if (event.getResult().isAllowed()) {
+        if (event.getResult().getIds().isEmpty()) {
           for (UUID uuid : infoPacket.getProfilesToRemove()) {
             this.entries.remove(uuid);
           }
+
+          connection.write(infoPacket);
+        } else {
+          List<UUID> uuids = new ArrayList<>();
+          for (UUID uuid : infoPacket.getProfilesToRemove()) {
+            if (event.getResult().getIds().contains(uuid)) {
+              this.entries.remove(uuid);
+              uuids.add(uuid);
+            }
+          }
+
+          this.connection.write(new RemovePlayerInfoPacket(uuids));
+        }
+      }
+    });
   }
 }

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

@@ -34,7 +34,7 @@ public class VelocityTabListEntry implements TabListEntry {
 
   private final VelocityTabList tabList;
   private final GameProfile profile;
-  private Component displayName;
+  private @Nullable Component displayName;
   private int latency;
   private int gameMode;
   private boolean listed;
@@ -43,7 +43,7 @@ public class VelocityTabListEntry implements TabListEntry {
   /**
    * Constructs the instance.
    */
-  public VelocityTabListEntry(VelocityTabList tabList, GameProfile profile, Component displayName,
+  public VelocityTabListEntry(VelocityTabList tabList, GameProfile profile, @Nullable Component displayName,
                               int latency,
                               int gameMode, @Nullable ChatSession session, boolean listed) {
     this.tabList = tabList;

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

@@ -17,16 +17,18 @@
 
 package com.velocitypowered.proxy.tablist;
 
+import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
+import com.velocitypowered.api.event.player.ServerUpdateTabListEvent;
 import com.velocitypowered.api.proxy.ProxyServer;
 import com.velocitypowered.api.proxy.player.TabListEntry;
 import com.velocitypowered.api.util.GameProfile;
 import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
 import com.velocitypowered.proxy.protocol.packet.LegacyPlayerListItemPacket;
-import com.velocitypowered.proxy.protocol.packet.LegacyPlayerListItemPacket.Item;
 import java.util.Collections;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
 import net.kyori.adventure.text.Component;
@@ -82,11 +84,111 @@ public class VelocityTabListLegacy extends KeyedVelocityTabList {
   }
 
   @Override
-  public void processLegacy(LegacyPlayerListItemPacket packet) {
+  public void processLegacyUpdate(LegacyPlayerListItemPacket packet) {
-    Item item = packet.getItems().get(0); // Only one item per packet in 1.7
+    ServerUpdateTabListEvent.Action action = mapToEventAction(packet.getAction());
+    Preconditions.checkNotNull(action, "action");
 
-    switch (packet.getAction()) {
+    UpdateEventTabListEntry entry = mapToEventEntry(packet.getAction(), packet.getItems().get(0)); // Only one item per packet in 1.7
-      case LegacyPlayerListItemPacket.ADD_PLAYER:
+
+    proxyServer.getEventManager().fire(
+        new ServerUpdateTabListEvent(
+            player,
+            Set.of(action),
+            Collections.singletonList(entry)
+        )
+    ).thenAcceptAsync(event -> {
+      if (event.getResult().isAllowed()) {
+        if (event.getResult().getIds().isEmpty()) {
+          if (entry.isRewrite()) {
+            //listeners have modified the entry, requires manual processing
+            if (action != ServerUpdateTabListEvent.Action.REMOVE_PLAYER) {
+              if (this.entries.containsKey(entry.getProfile().getId())) {
+                removeEntry(entry.getProfile().getId());
+              }
+
+              addEntry(entry);
+            } else {
+              removeEntry(entry.getProfile().getId());
+            }
+          } else {
+            //listeners haven't modified the entry
+            processLegacy(packet.getAction(), packet.getItems().get(0));
+
+            connection.write(packet);
+          }
+        } else {
+          //listeners have denied entries (and may have modified others), requires manual processing
+          // (doesn't make much sense as there can only be one entry)
+          if (action != ServerUpdateTabListEvent.Action.REMOVE_PLAYER) {
+            if (event.getResult().getIds().contains(entry.getProfile().getId())) {
+              if (this.entries.containsKey(entry.getProfile().getId())) {
+                removeEntry(entry.getProfile().getId());
+              }
+
+              addEntry(entry);
+            }
+          } else {
+            if (event.getResult().getIds().contains(entry.getProfile().getId())) {
+              removeEntry(entry.getProfile().getId());
+            }
+          }
+        }
+      }
+    });
+  }
+
+  private UpdateEventTabListEntry mapToEventEntry(int action, LegacyPlayerListItemPacket.Item packetItem) {
+    UpdateEventTabListEntry currentEntry = null;
+
+    switch (action) {
+      case LegacyPlayerListItemPacket.ADD_PLAYER -> {
+        if (nameMapping.containsKey(packetItem.getName())) { // ADD_PLAYER also used for updating ping
+          KeyedVelocityTabListEntry oldCurrentEntry = this.entries.get(nameMapping.get(packetItem.getName()));
+
+          if (oldCurrentEntry != null) {
+            currentEntry = new UpdateEventTabListEntry(
+                this,
+                oldCurrentEntry.getProfile(),
+                oldCurrentEntry.getDisplayNameComponent().orElse(null),
+                oldCurrentEntry.getLatency(),
+                oldCurrentEntry.getGameMode(),
+                oldCurrentEntry.getChatSession(),
+                oldCurrentEntry.isListed()
+            );
+          }
+
+          if (currentEntry != null) {
+            currentEntry.setLatencyWithoutRewrite(packetItem.getLatency());
+          }
+        } else {
+          UUID uuid = UUID.randomUUID(); // Use a fake uuid to preserve function of custom entries
+
+          nameMapping.put(packetItem.getName(), uuid);
+          currentEntry = new UpdateEventTabListEntry(
+              this,
+              new GameProfile(uuid, packetItem.getName(), ImmutableList.of()),
+              null,
+              packetItem.getLatency(),
+              0,
+              null,
+              true
+          );
+        }
+      }
+      case LegacyPlayerListItemPacket.REMOVE_PLAYER -> {
+        //Nothing should be done here as all entries which are not allowed are removed if the action is ServerUpdateTabListEvent.Action.REMOVE_PLAYER
+      }
+      default -> {
+        // For 1.7 there is only add and remove
+      }
+    }
+
+    return currentEntry;
+  }
+
+  private void processLegacy(int action, LegacyPlayerListItemPacket.Item item) {
+    switch (action) {
+      case LegacyPlayerListItemPacket.ADD_PLAYER -> {
         if (nameMapping.containsKey(item.getName())) { // ADD_PLAYER also used for updating ping
           KeyedVelocityTabListEntry entry = entries.get(nameMapping.get(item.getName()));
           if (entry != null) {
@@ -101,16 +203,16 @@ public class VelocityTabListLegacy extends KeyedVelocityTabList {
               .latency(item.getLatency())
               .build());
         }
-        break;
+      }
-      case LegacyPlayerListItemPacket.REMOVE_PLAYER:
+      case LegacyPlayerListItemPacket.REMOVE_PLAYER -> {
         UUID removedUuid = nameMapping.remove(item.getName());
         if (removedUuid != null) {
           entries.remove(removedUuid);
         }
-        break;
+      }
-      default:
+      default -> {
         // For 1.7 there is only add and remove
-        break;
+      }
     }
   }