FakePlayerGist.java

package net.bicrypt.gist;

import com.comphenix.protocol.ProtocolLibrary;
import com.comphenix.protocol.ProtocolManager;
import com.comphenix.protocol.events.PacketContainer;
import com.comphenix.protocol.wrappers.EnumWrappers.NativeGameMode;
import com.comphenix.protocol.wrappers.EnumWrappers.PlayerInfoAction;
import com.comphenix.protocol.wrappers.PlayerInfoData;
import com.comphenix.protocol.wrappers.WrappedChatComponent;
import com.comphenix.protocol.wrappers.WrappedDataWatcher;
import com.comphenix.protocol.wrappers.WrappedDataWatcher.Registry;
import com.comphenix.protocol.wrappers.WrappedDataWatcher.WrappedDataWatcherObject;
import com.comphenix.protocol.wrappers.WrappedGameProfile;
import java.lang.reflect.InvocationTargetException;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicInteger;
import lombok.RequiredArgsConstructor;
import lombok.SneakyThrows;
import org.bukkit.Location;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.scheduler.BukkitRunnable;

import static java.util.Collections.singletonList;

import static com.comphenix.protocol.PacketType.Play.Server.ENTITY_HEAD_ROTATION;
import static com.comphenix.protocol.PacketType.Play.Server.ENTITY_METADATA;
import static com.comphenix.protocol.PacketType.Play.Server.NAMED_ENTITY_SPAWN;
import static com.comphenix.protocol.PacketType.Play.Server.PLAYER_INFO;

@RequiredArgsConstructor
public class FakePlayerGist implements Listener {

    private static final ProtocolManager PROTOCOL_MANAGER;

    static {
        PROTOCOL_MANAGER = ProtocolLibrary.getProtocolManager();
    }

    private final JavaPlugin plugin;

    @EventHandler
    public void onPlayerJoin(PlayerJoinEvent event) {
        final Player player = event.getPlayer();
        final Location location = player.getLocation().clone();
        new BukkitRunnable() {
            @Override
            public void run() {
                if (!player.isOnline()) {
                    cancel();
                    return;
                }
                FakePlayer fakePlayer = new FakePlayer(plugin, player, location);
                // spawn fake player
                fakePlayer.spawn();
            }
        }.runTaskLaterAsynchronously(plugin, 40L);
    }

    private static class FakePlayer {

        private static final AtomicInteger GENERATOR;

        static {
            GENERATOR = new AtomicInteger(1);
        }

        private final int entityId;
        private final JavaPlugin plugin;
        private final Player player;
        private final UUID uniqueId;
        private final String username;
        private final WrappedGameProfile gameProfile;
        private final Location location;

        FakePlayer(JavaPlugin plugin, Player player, Location location) {
            this.entityId = nextEntityId();
            this.plugin = plugin;
            this.player = player;
            this.uniqueId = player.getUniqueId();
            this.username = player.getName();
            // use player skin for fake player
            this.gameProfile = WrappedGameProfile.fromPlayer(player);
            this.location = location;
        }

        static synchronized int nextEntityId() {
            return GENERATOR.getAndIncrement();
        }

        @SneakyThrows(value = InvocationTargetException.class)
        void spawn() {
            // add player to tab list
            PROTOCOL_MANAGER.sendServerPacket(player, getPlayerInfoPacket(PlayerInfoAction.ADD_PLAYER));
            // spawn fake player with skin data
            PROTOCOL_MANAGER.sendServerPacket(player, getNamedEntitySpawnPacket());
            // update the fake player's metadata (try to send skin parts yet another time)
            PROTOCOL_MANAGER.sendServerPacket(player, getEntityMetadataPacket());
            // send head rotation packet to ensure the player is facing the intended direction
            PROTOCOL_MANAGER.sendServerPacket(player, getHeadRotationPacket());
            new BukkitRunnable() {
                @SneakyThrows(value = InvocationTargetException.class)
                @Override
                public void run() {
                    if (!player.isOnline()) {
                        cancel();
                        return;
                    }
                    // try to display skin parts for the last time
                    PROTOCOL_MANAGER.sendServerPacket(player, getEntityMetadataPacket());
                    // remove fake player from the tab list
                    PROTOCOL_MANAGER.sendServerPacket(player, getPlayerInfoPacket(PlayerInfoAction.REMOVE_PLAYER));
                }
            }.runTaskLaterAsynchronously(plugin, 2L);
        }

        private PacketContainer getPlayerInfoPacket(PlayerInfoAction action) {
            PacketContainer container = PROTOCOL_MANAGER.createPacket(PLAYER_INFO);
            container.getModifier().writeDefaults();
            container.getPlayerInfoAction().write(0, action);
            PlayerInfoData infoData = new PlayerInfoData(
                gameProfile,
                1,
                NativeGameMode.NOT_SET,
                WrappedChatComponent.fromText(username)
            );
            container.getPlayerInfoDataLists().write(0, singletonList(infoData));
            return container;
        }

        private PacketContainer getNamedEntitySpawnPacket() {
            PacketContainer container = PROTOCOL_MANAGER.createPacket(NAMED_ENTITY_SPAWN);
            container.getModifier().writeDefaults();
            container.getIntegers().write(0, entityId);
            container.getUUIDs().write(0, uniqueId);
            container.getDoubles()
                .write(0, location.getX())
                .write(1, location.getY())
                .write(2, location.getZ());
            container.getBytes()
                .write(0, (byte) (location.getYaw() * 256.0F / 360.0F))
                .write(1, (byte) (location.getPitch() * 256.0F / 360.0F));
            container.getDataWatcherModifier().write(0, getFakePlayerDataWatcher());
            return container;
        }

        private PacketContainer getEntityMetadataPacket() {
            PacketContainer container = PROTOCOL_MANAGER.createPacket(ENTITY_METADATA);
            container.getModifier().writeDefaults();
            container.getIntegers().write(0, entityId);
            container.getWatchableCollectionModifier().write(0, getFakePlayerDataWatcher().getWatchableObjects());
            return container;
        }

        private PacketContainer getHeadRotationPacket() {
            PacketContainer container = PROTOCOL_MANAGER.createPacket(ENTITY_HEAD_ROTATION);
            container.getModifier().writeDefaults();
            container.getIntegers().write(0, entityId);
            container.getBytes().write(0, (byte) (location.getYaw() * 256.0F / 360.0F));
            return container;
        }

        private WrappedDataWatcher getFakePlayerDataWatcher() {
            WrappedDataWatcher watcher = new WrappedDataWatcher();
            /*
             * According to https://wiki.vg/Entity_metadata#Player one has to send
             * the desired bitmask at index 13 in order to display certain parts of
             * the players skin.
             *
             * In this case we set the value to the sum of all available masks
             * (0x01 + 0x02 + 0x04 + 0x08 + 0x10 + 0x20 + 0x40 = 127)
             *
             * Somehow no skin parts are being displayed!
             *
             * On a 1.8 paper spigot instance at index 10 (was the index to use back in
             * the day) it works perfectly with 127 as value.
             *
             * Seems to be broken in 1.14 and latest paper spigot build though.
             */
            watcher.setObject(new WrappedDataWatcherObject(13, Registry.get(Byte.class)), (byte) 127);
            return watcher;
        }
    }
}