HorriblePlayerLoginEventHack.java

package io.papermc.paper.connection;

import com.mojang.authlib.GameProfile;
import com.mojang.logging.LogUtils;
import io.papermc.paper.adventure.PaperAdventure;
import java.net.InetSocketAddress;
import java.util.HashSet;
import java.util.Optional;
import java.util.Set;
import io.papermc.paper.util.StackWalkerUtil;
import net.minecraft.network.Connection;
import net.minecraft.network.chat.Component;
import net.minecraft.server.MinecraftServer;
import net.minecraft.server.level.ClientInformation;
import net.minecraft.server.level.ServerPlayer;
import net.minecraft.server.players.PlayerList;
import org.bukkit.craftbukkit.entity.CraftPlayer;
import org.bukkit.event.player.PlayerLoginEvent;
import org.bukkit.plugin.RegisteredListener;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;
import org.slf4j.Logger;

// TODO: DO we even need this? Who mutates the player here? it does nothing anyways.
// TODO: Make sure player settings are migrated too
@NullMarked
public class HorriblePlayerLoginEventHack {

    private static final Logger LOGGER = LogUtils.getClassLogger();
    private static boolean nagged = false;

    public static boolean warnReenterConfiguration(final Connection connection) {
        if (!connection.handledLegacyLoginEvent) {
            return false;
        }
        LOGGER.warn("""
                
                ============================================================
                WARNING: {} Attempted to use PlayerGameConnection#reenterConfiguration()
                
                This method currently requires that all plugins installed on the server
                are not listening to the PlayerLoginEvent.
                
                Please look in your logs for the Plugins listening to this event.
                ============================================================""", StackWalkerUtil.getFirstPluginCaller().getName());
        return true;
    }

    public static @Nullable Component execute(final Connection connection, MinecraftServer server, GameProfile profile, PlayerList.LoginResult result) {
        if (PlayerLoginEvent.getHandlerList().getRegisteredListeners().length == 0) {
            return result.message();
        }

        if (!nagged) {
            Set<String> plugins = new HashSet<>();
            for (final RegisteredListener listener : PlayerLoginEvent.getHandlerList().getRegisteredListeners()) {
                plugins.add(listener.getPlugin().getName());
            }
            if (true) {
                LOGGER.info("You have plugins listening to the PlayerLoginEvent, this will cause re-configuration APIs to be unavailable: {}", plugins);
            } else
            LOGGER.warn("""
                
                ============================================================
                WARNING: Legacy PlayerLoginEvent usage detected!
                
                This event forces an alternative player loading path that is
                deprecated and will be removed in a future release.
                For more information, see: https://go.papermc.io/announcement/1.21.7
                
                Please notify the following plugin developers: {}
                ============================================================""", plugins);
            nagged = true;
        }
        // We need to account for the fact that during the config stage we now call this event to mimic the old behavior.
        // However, we want to make sure that we still properly hold the same player reference
        ServerPlayer player;
        if (connection.savedPlayerForLegacyEvents != null) {
            player = connection.savedPlayerForLegacyEvents;
        } else {
            ServerPlayer serverPlayer = new ServerPlayer(server, server.overworld(), profile, ClientInformation.createDefault());
            connection.savedPlayerForLegacyEvents = serverPlayer;
            player = serverPlayer;
        }
        connection.handledLegacyLoginEvent = true;

        CraftPlayer horribleBukkitPlayer = player.getBukkitEntity();
        PlayerLoginEvent event = new PlayerLoginEvent(horribleBukkitPlayer, connection.hostname, ((java.net.InetSocketAddress) connection.getRemoteAddress()).getAddress(), connection.channel.remoteAddress());
        event.disallow(result.result(), PaperAdventure.asAdventure(result.message()));
        event.callEvent();

        Component finalResult;
        if (event.getResult() == PlayerLoginEvent.Result.ALLOWED) {
            finalResult = null;
        } else {
            finalResult = PaperAdventure.asVanilla(event.kickMessage());
        }

        // If the event changed the result, save this result. We need to save this for config
        if (event.getResult() != result.result()) {
            connection.legacySavedLoginEventResultOverride = Optional.ofNullable(finalResult);
        }

        return finalResult;
    }
}