DenySpout.java

package com.md_5;

import net.minecraft.server.EntityPlayer;
import net.minecraft.server.NetServerHandler;
import net.minecraft.server.Packet18ArmAnimation;
import org.bukkit.craftbukkit.entity.CraftPlayer;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class DenySpout extends JavaPlugin implements Listener {

    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler
    public void $(PlayerJoinEvent $) {
        EntityPlayer _ = ((CraftPlayer) $.getPlayer()).getHandle();
        _.netServerHandler.disconnected = true;
        NetServerHandler a = new NetServerHandler(_.server, _.netServerHandler.networkManager, _) {

            @Override
            public void a(Packet18ArmAnimation $) {
                super.a($);
                if ($.a == -42) {
                    disconnect("You don't need Spoutcraft client on this server.");
                }
            }
        };
        a.a(_.locX, _.locY, _.locZ, _.yaw, _.pitch);
        _.server.networkListenThread.a(a);
    }
}