ReflPackets.java

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class ReflPackets {
    private String serverVersion;

    public ReflPackets() {
        String name = Bukkit.getServer().getClass().getName();
        String[] parts = name.split("\\.");
        serverVersion = parts[3];
        TabHFBukkit.instance.getLogger().info("Detected NMS/OBC package version " + serverVersion);
    }

    public Class<?> getNMSClass(String className) {
        String fullName = "net.minecraft.server." + serverVersion + "." + className;
        Class<?> clazz = null;
        try {
            clazz = Class.forName(fullName);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return clazz;
    }

    private Method getHandle;
    private Field playerConnection;

    private Class<?> chatSerializer;
    private Method serialize;

    private Method sendPacket;

    public void sendTabPacket(Player p) {
        try {
            if (getHandle == null) {
                getHandle = p.getClass().getDeclaredMethod("getHandle");
                getHandle.setAccessible(true);
            }
            Object entityPlayer = getHandle.invoke(p);
            if (playerConnection == null) {
                playerConnection = entityPlayer.getClass().getDeclaredField("playerConnection");
                playerConnection.setAccessible(true);
            }
            Object conn = playerConnection.get(entityPlayer);
            if (chatSerializer == null) {
                chatSerializer = getNMSClass("IChatBaseComponent$ChatSerializer");
                // still null?
                if (chatSerializer == null) {
                    chatSerializer = getNMSClass("ChatSerializer");
                }
            }
            if (serialize == null) {
                serialize = chatSerializer.getDeclaredMethod("a", String.class);
                serialize.setAccessible(true);
            }
            String header = TabHFBukkit.instance.header;
            String footer = TabHFBukkit.instance.footer;
            int onlinePlayers = Bukkit.getServer().getOnlinePlayers().size();
            Object headerComp = serialize.invoke(null, header.replace("{PLAYER}", p.getName())
                    .replace("{ONLINE}", Integer.toString(onlinePlayers)));
            Object footerComp = serialize.invoke(null, footer.replace("{PLAYER}", p.getName())
                    .replace("{ONLINE}", Integer.toString(onlinePlayers)));
            if (sendPacket == null) {
                sendPacket = conn.getClass().getDeclaredMethod("sendPacket", getNMSClass("Packet"));
                sendPacket.setAccessible(true);
            }
            Object headerFooterPacket = getHeaderFooterPacket(headerComp, footerComp);
            sendPacket.invoke(conn, headerFooterPacket);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private Constructor headerFooterPacketConstructor;
    private Field bField;

    private Object getHeaderFooterPacket(Object header, Object footer) {
        try {
            Class<?> packetClass = getNMSClass("PacketPlayOutPlayerListHeaderFooter");
            if (headerFooterPacketConstructor == null) {
                headerFooterPacketConstructor = packetClass.getDeclaredConstructor(getNMSClass("IChatBaseComponent"));
                headerFooterPacketConstructor.setAccessible(true);
            }
            Object headerFooter = headerFooterPacketConstructor.newInstance(header);
            if (bField == null) {
                bField = headerFooter.getClass().getDeclaredField("b");
                bField.setAccessible(true);
            }
            bField.set(headerFooter, footer);
            return headerFooter;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}