PayloadAdapter.java

public class PayloadAdapter extends PacketAdapter {

    private static final Method ARRAY_METHOD;
    static {
        try {
            ARRAY_METHOD = Class.forName("io.netty.buffer.UnpooledHeapByteBuf").getMethod("array");
        } catch (NoSuchMethodException | ClassNotFoundException ex) {
            throw new RuntimeException(ex);
        }
    }

    private final Map<String, Class<? extends Payload>> channels = new HashMap<>();
    private final PayloadDirection direction;

    public PayloadAdapter(Plugin plugin, PayloadDirection direction) {
        super(plugin, ListenerPriority.NORMAL, direction.getPayloadPacket());
        this.direction = direction;
    }

    public void bind(Class<? extends Payload> payload, String... channels) {
        Arrays.stream(channels).forEach(channel -> this.channels.put(channel, payload));
    }

    private Payload newPayload(String channel, byte[] bytes) {
        try {
            final Class<? extends Payload> clazz = channels.getOrDefault(channel, Payload.class);
            if (!clazz.equals(Payload.class)) return clazz.getConstructor(byte[].class).newInstance((Object) bytes);
            else return clazz.getConstructor(byte[].class, BiFunction.class).newInstance(bytes, (BiFunction<ByteBuffer, Integer, Object>) (buffer, index) -> null);
        } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException | InstantiationException ex) {
            throw new RuntimeException(ex);
        }
    }

    private void handleInternal(PacketEvent event) {
        try {
            final PacketContainer container = event.getPacket();
            final String channel = container.getStrings().readSafely(0);
            final byte[] bytes = (byte[]) ARRAY_METHOD.invoke(container.getModifier().readSafely(1));
            Bukkit.getPluginManager().callEvent(new PayloadInOutEvent(event.getPlayer(), direction, channel, newPayload(channel, bytes)));
        } catch (IllegalAccessException | InvocationTargetException ex) {
            ex.printStackTrace();
        }
    }

    @Override
    public void onPacketSending(PacketEvent event) {
        if(direction == PayloadDirection.SERVERBOUND) handleInternal(event);
    }

    @Override
    public void onPacketReceiving(PacketEvent event) {
        if(direction == PayloadDirection.CLIENTBOUND) handleInternal(event);
    }

}