Listening to Packets

In this guide, you'll learn how to listen to packets that are being sent or received from the Client.

Packets are defined in com.hypixel.hytale.protocol and organized by category in com.hypixel.hytale.protocol.packets. Base class is Packet and the sub-packages contain actual packet classes. The low-level Netty handler is com.hypixel.hytale.server.core.io.netty.PlayerChannelHandler, it delegates packet processing logic to com.hypixel.hytale.server.core.io.adapter.PacketAdapters.

The server has a built-in adapter system that makes injection very straightforward. You don't need to hook into Netty manually. You can use the PacketAdapters class to register inbound (Client -> Server) and outbound (Server -> Client) watchers. The process for registering inbound packets is the same as for outbound.

The PacketAdapters class provides several registerInbound method overloads. Possible argument types are PacketWatcher, PacketFilter, PlayerPacketWatcher and PlayerPacketFilter.

The difference between PacketWatcher and PacketFilter is that the PacketFilter can prevent packet processing and block the packet from reaching the server (for inbound) or reaching the player (for outbound).

Injecting our own function to the PacketAdapter.

We can inject our own function to the PacketAdapter by using one of the methods mentioned above, here is an example that prints all packets sent from the server to the client.

PacketAdapters.registerOutbound((PacketHandler handler, Packet packet) -> {
    var handlerName = handler.getClass().getSimpleName();
    var packetName = packet.getClass().getSimpleName();

    // some common packets excluded to reduce spam
    if (!"EntityUpdates".equals(packetName) && !"CachedPacket".equals(packetName)) {
        logger.at(Level.INFO)
              .log("[" + handlerName + "] Sent packet id=" + packet.getId() + ": " + packetName);
    }
});

Modfying an incoming packet

In the following example, we modify a incoming packet containing skin data to remove that data from the packet. With this, every player will have default skin.

PacketAdapters.registerInbound((PacketHandler handler, Packet packet) -> {
    if (packet instanceof PlayerOptions skinPacket) {
        skinPacket.skin = null;
    }
});

Packet handlers

Packet Handlers and the incoming packet types and corresponding packet ids of the packets they handle. Packets can be present in multiple handlers. If any other type of packet comes in during wrong phase, the handler will disconnect the sender. These are serverbound (inbound) packets. Some packets are used in both directions, such as SyncInteractionChains. Packets not mentioned here are likely clientbound (outbound), but will be added soon.