ProtocolLib

Services.get("ProtocolLib")

Overview

registerListener(priority, handler, packetTypes) ⇒ listener
unregisterListener(listener)

API Reference

registerListener()

ProtocolLib.registerListener(priority, handler, packetTypes)

Registers a new packet listener.

• priority: "LOW", "NORMAL", "HIGH", or "MONITOR"

• handler: JavaScript object containing onSend(event) and/or onReceive(event)

• packetTypes: Array of packet names, e.g., "Play.Server.BLOCK_CHANGE"

Returns: a listener object

const ProtocolLib = Services.get("ProtocolLib")
const listener = ProtocolLib.registerListener("NORMAL", {
  onSend(event) {
    const packet = event.getPacket();
    // handle packet here
  }
}, ["Play.Server.BLOCK_CHANGE"]);

Additional info on packetTypes:

The packetType is specified relative to the com.comphenix.protocol.PacketType class. For example, Play.Server.BLOCK_CHANGE corresponds to com.comphenix.protocol.PacketType.Play.Server.BLOCK_CHANGE. All provided packet types follow this structure and are based on their original class path.

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unregisterListener()

ProtocolLib.unregisterListener(listener)

Unregisters a previously registered packet listener.

ProtocolLib.unregisterListener(listener);

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Packet Event Object

The event passed into your handler (onSend / onReceive) provides access to:

Method	Description
getPacket()	Returns the actual ProtocolLib packet
getPacketType()	Returns packet type as enum (e.g. Play.Server.CHAT)

You can use:

• read(index) / write(index, value) to access fields

• Packet-specific methods like getBlockData() or getBlockDataArrays()

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Example Script: Block Spoofing

This script replaces all changing blocks with a spoofed OAK_LOG block:

const ProtocolLib = Services.get("ProtocolLib")
const WrappedBlockData = importClass("com.comphenix.protocol.wrappers.WrappedBlockData")
const Material = org.bukkit.Material;
const createDataMethod = getMethod(WrappedBlockData, "createData", ["org.bukkit.Material"]);

let SpoofedBlock = createDataMethod.invoke(null, [Material.OAK_LOG]);

const handler = {
  onSend(event) {
    const packet = event.getPacket();
    const type = event.getPacketType().name();

    if (type === "BLOCK_CHANGE") {
      const blockData = packet.getBlockData().read(0);
      if (!blockData.getType().equals(Material.AIR)) {
        packet.getBlockData().write(0, SpoofedBlock);
      }
    }

    if (type === "MULTI_BLOCK_CHANGE") {
      let blocks = packet.getBlockDataArrays().read(0);
      for (let i = 0; i < blocks.length; i++) {
        if (!blocks[i].getType().equals(Material.AIR)) {
          blocks[i] = SpoofedBlock;
        }
      }
      packet.getBlockDataArrays().write(0, blocks);
    }
  }
};

const listener = ProtocolLib.registerListener("NORMAL", handler, [
  "Play.Server.BLOCK_CHANGE",
  "Play.Server.MULTI_BLOCK_CHANGE"
]);

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Best Practices

• Unregister unused listeners with ProtocolLib.unregisterListener(...)

• Avoid modifying packets in "MONITOR" priority (read-only phase)

• Use getMethod() and invoke() carefully for wrapper class access