Packet event

var C00Handshake = Java.type("net.minecraft.network.handshake.client.C00Handshake");

...

module.on("packet", function(eventData) {
    var packet = eventData.getPacket();

    if (packet instanceof C00Handshake) {
        Chat.print("Cancelling handshake.");
        eventData.cancelEvent();
    }
});

Why not do it like this?

module.on("packet", function(event) {
    var packet = event.getPacket();

    if (packet instanceof Java.type("net.minecraft.network.play.client.C03PacketPlayer")) {
        Chat.print("you send a c03 packet!");   
    }
});

i thought the code will be execute when i RECEIVE (not send) a packet?

module.on("packet", function(event) {
    var packet = event.getPacket();

    if (packet instanceof Java.type("net.minecraft.network.play.client.C03PacketPlayer")) {
        Chat.print("you send a c03 packet!");   
    }
});

Why would you need a onPacketSend event? Packet names either start with a C or an S. Packets whose name begins with a C are client packets, those that begin with an S are server packets.

i mean i want to execute sth when sending a packet, example:

this.onSendPacket = function(event) {
      if(event.sendPacket() instanceof C03PacketPlayer) {
     Chat.print("you send a c03 packet!")
      }
}