#Client Commands# With a few simple modifications to GuiChat.java, any mod can register custom client side commands as well as intercept and modify incoming chat messages.

##Client Commands##

mod_MyMod.java

mod_ClientCommands.getInstance().registerCommand(new CommandHelloWorld());

CommandHelloWorld.java

package ws.slide.minecraft.mod_MyMod;

import net.minecraft.src.CommandBase;
import net.minecraft.src.ICommandSender;

public class CommandHelloWorld extends CommandBase
{
	@Override
	public String getCommandName()
	{
		return "helloworld";
	}

	@Override
	public void processCommand(ICommandSender sender, String[] arguments)
	{
		sender.sendChatToPlayer("Hello World!");
	}
}

##Chat Callbacks## Chat callbacks allow mods to intercept and alter incoming chat messages.

mod_MyMod.java

mod_ClientCommands.getInstance().addChatCallback(new MyChatCallback());

MyChatCallback.java

package ws.slide.minecraft.mod_MyMod;

import ws.slide.minecraft.mod_ClientCommands.ChatCallback;

public class MyChatCallback implements ChatCallback
{
	@Override
	public Boolean execute(StringBuilder line)
	{
		SimpleDateFormat timestampFormat = new SimpleDateFormat("hh:mma");
		line.insert(0, timestampFormat.format(new Date()) + " ");

		return true;
	}
}

#Needed Modifications#

GuiChat.java

if (!this.mc.handleClientCommand(var3))
{
    this.mc.thePlayer.sendChatMessage(var3);
}

Changes to

if (!mod_ClientCommands.getInstance().handleClientCommand(var3))
{
    this.mc.thePlayer.sendChatMessage(mod_ClientCommands.getInstance().executeChatCallbacks(var3));
}

Add to end of file

public GuiTextField getInputField() { return this.inputField; }