Hi, i need to add additional field in login packet from client.

Reason is: i need to check hwid of clients for ban(i have implemented and working hwid class).

 

I have working mod on 1.7.10, its uses ASM to modify login packet on clientside and bukkit to read it on clien.

 

package my_class.hwidmod.coremod;

import net.minecraft.launchwrapper.IClassTransformer;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.tree.*;

import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;

import static org.objectweb.asm.Opcodes.*;

@SuppressWarnings("unused")
public final class ASMTransformer implements IClassTransformer
{
	private static final String HWID_UTILS_CLASS_NAME = "my_class_here/HwidUtils";
	private static final String HWID_UTILS_METHOD_GET_HWID_NAME = "getHwid";
	private static final String HWID_UTILS_METHOD_GET_HWID_DESC = "()[B";

	private static final String FIELD_HWID_NAME = "hwid";
	private static final String FIELD_HWID_DESC = "[B";
	private static final String METHOD_GET_HWID_NAME = "getHwid";
	private static final String METHOD_GET_HWID_DESC = "()[B";

	@Override
	public byte[] transform(String name, String transformedName, byte[] basicClass)
	{
		if (transformedName.equals("net.minecraft.network.login.client.C00PacketLoginStart"))
			return transformLoginPacket(basicClass);
		return basicClass;
	}

	private static byte[] transformLoginPacket(byte[] basicClass)
	{
		ClassNode classNode = new ClassNode();
		new ClassReader(basicClass).accept(classNode, 0);

		// May be need add it before static field __OBFID?
		classNode.visitField(ACC_PRIVATE, FIELD_HWID_NAME, FIELD_HWID_DESC, null, null).visitEnd();

		MethodVisitor getterVisitor = classNode.visitMethod(ACC_PUBLIC, METHOD_GET_HWID_NAME, METHOD_GET_HWID_DESC, null, null);
		getterVisitor.visitVarInsn(ALOAD, 0);
		getterVisitor.visitFieldInsn(GETFIELD, classNode.name, FIELD_HWID_NAME, FIELD_HWID_DESC);
		getterVisitor.visitInsn(ARETURN);
		getterVisitor.visitEnd();

		MethodNode methodNode = findMethod(classNode, "<init>", "()V");
		for (AbstractInsnNode returnInsnNode : findAllInsnNodes(methodNode, RETURN))
		{
			InsnList insnList = new InsnList();
			insnList.add(new VarInsnNode(ALOAD, 0));
			insnList.add(new FieldInsnNode(GETSTATIC, "org/apache/commons/lang3/ArrayUtils", "EMPTY_BYTE_ARRAY", "[B"));
			insnList.add(new FieldInsnNode(PUTFIELD, classNode.name, FIELD_HWID_NAME, FIELD_HWID_DESC));
			methodNode.instructions.insertBefore(returnInsnNode, insnList);
		}

		methodNode = findMethod(classNode, "<init>", "(Lcom/mojang/authlib/GameProfile;)V");
		for (AbstractInsnNode returnInsnNode : findAllInsnNodes(methodNode, RETURN))
		{
			InsnList insnList = new InsnList();
			insnList.add(new VarInsnNode(ALOAD, 0));
			insnList.add(new MethodInsnNode(INVOKESTATIC, HWID_UTILS_CLASS_NAME, HWID_UTILS_METHOD_GET_HWID_NAME, HWID_UTILS_METHOD_GET_HWID_DESC, false));
			insnList.add(new FieldInsnNode(PUTFIELD, classNode.name, FIELD_HWID_NAME, FIELD_HWID_DESC));
			methodNode.instructions.insertBefore(returnInsnNode, insnList);
		}

		methodNode = findMethod(classNode, CoreMod.isObfuscated() ? "func_148837_a" : "readPacketData", "(Lnet/minecraft/network/PacketBuffer;)V");
		for (AbstractInsnNode returnInsnNode : findAllInsnNodes(methodNode, RETURN))
		{
			InsnList insnList = new InsnList();
			insnList.add(new VarInsnNode(ALOAD, 0));
			insnList.add(new VarInsnNode(ALOAD, 1));
			insnList.add(new MethodInsnNode(INVOKESTATIC, "net/minecraft/network/Packet", CoreMod.isObfuscated() ? "func_148834_a" : "readBlob", "(Lio/netty/buffer/ByteBuf;)[B", false));
			insnList.add(new FieldInsnNode(PUTFIELD, classNode.name, FIELD_HWID_NAME, FIELD_HWID_DESC));
			methodNode.instructions.insertBefore(returnInsnNode, insnList);
		}

		methodNode = findMethod(classNode, CoreMod.isObfuscated() ? "func_148840_b" : "writePacketData", "(Lnet/minecraft/network/PacketBuffer;)V");
		for (AbstractInsnNode returnInsnNode : findAllInsnNodes(methodNode, RETURN))
		{
			InsnList insnList = new InsnList();
			insnList.add(new VarInsnNode(ALOAD, 1));
			insnList.add(new VarInsnNode(ALOAD, 0));
			insnList.add(new FieldInsnNode(GETFIELD, classNode.name, FIELD_HWID_NAME, FIELD_HWID_DESC));
			insnList.add(new MethodInsnNode(INVOKESTATIC, "net/minecraft/network/Packet", CoreMod.isObfuscated() ? "func_148838_a" : "writeBlob", "(Lio/netty/buffer/ByteBuf;[B)V", false));
			methodNode.instructions.insertBefore(returnInsnNode, insnList);
		}

		ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_MAXS);
		classNode.accept(classWriter);
		return classWriter.toByteArray();
	}

	private static MethodNode findMethod(ClassNode classNode, String name, String desc)
	{
		for (MethodNode methodNode : classNode.methods)
		{
			if (methodNode.name.equals(name) && methodNode.desc.equals(desc))
				return methodNode;
		}
		throw new NullPointerException("Method " + classNode.name + '.' + name + desc + " not found");
	}

	private static List<AbstractInsnNode> findAllInsnNodes(MethodNode methodNode, int opcode)
	{
		return findAllInsnNodes(methodNode.instructions, opcode);
	}

	private static List<AbstractInsnNode> findAllInsnNodes(InsnList insnList, int opcode)
	{
		List<AbstractInsnNode> list = new ArrayList<AbstractInsnNode>(1);
		for (ListIterator<AbstractInsnNode> iterator = insnList.iterator(); iterator.hasNext(); )
		{
			AbstractInsnNode insnNode = iterator.next();
			if (insnNode.getOpcode() == opcode)
				list.add(insnNode);
		}
		return list;
	}
}

 

But, as far as i know asm is bad practice and dont have suport now. And theris zero documentation on this.

 

So how can i achive custom field in login packet in 1.12.2?

 

Iam thinking about modifying userPropertis but don know how to do it with forge.

38 minutes ago, diesieben07 said:

What is "HWID"?

Any kind of ban system that relies on the client to send data is completely flawed. It can be bypassed stupidly easily.

What is wrong with the default ban system?

HardwareID. default ban system can be bypased with 1 click. But lets return to forum topic. Is there way to send additional info in login packet?

1 hour ago, diesieben07 said:

I'd be very interested to know how you bypass it with 1 click, as it is based on Authentication with Mojang's servers.

Your "hardware id" can also be bypassed "with 1 click".

not shure u can change serial of your cpu with 1 click.

 

Quote

No.

Ok. Moderator can close topic now.

6 minutes ago, diesieben07 said:

No, you can't do that.

But you cannot force the client to actually send the serial of the CPU. It can just send a random number.

ofc u can. and its working for my 1.7.10 server. https://github.com/oshi/oshi