Packet IO Transformer

PacketIOTransformer.java

package mnm.mods.protocol4.asm;

import com.mumfrey.liteloader.core.runtime.Obf;
import com.mumfrey.liteloader.transformers.ClassTransformer;

import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.MethodInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.VarInsnNode;

import java.util.ListIterator;

public abstract class PacketIOTransformer extends ClassTransformer implements Opcodes {

    private static final String READ_PACKET = "readPacketData";
    private static final String WRITE_PACKET = "writePackeDatat";

    protected Obf className;
    private String packetIO;;

    protected PacketIOTransformer(Obf className, String packetIOClass) {
        this.className = className;
        this.packetIO = packetIOClass;
    }

    @Override
    public final byte[] transform(String name, String transformedName, byte[] basicClass) {
        if (className.name.equals(name) && basicClass != null) {
            ClassNode classNode = readClass(basicClass, false);

            for (MethodNode mn : classNode.methods) {
                if (mn.name.equals("readPacketData")) {
                    transformReadPacket(mn);
                }

                if (mn.name.equals("writePacketData")) {
                    transformWritePacket(mn);
                }
            }

            basicClass = writeClass(classNode);
        }
        return basicClass;
    }

    protected void transformReadPacket(MethodNode mn) {
        InsnList insn = mn.instructions;

        InsnList list = new InsnList();
        {
            list.add(new VarInsnNode(ALOAD, 0));
            list.add(new MethodInsnNode(INVOKESTATIC, packetIO, READ_PACKET, mn.desc));
            list.add(new VarInsnNode(ASTORE, 0));
        }
        // Insert at beginning
        insn.insert(list);
    }

    protected void transformWritePacket(MethodNode mn) {
        InsnList insn = mn.instructions;

        InsnList list = new InsnList();
        {
            list.add(new VarInsnNode(ALOAD, 0));
            list.add(new MethodInsnNode(INVOKESTATIC, packetIO, WRITE_PACKET, mn.desc));
            list.add(new VarInsnNode(ASTORE, 0));
        }
        // Insert before return
        ListIterator<AbstractInsnNode> iter = insn.iterator();
        while (iter.hasNext()) {
            AbstractInsnNode node = iter.next();
            if (node.getOpcode() == RETURN) {
                insn.insertBefore(node, list);
            }
        }
    }
}