3. Creating your own Transformer

🪄 What are transformers?

The whole deobfuscation process is based on transformers. Transformers are smaller pieces that are responsible for deobfuscating specific obfuscation techniques. In simple words - transformers are transforming obfuscated code into a more readable form.

🔧 How to create your own transformer?

Create a new class in deobfuscator-transformers module. The most basic transformer can look like this:

import uwu.narumi.deobfuscator.api.asm.ClassWrapper;
import uwu.narumi.deobfuscator.api.context.Context;
import uwu.narumi.deobfuscator.api.transformer.Transformer;

public class SomeTransformer extends Transformer {
  @Override
  protected void transform() throws Exception {
    scopedClasses().forEach(classWrapper -> classWrapper.methods().forEach(methodNode -> {
      // Code here
    }));
  }
}

For example, this transformer replaces every "Hello, World!" string with "Bye, World!":

import org.objectweb.asm.tree.LdcInsnNode;
import uwu.narumi.deobfuscator.api.asm.ClassWrapper;
import uwu.narumi.deobfuscator.api.context.Context;
import uwu.narumi.deobfuscator.api.transformer.Transformer;

import java.util.Arrays;

public class SomeTransformer extends Transformer {
  @Override
  protected void transform() throws Exception {
    scopedClasses().forEach(classWrapper -> classWrapper.methods().forEach(methodNode -> {
      
      // Iterate over all LDC instructions in the method
      Arrays.stream(methodNode.instructions.toArray())
          .filter(insn -> insn.getOpcode() == LDC) // Check if opcode is LDC
          .map(LdcInsnNode.class::cast) // Cast to LdcInsnNode so we can access the constant value (ldcInsn.cst)
          .forEach(ldcInsn -> {
            // Replace all "Hello, World!" strings with "Bye, World!"
            if (ldcInsn.cst.equals("Hello, World!")) {
              ldcInsn.cst = "Bye, World!";
            }
          });
    }));
  }
}