Forge 1.12.2 Coremodding: java.lang.StringIndexOutOfBoundsException

I try to make a coremod on 1.12.2 Forge in order to patch some missing stuff in the Lost Cities mod. (Source: https://github.com/McJtyMods/LostCities/blob/1.12/src/main/java/mcjty/lostcities/dimensions/world/lost/BuildingInfo.java)

A friend and I have written this LostCitiesClassTransformer.java: (Full source: https://github.com/Nick1st/LCPatches)

package seemdmax.lcpatches;

import static org.objectweb.asm.Opcodes.ALOAD;
import static org.objectweb.asm.Opcodes.IFGT;
import static org.objectweb.asm.Opcodes.IFLE;
import static org.objectweb.asm.Opcodes.IFNE;
import static org.objectweb.asm.Opcodes.ILOAD;
import static org.objectweb.asm.Opcodes.INVOKEINTERFACE;
import static org.objectweb.asm.Opcodes.INVOKESTATIC;
import static org.objectweb.asm.Opcodes.INVOKEVIRTUAL;
import static org.objectweb.asm.Opcodes.GETFIELD;

import java.util.Arrays;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Type;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.JumpInsnNode;
import org.objectweb.asm.tree.LabelNode;
import org.objectweb.asm.tree.LdcInsnNode;
import org.objectweb.asm.tree.MethodInsnNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.VarInsnNode;

import mcjty.lostcities.api.ILostCityBuilding;
import net.minecraft.launchwrapper.IClassTransformer;

public class LostCitiesClassTransformer implements IClassTransformer {
    private static final String[] classesBeingTransformed = { "mcjty.lostcities.dimensions.world.lost.BuildingInfo", "mcjty.lostcities.dimensions.world.terraingen.LostCitiesTerrainGenerator"};

    @Override
    public byte[] transform(String name, String transformedName, byte[] classBeingTransformed) {
        boolean isObfuscated = !name.equals(transformedName);
        int index = Arrays.asList(classesBeingTransformed).indexOf(transformedName);
        return index != -1 ? transform(index, classBeingTransformed, isObfuscated) : classBeingTransformed;
    }

    private static byte[] transform(int index, byte[] classBeingTransformed, boolean isObfuscated) {
        System.out.println("Transform " + classesBeingTransformed[index] + " got called!");
        try {
            ClassNode classNode = new ClassNode();
            ClassReader classReader = new ClassReader(classBeingTransformed);
            classReader.accept(classNode, 2);

            System.out.println("Transforming " + classesBeingTransformed[index] + " Is Obf: " + isObfuscated);
            switch (index) {
            case 0:
                transformLCCellars(classNode, isObfuscated);
                break;
            case 1:
                transformBuildingBorders(classNode, isObfuscated);
                break;
            }

            ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_MAXS /*| ClassWriter.COMPUTE_FRAMES*/);
            classNode.accept(classWriter);
            return classWriter.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return classBeingTransformed;
    }

    private static void transformBuildingBorders(ClassNode terrainGenClass, boolean isObfuscated) {
        final String METHOD = isObfuscated ? "generateBuilding" : "generateBuilding";
        final String METHOD_DESC = isObfuscated
                ? "(Lmcjty/lostcities/dimensions/world/lost/BuildingInfo;Lmcjty/lostcities/dimensions/world/ChunkHeightmap;)V"
                : "(Lmcjty/lostcities/dimensions/world/lost/BuildingInfo;Lmcjty/lostcities/dimensions/world/ChunkHeightmap;)V";
        
        for (MethodNode method : terrainGenClass.methods) {
            if (method.name.equals(METHOD) && method.desc.equals(METHOD_DESC)) {
                System.out.println("Found method in BuildingInfo to transform");
                AbstractInsnNode targetNode = null;
                for (AbstractInsnNode instruction : method.instructions.toArray()) {
                    if (instruction.getOpcode() == ALOAD) {
                        if (((VarInsnNode) instruction).var == 1 & instruction.getNext().getOpcode() == GETFIELD & instruction.getNext().getNext().getOpcode() == IFLE) {
                            System.out.println("Matched");
                            targetNode = instruction.getNext().getNext();
                            break;
                        }
                    }
                }
                if (targetNode != null) {
                    System.out.println("Target Node valid");

                    InsnList toInsert = new InsnList();
                    toInsert.add(new VarInsnNode(ALOAD, 1));
                    toInsert.add(
                            new MethodInsnNode(INVOKEVIRTUAL, "mcjty/lostcities/dimensions/world/lost/BuildingInfo",
                                    "floorsBelowGround", "I", false));
                    toInsert.add(
                            new MethodInsnNode(INVOKEVIRTUAL, "seemdmax/lcpatches/Constants",
                                    "getKey", "()Ljava/lang/String;", false));
                    toInsert.add(
                            new MethodInsnNode(INVOKEVIRTUAL, "java/lang/String", "endsWith", "(Ljava/lang/String;)Z", false));
                    toInsert.add(new JumpInsnNode(IFNE, ((JumpInsnNode) targetNode).label));

                    method.instructions.insert(targetNode, toInsert);
                    System.out.println("Transform done!");
                } else {
                    System.out.println("Something went wrong transforming LostCitiesTerrainGenerator!");
                }
            }
        }
        
    }

    private static void transformLCCellars(ClassNode buildingInfoClass, boolean isObfuscated) {
      //This is already working
    }
}

The original code I want to patch (Bytecode Outline):

L55
    LINENUMBER 2338 L55
   FRAME CHOP 3
    ALOAD 1
    GETFIELD mcjty/lostcities/dimensions/world/lost/BuildingInfo.floorsBelowGround : I
    IFLE L68

The Bytecode Outline containing my changes:

L55
    LINENUMBER 2338 L55
   FRAME CHOP 3
    ALOAD 1
    GETFIELD mcjty/lostcities/dimensions/world/lost/BuildingInfo.floorsBelowGround : I
    IFLE L68
    ALOAD 1
    INVOKEVIRTUAL mcjty/lostcities/dimensions/world/lost/BuildingInfo.getBuildingType ()Ljava/lang/String;
    LDC "#NOBORDER"
    INVOKEVIRTUAL java/lang/String.endsWith (Ljava/lang/String;)Z
    IFNE L68

The stacktrace I get:

java.lang.StringIndexOutOfBoundsException: String index out of range: 1
    at java.lang.String.charAt(String.java:658)
    at org.objectweb.asm.Type.getArgumentsAndReturnSizes(Type.java:420)
    at org.objectweb.asm.MethodWriter.visitMethodInsn(MethodWriter.java:931)
    at org.objectweb.asm.tree.MethodInsnNode.accept(MethodInsnNode.java:133)
    at org.objectweb.asm.tree.InsnList.accept(InsnList.java:162)
    at org.objectweb.asm.tree.MethodNode.accept(MethodNode.java:817)
    at org.objectweb.asm.tree.MethodNode.accept(MethodNode.java:727)
    at org.objectweb.asm.tree.ClassNode.accept(ClassNode.java:412)
    at seemdmax.lcpatches.LostCitiesClassTransformer.transform(LostCitiesClassTransformer.java:59)
    at seemdmax.lcpatches.LostCitiesClassTransformer.transform(LostCitiesClassTransformer.java:38)
    at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:256)
    at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279)
    at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
    at mcjty.lostcities.dimensions.world.LostCityChunkGenerator.<init>(LostCityChunkGenerator.java:170)
    at mcjty.lostcities.dimensions.world.LostWorldType.getChunkGenerator(LostWorldType.java:55)
    at net.minecraft.world.WorldProvider.createChunkGenerator(WorldProvider.java:86)
    at net.minecraft.world.WorldServer.createChunkProvider(WorldServer.java:890)
    at net.minecraft.world.WorldServer.<init>(WorldServer.java:124)
    at net.minecraft.server.integrated.IntegratedServer.loadAllWorlds(IntegratedServer.java:122)
    at net.minecraft.server.integrated.IntegratedServer.init(IntegratedServer.java:160)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:552)
    at java.lang.Thread.run(Thread.java:748)

Why do I monkey-patch a open-source mod? I need it for a modpack; Curseforge doesn’t allow modified jars in modpacks. McJty said, that he don’t want a second LC Project, but he’s fine with patching LC using coremods/mixins etc.

Any help would be appreciated. If you need to know more details, feel free to ask. Thanks in advance.

Answer

Here’s the problem:

                    toInsert.add(
                            new MethodInsnNode(INVOKEVIRTUAL, "mcjty/lostcities/dimensions/world/lost/BuildingInfo",
                                    "floorsBelowGround", "I", false));

You’re trying to call floorsBelowGround like it’s a method, but it’s actually a field. You need to make a GETFIELD FieldInsnNode instead of an INVOKEVIRTUAL MethodInsnNode.