gistfile1.java

package cpw.mods.fml.common.asm.transformers;

import java.util.Map;
import java.util.Set;

import net.minecraft.launchwrapper.IClassTransformer;

import org.objectweb.asm.*;
import org.objectweb.asm.commons.Method;

import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Maps;

public class TestTransformer implements IClassTransformer {

    private final static String bedHookCls = "openblocks/BedHook";

    private static class HookMethodVisitor extends MethodVisitor {

        private final String methodName;

        public HookMethodVisitor(MethodVisitor mv, String methodName) {
            super(Opcodes.ASM4, mv);
            this.methodName = methodName;
        }

        @Override
        public void visitCode() {
            mv.visitCode();
            mv.visitVarInsn(Opcodes.ALOAD, 0); //EntityPlayer this
            mv.visitMethodInsn(Opcodes.INVOKESTATIC, bedHookCls, "hook", "(Lnet/minecraft/entity/player/EntityPlayer;)Z");
            Label skipReturn = new Label();
            mv.visitJumpInsn(Opcodes.IFEQ, skipReturn);
            mv.visitLdcInsn(true);
            mv.visitInsn(Opcodes.IRETURN);
            mv.visitLabel(skipReturn);
        }
    }

    public class HookClassVistor extends ClassVisitor {
        private final Set<Method> methods;

        public HookClassVistor(ClassVisitor cv, Set<Method> methods) {
            super(Opcodes.ASM4, cv);
            this.methods = ImmutableSet.copyOf(methods);
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
            Method type = new Method(name, desc);
            MethodVisitor parent = super.visitMethod(access, name, desc, signature, exceptions);
            return methods.contains(type) ? new HookMethodVisitor(parent, name) : parent;
        }
    }

    private Map<String, Set<Method>> classes = Maps.newHashMap();

    {
        classes.put("net.minecraft.entity.player.EntityPlayer", ImmutableSet.<Method>of(new Method("isInBed", "()Z")));
    }

    @Override
    public byte[] transform(String name, String transformedName, byte[] bytes) {
        Set<Method> methodsToModify = classes.get(transformedName);
        if (methodsToModify == null)
            return bytes;
        ClassReader cr = new ClassReader(bytes);
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
        HookClassVistor mod = new HookClassVistor(cw, methodsToModify);
        cr.accept(mod, 0);
        return cw.toByteArray();
    }

}