Migrating from ASM to ByteBuddy

[rupinder10]

I have migrated from ASM to ByteBuddy and have been able to replace by ClassFileTransformer to use Advice instead. In my old code, I used to be able to add and remove instrumentation using a switch. It was roughly like this:

ClassFileTransformer transformer = ...
if (config.enable) {
  instrumentation.addTransformer(tranformer, true);
} else {
  instrumentation.removeTransformer(tranformer);
}
instrumentation.retransformClasses(classes);

The corresponding code with ByteBuddy that works:

AgentBuilder agentBuilder = new AgentBuilder.Default().disableClassFormatChanges()
                .with(RedefinitionStrategy.RETRANSFORMATION);

agentBuilder = agentBuilder.type(ElementMatchers.named(className))
        .transform((builder, typeDescription, classLoader, module, protectionDomain) -> builder
        .visit(getAdvice(MyAdvice.class).on(ElementMatchers.nameEndsWith(methodName))));

agentBuilder.installOn(instrumentation);

But there are two aspects I need help with:

1. How do remove the instrumentation and switch back to the original class ?
2. I also need to sometimes need the original byte[] of the uninstrumented class. How do I that ?

[dogourd]

After calling installOn, you will get a ResettableClassFileTransformer, you can remove the ClassFileTransformer and retransform the classes by calling the reset method.

You can use AgentBuilder#with(TransformerDecorator) to specify a decorator where you can get the byte array of the class passed to ClassFileTransformer. You can also use net.bytebuddy.dynamic.DynamicType.Builder.make().getBytes() in the implementation of net.bytebuddy.agent.builder.AgentBuilder.Transformer#transform to get it, depending on your needs

[rupinder10]

I will try those. Just to clarify for the reset you means something like this ?

When I want to instrument :

ResettableClassFileTransformer resettableClassFileTransformer = agentBuilder.installOn(instrumentation);

and then we I want to remove the instrumentation :

instrumentation.removeTransformer(resettableClassFileTransformer);
resettableClassFileTransformer.reset(instrumentation, RedefinitionStrategy.RETRANSFORMATION);

[rupinder10]

Another question. Is there a way for me to check the results of a transformation to determine whether the class was changed at all ? Using your suggestions I can get the bytes before and after to compare. but is there a simpler approach ?

[raphw]

The first line will break the second. With reset, you undo the instrumentation by transforming back the classes. By removing the transformer, you will simply no longer transform classes later.

[rupinder10]

Thanks