Parameterize Advice Methods

[AndreasMili]

In a nutshell, I want to change parameter values of several methods using the same @Advice.OnMethodEnter and @Advice.OnMethodExit advice methods.
Moreover, I want the advice methods to behave differently (change different parameters), depending on which method they instrument.

        new AgentBuilder.Default()
                .type(named("com.example.MyClass"))
                .transform((builder, typeDescription, classLoader, module) ->
                        builder
                                .visit(Advice.to(MyAdvice.class).on(named("doSomething1").and(...)))
                                .visit(Advice.to(MyAdvice.class).on(named("doSomething2").and(...)))
        );

Referring to the example, I want the @Advice.OnMethodEnter and @Advice.OnMethodExit method in MyAdvice to change different parameters for doSomething1() and doSomething2(), but by using the same logic. Therefore, I would need to parameterize MyAdvice.

Since the @Advice.OnMethodEnter and @Advice.OnMethodExit methods are static, are there any ByteBuddy-way solutions for parameterizing them?
Otherwise I would need to use a global state and do the same kind of matching again which I've already done with the ElementMatchers, which bould be cumbersome.

Unfortunately, the interception api is not an option for me, since I don't want to change the class schema.

Thanks in advance!

[raphw]

Advice works due to reusing compiled byte code; even if you parameterized the advice class, Byte Buddy could not simply "copy-paste" the code over. What you can do is to use Advice.AllArguments and change only specific argument values programmatically depending on what method you run.

If you need to provide method specific arguments to an advice, note that you can add your custom annotations using Advice.withCustomConfiguration().bind(...).to(MyAdvice.class).

[AndreasMili]

What you can do is to use Advice.AllArguments and change only specific argument values programmatically depending on what method you run.

What I basically need is to pass a list describing which parameters to change, like this:

    @Advice.OnMethodEnter
    public static void onEnter(@Advice.This Object obj, @Advice.Origin String method,
                               @Advice.AllArguments Object[] args, List<Integer> paramsToChange) {
        paramsToChange.forEach(i -> {
            // do something with args[i]
        });
    }

So this is possible with Advice.withCustomMapping().bind(...).to(MyAdvice.class)?

[raphw]

Yes, you can bind any StackManipulation to a custom annotation. You will need to implement a custom binder that creates the array, have a look at ArrayFactory to create an int[]. Also, use standard iteration, lambdas create methods to invoke in the advice class that will not be accessible to your instrumented class.

[AndreasMili]

Thanks for your blazing fast answers. I'm trying to wrap my head around on how to the custom annotation has to look like.

So basically I can achieve this:

int[] paramsToChange = // read from file
int[] paramsToChange2 = // read from file
                
builder.visit(Advice.withCustomMapping().bind(MyAnnotation.class, paramsToChange)
                   .to(MyAdvice.class).on(named("doSomething1")))
      .visit(Advice.withCustomMapping().bind(MyAnnotation.class, paramsToChange2)
                   .to(MyAdvice.class).on(named("doSomething2")));

@Advice.OnMethodEnter
public static void onEnter(@Advice.This Object obj, @Advice.Origin String method,
                           @Advice.AllArguments Object[] args, @MyAnnotation int[] params) {
}

With an annotation like that?

@Documented
@Retention(RetentionPolicy.RUNTIME)
@java.lang.annotation.Target(ElementType.PARAMETER)
public @interface MyAnnotation {
// Use ArrayFactory here?
}

If I'm on the right track, I'll try to figure it out and post an answer as soon as I got something working :)

[raphw]

Yes, this is right. All that is leat to do is to combine array factory with integer constant to produce a stack manipulation that loads the integers.

[raphw]

Please reopen the ticket if you have further questions.