Piping methods with void return type

[tomola]

I'm currently porting one of our libraries from CGLib to ByteBuddy and I've encounter a problem with @pipe. I've got a simple proxy that delegates all calls to the wrapped target object. Everything is OK until there is a method returning void on the target object.

My setup is like:

public class X {
    public static class WrappedObject {
        Object method1() {...}
        void method2() {...}
    }

    public static interface Forwarder<T, S> {
        T to(S target);
    }

    public static class Handler {
        protected final WrappedObject wrappedObject;

        public Handler(WrappedObject wrappedObject) {
            this.wrappedObject = wrappedObject;
        }

        @RuntimeType
        public Object delegate(@Pipe Forwarder<Object, WrappedObject> pipe) {
            return pipe.to(wrappedObject);
        }
    }

    public static void main(String... args) throws Exception {
        WrappedObject proxiedObject = new ByteBuddy()
          .subclass(WrappedObject.class)
          .method(any())
          .intercept(MethodDelegation.to(new Handler(new WrappedObject())).appendParameterBinder(Pipe.Binder.install(Forwarder.class)))
          .make()
          .load(X.class.getClassLoader(), ClassLoadingStrategy.Default.WRAPPER)
          .getLoaded()
          .newInstance();
    }
}

The proxy cannot be created:

Exception in thread "main" java.lang.IllegalStateException: An illegal stack manipulation must not be applied
    at net.bytebuddy.instrumentation.method.bytecode.stack.StackManipulation$Illegal.apply(StackManipulation.java:46)
    at net.bytebuddy.instrumentation.method.bytecode.stack.StackManipulation$Compound.apply(StackManipulation.java:194)
    at net.bytebuddy.instrumentation.method.bytecode.bind.annotation.Pipe$Binder$Redirection$MethodCall$Appender.apply(Pipe.java:589)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Entry$Simple.apply(TypeWriter.java:1055)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Engine$ForCreation.create(TypeWriter.java:688)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1143)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:219)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$AbstractDelegatingBuilder.make(DynamicType.java:1611)
    at net.bytebuddy.instrumentation.method.bytecode.bind.annotation.Pipe$Binder$Redirection.make(Pipe.java:332)
    at net.bytebuddy.instrumentation.Instrumentation$Context$Default.register(Instrumentation.java:808)
    at net.bytebuddy.instrumentation.method.bytecode.bind.annotation.Pipe$Binder$Redirection.apply(Pipe.java:342)
    at net.bytebuddy.instrumentation.method.bytecode.bind.MethodDelegationBinder$ParameterBinding$Anonymous.apply(MethodDelegationBinder.java:192)
    at net.bytebuddy.instrumentation.method.bytecode.bind.MethodDelegationBinder$MethodBinding$Builder$Build.apply(MethodDelegationBinder.java:507)
    at net.bytebuddy.instrumentation.method.bytecode.stack.StackManipulation$Compound.apply(StackManipulation.java:194)
    at net.bytebuddy.instrumentation.MethodDelegation$Appender.apply(MethodDelegation.java:998)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Entry$Simple.apply(TypeWriter.java:1055)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Engine$ForCreation.create(TypeWriter.java:688)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1143)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:219)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase$AbstractDelegatingBuilder.make(DynamicType.java:1611)
    at X.main(X.java:40)

When I change WrappedObject class to:

    public static class WrappedObject {
        Object method1() {...}
        Object method2() {...}
    }

it runs fine.

So, is @pipe capable of delegation to void returning methods? Or am I doing something wrong?

[raphw]

This is indeed a bug, rather a faulty default setup. You can resolve this by setting a different Assigner which knows how to assign a void type to an Object type.

When defining the MethodDelegation, set

new VoidAwareAssigner(new PrimitiveTypeAwareAssigner(ReferenceTypeAwareAssigner.INSTANCE), true)

using the withAssigner method.

This is of course inconvenient and the upcoming version will provide a better solution and you will not longer be required to do so. Thanks for reporting this and for using Byte Buddy.

[raphw]

As a matter of fact, due to another bug, I planed a bug-fix release later this day. Simply upgrade to version 0.4.1 once this version is available.

[raphw]

The bug-fix release 0.4.1 is already available in JCenter and is currently synchronized to Maven Central. It should be available from there in a couple of hours.

[tomola]

Thanks Rafael, I can confirm now it works as I expected.

[raphw]

You are welcome. And thanks for reporting this and helping to improve Byte Buddy.