QUESTION: Can bytebuddy enhance native method in jdk libraries?

[RTxin]

The test cases under the test package seem to be supported by the native method that can enhance the custom class.
I tried to modify the test case with the intention of enhancing java.lang.string#intern and it seemed to cause a java SecurityException.
So I want to consult you, how should I operate this example.

        classLoader = new ByteArrayClassLoader.ChildFirst(getClass().getClassLoader(),
                ClassFileLocator.ForClassLoader.readToNames(String.class),
                ByteArrayClassLoader.PersistenceHandler.MANIFEST);
        assertThat(ByteBuddyAgent.install(), instanceOf(Instrumentation.class));
        AgentBuilder builder = new AgentBuilder.Default()
                .disableClassFormatChanges()
                .enableNativeMethodPrefix("bar")
                .ignore(none())
                .with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE)
                .type(ElementMatchers.is(String.class), ElementMatchers.is(classLoader))
                .transform(new FooTransformer())
                ;
        ClassFileTransformer classFileTransformer=builder.installOnByteBuddyAgent();
        try {
            Class<?> type = classLoader.loadClass(String.class.getName());
            System.out.println(type.getDeclaredMethod("intern").invoke(type.getDeclaredConstructor(String.class).newInstance("foo")));
        } finally {
            assertThat(ByteBuddyAgent.getInstrumentation().removeTransformer(classFileTransformer), is(true));
        }

[raphw]

This would require adding a method to a loaded class for a native method prefix. That is not possible.

[RTxin]

hi @raphw ,So you mean ByteBuddy has no way to enhance all classes native method? Can it only enhance the custom class that has not been loaded by ClassLoader's Native Method?

Can't you replace the whole method using the annotations' @RunTimeType 'and' @supercall '?

@RuntimeType
public static Object intercept(@SuperCall Callable<?> zuper) throws Throwable;

This is just found a replaceable bytecode demo

protected TServer(AbstractServerArgs abstractServerArgs) {
    TServer tServer = this;
    // enhance by first agent.
    delegate$6386i10.intercept((Object)tServer, new Object[]{abstractServerArgs2});
}
private /* synthetic */ TServer(AbstractServerArgs args, auxiliary.Ig29GTq8 ig29GTq8) {
    /*117*/     ...
    /*120*/    .....
}

[RTxin]

My problem is similar to issue #716

[raphw]

Using a prefix requires adding a method to the class file and that is not possible if the class is already loaded. That's why this is not possible

[RTxin]

I've got it,Thanks!