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Comment by vips7L | Hacker News Reader

As an application developer I love these changes. I do not want some library calling out to architecture specific binaries without me knowing. I want to have to enable that for them so I know that my application is portable. I do not want random code outside of my package to be able to reflect on my class and pull data out of a private variable or set its data breaking any type of encapsulation or rules I have written.

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> I do not want random code outside of my package to be able to reflect on my class and pull data out of a private variable or set its data breaking any type of encapsulation or rules I have written.

You have a very strange threat model given how stunningly trivial it is to decompile .class files

I'm with you on the JNI but I am not willing to "baby with the bathwater" the Reflection API just avoid having to check the bytecode for Runtime.loadLibrary

> You have a very strange threat model given how stunningly trivial it is to decompile .class files

I don't see how this is relevant. I'm talking at runtime. If I have a class:

    class Point {
        private final int x;
        private final int y;
        
        Point(int x, int y) {
            if (x < 0) throw new IllegalArgumentException("x less than 0");
            if (y < 0) throw new IllegalArgumentException("y less than 0");
            this.x = x;
            this.y = y;
        }
    }

You should not be able to use reflection to remove the private-ness of my field to set Y to -42, unless you are code within my module that I control.

Serious question - why not?

Because implementation details are not an interface. Say that, for example, in the future the module code evolves and `y` becomes cached or lazy loaded. Then your external code reaching in and setting `y` to -42 directly may no longer have the effect that it did when you wrote your "monkey patch".

https://en.wikipedia.org/wiki/Monkey_patch#Pitfalls

They are an interface, just clearly not the intended interface in this case. In the tower of abstraction, it is simply a lower level of abstraction than the public interface. It's important to speak at the appropriate level of abstraction for the problem at hand, and I believe library writers may not perfectly forsee the appropriate level of abstraction for everyone who uses the library.

For debugging, accessing private innards is fine because the version doesn't change before you're done. For long-lasting features, you can perform a risk-based analysis as to the likely stability of the implementation details you're accessing.

But as a general rule: as a library author I deeply resent people who cause ME to get blamed when I change an implementation detail and their fragile code breaks when my library gets upgraded.

https://xkcd.com/1172/

> This update broke my workflow! My control key is hard to reach, so I hold spacebar instead, and I configured Emacs to interpret a rapid temperature rise as "control".

That would only would be an issue if there is untrusted code running in the same jvm. The security manager was a really difficult way to stop this. Another approach I’ve used is to scan the jar and disallow all but whitelisted classes in the bytecode. Worked well.

It really isn't. Most security problems are caused by accidental vulnerabilities in trusted code, which is far more risky than untrusted code. (Untrusted code is really easy to deal with -- you just run it in a sandbox; it's trusted, benevolent, well-meaning code you should be afraid of.)

But security is just a small part of the problem. Remember all the breakages people had upgrading from 8 to 9+? Virtually all of them were do to libraries reaching into internals that then changed. If no internal method could change because someone might be relying on it then the platform can't evolve. If an application author cannot know which of her dependencies may be non-portable, they can't weigh the risk.

Yet another problem is optimisations. We can't optimise code if any dependency can freely decide to change the meaning of any line of code in the program.

How is decompiling the bytecode relevant? The issue isn't hiding secrets in the code, it's the application breaking at runtime due to violating invariants or assumptions.

  private java.security.PrivateKey _key;

  $ java -jar cfr.jar ...
  $ sed -i"" -e s/private/public/g $(find . -name "*.java")
  $ javac ...

and now Reflection doesn't need setAccessible and your threat model of "but my field is private!!11" has gone poof

Awesome, you now have a private fork! You the application developer now know your code isn't portable with the library! The JVM also can do its optimizations without having integrity change from under its feet at runtime! Win win!

Ok, I hear you, so let's mandate that every class have a .gpg signature to really double down on integrity. The JVM should have to have every gpg public key registered as a Trusted Platform Module Author. Win win on how sekure everything will be, and I can always resign every class with my .gpg signature. That really sounds like a win for the day-to-day Java developer, doesn't it? I'm sure that would never cause weird errors in day to day work just to address some niche audience who is really, really into chain of trust

The point I'm making is that I don't understand for the life of me whose problem this egregiously disruptive change is solving outside of the NSA, who I'm sure have their own JVM builds and can leave the rest of us out of it

You're thinking about security, and this enhancement is about integrity. The idea is simply that some third-level dependency won't be able to make global changes to the program -- like making it non-portable (i.e. not allowing the upgrade of the JDK) -- without the application knowing about it. This is a brand new functionality that solves the problem that led to the 8 -> 9+ migration pain (and I hope you'll agree that was a relatively big problem).

Integrity is also a prerequisite to writing any security mechanism in any layer of the code that is less prone to accidental vulnerabilities in a third-level dependency, and it's also a prerequisite to performance optimisations. For example, if Java strings were immutable, the compiler would be able to optimise some operations on them. Except it can't because even thought they're almost always immutable, some third-level dependency may decide to mutate one string in the program, and because of that the compiler can't optimise any.

Such new and powerful functionality is indeed disruptive (in a good way), and all it demands is that libraries that need to, say, mutate Java strings or final fields let the application know so it could add a flag (if it's willing to take the portability/performance/security risks involved). That's it.

Again I think you have a deep misunderstanding of how this works. This puts control into the hands of the everyday application developer! It ensures that the application developer knows what correctness, portability, and integrity guarantees their program has.

And I don't want the JVM hamstrung from a whole host of optimizations because this random stuff could be happening at any point.

Any general-purpose JVM is already going to have JNI entry points which bypass privacy. They can certainly restrict JNI as a whole and make users jump through hoops to enable it, but they're not going to be tearing it out for a long, long time.

Do you think you're like Apple: not allowing people to fix their phones, laptops ...?

I don’t want the community hijacking my library by fossilizing some implementation detail. If you want to fork it, own it and do it, but don’t force that on me by using something you weren’t meant to and then bitch and moan when I break your code by changing some detail.

You can make that argument either way. People will always complain about the decisions you make and the ones you don't.

The semantics of encapsulation are sufficient. Anyone who breaks them knows it's on them, and if they don't, they certainly should have. It's not worth sweating all the maybes and what-ifs.

> Anyone who breaks them knows it's on them, and if they don't, they certainly should have.

I agree, the issue arises when library developers make this decision and application developers have to deal with the fall out of that. Application developers need to know when things like this happen.

So use an older version of the library, or stop using the library, or work around it. Libraries with such bad behavior are going to be infrequently used, or abandoned quickly regardless.

I don't see how this is relevant. This purely puts control into the hands of application developers. It lets them know exactly what correctness, portability, and integrity guarantees their application has. The application developer STILL can "fix their phone", but they have to enable it at the command line. It pevents library developers from making decisions for application developers without them knowing.

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