feat(pass-style): add selector

[kumavis]

No description provided.

[mhofman]

What's a selector?

[kriskowal]

What's a selector?

OCapN Selector corresponds to Syrup symbol and Scheme symbol. Because we can’t use JavaScript symbols (risk of registry stuffing attacks), MarkM insisted we give this a distinguishing name. It follows that it should have its own passStyle, which should replace symbols entirely in the long run.

https://github.com/ocapn/ocapn/blob/main/draft-specifications/Model.md#selector

[kriskowal]

I defer to @erights and @mhofman in this package. I have questions about whether Selector (née Symbol) fits in the established categories. It represents an Atom on the wire, but one we are obliged to reïfy as an Object.

[kriskowal]

I don’t believe selector qualifies as a container. It’s more like a string. But, the reïfication of a selector is an object, so that might be the distinguishing feature for containers. I do not know.

[kumavis]

its a container for a string! yeah ok was mostly just following 'tagged' around the code base

[gibson042]

It's definitely not a container. Our best documentation is at https://endojs.github.io/endo/types/_endo_pass_style.Passable.html , and we could describe Selector as primitive if we're taking a data model perspective, or otherwise a new special case (because, unlike the existing primitives, Object.is will differentiate identical values).

[kriskowal]

Selector definitely does not belong in this union.

[kumavis]

we can’t use JavaScript symbols (risk of registry stuffing attacks)

is the concern here only from using Symbol.for? would making our own symbol registry as a WeakRefMap (map to weakly held values) resolve the attack vector?

here is an example showing a Symbol being GC'd in nodejs

❯ node --expose-gc
Welcome to Node.js v20.18.0.
Type ".help" for more information.
> const registry = new FinalizationRegistry((heldValue) => console.log(`Object with value '${heldValue}' has been garbage collected.`));
undefined
> registry.register(Symbol('foo'), 'foo');
undefined
> gc()
undefined
> Object with value 'foo' has been garbage collected.

[erights]

Seeing this thread, I realize I gave you bad advise. Selector is like Tagged in some ways, but is like Symbol in other ways. I'll make a PR staged on this one as my corrected review suggestions. Hold on.

would making our own symbol registry as a WeakRefMap (map to weakly held values) resolve the attack vector?

Would be an interesting experiment, but I don't expect it to be a better solution than what this PR is attempting.

[erights]

#2777

Thanks for the great idea, and sorry for how long it took for me to get it.

[kumavis]

closed for #2777