Illegal invocation error using ES6 Proxy and node.js

[FranckFreiburger]

Hello,
I am unable to call a node.js native function through a No-op forwarding proxy.

The following case works properly with a v8 native function:

var p = new Proxy(Math, {});
console.log( p.cos.toString() ); // function cos() { [native code] }
console.log( p.cos(0) ); // 1

Whereas the following case throw TypeError: Illegal invocation

var p = new Proxy(require('os'), {});
console.log( p.cpus.toString() ); // function getCPUs() { [native code] }
console.log( p.cpus() ); // TypeError: Illegal invocation

what's wrong ?

[vsemozhetbyt]

Maybe it is because the Math methods are static, while the Node.js modules' methods could require an appropriate receiver. This works:

const os = require('os');
const p = new Proxy(os, {});
console.log(p.cpus);
console.log(p.cpus.call(os));

[vsemozhetbyt]

See also: Exploring ES6 by Dr. Axel Rauschmayer: 28. Metaprogramming with proxies: 28.3.2 Intercepting method calls

[FranckFreiburger]

receiver for the default get proxy handler is handled with Reflect.get(target, property, receiver)

[FranckFreiburger]

This case is also weird (note that I use node.js v7.7.1):

const p = new Proxy(require('os'), {});

var cpus = p.cpus;
console.log(cpus()); // ok

console.log(p.cpus()); // Illegal invocation

[vsemozhetbyt]

@FranckFreiburger
Maybe this is somehow connected with C++ bindings, This works:

var p = new Proxy(require('os'), {});
console.log(p.arch.toString());
console.log(p.arch());

os.arch() does not use bindings. os.cpus() does use them.

[TimothyGu]

This issue isn't reproducible on master or v7.x-staging, probably as a side effect of #11564. Either way, the next release of v7.x will have this fixed.

[TimothyGu]

cpus is only one function affected by this bug. Other methods that directly call C++ bindings are also vulnerable. On the V8 level, it is probably because the API call helper cannot find a compatible receiver in a Proxy object.

This bug has already been reported upstream by as issue 5773.

/cc @nodejs/v8

[FranckFreiburger]

Note that all binding.* functions seems to be affected by this bug.

new Proxy(require('os'), {}).hostname() // Illegal invocation ...

[Trott]

Is there anything Node.js can/should do about this other than await https://bugs.chromium.org/p/v8/issues/detail?id=5773 getting fixed in V8? Should this issue remain open?

[targos]

This is still an issue but AFAICT there is nothing Node.js can do about it.

Repro on v8.x:

const binding = process.binding('util');
const isDate = binding.isDate;
console.log(isDate(new Date)); // true
console.log(isDate.call(binding, new Date)); // true
console.log(isDate.call(new Proxy(binding, {}), new Date)); // illegal invocation

[mappum]

This is still an issue as of Node v9.8.0. Can/should anyone push for a v8 fix, or should there be any sort of Node workaround? Or are users expected to rebind to the unproxied contexts for all of these calls?

[mappum]

BTW, this comes up in surprisingly common places, e.g. trying to stringify a Proxied Buffer.

let buf = new Proxy(Buffer.from('test'), { get: (t, n) => t[n] })
console.log(buf)

[devsnek]

fwiw this is intended behavior on the side of proxies. check out https://github.com/nodejs/node/pull/18131/files#diff-cc63475f116262e9cbea02374e344c01R671 for an example of a proxy that covers this use case.

[mappum]

Even if this is fully compliant with the spec, it's quite a pain. As Proxies become a more widely adopted feature I expect many more people will run into this. At the very least, there should be a workaround on the Node side.

[devsnek]

@mappum that's the general idea of the membrane concept: https://www.npmjs.com/package/es7-membrane

[bnoordhuis]

The examples listed in this issue work with master so I think this can be closed out.

As to this example (edited for brevity):

new Proxy(Buffer.from('test'), { get: (t, n) => t[n] }).toString()

That invokes Buffer.prototype.toString() with the proxy as the receiver and fails the way it is expected to.

Talk of "there should be a workaround on the Node side" is misguided because it's not a sensible construct. Write it like this and note the .bind() call:

new Proxy(Buffer.from('test'), { get: (t, n) => t[n].bind(t) }).toString()

[kamil-kielczewski]

On chrome I have same problem for events (eg. click event) - here is solution

const eventProxy = new Proxy(event, {
    get: (target, prop) => ()=> target[prop].apply(target),
});

working editable example here which shows how to add your code before/after original function execution