sandbox inheritied properties flattened after vm.runInNewContext

[waynedpj]

on node-4.5.1 when using a sandbox Object with inherited properties, after running sandbox in vm.runInNewContext all properties up the prototype chain are copied to sandbox Object, even if they are not changed by code, though the prototype chain is still there. here is a failing test case

'use strict';

let vm = require('vm'), assert = require('assert');

let base = Object.create(null);
base.x = 1;
base.y = 2;

let sandbox = Object.create(base);
sandbox.z = 3;

console.log('base:\n%j', base);
console.log('sandbox:\n%j', sandbox);
console.log("sandbox's own keys:\n%j", Object.keys(sandbox));

let code = 'x = 0; z = 4;';
let result = vm.runInNewContext(code, sandbox);
console.log('result: %s', result);

console.log('base:\n%j', base);
console.log('sandbox:\n%j', sandbox);
console.log("sandbox's own keys:\n%j", Object.keys(sandbox));

assert((Object.keys(sandbox)).indexOf('y') === -1);  // fails

note that the same problem occurs even if code is empty, as well as with vm.runInContext.

not sure if this is expected behavior or not, but i was surprised to have sandbox modified like that. if it is normal, i did not find any mention of it in the docs, and would ask if someone could kindly explain why?

thanks.

[abenhamdine]

@waynedpj do you see the same behaviour with the last stable version of nodejs ?
I also see some strange behaviours with the sandbox object properties on node 5.7 (but not exactly the same problem as your), but i'm still investigating before opening an issue.

[waynedpj]

@abenhamdine yes, i still see the same issue w/ 5.7. i have been investigating this further, and though i am not totally following what is going on yet, i suspect that this flattening of sandbox's prototype chain might be happening here in CopyProperties. but i am not familiar enough yet w/ Node.js's C++ code yet ;)

does your issue involve the sandbox being modified unexpectedly?

please let us know if you find anything and thanks.

[waynedpj]

PS. @abenhamdine which strange behaviors are you seeing?

[abenhamdine]

I just opened an issue : #5491

[jasnell]

Pretty certain this is the same issue as #2734

[jasnell]

@nodejs/v8 ... can anyone on the v8 site assist with this one?

[jeisinger]

I'll sync with Domenic and Ali to understand the exact requirements here.