utimes precision errors

[jorangreef]

Version: v7.10.0
Platform: Windows 10 64-bit
Subsystem: fs

I was working on a fuzz test to test the accuracy of timestamps set using fs.utimes() and found the following two precision bugs on Windows:

NEGATIVE MTIME:
expect mtime=2159345162531
actual mtime=-2135622133469

INACCURATE MTIME:
expect mtime=1713037251360
actual mtime=1713037251359

Here's the gist to reproduce (on a Windows fs with support for at least millisecond timestamps):

var fs = require('fs');
var path = 'test-utimes-precision';
fs.writeFileSync(path, '');

console.log('\r\nNEGATIVE MTIME:');
var mtime = 2159345162531;
fs.utimesSync(path, mtime / 1000, mtime / 1000);
var stats = fs.statSync(path);
console.log('expect mtime=' + mtime);                 // 2159345162531
console.log('actual mtime=' + stats.mtime.getTime()); // -2135622133469

console.log('\r\nINACCURATE MTIME:');
var mtime = 1713037251360;
fs.utimesSync(path, mtime / 1000, mtime / 1000);
var stats = fs.statSync(path);
console.log('expect mtime=' + mtime);                 // 1713037251360
console.log('actual mtime=' + stats.mtime.getTime()); // 1713037251359

On Mac, the negative mtime is also an issue.

[jorangreef]

Actually on Mac, there is no issue, only Windows.

[jorangreef]

I think the negative mtime has to do with a limit in NTFS (https://articles.forensicfocus.com/2013/04/06/interpretation-of-ntfs-timestamps/).

[jorangreef]

That leaves the rounding error. Perhaps there could be an exception for an mtime that would overflow NTFS on Windows.

[refack]

Hello @jorangreef , we already have a fix for the second issue (the bad rounding of time) #12607 (and it's spinoff #12818).
The second issue is caused by an overflow of the double that is the underlying type for JS number, and for that we have #13173

[jorangreef]

Regarding an exception for an mtime that would overflow NTFS on Windows and lead to a negative mtime returned by fs.stats:

2147483647999 is the highest btime/mtime/atime value supported by NTFS.

Anything more than that overflows NTFS' internal structures. statSync then returns a valid Date object, but the getTime() on this Date object returns a negative Unix timestamp (negative relative to the Unix epoch).

[refack]

@jorangreef It's not exactly an overflow, it's just bad interpretation. I think I have a fix in #13281