Provide access to file system times with nanoseconds resolution

[haraldrudell]

Node.js should provide nanosecond time values in the fs.stat() response structure similar to how process.hrtime() does it.

If there is a module or trick to provide ns I would be happy to use that

Generally on Linux, human readable stat provides the nanoseconds, and epoch time provides the UTC second-level value. The combination is complete. Since Node.js uses ECMAScript Date objects, there is only millisecond resolution.

• ext4 and Android has nanosecond time resolution since long time
• Most Linux utilities still drop sub-seconds and Linux cannot display birth date easily
• Some Android won't give you UTC allowing you to create lots of bugs calculating it

Here's Linux human readable

stat 0 --format %z
2016-06-14 00:50:44.920739523 -0700

uname --all && node --version
Linux c89 4.4.0-34-generic #53-Ubuntu SMP Wed Jul 27 16:06:39 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
v6.4.0

I have some utilities moving large data around that uses recursive md5 and metadata before-after to verify integrity

[bnoordhuis]

If there is a module or trick to provide ns I would be happy to use that

If there isn't one already, you can write your own bindings for uv_fs_stat/uv_fs_fstat/uv_fs_lstat. That is what node.js itself uses and they support nanosecond resolution on file systems that support them and with the usual caveats.

Adding nanoseconds to fs.Stats is something I'd probably veto because of the performance implications. They're already expensive to create; tacking on more properties would only make it worse.

It might be possible to do something clever with interceptors and create values lazily but that would have to be benchmarked very carefully.

[haraldrudell]

The performance impact is to copy 4 C long to ECMAScript number

fs.*utimes() api needs update, too

• some file properties are not supported here
• it might be more future proof to use an object

[bnoordhuis]

The performance impact is to copy 4 C long to ECMAScript number

With all due respect but that comment betrays a certain ignorance of node's and V8's inner workings.

[haraldrudell]

Both nanoseconds (kernel 2.6) and birth date (ext4) predates Node.js

These fs api calls should not have been designed this way in the first place. They knowingly lack file system features. The design of fs.*utimes does not adhere to good software engineering practices.

Additional constructive suggestions would be great!

[bnoordhuis]

I already provided one:

It might be possible to do something clever with interceptors and create values lazily but that would have to be benchmarked very carefully.

[refack]

In #12607 we are considering exposing the raw numbers in addition to the Date values