Stop using process.umask()

[isaacs]

Refs: nodejs/node#32321

Summary: process.umask() (no args) will be deprecated and removed.

I couldn't quite divine what lib/config/defaults.js uses process.umask() for but in most cases you don't need to deal with the umask directly - the operating system will apply it automatically.

Example:

const mode = 0o777 & ~process.umask();
fs.mkdirSync(dir, mode);

Computing the file mode that way is superfluous, it can be replaced with just this:

fs.mkdirSync(dir, 0o777);

nodejs/node#32321 (comment)

cc @bnoordhuis

[isaacs]

• Add a chmod: false option to unpack. In this mode, just create the file with the entry mode, and let it ride with whatever the OS gives us.
• If chmod:false is not set, then create the file with the entry.mode, stat the file, and chmod if different. This will be slower than the current approach, unfortunately.

[isaacs]

Note: even though it's potentially slower, creating the file and then checking the mode is a more technically correct approach, as it is resilient against process.umask() changing during the unpack, or returning an incorrect value.

[bnoordhuis]

FWIW, I did some quick, completely unscientific benchmarks on Linux and changing create-close to create-fchmod-close slows it down by just under 15%:

// As root, run `echo 3 > /proc/sys/vm/drop_caches` first
'use strict';
const { O_CREAT, O_WRONLY } = require('fs').constants;
const { openSync, closeSync, unlinkSync } = require('fs');
let { fchmodSync } = require('fs');
if (process.argv[2]) fchmodSync = () => {};

const N = 1e4;
const files = [];
for (let i = 0; i < N; i++) files.push('/tmp/xyzzy' + i);

const start = Date.now();
for (const file of files) {
  const fd = openSync(file, O_CREAT|O_WRONLY);
  fchmodSync(fd, 0o666);
  closeSync(fd);
}
const end = Date.now();

console.log(start, end, end - start);
for (const file of files) unlinkSync(file);

15% sounds like a lot, however:

1. The benchmark doesn't write any data. Writing 4x4k blocks shrinks the relative gap to <5%.

2. There is only a statistically significant difference when the cache is already warmed up.

I assume cold caches are the common case for node-tar because you don't normally unpack the same tarball to the same location 10 times in a row. (Well, I don't, anyway.)

[ql-nano]

If you really need to use

process.umask()

(without args), then you may use get-umask module. It suppresses those annoying warnings. And yeah, it's written by me.

[isaacs]

Suppress warnings by using { noChmod: true }, so that it won't have to calculate anything. Otherwise, there's no way around having to get the process umask, or else it's a big security problem.