fs.writeFile(Sync): mode option is ignored in some cases

[targos]

Original issue: nodejs/node-v0.x-archive#25756

fs.writeFile(Sync) has a bug regarding the mode option:

• If the file is not existing, it is sometimes created with a different mode (see test case, I didn't try all possible combinations). (not-a-bug, umask at work)
• If the file is already existing, its mode is kept unchanged.

Our tests are not catching this because we use 755 and it is one of the working cases.

I suspect a bug in libuv's open method. The mode seems to be correctly passed from our code.

Test case (tested on OSX 10.10):

'use strict';

const filename = 'a00.txt';
const fs = require('fs');

remove(); write();
logMode('new file, 666 (default)');
remove(); write(0o756);
logMode('new file, 756');
remove(); write(0o565);
logMode('new file, 565');
remove(); write(0o755);
logMode('new file, 755');
remove(); write(0o444);
logMode('new file, 444');
chmod(0o777);
logMode('chmod, 777');
write(0o666);
logMode('replace, 666');
write(0o756);
logMode('replace, 756');
write(0o565);
logMode('replace, 565');
write(0o755);
logMode('replace, 755');
write(0o444);
logMode('replace, 444');

function remove() {
    try {
        fs.unlinkSync(filename);
    } catch (e) {}
}
function chmod(mode) {
    fs.chmodSync(filename, mode);
}
function write(mode) {
    fs.writeFileSync(filename, 'hello', {mode: mode});
}
function logMode(message) {
    console.log(fs.statSync(filename).mode.toString(8) + ' (' + message + ')');
}

Output :

100644 (new file, 666 (default))
100754 (new file, 756)
100545 (new file, 565)
100755 (new file, 755)
100444 (new file, 444)
100777 (chmod, 777)
100777 (replace, 666)
100777 (replace, 756)
100777 (replace, 565)
100777 (replace, 755)
100777 (replace, 444)

/cc @saghul ?

[targos]

OK I did a bad pre-search, first issue is not an issue: #1104

But the second one is different and it feels wrong that the mode is not altered when replacing the file.

[targos]

I think it may be just a documentation issue.

[bnoordhuis]

If the file is already existing, its mode is kept unchanged.

This is the expected behavior, at least if you're a POSIX C programmer. From man 2 open:

mode specifies the permissions to use in case a new file is created.

[targos]

I get it now, thank you :)