fs.watch - on change returns incorrect file name

[captainrdubb]

In another project, I ran into the following scenario:

The function os.tmpDir returns a path with the 8.3 short name for the user name, example "C:\Users\<FIRST SIX CHARS OF NAME>~1\AppData\Local\Temp".

The Windows api returns the changed file name including the long version of the user name, example,
"C:\Users\<actual 18 char user name>\AppData\Local\Temp".

Pretend we are monitoring, "C:\Users\<8.3 file name>\AppData\Local\Temp\Configuration", expecting the file "config.json" to change. We would then expect the FSWatcher change event to return "config.json" as the name of the changed file. Instead, it returns something like "figuration\config.json", depending on the difference in length between the 8.3 file name and the actual file name.

It seems that node is saving an index so that it can quickly determine the part of the uri that is the file name, but the uri passed to fs.watch is a different length than the uri returned by the Windows api.

[seishun]

It's not clear from your description how one can reproduce this issue. Can you provide a test case?

[captainrdubb]

@seishun

var os = require('os');
var fs = require('fs');
var path = require('path');
var assert = require('assert');

var expectedFilename = 'testFile.txt';

var tmpDir = os.tmpdir();
var testDir = path.join(tmpDir, 'testCase');
var testFile = path.join(testDir, expectedFilename);

if (!fs.existsSync(testDir)) {
    fs.mkdirSync(testDir);
}

fs.watch(testDir, function (eventType, filename) {
    var areEqual = filename === expectedFilename;

    //This assert will fail if testDir contains an 8.3 short filename https://en.wikipedia.org/wiki/8.3_filename
    assert.deepStrictEqual(filename, expectedFilename, `"${filename}\" ${areEqual ? '=' : '!'}== \"${expectedFilename}\"`);
});


if (!fs.exists(testFile)) {
    fs.writeFileSync(testFile);
} else {
    fs.appendFileSync(testFile, 'data');
}

[bzoz]

Its a libuv issue. The wrong relative filename is created in fs-event.c.

[captainrdubb]

@bzoz Maybe we need the long_dirw, instead of passing handle->dirw

[bzoz]

I think we should get long directory name here: https://github.com/libuv/libuv/blob/v1.x/src/win/fs-event.c#L200.

[bzoz]

@seishun fixed this in libuv