fs.watch(): EINVAL on Windows watching a root file

[bpasero]

node.js: 4.2.1
OS: Win10

• have a file test.txt directly on C:
• try to watch it: fs.watch("C:\\test.txt")

=>

> fs.watch("C:\\test.txt")
Error: watch C:\test.txt EINVAL
    at exports._errnoException (util.js:874:11)
    at FSWatcher.start (fs.js:1239:19)
    at Object.fs.watch (fs.js:1267:11)
    at repl:1:4
    at REPLServer.defaultEval (repl.js:164:27)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
    at REPLServer.<anonymous> (repl.js:393:12)
    at emitOne (events.js:82:20)
    at REPLServer.emit (events.js:169:7)

[mscdex]

/cc @nodejs/platform-windows

[jorangreef]

When watching files, I think libuv actually creates a watch on the parent directory of the file (https://github.com/libuv/libuv/blob/v1.x/src/win/fs-event.c#L188), in this case C:\\. Could that have something to do with it? Also, do you have appropriate permissions to access C:\\?

[bpasero]

Yes, otherwise you will get an EPERM

[orangemocha]

This looks like a bug in libuv. If the file is at the root, and we try split the path into a directory name and file name (https://github.com/libuv/libuv/blob/f1a13e9b4abe8c97768a1d38b12ca3766c8a9b34/src/win/fs-event.c#L198-L206), we end up with a directory name that doesn't have a trailing backslash, e.g. \\?\C:. When passing that to CreateFile() Windows thinks we are trying to open the drive rather than the root directory. Adding a trailing backslash fixes the issue.

I'll add this to my queue of fixes. If anyone else wants to open a PR to https://github.com/libuv/libuv, you are welcome to do so. Thanks for reporting this issue!

[CxRes]

@saghul @seishun Has this change been upstreamed? I still have this problem with node 5.9.0.

[saghul]

@CxRes It's part of libuv but not yet of any release. It will be part of the next one, which should happen by Node 6.0.

[CxRes]

@saghul Thanks!