fs.open differences on windows vs *nix

[evanlucas]

If you create a directory, and then try to use fs.open to open it, you get differing behavior on windows and *nix if the flags are a+.

Example:

// OS X
fs.open('<directory>', 'a+', console.log)
// => [Error: EISDIR: illegal operation on a directory, open <directory>]

// Windows
fs.open('<directory>', 'a+', console.log)
// => null <fd>

After looking through the libuv code, it looks like https://github.com/libuv/libuv/blob/v1.x/src/win/fs.c#L479-L480 is responsible for this. Is this intended or should this operation show the same behavior on all platforms?

[bnoordhuis]

Libuv lets you do that on freebsd as well, FWIW, so it's not entirely without precedent.

[jasnell]

I believe this is working as expected but additional documentation may be worthwhile.
@nodejs/documentation

[eljefedelrodeodeljefe]

Added a PR for this.