Windows: ftruncate to shrink file gives EPERM

[jorangreef]

I have a file with the following stats in a Windows VM:

{"dev":-24039965,"mode":33206,"nlink":1,"uid":0,"gid":0,"rdev":0,"ino":562949953548321,"size":39035842,"atime":"2015-10-03T09:59:32.677Z","mtime":"2015-10-03T10:00:17.241Z","ctime":"2015-10-03T10:00:17.241Z","birthtime":"2015-10-03T09:59:32.677Z"}

Truncating this file using ftruncate from 39035842 to 38839234 byte (to make it smaller) gives EPERM.

Is ftruncate simply not supported at all on Windows? I thought it was only ftruncate to enlarge a file that was not permitted on Windows?

[bnoordhuis]

/cc @nodejs/platform-windows - I don't know the answer to this question. I thought that as long as you have the appropriate privileges and the file is opened for writing (not appending), you should be able to truncate it in either direction.

[jorangreef]

Thanks Ben, that was the problem. I had the file opened on Windows using "a+".

On Mac however, ftruncate still works if the file is opened with "a+".

[sam-github]

This behaviour is undocumented in node, and I'd welcome a PR for that, but node doesn't reduce Windows and Unixen to a "lowest common denominator", there are differences.