VB Forum / Win API / November 2007

I have some code which compresses a whole folder structure, and it works OK,
but I have admin privileges.  For someone who doesn't, my code fails --
however they can successfully right-click a folder, choose Properties, and
use the Advanced button to compress its whole structure and all contents.  So
the problem is, I'm asking for too much permission in my code.

Here's the essence of my VB code:

Sub Compress(sFileOrFolder as String)
   Dim lFileHwnd As Long, lBytesRtn As Long, iOutput As Integer, lResult as
Long

   lFileHwnd = CreateFile(sFileOrFolder, GENERIC_ALL, 0&, 0&,
OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0&)

   lResult = DeviceIoControl(lFileHwnd, FSCTL_SET_COMPRESSION,
COMPRESSION_FORMAT_DEFAULT, 2&, iOutput, 2&, lBytesRtn, 0&)

End Sub

I've found other code out there with many different settings for the
parameters to CreateFile, even one with dwDesiredAccess (#2) set to only
GENERIC_READ, but none mentioning FILE_WRITE_EA or FILE_WRITE_ATTRIBUTES,
which seems to make sense.  Also, it seems to me there should be no sharing
during compression, but I see code with dwShareMode (#3) set to SHARE_ALL,
etc., all over.

What's the bare minimum access and sharing I really need to compress files
and folders?  Thanks.