[python-win32] Interacting with the desktop as a service on Vista

[Matt Herbert (matherbe)]

Hey all,

So I have a service that needs to interact with the desktop on a Vista
machine. I've read multiple articles about Vista's updated security and
it's restrictions on services. So I realize that in order for the
service to interact with desktop, I'm going to need to create a new
process as a "normal" user, and use some form of IPC between the child
process and my service to get at the information I need.

I've done some research and found an example program on MSDN titled
"Starting an Interactive Client Process in C++"
(http://msdn.microsoft.com/en-us/library/aa379608(VS.85).aspx). With a
little patience, I translated the program into various win32api calls,
and got almost everything working. The one thing I can't seem to get
working, is the new child process I create (via CreateProcessAsUser)
does not seem to be attached to the winsta0\default desktop. Even though
I have explicitly created a STARTUPINFO object and set the lpDesktop to
'winsta0\\default':

si = win32process.STARTUPINFO()
si.lpDesktop = 'winsta0\\default'
pinfo = win32process.CreateProcessAsUser(
    hToken,
    None,
    command,
    None,
    None,
    False,
    win32con.NORMAL_PRIORITY_CLASS | win32con.CREATE_NEW_CONSOLE,
    None,
    None,
    si)

My child process starts up just fine, but is not able to interact with
the desktop in any way. When I check in task manager, it shows the
session id for the child process as 0, while my "normal" applications
(such as firefox) are running under session id 1. (FWIW, the user of the
child process is my "normal" (non SYSTEM) user in task manager). 

I've also tried to force my way onto the default desktop in the child
process:

hwinsta = win32service.OpenWindowStation(
                "winsta0", False, win32con.READ_CONTROL)
hwinsta.SetProcessWindowStation()
hdesk = win32service.OpenDesktop('default', 0, False, DESKTOP_ALL)
hdesk.SetThreadDesktop()

But when the child tries to do this, it dies with the following
exception:

Traceback (most recent call last):
  File "C:\Spawn.py", line 723, in <module>
    hdesk.SetThreadDesktop()
pywintypes.error: (170, 'SetThreadDesktop', 'The requested resource is
in use.')

I can't figure out where to go from here, so any hints would be greatly
appreciated.

-Matt