NetUserModalsGet() returns strings incorrectly for C#.NET

Question

EDIT: Yet another followup at https://stackoverflow.com/questions/1799742/shouldnt-netusermodalsget-tell-me-what-domain-a-machine-is-part-of-and-where

Thanks to Gonzalo's help, I'm able to use the NetUserModalsGet() from C# . But there's still some kinks: the string members ( usrmod1_primary and usrmod2_domain_name ) come out messed up. Here's the code:

[DllImport("netapi32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall, SetLastError = true)]
public static extern uint NetUserModalsGet(
    string server,
    int level,
    out IntPtr BufPtr
);

[DllImport("netapi32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall, SetLastError = true)]
public static extern uint NetApiBufferFree(
    IntPtr bufptr
);

public struct USER_MODALS_INFO_0
{
    public uint usrmod0_min_passwd_len;
    public uint usrmod0_max_passwd_age;
    public uint usrmod0_min_passwd_age;
    public uint usrmod0_force_logoff;
    public uint usrmod0_password_hist_len;
};

public struct USER_MODALS_INFO_1
{
    public uint usrmod1_role;
    public string usrmod1_primary;
};

public struct USER_MODALS_INFO_2
{
    public string usrmod2_domain_name;
    public uint usrmod2_domain_id;
};

public struct USER_MODALS_INFO_3
{
    public uint usrmod3_lockout_duration;
    public uint usrmod3_lockout_observation_window;
    public uint usrmod3_lockout_threshold;
};

...

uint retVal;
IntPtr myBuf;
USER_MODALS_INFO_0 myInfo0 = new USER_MODALS_INFO_0();
USER_MODALS_INFO_1 myInfo1 = new USER_MODALS_INFO_1();
USER_MODALS_INFO_2 myInfo2 = new USER_MODALS_INFO_2();
USER_MODALS_INFO_3 myInfo3 = new USER_MODALS_INFO_3();

retVal = NetUserModalsGet("\\\\" + tbHost.Text, 0, out myBuf);
if (retVal == 0)
{
    myInfo0 = (USER_MODALS_INFO_0)Marshal.PtrToStructure(myBuf, typeof(USER_MODALS_INFO_0));
    myResults += String.Format("usrmod0_force_logoff={0}\nusrmod0_max_passwd_age={1}\nusrmod0_min_passwd_age={2}\nusrmod0_min_passwd_len={3}\nusrmod0_password_hist_len={4}\n",
        myInfo0.usrmod0_force_logoff.ToString("X8"),
        myInfo0.usrmod0_max_passwd_age.ToString("X8"),
        myInfo0.usrmod0_min_passwd_age.ToString("X8"),
        myInfo0.usrmod0_min_passwd_len.ToString("X8"),
        myInfo0.usrmod0_password_hist_len.ToString("X8")
        );
}
myResults += String.Format("retVal={0}\n\n", retVal);
retVal = NetApiBufferFree(myBuf);

retVal = NetUserModalsGet("\\\\" + tbHost.Text, 1, out myBuf);
if (retVal == 0)
{
    myInfo1 = (USER_MODALS_INFO_1)Marshal.PtrToStructure(myBuf, typeof(USER_MODALS_INFO_1));
    myResults += String.Format("usrmod1_primary={0}\nusrmod1_role={1}\n",
        myInfo1.usrmod1_primary,
        myInfo1.usrmod1_role.ToString("X8")
        );
}
myResults += String.Format("retVal={0}\n\n", retVal);
retVal = NetApiBufferFree(myBuf);

retVal = NetUserModalsGet("\\\\" + tbHost.Text, 2, out myBuf);
if (retVal == 0)
{
    myInfo2 = (USER_MODALS_INFO_2)Marshal.PtrToStructure(myBuf, typeof(USER_MODALS_INFO_2));
    myResults += String.Format("usrmod2_domain_id={0}\nusrmod2_domain_name={1}\n",
        myInfo2.usrmod2_domain_id.ToString("X8"),
        myInfo2.usrmod2_domain_name
        );
}
myResults += String.Format("retVal={0}\n\n", retVal);
retVal = NetApiBufferFree(myBuf);

retVal = NetUserModalsGet("\\\\" + tbHost.Text, 3, out myBuf);
if (retVal == 0)
{
    myInfo3 = (USER_MODALS_INFO_3)Marshal.PtrToStructure(myBuf, typeof(USER_MODALS_INFO_3));
    myResults += String.Format("usrmod3_lockout_duration={0}\nusrmod3_lockout_observation_window={1}\nusrmod3_lockout_threshold={2}\n",
        myInfo3.usrmod3_lockout_duration.ToString("X8"),
        myInfo3.usrmod3_lockout_observation_window.ToString("X8"),
        myInfo3.usrmod3_lockout_threshold.ToString("X8")
        );
}
myResults += String.Format("retVal={0}\n\n", retVal);
retVal = NetApiBufferFree(myBuf);

What I get as a result is:

usrmod0_force_logoff=FFFFFFFF
usrmod0_max_passwd_age=00375F00
usrmod0_min_passwd_age=00000000
usrmod0_min_passwd_len=00000000
usrmod0_password_hist_len=00000000
retVal=0

usrmod1_primary=
usrmod1_role=00000003
retVal=0

usrmod2_domain_id=08C409B0
usrmod2_domain_name=M
retVal=0

usrmod3_lockout_duration=0000012C
usrmod3_lockout_observation_window=0000012C
usrmod3_lockout_threshold=00000000
retVal=0

All of that except usrmod1_primary and usrmod2_domain_name makes sense. The tested machine is a member of a domain, whose name does start with an M. I smell some Unicode hijinx, but I can't see what's wrong.

Answer 1

The strings in your structs are marshaled as ANSI by default, but the Net* APIs work almost exclusively with Unicode strings. So apply the attribute

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]

to USER_MODALS_INFO_1 and _2 and your should be good.

A couple of other things:

• There's no point in specifying SetLastError=true in yor DllImport attributes in this case, because NetUserModalsGet doesn't return error info via SetLastError (you get it in the return value).

• USER_MODALS_INFO_2.usrmod2_domain_id is a pointer and therefore better modeled as an IntPtr (for x64 compatibility).