X11 binding, XGetWindowProperty, and different behaviour for similar code between D and C++ (D fails)

[Simon Gomizelj]

On Fri, 03 Apr 2009 04:09:25 -0400, Simon Gomizelj <simongmzlj at gmail.com>  
wrote:

> As a personal learning D/learn X11 project, I thought it would be  
> interesting to try to port dwm over to D. Building it up nice and  
> slowly, right now I'm trying to collect a list of windows and their  
> states a-la dwm.c code.
>
> The D code, which is translated from C code, does not work, it returns:
> X Error of failed request:  BadValue (integer parameter out of range for  
> operation)
>    Major opcode of failed request:  20 (X_GetProperty)
>    Value in failed request:  0x2
>    Serial number of failed request:  29
>    Current serial number in output stream:  29
>
> The C++ code, which is the D code translated back, does work. The code  
> fails on a call to XGetWindowProperty. Debugging each shows that both  
> the C++ and D code pass the same atom, display, and window. Setting  
> WM_STATE_ELEMENTS < 2 causes the D code to start to segfault while the  
> C++ code still seems to work.
>
> The std.c.linux.X11.X and std.c.linux.X11.Xlib modules I grabbed off of  
> http://www.dsource.org/projects/bindings/browser/trunk/X11?order=date.  
> The rest are hand translated (but unconsequential, XGetWindowProperty is  
> contained in Xlib). X.d and Xlib.d look correct enough.
>
> I've spent a full day looking at this code, and I can't seem to  
> determine why the D code fails. Anyone have any ideas? Thanks in advance.
>

C++ code:
long getstate(Window window)
{
     static const long WM_STATE_ELEMENTS = 2L;

     unsigned long nitems;
     unsigned long leftover;
     Atom xa_WM_STATE, actual_type;
     int actual_format;
     int status;
     unsigned char* p = NULL;

     xa_WM_STATE = XInternAtom(display, "WM_STATE", false);
     cout << "debug: atom " << xa_WM_STATE << endl;

     cout << "debug: XGetWindowProperty on window " << window << endl;
     status = XGetWindowProperty(display, window,
                   xa_WM_STATE, 0L, WM_STATE_ELEMENTS,
                   false, xa_WM_STATE, &actual_type, &actual_format,
                   &nitems, &leftover, &p);

     if(status == 0)
     {
         cout << "RETURN:" << ((p != NULL) ? (long)*p : -1) << " leftover:"  
<< leftover << " nitems:" << nitems << endl;
         XFree(p);
         return (p != NULL) ? (long)*p : -1;
     }
     return -1;
}

D code:
long getstate(Window window)
{
     static const long WM_STATE_ELEMENTS = 2L;

     uint nitems;
     uint leftover;
     Atom xa_WM_STATE, actual_type;
     int actual_format;
     int status;

     ubyte* p = null;
     scope(exit) XFree(p);

     byte[] name = cast(byte[])"WM_STATE\0";
     xa_WM_STATE = XInternAtom(display, name.ptr, Bool.False);
     debug output(color.green, "debug: atom {}", xa_WM_STATE);

     debug output(color.cyan, "debug: XGetWindowProperty on window {}",  
window);
     status = XGetWindowProperty(display, window,
                   xa_WM_STATE, 0L, WM_STATE_ELEMENTS,
                   Bool.False, xa_WM_STATE, &actual_type, &actual_format,
                   &nitems, &leftover, &p);
     debug output(color.cyan, "debug: XGetWindowProperty, result:{}",  
status);

     if(status == 0)
         return (p != null) ? cast(long)*p : -1;
     return -1;
}

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