#include <X11/Xlib.h>
#include <X11/Xproto.h>
#include <X11/Xlibint.h>
#include <X11/Xlib-xcb.h>
#include <stdio.h>
#include <assert.h>

static int handler(Display *dpy, XErrorEvent *err)
{
	(void) dpy, (void) err;
	puts("in error handler");
	return 0;
}

static void __glXSendError(Display * dpy, int errorCode, int resourceID, int minorCode)
{
   xError error;

   XLockDisplay(dpy);

   error.type = X_Error;

      error.errorCode = errorCode;

   error.sequenceNumber = dpy->request;
   error.resourceID = resourceID;
   error.minorCode = minorCode;
   error.majorCode = minorCode;

   _XError(dpy, &error);

   XUnlockDisplay(dpy);
}

static void sync_xcb(xcb_connection_t *c)
{
	xcb_get_input_focus_reply(c, xcb_get_input_focus(c), NULL);
}

int main()
{
	Window own;
	Display *dpy = XOpenDisplay(NULL);
	xcb_connection_t *c = XGetXCBConnection(dpy);
	XSetErrorHandler(handler);

	/* Sequence 7: CreateWindow */
	own = xcb_generate_id(c);
	xcb_create_window(c, 24, own, RootWindow(dpy, 0), 0, 0, 10, 10, 0, XCB_COPY_FROM_PARENT, XCB_COPY_FROM_PARENT,
			XCB_CW_EVENT_MASK, (uint32_t[]) { XCB_EVENT_MASK_KEY_PRESS });

	XKeyEvent event;
	event.type=KeyPress;
	event.keycode=42;
	event.display=dpy;
	event.root=own;

	/* Sequence 8: Send us an event */
	XSendEvent(dpy,own,True,KeyPressMask,(XEvent *)&event);

	/* To avoid a race with the X11 server: Make sure the event we
	 * just sent was already received by xcb (but not yet Xlib)
	 * Sequence 9
	 */
	sync_xcb(c);

	/* Send us another event */
	/* Sequence 10: */
	XSendEvent(dpy,own,True,KeyPressMask,(XEvent *)&event);
	assert(dpy->request == 10 && XNextRequest(dpy) == 11);
	assert(dpy->last_request_read == 8);

	/* Increase dpy->request some more */
	/* Sequence 11: */
	XNoOp(dpy);
	assert(dpy->request == 11 && XNextRequest(dpy) == 12);

	/* To avoid a race with the X11 server: Make sure the event we
	 * just sent was already received by xcb (but not yet Xlib)
	 * Sequence 12:
	 */
	sync_xcb(c);
	assert(dpy->request == 11);
	assert(dpy->last_request_read == 8);

	/* Set last_request_read into the future (incorrectly) */

	__glXSendError(dpy, 42, 42, 42);
	assert(dpy->request == 11);
	assert(dpy->last_request_read == 11);

	/* XLib will now read the event we generated above (sequence number 10).
	 * Thanks to XNoOp(), dpy->request was already 11. The call to _XError()
	 * thus caused request_read to be 11. Since 10 is less than 11, widen()
	 * assumes an overflow and adds 1 << 32 to the sequence.
	 *
	 * Something else that I just got right by trial and error makes sure
	 * that dpy->xcb->pending_requests is NULL.
	 */
	XEvent xevent;
	XNextEvent(dpy, &xevent);

	XCloseDisplay(dpy);
	return 0;
}