mc/src/x11conn.c

/*
   X11 support for the Midnight Commander.

   Copyright (C) 2005 The Free Software Foundation

   Written by:
   Roland Illig <roland.illig@gmx.de>, 2005.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

/*
   !!! WARNING !!!

   This code uses setjmp() and longjmp(). Before you modify _anything_
   here, please read the relevant sections of the C standard.
*/

#include <config.h>

#ifndef HAVE_TEXTMODE_X11_SUPPORT
typedef int dummy;		/* C99 forbids empty compilation unit */
#else

#include <setjmp.h>

#include <X11/Xlib.h>

#include "../src/global.h"

#ifdef HAVE_GMODULE
#  include <gmodule.h>
#endif

#include "x11conn.h"

/*** file scope type declarations **************************************/

typedef int (*mc_XErrorHandler_callback) (Display *, XErrorEvent *);
typedef int (*mc_XIOErrorHandler_callback) (Display *);

/*** file scope variables **********************************************/

#ifdef HAVE_GMODULE

static Display * (*func_XOpenDisplay) (_Xconst char *);
static int (*func_XCloseDisplay) (Display *);
static mc_XErrorHandler_callback (*func_XSetErrorHandler)
	(mc_XErrorHandler_callback);
static mc_XIOErrorHandler_callback (*func_XSetIOErrorHandler)
	(mc_XIOErrorHandler_callback);
static Bool (*func_XQueryPointer) (Display *, Window, Window *, Window *,
	int *, int *, int *, int *, unsigned int *);

static GModule *x11_module;

#else

#define func_XOpenDisplay	XOpenDisplay
#define func_XCloseDisplay	XCloseDisplay
#define func_XSetErrorHandler	XSetErrorHandler
#define func_XSetIOErrorHandler	XSetIOErrorHandler
#define func_XQueryPointer	XQueryPointer

#endif

static gboolean handlers_installed = FALSE;

/* This flag is set as soon as an X11 error is reported. Usually that
 * means that the DISPLAY is not available anymore. We do not try to
 * reconnect, as that would violate the X11 protocol. */
static gboolean lost_connection = FALSE;

static jmp_buf x11_exception; /* FIXME: get a better name */
static gboolean longjmp_allowed = FALSE;

/*** file private functions ********************************************/

static int x_io_error_handler (Display *dpy)
{
    (void) dpy;

    lost_connection = TRUE;
    if (longjmp_allowed) {
	longjmp_allowed = FALSE;
	longjmp(x11_exception, 1);
    }
    return 0;
}

static int x_error_handler (Display *dpy, XErrorEvent *ee)
{
    (void) ee;
    (void) func_XCloseDisplay (dpy);
    return x_io_error_handler (dpy);
}

static void install_error_handlers(void)
{
    if (handlers_installed) return;

    (void) func_XSetErrorHandler (x_error_handler);
    (void) func_XSetIOErrorHandler (x_io_error_handler);
    handlers_installed = TRUE;
}

static gboolean x11_available(void)
{
#ifdef HAVE_GMODULE
    gchar *x11_module_fname;

    if (lost_connection)
	return FALSE;

    if (x11_module != NULL)
	return TRUE;

    x11_module_fname = g_module_build_path (NULL, "X11");

    if (x11_module_fname == NULL)
	return FALSE;

    x11_module = g_module_open (x11_module_fname, G_MODULE_BIND_LAZY);
    g_free (x11_module_fname);

    if (x11_module == NULL)
	return FALSE;

    if (!g_module_symbol (x11_module, "XOpenDisplay",
			(void *) &func_XOpenDisplay))
	goto cleanup;
    if (!g_module_symbol (x11_module, "XCloseDisplay",
			(void *) &func_XCloseDisplay))
	goto cleanup;
    if (!g_module_symbol (x11_module, "XQueryPointer",
			(void *) &func_XQueryPointer))
	goto cleanup;
    if (!g_module_symbol (x11_module, "XSetErrorHandler",
			(void *) &func_XSetErrorHandler))
	goto cleanup;
    if (!g_module_symbol (x11_module, "XSetIOErrorHandler",
			(void *) &func_XSetIOErrorHandler))
	goto cleanup;

    install_error_handlers();
    return TRUE;

cleanup:
    func_XOpenDisplay = 0;
    func_XCloseDisplay = 0;
    func_XQueryPointer = 0;
    func_XSetErrorHandler = 0;
    func_XSetIOErrorHandler = 0;
    g_module_close (x11_module);
    x11_module = NULL;
    return FALSE;
#else
    install_error_handlers();
    return !(lost_connection);
#endif
}

/*** public functions **************************************************/

Display *mc_XOpenDisplay (const char *displayname)
{
    Display *retval;

    if (x11_available()) {
	if (setjmp(x11_exception) == 0) {
	    longjmp_allowed = TRUE;
	    retval = func_XOpenDisplay (displayname);
	    longjmp_allowed = FALSE;
	    return retval;
	}
    }
    return NULL;
}

int mc_XCloseDisplay (Display *display)
{
    int retval;

    if (x11_available()) {
	if (setjmp(x11_exception) == 0) {
	    longjmp_allowed = TRUE;
	    retval = func_XCloseDisplay (display);
	    longjmp_allowed = FALSE;
	    return retval;
	}
    }
    return 0;
}

Bool mc_XQueryPointer (Display *display, Window win, Window *root_return,
	Window *child_return, int *root_x_return, int *root_y_return,
	int *win_x_return, int *win_y_return, unsigned int *mask_return)
{
    Bool retval;

    if (x11_available()) {
	if (setjmp(x11_exception) == 0) {
	    longjmp_allowed = TRUE;
	    retval = func_XQueryPointer (display, win, root_return,
		child_return, root_x_return, root_y_return,
		win_x_return, win_y_return, mask_return);
	    longjmp_allowed = FALSE;
	    return retval;
	}
    }
    *root_return = None;
    *child_return = None;
    *root_x_return = 0;
    *root_y_return = 0;
    *win_x_return = 0;
    *win_y_return = 0;
    *mask_return = 0;
    return False;
}

#endif /* HAVE_TEXTMODE_X11_SUPPORT */