#
# GetDisplayNumber gets the lowest available display number.  A display number
# n is taken if something is listening on the VNC server port (5900+n) or the
# X server port (6000+n).
#
sub GetDisplayNumber
{
    foreach $n (1..99) {
        if (&CheckDisplayNumber($n)) {
            return $n+0; # Bruce Mah's workaround for bug in perl 5.005_02
        }
    }
    die "$prog: no free display number on $host.\n";
}
 
#
# CheckDisplayNumber checks if the given display number is available.  A
# display number n is taken if something is listening on the VNC server port
# (5900+n) or the X server port (6000+n).
#
sub CheckDisplayNumber
{
    local ($n) = @_;
    socket(S, $AF_INET, $SOCK_STREAM, 0) || die "$prog: socket failed: $!\n";
    eval 'setsockopt(S, &SOL_SOCKET, &SO_REUSEADDR, pack("l", 1))';
    if (!bind(S, pack('S n x12', $AF_INET, 6000 + $n))) {
        close(S);
        return 0;
    }
    close(S);
    socket(S, $AF_INET, $SOCK_STREAM, 0) || die "$prog: socket failed: $!\n";
    eval 'setsockopt(S, &SOL_SOCKET, &SO_REUSEADDR, pack("l", 1))';
    if (!bind(S, pack('S n x12', $AF_INET, 5900 + $n))) {
        close(S);
        return 0;
    }
    close(S);
    if (-e "/tmp/.X$n-lock") {
        warn "\nWarning: $host:$n is taken because of /tmp/.X$n-lock\n";
        warn "Remove this file if there is no X server $host:$n\n";
        return 0;
    }
    if (-e "/tmp/.X11-unix/X$n") {
        warn "\nWarning: $host:$n is taken because of /tmp/.X11-unix/X$n\n";
        warn "Remove this file if there is no X server $host:$n\n";
        return 0;
    }
    if (-e "/usr/spool/sockets/X11/$n") {
        warn("\nWarning: $host:$n is taken because of ".
             "/usr/spool/sockets/X11/$n\n");
        warn "Remove this file if there is no X server $host:$n\n";
        return 0;
    }
    return 1;
}