sub _slow_is_ipv4 {
    shift if ref $_[0];
    my $value = shift;
 
    return undef unless defined($value);
 
    my (@octets) = $value =~ /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/;
    return undef unless (@octets == 4);
    foreach (@octets) {
        return undef if $_ < 0 || $_ > 255;
        return undef if $_ =~ /^0\d{1,2}$/;
    }
 
    return join('.', @octets);
}