/**
* @brief Generates a Universally Unique IDentifier, version 4.
*
* This function generates a truly random UUID. The built in CakePHP String::uuid() function
* is not cryptographically secure. You should uses this function instead.
*
* @see http://tools.ietf.org/html/rfc4122#section-4.4
* @see http://en.wikipedia.org/wiki/UUID
* @return {string} A UUID, made up of 32 hex digits and 4 hyphens.
*/
static function uuid()
{
if (!self::$urand) {
self::$urand = @fopen('/dev/urandom', 'rb');
}
$pr_bits = false;
if (is_resource(self::$urand)) {
$pr_bits .= @fread(self::$urand, 16);
}
if (!$pr_bits) {
$fp = @fopen('/dev/urandom', 'rb');
if ($fp !== false) {
$pr_bits .= @fread($fp, 16);
@fclose($fp);
} else {
// If /dev/urandom isn't available (eg: in non-unix systems), use mt_rand().
$pr_bits = "";
for ($cnt = 0; $cnt < 16; $cnt++) {
$pr_bits .= chr(mt_rand(0, 255));
}
}
}
$time_low = bin2hex(substr($pr_bits, 0, 4));
$time_mid = bin2hex(substr($pr_bits, 4, 2));
$time_hi_and_version = bin2hex(substr($pr_bits, 6, 2));
$clock_seq_hi_and_reserved = bin2hex(substr($pr_bits, 8, 2));
$node = bin2hex(substr($pr_bits, 10, 6));
/**
* Set the four most significant bits (bits 12 through 15) of the
* time_hi_and_version field to the 4-bit version number from
* Section 4.1.3.
* @see http://tools.ietf.org/html/rfc4122#section-4.1.3
*/
$time_hi_and_version = hexdec($time_hi_and_version);
$time_hi_and_version = $time_hi_and_version >> 4;
$time_hi_and_version = $time_hi_and_version | 0x4000;
/**
* Set the two most significant bits (bits 6 and 7) of the
* clock_seq_hi_and_reserved to zero and one, respectively.
*/
$clock_seq_hi_and_reserved = hexdec($clock_seq_hi_and_reserved);
$clock_seq_hi_and_reserved = $clock_seq_hi_and_reserved >> 2;
$clock_seq_hi_and_reserved = $clock_seq_hi_and_reserved | 0x8000;
return sprintf('%08s-%04s-%04x-%04x-%012s', $time_low, $time_mid, $time_hi_and_version, $clock_seq_hi_and_reserved, $node);
}
