Symfony SecureRandom mockup

SecureRandomMockup.php

<?php
namespace Symfony\Component\Security\Core\Util;

class SecureRandom
{
    /**
     * Generate a random string of bytes suitable for cryptographic use.
     *
     * @param int $nbBytes
     * @return string
     * @throws \RuntimeException
     */
    public function nextBytes($nbBytes)
    {
        $nbBytes = (int) $nbBytes;

        if ($nbBytes < 1)
        {
            throw new \RuntimeException('$nbBytes must be greater than 0');
        }

        $bytes = '';
        $hasBytes = false;

        // Try mcrypt_create_iv at first because it works also on the Windows
        if (function_exists('mcrypt_create_iv'))
        {
            $tmp = mcrypt_create_iv($nbBytes, MCRYPT_DEV_URANDOM);
            if ($tmp !== false)
            {
                $bytes = $tmp;
                $hasBytes = true;
            }
        }

        // Fall back trying to read straight from /dev/urandom
        if ($hasBytes === false && file_exists('/dev/urandom') && is_readable('/dev/urandom') && (false !== ($fh = fopen('/dev/urandom', 'rb'))))
        {
            if (function_exists('stream_set_read_buffer'))
            {
                stream_set_read_buffer($fh, 0);
            }

            $tmp = fread($fh, $nbBytes);
            fclose($fh);
            if ($tmp !== false)
            {
                $bytes = $tmp;
            }
        }

        if (strlen($bytes) === $nbBytes)
        {
            return $bytes;
        }
        else
        {
            throw new \RuntimeException('Could not generate random bytes');
        }
    }
}