php不可靠函数is_writable的另外一种安全实现

is_really_writable

if ( ! function_exists('is_really_writable'))
{
	/**
	 * Tests for file writability
	 *
	 * is_writable() returns TRUE on Windows servers when you really can't write to
	 * the file, based on the read-only attribute.
	 *
	 * @link	https://bugs.php.net/bug.php?id=54709
	 * @param	string
	 * @return	bool
	 */
	function is_really_writable($file)
	{
		// If we're on a UNIX-like server, just is_writable()
		if (DIRECTORY_SEPARATOR === '/')
		{
			return is_writable($file);
		}
		/* For Windows servers and safe_mode "on" installations we'll actually
		 * write a file then read it. Bah...
		 */
		if (is_dir($file))
		{
			$file = rtrim($file, '/').'/'.md5(mt_rand());
			if (($fp = @fopen($file, 'ab')) === FALSE)
			{
				return FALSE;
			}
			fclose($fp);
			@chmod($file, 0777);
			@unlink($file);
			return TRUE;
		}
		elseif ( ! is_file($file) OR ($fp = @fopen($file, 'ab')) === FALSE)
		{
			return FALSE;
		}
		fclose($fp);
		return TRUE;
	}
}