PHP stream_wrapper_register

<?php
/**
 * 引用：http://php.net/manual/en/function.stream-wrapper-register.php
 * 把变量当成文件读写的协议
 *
 * Class VariableStream
 */
class VariableStream
{
    private $postition;   // 当前的位置
    private $varname;     // 变量的名字

    /**
     * 打开
     *
     * @param $path
     * @param $mode
     * @param $options
     * @param $opened_path
     * @return bool
     */
    public function stream_open($path, $mode, $options, &$opened_path)
    {
        $url = parse_url($path);

        $this->varname   = $url['host'];
        $this->postition = 0;

        return true;
    }

    /**
     * 读取
     *
     * @param $count
     * @return string
     */
    public function stream_read($count)
    {

        $p   = $this->postition;
        $ret = substr($GLOBALS[$this->varname], $p,$count);
        $p  += $count;
        return $ret;
    }

    /**
     * 写入
     *
     * @param $data
     * @return int
     */
    public function stream_write($data)
    {
        $v = &$GLOBALS[$this->varname];
        $l = strlen($data);
        $p = &$this->postition;
        $v = substr($v,0,$p) .$data.substr($v,$p+=$l);

        return $l;
    }

    /**
     * 返回位置
     *
     * @return mixed
     */
    public function stream_tell()
    {
        return $this->postition;
    }

    /**
     * 寻位
     *
     * @param $offset
     * @param $whence
     * @return bool
     */
    public function stream_seek($offset, $whence)
    {
        $dp = $p = &$this->postition;
        $l  = strlen($GLOBALS[$this->varname]);

        switch($whence)
        {
            case SEEK_SET:
                $p = 0;
                break;
            case SEEK_END:
                $p = $l;
                break;
            default:
                return false;
        }
        $p += $offset;
        $ret = ($p >= 0 || $p <= $l);
        if(!$ret)
            $this->postition = $dp;
        return $ret;
    }

    public function stream_eof()
    {
        return strlen($GLOBALS[$this->varname])== $this->postition;
    }
}

// 撤销已注册的同名协议
if(in_array('var',stream_get_wrappers()))
{
    stream_wrapper_unregister('var');
}
// 注册自己的协议
stream_wrapper_register('var','VariableStream') or die('Failed to register protocol');

$myvar = "";
$fp = fopen('var://myvar','r+');
if(!$fp){
    die('Failed to open the file!');
}
$str = "Hello the world!";
fwrite($fp,$str,strlen($str));

echo 'The length of the string is ' .strlen($myvar) ."
";
echo 'The value of variable ,$myvar,is :' .$myvar ."
";
echo 'The position of the cursor is :' .ftell($fp) ."
";
echo 'Is at the end of the file :' .(feof($fp) ? 'true':'false') ."
";
if(fseek($fp,-16,SEEK_END))
{
    echo 'Now,the position is :' .ftell($fp);
}