php如何读取torrent种子文件内容？

<?php
/**
 * Class xBEncoder
 * Author: Angus.Fenying
 * Version: 0.1
 * Date: 2014-06-03
 *
 * This class helps stringify or parse BENC
 * codes.
 *
 * All Copyrights 2007 - 2014 Fenying Studio Reserved.
 */
class xBEncoder
{
 const READY = 0;
 const READ_STR = 1;
 const READ_DICT = 2;
 const READ_LIST = 3;
 const READ_INT = 4;
 const READ_KEY = 5;
 public $y;
 protected $z, $m, $n;
 protected $stat;
 protected $stack;
 /**
  * This method saves the status of current
  * encode/decode work.
  */
 protected function push($newY, $newStat)
 {
  array_push($this->stack, array($this->y, $this->z, $this->m, $this->n, $this->stat));
  list($this->y, $this->z, $this->m, $this->n, $this->stat) = array($newY, 0, 0, 0, $newStat);
 }
 /**
  * This method restore the saved status of current
  * encode/decode work.
  */
 protected function pop()
 {
  $t = array_pop($this->stack);
  if ($t) {
   if ($t[4] == self::READ_DICT) {
    $t[0]->{$t[1]} = $this->y;
    $t[1] = 0;
   } elseif ($t[4] == self::READ_LIST)
    $t[0][] = $this->y;
   list($this->y, $this->z, $this->m, $this->n, $this->stat) = $t;
  }
 }
 /**
  * This method initializes the status of work.
  * YOU SHOULD CALL THIS METHOD BEFORE EVERYTHING.
  */
 public function init()
 {
  $this->stat = self::READY;
  $this->stack = array();
  $this->z = $this->m = $this->n = 0;
 }
 /**
  * This method decode $s($l as length).
  * You can get $obj->y as the result.
  */
 public function decode($s, $l)
 {
  $this->y = 0;
  for ($i = 0; $i < $l; ++$i) {
   switch ($this->stat) {
    case self::READY:
     if ($s[$i] == 'd') {
      $this->y = new xBDict();
      $this->stat = self::READ_DICT;
     } elseif ($s[$i] == 'l') {
      $this->y = array();
      $this->stat = self::READ_LIST;
     }
     break;
    case self::READ_INT:
     if ($s[$i] == 'e') {
      $this->y->val = substr($s, $this->m, $i - $this->m);
      $this->pop();
     }
     break;
    case self::READ_STR:
     if (xBInt::isNum($s[$i]))
      continue;
     if ($s[$i] = ':') {
      $this->z = substr($s, $this->m, $i - $this->m);
      $this->y = substr($s, $i + 1, $this->z + 0);
      $i += $this->z;
      $this->pop();
     }
     break;
    case self::READ_KEY:
     if (xBInt::isNum($s[$i]))
      continue;
     if ($s[$i] = ':') {
      $this->n = substr($s, $this->m, $i - $this->m);
      $this->z = substr($s, $i + 1, $this->n + 0);
      $i += $this->n;
      $this->stat = self::READ_DICT;
     }
     break;
    case self::READ_DICT:
     if ($s[$i] == 'e') {
      $this->pop();
      break;
     } elseif (!$this->z) {
      $this->m = $i;
      $this->stat = self::READ_KEY;
      break;
     }
    case self::READ_LIST:
     switch ($s[$i]) {
      case 'e':
       $this->pop();
       break;
      case 'd':
       $this->push(new xBDict(), self::READ_DICT);
       break;
      case 'i':
       $this->push(new xBInt(), self::READ_INT);
       $this->m = $i + 1;
       break;
      case 'l':
       $this->push(array(), self::READ_LIST);
       break;
      default:
       if (xBInt::isNum($s[$i])) {
        $this->push('', self::READ_STR);
        $this->m = $i;
       }
     }
     break;
   }
  }
  $rtn = empty($this->stack);
  $this->init();
  return $rtn;
 }
 /**
  * This method encode $obj->y into BEncode.
  */
 public function encode()
 {
  return $this->_encDo($this->y);
 }
 protected function _encStr($str)
 {
  return strlen($str) . ':' . $str;
 }
 protected function _encDo($o)
 {
  if (is_string($o))
   return $this->_encStr($o);
  if ($o instanceof xBInt)
   return 'i' . $o->val . 'e';
  if ($o instanceof xBDict) {
   $r = 'd';
   foreach ($o as $k => $c)
    $r .= $this->_encStr($k) . $this->_encDo($c);
   return $r . 'e';
  }
  if (is_array($o)) {
   $r = 'l';
   foreach ($o as $c)
    $r .= $this->_encDo($c);
   return $r . 'e';
  }
 }
}
class xBDict
{
}
class xBInt
{
 public $val;
 public function __construct($val = 0)
 {
  $this->val = $val;
 }
 public static function isNum($chr)
 {
  $chr = ord($chr);
  if ($chr <= 57 && $chr >= 48)
   return true;
  return false;
 }
}
//使用实例
$s = file_get_contents("test.torrent");
$bc = new xBEncoder();
$bc->init();
$bc->decode($s, strlen($s));
var_dump($bc->y);