Lightbenc.php解析BT/BitTorrent种子的PHP类库

      我们在制作网站前段时有时会有显示bt种子内信息的需求，比如种子包含的服务器信息、包含哪些文件等等，可以通过下面的解析类库lightbenc.php来解决。

      调用示例：

<?php
require 'lightbenc.php';
$Lightbenc=new Lightbenc();
$btfile=$Lightbenc->bdecode_getinfo('11.torrent');
//获取种子文件信息
echo "<strong>种子文件名</strong>：".$btfile['info']['name'].'<br />';
echo "<strong>种子文件数</strong>：".$btfile['info']['filecount'].'<br />';
echo "<strong>种子大小</strong>：".$btfile['info']['size'].'<br />';
echo "<strong>磁力链接</strong>：".'magnet:?xt=urn:btih:'.$btfile['info_hash'].'<br />';
echo "<strong>下载种子</strong>：".'http://bt.box.n0808.com/'.substr($btfile['info_hash'],0,2).'/'.substr($btfile['info_hash'],38).'/'.$btfile['info_hash'].'.torrent'.'<br />';
echo "<strong>备用下载</strong>：".'http://torcache.net/torrent/'.$btfile['info_hash'].'.torrent'.'<br />';
echo "<strong>备用下载</strong>：".'http://btcache.sobt.org/'.$btfile['info_hash'].'.torrent'.'<br />';
echo "<strong>备用下载</strong>：".'https://zoink.it/torrent/'.$btfile['info_hash'].'.torrent'.'<br />';
echo '<br /><strong>文件信息</strong>：<br />';
foreach($btfile['info']['files'] as $f){
echo '—文件总大小：'.$f['length'].' byte<br />';
echo '—文件列表：<br />';
foreach($f['path'] as $path){
echo '——'.$path.'<br />';
}
echo '<br />';
}
?>

      解析后的效果如下：

      类库的完整代码如下：

<?php
/* lightbenc.php


	Dear Bram Cohen,
		You are an arse
	WHAT were you smoking ?



This implementation should use one order of magnitude less memory then the TBdev version.
The bdecoding speed is similar to TBdev, bencoding is faster, and much faster then bdecoding.

Call the bdecode() function with the bencoded string:

$str="d7:oneListl8:a stringe10:oneIntegeri34ee";
var_dump(bdecode($str));

array(3) {
  ["oneList"]=>
  array(1) {
    [0]=>
    string(8) "a string"
  }
  ["oneInteger"]=>
  int(34)
  ["isDct"]=>
  bool(true)
}

The returned value is a nested data type with the following type of elements:
 - ints    (test type with is_integer($x))
 - strings (test type with is_string($x))
 - lists   (test type with is_array($x) && !isset($x[isDct])
 - dicts   (test type with is_array($x) && isset($x[isDct])

All elements have the native PHP type, except for the dictionary which is an array with an "isDct" key.
This is necessary since PHP makes no distinction between flat and associative arrays. Note that the isDct
key is allways set as a bool, so that even if the dictionary contains an actual "isDct" value, the
functions behave transparently, i.e. they don't strip out or overwrite actual "isDct" keys.

As such, this implementation is not a drop-in replacement of the TBDev code, hence the new function names
For all practical purposes, it's just as flexible, and very easy to use. For example:

// decode the torrent file
$dict= bdecode_file($torrentfilename);
// change announce url
$dict['announce']='http://inferno.demonoid.com';
// add private tracker flag
$dict['info']['private']=1;
// compute infohash
$infohash = pack("H*", sha1(bencode($dict["info"])));
// recreate the torrent file
$torrentfile=bencode($dict);

After calling bencode(), the passed nested array will have all it's dictionaries sorted by key.
The bencoded data generated by bencode() will have sorted dictionaries, but bdecode() does not require
this in the input stream, and will keep the order unchanged.

This implementation is hereby released under the GFYPL, version 1.00.


	The Go Fuck Yourself Public License, version 1.00

	Article 1
	You can go fuck yourself.

	END OF ALL TERMS AND CONDITIONS

*/
class Lightbenc{
    public static function bdecode($s, &$pos=0) {
        if($pos>=strlen($s)) {
            return null;
        }
        switch($s[$pos]){
        case 'd':
            $pos++;
            $retval=array();
            while ($s[$pos]!='e'){
                $key=Lightbenc::bdecode($s, $pos);
                $val=Lightbenc::bdecode($s, $pos);
                if ($key===null || $val===null)
                    break;
                $retval[$key]=$val;
            }
            $retval["isDct"]=true;
            $pos++;
            return $retval;

        case 'l':
            $pos++;
            $retval=array();
            while ($s[$pos]!='e'){
                $val=Lightbenc::bdecode($s, $pos);
                if ($val===null)
                    break;
                $retval[]=$val;
            }
            $pos++;
            return $retval;

        case 'i':
            $pos++;
            $digits=strpos($s, 'e', $pos)-$pos;
            $val=(int)substr($s, $pos, $digits);
            $pos+=$digits+1;
            return $val;

    //	case "0": case "1": case "2": case "3": case "4":
    //	case "5": case "6": case "7": case "8": case "9":
        default:
            $digits=strpos($s, ':', $pos)-$pos;
            if ($digits<0 || $digits >20)
                return null;
            $len=(int)substr($s, $pos, $digits);
            $pos+=$digits+1;
            $str=substr($s, $pos, $len);
            $pos+=$len;
            //echo "pos: $pos str: [$str] len: $len digits: $digitsn";
            return (string)$str;
        }
        return null;
    }

    public static function bencode(&$d){
        if(is_array($d)){
            $ret="l";
            if(isset($d["isDct"])&&$d["isDct"]){
                $isDict=1;
                $ret="d";
                // this is required by the specs, and BitTornado actualy chokes on unsorted dictionaries
                ksort($d, SORT_STRING);
            }
            foreach($d as $key=>$value) {
                if(isset($isDict)&&$isDict){
                    // skip the isDct element, only if it's set by us
                    if($key=="isDct" and is_bool($value)) continue;
                    $ret.=strlen($key).":".$key;
                }
                if (is_string($value)) {
                    $ret.=strlen($value).":".$value;
                } elseif (is_int($value)){
                    $ret.="i${value}e";
                } else {
                    $ret.=Lightbenc::bencode ($value);
                }
            }
            return $ret."e";
        } elseif (is_string($d)) // fallback if we're given a single bencoded string or int
            return strlen($d).":".$d;
        elseif (is_int($d))
            return "i${d}e";
        else
            return null;
    }

    public static function bdecode_file($filename){
        $f=file_get_contents($filename, FILE_BINARY);
        return Lightbenc::bdecode($f);
    }

    public static function bdecode_getinfo($filename){
        $t = Lightbenc::bdecode(file_get_contents($filename, FILE_BINARY));
        $t['info_hash'] = sha1(Lightbenc::bencode($t['info']));

        if(is_array($t['info']['files'])){ //multifile
            $t['info']['size'] = 0;
            $t['info']['filecount'] = 0;

            foreach($t['info']['files'] as $file){
                $t['info']['filecount']++;
                $t['info']['size']+=$file['length'];
            }
        }else{
            $t['info']['size'] = $t['info']['length'];
            $t['info']["filecount"] = 1;
            $t['info']['files'][0]['path'] = $t['info']['name'];
            $t['info']['files'][0]['length'] = $t['info']['length'];
        }
        return $t;
    }
}
?>