function bdec($s) {
if (preg_match('/^(\d+):/', $s, $m)) {
$pl = strlen($m[1]) + 1;
$v = substr($s, $pl, $m[1]);
$ss = substr($s, 0, $pl + $m[1]);
if (strlen($v) != $m[1])
return;
return array('type' => "string", 'value' => $v, 'strlen' => strlen($ss), 'string' => $ss);
}
if (preg_match('/^i(\d+)e/', $s, $m)) {
$v = $m[1];
$ss = "i" . $v . "e";
if ($v === "-0")
return;
if ($v[0] == "0" && strlen($v) != 1)
return;
return array('type' => "integer", 'value' => $v, 'strlen' => strlen($ss), 'string' => $ss);
}
switch ($s[0]) {
case "l":
return bdec_list($s);
case "d":
return bdec_dict($s);
default:
return;
}
}
function bdec_list($s) {
if ($s[0] != "l")
return;
$sl = strlen($s);
$i = 1;
$v = array();
$ss = "l";
for (;;) {
if ($i >= $sl)
return;
if ($s[$i] == "e")
break;
$ret = bdec(substr($s, $i));
if (!isset($ret) || !is_array($ret))
return;
$v[] = $ret;
$i += $ret["strlen"];
$ss .= $ret["string"];
}
$ss .= "e";
return array('type' => "list", 'value' => $v, 'strlen' => strlen($ss), 'string' => $ss);
}
function bdec_dict($s) {
if ($s[0] != "d")
return;
$sl = strlen($s);
$i = 1;
$v = array();
$ss = "d";
for (;;) {
if ($i >= $sl)
return;
if ($s[$i] == "e")
break;
$ret = bdec(substr($s, $i));
if (!isset($ret) || !is_array($ret) || $ret["type"] != "string")
return;
$k = $ret["value"];
$i += $ret["strlen"];
$ss .= $ret["string"];
if ($i >= $sl)
return;
$ret = bdec(substr($s, $i));
if (!isset($ret) || !is_array($ret))
return;
$v[$k] = $ret;
$i += $ret["strlen"];
$ss .= $ret["string"];
}
$ss .= "e";
return array('type' => "dictionary", 'value' => $v, 'strlen' => strlen($ss), 'string' => $ss);
}

class BDecode
{

function numberdecode($wholefile, $start)
{
$ret[0] = 0;
$offset = $start;

// Funky handling of negative numbers and zero
$negative = false;
if ($wholefile[$offset] == '-')
{
$negative = true;
$offset++;
}
if ($wholefile[$offset] == '0')
{
$offset++;
if ($negative)
return array(false);
if ($wholefile[$offset] == ':' || $wholefile[$offset] == 'e')
{
$offset++;
$ret[0] = 0;
$ret[1] = $offset;
return $ret;
}
return array(false);
}
while (true)
{

if ($wholefile[$offset] >= '0' && $wholefile[$offset] <= '9')
{

$ret[0] *= 10;
$ret[0] += ord($wholefile[$offset]) - ord("0");
$offset++;
}
// Tolerate : or e because this is a multiuse function
else if ($wholefile[$offset] == 'e' || $wholefile[$offset] == ':')
{
$ret[1] = $offset+1;
if ($negative)
{
if ($ret[0] == 0)
return array(false);
$ret[0] = - $ret[0];
}
return $ret;
}
else
return array(false);
}

}

function decodeEntry($wholefile, $offset=0)
{
if ($wholefile[$offset] == 'd')
return $this->decodeDict($wholefile, $offset);
if ($wholefile[$offset] == 'l')
return $this->decodelist($wholefile, $offset);
if ($wholefile[$offset] == "i")
{
$offset++;
return $this->numberdecode($wholefile, $offset);
}
// String value: decode number, then grab substring
$info = $this->numberdecode($wholefile, $offset);
if ($info[0] === false)
return array(false);
$ret[0] = substr($wholefile, $info[1], $info[0]);
$ret[1] = $info[1]+strlen($ret[0]);
return $ret;
}

function decodeList($wholefile, $start)
{
$offset = $start+1;
$i = 0;
if ($wholefile[$start] != 'l')
return array(false);
$ret = array();
while (true)
{
if ($wholefile[$offset] == 'e')
break;
$value = $this->decodeEntry($wholefile, $offset);
if ($value[0] === false)
return array(false);
$ret[$i] = $value[0];
$offset = $value[1];
$i ++;
}

// The empy list is an empty array. Seems fine.
$final[0] = $ret;
$final[1] = $offset+1;
return $final;



}

// Tries to construct an array
function decodeDict($wholefile, $start=0)
{
$offset = $start;
if ($wholefile[$offset] == 'l')
return $this->decodeList($wholefile, $start);
if ($wholefile[$offset] != 'd')
return false;
$ret = array();
$offset++;
while (true)
{
if ($wholefile[$offset] == 'e')
{
$offset++;
break;
}
$left = $this->decodeEntry($wholefile, $offset);
if (!$left[0])
return false;
$offset = $left[1];
if ($wholefile[$offset] == 'd')
{
// Recurse
$value = $this->decodedict($wholefile, $offset);
if (!$value[0])
return false;
$ret[addslashes($left[0])] = $value[0];
$offset= $value[1];
continue;
}
else if ($wholefile[$offset] == 'l')
{
$value = $this->decodeList($wholefile, $offset);
if (!$value[0] && is_bool($value[0]))
return false;
$ret[addslashes($left[0])] = $value[0];
$offset = $value[1];
}
else
{
$value = $this->decodeEntry($wholefile, $offset);
if ($value[0] === false)
return false;
$ret[addslashes($left[0])] = $value[0];
$offset = $value[1];
}
}
if (empty($ret))
$final[0] = true;
else
$final[0] = $ret;
$final[1] = $offset;
return $final;


}


} // End of class declaration.



// Use this function. eg: BDecode("d8:announce44:http://www. ... e");
function BDecode($wholefile)
{
$decoder = new BDecode;
$return = $decoder->decodeEntry($wholefile);
return $return[0];
}