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<?php
/*
Programming info
All functions output a small array, which we'll call $return for now.
$return[0] is the data expected of the function
$return[1] is the offset over the whole bencoded data of the next
piece of data.
numberdecode returns [0] as the integer read, and [1]-1 points to the
symbol that was interprented as the end of the interger (either "e" or
":").
numberdecode is used for integer decodes both for i11e and 11:hello there
so it is tolerant of the ending symbol.
decodelist returns $return[0] as an integer indexed array like you would use in C
for all the entries. $return[1]-1 is the "e" that ends the list, so [1] is the next
useful byte.
decodeDict returns $return[0] as an array of text-indexed entries. For example,
$return[0]["announce"] = "http://www.whatever.com:6969/announce";
$return[1]-1 again points to the "e" that ends the dictionary.
decodeEntry returns [0] as an integer in the case $offset points to
i12345e or a string if $offset points to 11:hello there style strings.
It also calls decodeDict or decodeList if it encounters a d or an l.
Known bugs:
- The program doesn't pay attention to the string it's working on.
A zero-sized or truncated data block will cause string offset errors
before they get rejected by the decoder. This is worked around by
suppressing errors.
*/
// Protect our namespace using a class
class BDecode {
function numberdecode($wholefile, $offset) {
// 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'){
return array(0, ++$offset);
}
return array(false);
}
$ret[0] = 0;
for(;;) {
if ($wholefile[$offset] >= '0' && $wholefile[$offset] <= '9') {
$ret[0] *= 10;
//Added 2005.02.21 - VisiGod
//Changing the type of variable from integer to double to prevent a numeric overflow
settype($ret[0],'double');
//Added 2005.02.21 - VisiGod
$ret[0] += ord($wholefile[$offset]) - ord('0');
$offset++;
} else if ($wholefile[$offset] == 'e' || $wholefile[$offset] == ':') {
// Tolerate : or e because this is a multiuse function
$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')
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, $offset) {
if ($wholefile[$offset] != 'l')
return array(false);
$offset++;
$ret = array();
for ($i=0;;$i++) {
if ($wholefile[$offset] == 'e')
break;
$value = $this->decodeEntry($wholefile, $offset);
if ($value[0] === false)
return array(false);
$ret[$i] = $value[0];
$offset = $value[1];
}
// The empty list is an empty array. Seems fine.
return array(0=>$ret, 1=>++$offset);
}
// Tries to construct an array
function decodeDict($wholefile, $offset=0) {
if ($wholefile[$offset] == 'l')
return $this->decodeList($wholefile, $offset);
if ($wholefile[$offset] != 'd')
return false;
$ret=array();
$offset++;
for (;;) {
if ($wholefile[$offset] == 'e') {
$offset++;
break;
}
$left = $this->decodeEntry($wholefile, $offset);
if ($left[0]===false) {
die("stop...".$left[1]);
return false;
}
$offset = $left[1];
if ($wholefile[$offset] == 'd') {
// Recurse
$value = $this->decodedict($wholefile, $offset);
if ($value[0]) {
$ret[addslashes($left[0])] = $value[0];
$offset= $value[1];
}
continue;
}
if ($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];
continue;
}
$value = $this->decodeEntry($wholefile, $offset);
if ($value[0] === false)
return false;
$ret[addslashes($left[0])] = $value[0];
$offset = $value[1];
}
return array(0=>(empty($ret)?true:$ret), 1=>$offset);
}
} // 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];
}
?>
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