<?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 $offset points to 11:hello there style strings.
It also calls decodeDict or decodeList if it encounters a d or an l.
Known bugs:
- The program doesn't pay attention to the string it's working on.
A zero-sized or truncated data block will cause string offset errors
before they get rejected by the decoder. This is worked around by
suppressing errors.
*/
function numberdecode($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[$offset] == 'd')
return decodeDict($wholefile, $offset);
if ($wholefile[$offset] == 'l')
return decodelist($wholefile, $offset);
if ($wholefile[$offset] == "i")
{
$offset++;
return numberdecode($wholefile, $offset);
}
// String value: decode number, then grab substring
$info = numberdecode($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;
$value = decodeEntry($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[$offset] == 'l')
return decodeList($wholefile, $start);
if ($wholefile[$offset] != 'd')
return false;
$ret = array();
$offset++;
while (true)
{
if ($wholefile[$offset] == 'e')
{
$offset++;
break;
}
$left = decodeEntry($wholefile, $offset);
if (!$left[0])
return false;
$offset = $left[1];
if ($wholefile[$offset] == 'd')
{
// Recurse
$value = decodedict($wholefile, $offset);
if (!$value[0])
return false;
$ret[addslashes($left[0])] = $value[0];
$offset= $value[1];
continue;
}
else if ($wholefile[$offset] == 'l')
{
$value = decodeList($wholefile, $offset);
if (!$value[0] && is_bool($value[0]))
return false;
$ret[addslashes($left[0])] = $value[0];
$offset = $value[1];
}
else
{
$value = decodeEntry($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 $final;
}
// Use this function. eg: BDecode("d8:announce44:http://www. ... e");
function BDecode($wholefile)
{
$return = @decodeEntry($wholefile);
return $return[0];
}
?>
