<?php

ini_set("memory_limit","32M");

/*



Basic knowledge of how bencoding works is assumed. Details can be found

at <http://bitconjurer.org/BitTorrent/protocol.html>.







How to use these functions:



An "object" is defined to be an associative array with at least the keys

"type" and "value" present. The "type" key contains a string which is

one of "string", "integer", "list" or "dictionary". The "value" key

contains the appropriate thing, either a string, an integer, a list which

is just a flat array, or a dictionary, which is an associative array. In

the case of "list" and "dictionary", the values of the contained array

are agaib "objects".







Description of the functions:







string benc($obj);



Takes an object as argument and returns the bencoded form of it as string.

Returns the undefined/unset value on failure.



Examples:



benc(array(type => "string", value => "spam"))		returns "4:spam".

benc(array(type => "integer", value => 3))		returns "i3e".

benc(array(type => "list", value => array(

	array(type => "string", value => "spam"),

	array(type => "string", value => "eggs")

)))

						returns "l4:spam4:eggse"



benc(array(type => "dictionary", value => array(

	cow => array(type => "string", value => "moo"),

	spam => array(type => "string", value => "eggs"),

)))

					returns "d3:cow3:moo4:spam4:eggse"









object bdec($str);



Returns the object that results from bdecoding the given string. Note

that those aren't real php objects, but merely "objects" as described

above. The returned objects have two additional keys: "string" and

"strlen". They represent the bencoded form of the returned objects, as

it was given in the original bencoded string. Use this to extract

certain portions of a bencoded string without having to re-encode it

(and avoiding possible re-ordering of dictionary keys). $x["strlen"]

is always equivalent to strlen($x["string"]). The "string" attribute

of the top-level returned object will be the same as the original

bencoded string, unless there's trailing garbage at the end of the

string.



This function returns the undefined/unset value on failure.



Example:



bdec("d4:spaml11:spiced pork3:hamee")

	returns this monster:



Array

(

    [type] => dictionary

    [value] => Array

        (

            [spam] => Array

                (

                    [type] => list

                    [value] => Array

                        (

                            [0] => Array

                                (

                                    [type] => string

                                    [value] => spiced pork

                                    [strlen] => 14

                                    [string] => 11:spiced pork

                                )



                            [1] => Array

                                (

                                    [type] => string

                                    [value] => ham

                                    [strlen] => 5

                                    [string] => 3:ham

                                )



                        )



                    [strlen] => 21

                    [string] => l11:spiced pork3:hame

                )



        )



    [strlen] => 29

    [string] => d4:spaml11:spiced pork3:hamee

)











object bdec_file($filename, $maxsize);



Opens the specified file, reads its contents (up to the specified length),

and returns whatever bdec() returns for those contents. This is a simple

convenience function.



*/



function benc($obj) {

	if (!is_array($obj) || !isset($obj["type"]) || !isset($obj["value"]))

		return;

	$c = $obj["value"];

	switch ($obj["type"]) {

		case "string":

			return benc_str($c);

		case "integer":

			return benc_int($c);

		case "list":

			return benc_list($c);

		case "dictionary":

			return benc_dict($c);

		default:

			return;

	}

}



function benc_str($s) {

	return strlen($s) . ":$s";

}



function benc_int($i) {

	return "i" . $i . "e";

}



function benc_list($a) {

	$s = "l";

	foreach ($a as $e) {

		$s .= benc($e);

	}

	$s .= "e";

	return $s;

}



function benc_dict($d) {

	$s = "d";

	$keys = array_keys($d);

	sort($keys);

	foreach ($keys as $k) {

		$v = $d[$k];

		$s .= benc_str($k);

		$s .= benc($v);

	}

	$s .= "e";

	return $s;

}



function bdec_file($f, $ms) {

	$fp = fopen($f, "rb");

	if (!$fp)

		return;

	$e = fread($fp, $ms);

	fclose($fp);

	return bdec($e);

}



function bdec($s) {

	if (preg_match('/^(\d+):/', $s, $m)) {

		$l = $m[1];

		$pl = strlen($l) + 1;

		$v = substr($s, $pl, $l);

		$ss = substr($s, 0, $pl + $l);

		if (strlen($v) != $l)

			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);

}



?>