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Bencode.php
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Bencode.php
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<?php
namespace FloFaber\Bencode;
use Exception;
// Starting with PHP 8.1 this is a built-in function
if(!function_exists("array_is_list")){
function array_is_list(array $array) : bool {
$i = 0;
foreach ($array as $k => $v) {
if ($k !== $i++) {
return false;
}
}
return true;
}
}
class Decoder
{
private int $len = 0;
private int $offset = 0;
private string $data = "";
/**
* @throws Exception
*/
public function decode($data)
{
$this->data = $data;
$this->len = strlen($this->data);
$ret = [];
while ($this->offset < $this->len - 1) {
array_push($ret, $this->decode_next());
}
if (count($ret) === 1) {
$ret = $ret[0];
}
return $ret;
}
/**
* @throws Exception
*/
private function decode_next()
{
$char = $this->data[$this->offset];
if (is_numeric($char)) {
return $this->decode_string();
} elseif ($char === "d") {
return $this->decode_dict();
} elseif ($char === "i") {
return $this->decode_int();
} elseif ($char === "l") {
return $this->decode_list();
} else {
throw new Exception("Unexpected character at offset $this->offset: $char");
}
}
/**
* @throws Exception
*/
// i1337e
private function decode_int(): int
{
$e = strpos($this->data, "e", $this->offset);
if ($e === false) {
throw new Exception("Unterminated integer at offset $this->offset");
}
$n = "";
$this->offset++;
while ($this->offset < $e) {
$n .= $this->data[$this->offset];
$this->offset++;
}
$this->offset++;
return (int)$n;
}
/**
* @throws Exception
*/
private function decode_string(): string
{
$len = "";
// 4:pear
// first get the length of the upcoming string
while ($this->offset < $this->len) {
if (is_numeric($this->data[$this->offset])) {
$len .= $this->data[$this->offset];
} else {
break;
}
$this->offset++;
}
$len = (int)$len;
// skip ":"
$this->offset++;
// then get read from current offset to offset + len
$stop = $this->offset + $len;
if ($stop > $this->len) {
throw new Exception("String longer than length of data at offset $this->offset");
}
$s = "";
while ($this->offset < $stop) {
$s .= $this->data[$this->offset];
$this->offset++;
}
return $s;
}
/**
* @throws Exception
*/
private function decode_dict(): array
{
$ret = [];
while ($this->offset < $this->len) {
$k = $this->decode_next();
$v = $this->decode_next();
$ret[$k] = $v;
if ($this->data[$this->offset] === "e") {
$this->offset++;
break;
}
}
return $ret;
}
/**
* @throws Exception
*/
private function decode_list(): array
{
$this->offset++;
$ret = [];
while ($this->offset < $this->len) {
array_push($ret, $this->decode_next());
if ($this->data[$this->offset] === "e") {
$this->offset++;
break;
}
}
return $ret;
}
}
class Encoder
{
/**
* @throws Exception
*/
public function encode($x): string
{
switch (gettype($x)) {
case "string":
return $this->encode_string($x);
case "integer":
return $this->encode_int((int)$x);
case "array":
return $this->encode_array((array)$x);
default:
throw new Exception("Unknown type: " . gettype($x));
}
}
private function encode_string(string $str): string
{
return strlen($str) . ":" . $str;
}
private function encode_int(int $num): string
{
return "i" . $num . "e";
}
/**
* @throws Exception
*/
private function encode_array(array $arr): string
{
if (array_is_list($arr)) {
return $this->encode_list($arr);
} else {
$x = "";
foreach ($arr as $key => $value) {
$k = $this->encode($key);
$v = $this->encode($value);
$x .= $k . $v;
}
return "d" . $x . "e";
}
}
/**
* @throws Exception
*/
private function encode_list(array $list): string
{
$x = "";
foreach ($list as $item) {
$x .= $this->encode($item);
}
return "l" . $x . "e";
}
}
class Bencode
{
/**
* @throws Exception
*/
public static function decode($data)
{
return (new Decoder())->decode($data);
}
/**
* @throws Exception
*/
public static function encode($data): string
{
return (new Encoder())->encode($data);
}
}