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<?php declare(strict_types=1); |
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/** |
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* @package s9e\Bencode |
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* @copyright Copyright (c) 2014-2020 The s9e authors |
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* @license http://www.opensource.org/licenses/mit-license.php The MIT License |
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*/ |
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namespace s9e\Bencode; |
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use ArrayObject; |
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use InvalidArgumentException; |
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use RuntimeException; |
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class Decoder |
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{ |
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/** |
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* @var string Bencoded string being decoded |
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*/ |
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protected string $bencoded; |
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/** |
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* @var int Length of the bencoded string |
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*/ |
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protected int $len; |
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/** |
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* @var int Safe rightmost boundary |
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*/ |
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protected int $max; |
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/** |
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* @var int Position of the cursor while decoding |
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*/ |
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protected int $pos; |
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protected function __construct(string $bencoded) |
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{ |
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if ($bencoded === '') |
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{ |
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throw new InvalidArgumentException; |
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} |
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$this->bencoded = $bencoded; |
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$this->len = strlen($bencoded); |
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$this->pos = 0; |
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$this->computeSafeBoundary(); |
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} |
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public static function decode(string $bencoded) |
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{ |
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$decoder = new static($bencoded); |
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$value = $decoder->decodeAnything(); |
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$decoder->checkCursorPosition(); |
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return $value; |
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} |
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protected function checkBoundary(): void |
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{ |
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if ($this->max < 1) |
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{ |
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if (strpos('-e', $this->bencoded[0]) !== false) |
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{ |
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throw new RuntimeException('Illegal character found at offset 0'); |
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} |
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throw new RuntimeException('Premature end of data'); |
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} |
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} |
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protected function checkCursorPosition(): void |
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{ |
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if ($this->pos !== $this->len) |
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{ |
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if ($this->pos > $this->len) |
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{ |
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throw new RuntimeException('Premature end of data'); |
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} |
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$this->nonFatalError('Superfluous content found at offset ' . $this->pos); |
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} |
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} |
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/** |
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* Adjust the rightmost boundary to the last safe character |
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* |
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* Will rewind the boundary to skip the rightmost digits, optionally preceded by "i" or "i-" |
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*/ |
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protected function computeSafeBoundary(): void |
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{ |
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$boundary = $this->len - 1; |
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$c = $this->bencoded[$boundary]; |
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while (is_numeric($c) && --$boundary >= 0) |
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{ |
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$c = $this->bencoded[$boundary]; |
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} |
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if ($c === '-') |
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{ |
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$boundary -= 2; |
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} |
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elseif ($c === 'i') |
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{ |
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--$boundary; |
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} |
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$this->max = $boundary; |
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$this->checkBoundary(); |
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} |
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protected function decodeAnything() |
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{ |
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$c = $this->bencoded[$this->pos]; |
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if ($c === 'i') |
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{ |
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return $this->decodeInteger(); |
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} |
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if ($c === 'd') |
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{ |
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return $this->decodeDictionary(); |
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} |
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if ($c === 'l') |
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{ |
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return $this->decodeList(); |
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} |
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return $this->decodeString(); |
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} |
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protected function decodeDictionary(): ArrayObject |
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{ |
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$dictionary = new ArrayObject; |
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$dictionary->setFlags(ArrayObject::ARRAY_AS_PROPS); |
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++$this->pos; |
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while ($this->pos <= $this->max) |
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{ |
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if ($this->bencoded[$this->pos] === 'e') |
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{ |
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++$this->pos; |
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return $dictionary; |
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} |
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$pos = $this->pos; |
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$key = $this->decodeString(); |
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if (isset($dictionary->$key)) |
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{ |
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$this->nonFatalError("Duplicate dictionary entry '" . $key . "' at pos " . $pos); |
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} |
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if ($this->pos > $this->max) |
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{ |
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break; |
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} |
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$dictionary->$key = $this->decodeAnything(); |
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} |
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throw new RuntimeException('Premature end of data'); |
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} |
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protected function decodeDigits(string $terminator): int |
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{ |
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// Digits sorted by decreasing frequency as observed on a random sample of torrent files |
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$spn = strspn($this->bencoded, '4615302879', $this->pos); |
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if (!$spn) |
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{ |
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throw new RuntimeException('Illegal character found at offset ' . $this->pos); |
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} |
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elseif ($spn > 1 && $this->bencoded[$this->pos] === '0') |
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{ |
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$this->nonFatalError('Illegal character found at offset ' . $this->pos); |
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} |
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// Capture the value and cast it as an integer |
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$value = (int) substr($this->bencoded, $this->pos, $spn); |
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$this->pos += $spn; |
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if ($this->bencoded[$this->pos] !== $terminator) |
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{ |
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throw new RuntimeException('Illegal character found at offset ' . $this->pos); |
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} |
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++$this->pos; |
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return $value; |
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} |
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protected function decodeInteger(): int |
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{ |
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$negative = ($this->bencoded[++$this->pos] === '-'); |
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if ($negative && $this->bencoded[++$this->pos] === '0') |
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{ |
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$this->nonFatalError('Illegal character found at offset ' . $this->pos); |
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} |
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$value = $this->decodeDigits('e'); |
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return ($negative) ? -$value : $value; |
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} |
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protected function decodeList(): array |
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{ |
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++$this->pos; |
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$list = []; |
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while ($this->pos <= $this->max) |
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{ |
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if ($this->bencoded[$this->pos] === 'e') |
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{ |
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++$this->pos; |
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return $list; |
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} |
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$list[] = $this->decodeAnything(); |
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} |
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throw new RuntimeException('Premature end of data'); |
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} |
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protected function decodeString(): string |
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{ |
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$len = $this->decodeDigits(':'); |
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$string = substr($this->bencoded, $this->pos, $len); |
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$this->pos += $len; |
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return $string; |
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} |
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protected function nonFatalError(string $message): void |
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{ |
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throw new RuntimeException($message); |
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} |
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} |
s9e /
Bencode
