<?php
/*********************************************************************
 *  Author:     Andris Causs
 *  Email:      cypher[at]inbox[dot]lv
 *  Date:       July 07, 2006
 *  Purpose:    Parse binary encoded (torrent) files into nested array.
 *
 *  You are free to use and modify the code. Just do not copy it and post
 *  somewhere as your own.
 *  Therefore I reserve all rights to this code in modified or unmodified form.
 *
 *
 *  Class form:
 *    BDecode(string filepath);
 *
 *  Basic usage:
 *  -- Require this file:
 *  require_once 'class.bdecode.php';
 *
 *  -- Initialize new class instance like this:
 *  $torrent = new BDecode('C:\\path\\to\file.torrent');
 *  -- if your web server is running on Windows
 *  -- or
 *  $torrent = new BDecode('/path/to/file.torrent');
 *
 *  -- You can access the resulting value this way:
 *  $torrent->result['my_value_name']
 *
 *  -- Here is a list of some of the most used properties:
 *    $torrent->result['announce']                    // string
 *    $torrent->result['announce-list']               // array
 *    $torrent->result['comment']                     // string
 *    $torrent->result['created by']                  // string
 *    $torrent->result['creation date']               // unix timestamp
 *    $torrent->result['encoding']                    // string
 *    $torrent->result['info']['files']               // array
 *    $torrent->result['info']['files'][?]['length']  // integer
 *    $torrent->result['info']['files'][?]['path']    // string
 *    $torrent->result['info']['name']                // string
 *    $torrent->result['info']['piece length']        // integer
 *    $torrent->result['info']['pieces']              // string
 *    $torrent->result['info']['private']             // integer
 *    $torrent->result['modified-by']                 // array
 *
 *  See http://wiki.theory.org/BitTorrentSpecification for bittorrent specification
 */

    final class BDecode {
        private $content;            // string containing contents of file
        private $pointer = 0;        // current position pointer in content
        public $result = array();    // result array containing all decoded elements


        /**************************************************************************
         * Info: Parses bencoded file into array.
         * Args: {string} filepath: full or relative path to bencoded file
         **************************************************************************/
        function __construct($filepath) {
            $this->content = @file_get_contents($filepath);

            if (!$this->content) {
                $this->throwException('File does not exist!');
            } else {
                if (!isset($this->content)) {
                    $this->throwException('Error opening file!');
                } else {
                    $this->result = $this->processElement();
                }
            }
            unset($this->content);
        }


        /**************************************************************************
         * Info: Clear class variables.
         * Args: none
         **************************************************************************/
        function __destruct() {
            unset($this->content);
            unset($this->result);
        }


        /**************************************************************************
         * Info: Terminates decoding process and returns error.
         * Args: {string} error [optional] - error description
         **************************************************************************/
        private function throwException($error = 'error parsing file') {
                $this->result = array();
                $this->result['error'] = $error;
        }

        /**************************************************************************
         * Info: Processes element depending on its type.
         *       Results in error if no valid identifier is found.
         * Args: none
         **************************************************************************/
        private function processElement() {
            switch($this->content[$this->pointer]) {
            case 'd':
                return $this->processDictionary();
                break;
            case 'l':
                return $this->processList();
                break;
            case 'i':
                return $this->processInteger();
                break;
            default:
                if (is_numeric($this->content[$this->pointer])) {
                    return $this->processString();
                } else {
                    $this->throwException('Unknown BEncode element');
                }
                break;
            }
        }

        /**************************************************************************
         * Info: Processes dictionary entries.
         *       Returns array of dictionary entries.
         * Args: none
         **************************************************************************/
        private function processDictionary() {
            if (!$this->isOfType('d'))
                $this->throwException();

            $res = array();
            $this->pointer++;

            while (!$this->isOfType('e')) {
                $elemkey = $this->processString();

                switch($this->content[$this->pointer]) {
                case 'd':
                    $res[$elemkey] = $this->processDictionary();
                    break;
                case 'l':
                    $res[$elemkey] = $this->processList();
                    break;
                case 'i':
                    $res[$elemkey] = $this->processInteger();
                    break;
                default:
                    if (is_numeric($this->content[$this->pointer])) {
                        $res[$elemkey] = $this->processString();
                    } else {
                        $this->throwException('Unknown BEncode element!');
                    }
                    break;
                }
            }

            $this->pointer++;
            return $res;
        }

        /**************************************************************************
         * Info: Processes list entries.
         *       Returns array of list entries found between 'l' and 'e' identifiers.
         * Args: none
         **************************************************************************/
        private function processList() {
            if (!$this->isOfType('l'))
                $this->throwException();

            $res = array();
            $this->pointer++;

            while (!$this->isOfType('e'))
                $res[] = $this->processElement();

            $this->pointer++;
            return $res;
        }

        /**************************************************************************
         * Info: Processes integer value.
         *       Returns integer value found between 'i' and 'e' identifiers.
         * Args: none
         **************************************************************************/
        private function processInteger() {
            if (!$this->isOfType('e'))
                $this->throwException();

            $this->pointer++;

            $delim_pos = strpos($this->content, 'e', $this->pointer);
            $integer = substr($this->content, $this->pointer, $delim_pos - $this->pointer);
            if (($integer == '-0') || ((substr($integer, 0, 1) == '0') && (strlen($integer) > 1)))
                $this->throwException();

            $integer = abs(intval($integer));
            $this->pointer = $delim_pos + 1;
            return $integer;
        }

        /**************************************************************************
         * Info: Processes string value.
         *       Returns string value found after '%:' identifier, where '%' is any
         *       valid integer.
         * Args: none
         **************************************************************************/
        private function processString() {
            if (!is_numeric($this->content[$this->pointer])) {
                $this->throwException();
            }

            $delim_pos = strpos($this->content, ':', $this->pointer);
            $elem_len = intval(substr($this->content, $this->pointer, $delim_pos - $this->pointer));
            $this->pointer = $delim_pos + 1;

            $elem_name = substr($this->content, $this->pointer, $elem_len);

            $this->pointer += $elem_len;
            return $elem_name;
        }

        /**************************************************************************
         * Info: Checks if identifier at current pointer is of supplied type.
         * Args: {char} type - character denoting required type.
         *   Usually one of [d,l,i,e].
         **************************************************************************/
        private function isOfType($type) {
            return ($this->content[$this->pointer] == $type);
        }
    }
?>