.torrent creator in PHP, for easier Drupal integration in the future.

opentracker.torrent.php

<?php


/**
 * Converts a specified structure into its bencoded form. Acceptable values
 * include: integers, strings, arrays, and assoc. arrays.
 * Note that associative arrays are encoded into dictionaries while
 * non-associative arrays are encoded into lists.
 *
 * This was copied from http://drupal.org/project/bittorrent
 *
 * @param $struct
 *    This is the structure to bencode example passing the value 'hi' would
 *    return '2:hi'.
 * @return
 *    The bencoded form of $struct.
 */
function opentracker_bencode($struct) {
  if (is_array($struct)) {
    $numeric = true;
    foreach(array_keys($struct) as $key) {
      if (!is_numeric($key)) {
        $numeric = false;
        break;
      }
    }

    if (!$numeric) {
      $out = 'd';
      ksort($struct);
      foreach($struct as $key => $value) {
        $out .= opentracker_bencode($key);
        $out .= opentracker_bencode($value);
      }
      $out .= 'e';
    }
    else {
      $out = 'l';
      ksort($struct);
      foreach($struct as $key => $value) {
        $out .= opentracker_bencode($value);
      }
      $out .= 'e';
    }

    return $out;
  }
  elseif (preg_match('/^(\+|\-)?\d+$/', $struct)) {
    return 'i' . $struct . 'e';
  }
  else {
    return strlen($struct) . ':' . $struct;
  }
  return;
}


function opentracker_torrent_create($announce, $input_file, $torrent_file, $publisher, $publisher_url, $comment, $creation_date) {
  $length = filesize($input_file);

  // 512 KB is the default maximum piece length
  //
  // From http://wiki.theory.org/BitTorrentSpecification:
  //  "Current best-practice is to keep the piece size to 512KB or less, for
  //   torrents around 8-10GB, even if that results in a larger .torrent file.
  //   This results in a more efficient swarm for sharing files.""
  $piece_length = 524288;

  // Keep making the piece length:
  // - smaller until there is >1 piece, or;
  // - larger until there are <1500 pieces
  // From http://wiki.vuze.com/w/Torrent_Piece_Size:
  //  "All in all, a torrent should have around 1000-1500 pieces, to get a
  //   reasonably small torrent file and an efficient client and swarm
  //   download."
  while (ceil($length / $piece_length) == 1) {
    $piece_length /= 2;
  }
  while (ceil($length / $piece_length) > 1500) {
    $piece_length *= 2;
  }

  // Build pieces.
  if (($fp = fopen($input_file, 'r')) == FALSE) {
    return FALSE;
  }
  $pieces = '';
  while (!feof($fp)) {
    $pieces .= pack('H*', sha1(fread($fp, $piece_length)));
  }
  fclose($fp);

  // Build the torrent data structure.
  $torrent = array(
    'announce'      => $announce,
    'creation date' => $creation_date,
    'created by'    => $publisher,
    'publisher'     => $publisher,
    'publisher-url' => $publisher_url,
    'comment'       => $comment,
    'info' => array(
      'length'       => $length,
      'name'         => basename($input_file),
      'piece length' => $piece_length,
      'pieces'       => $pieces,
      'md5sum'       => md5_file($input_file),
    ),
  );

  // Save the .torrent file.
  file_put_contents($torrent_file, opentracker_bencode($torrent));

  return $torrent;
}

opentracker_torrent_create(
  'http://tracker.driverpacks.net:6969/announce',
  '/Users/wimleers/Downloads/DP_CPU_wnt5_x86-32_1005.7z',
  '/Users/wimleers/Downloads/DP_CPU_wnt5_x86-32_1005.torrent',
  'DriverPacks.net',
  'http://driverpacks.net',
  "DriverPack CPU 10.05 for Windows 2000/XP/2003 (x86)\n\nURL: http://driverpacks.net/driverpacks/windows/xp/x86/cpu/10.05",
  1290176462
);