index.js

module.exports = decodeTorrentFile
module.exports.decode = decodeTorrentFile
module.exports.encode = encodeTorrentFile

var bencode = require('bencode')
var path = require('path')
var sha1 = require('simple-sha1')
var uniq = require('uniq')

/**
 * Parse a torrent. Throws an exception if the torrent is missing required fields.
 * @param  {Buffer|Object} torrent
 * @return {Object}        parsed torrent
 */
function decodeTorrentFile (torrent) {
  if (Buffer.isBuffer(torrent)) {
    torrent = bencode.decode(torrent)
  }

  // sanity check
  ensure(torrent.info, 'info')
  ensure(torrent.info['name.utf-8'] || torrent.info.name, 'info.name')
  ensure(torrent.info['piece length'], 'info[\'piece length\']')
  ensure(torrent.info.pieces, 'info.pieces')

  if (torrent.info.files) {
    torrent.info.files.forEach(function (file) {
      ensure(typeof file.length === 'number', 'info.files[0].length')
      ensure(file['path.utf-8'] || file.path, 'info.files[0].path')
    })
  } else {
    ensure(typeof torrent.info.length === 'number', 'info.length')
  }

  var result = {}
  result.info = torrent.info
  result.infoBuffer = bencode.encode(torrent.info)
  result.infoHash = sha1.sync(result.infoBuffer)
  result.infoHashBuffer = new Buffer(result.infoHash, 'hex')

  result.name = (torrent.info['name.utf-8'] || torrent.info.name).toString()

  if (torrent.info.private !== undefined) result.private = !!torrent.info.private

  if (torrent['creation date']) result.created = new Date(torrent['creation date'] * 1000)
  if (torrent['created by']) result.createdBy = torrent['created by'].toString()

  if (Buffer.isBuffer(torrent.comment)) result.comment = torrent.comment.toString()

  // announce and announce-list will be missing if metadata fetched via ut_metadata
  result.announce = []
  if (torrent['announce-list'] && torrent['announce-list'].length) {
    torrent['announce-list'].forEach(function (urls) {
      urls.forEach(function (url) {
        result.announce.push(url.toString())
      })
    })
  } else if (torrent.announce) {
    result.announce.push(torrent.announce.toString())
  }

  // handle url-list (BEP19 / web seeding)
  if (Buffer.isBuffer(torrent['url-list'])) {
    // some clients set url-list to empty string
    torrent['url-list'] = torrent['url-list'].length > 0
      ? [ torrent['url-list'] ]
      : []
  }
  result.urlList = (torrent['url-list'] || []).map(function (url) {
    return url.toString()
  })

  uniq(result.announce)
  uniq(result.urlList)

  var files = torrent.info.files || [ torrent.info ]
  result.files = files.map(function (file, i) {
    var parts = [].concat(result.name, file['path.utf-8'] || file.path || []).map(function (p) {
      return p.toString()
    })
    return {
      path: path.join.apply(null, [path.sep].concat(parts)).slice(1),
      name: parts[parts.length - 1],
      length: file.length,
      offset: files.slice(0, i).reduce(sumLength, 0)
    }
  })

  result.length = files.reduce(sumLength, 0)

  var lastFile = result.files[result.files.length - 1]

  result.pieceLength = torrent.info['piece length']
  result.lastPieceLength = ((lastFile.offset + lastFile.length) % result.pieceLength) || result.pieceLength
  result.pieces = splitPieces(torrent.info.pieces)

  return result
}

/**
 * Convert a parsed torrent object back into a .torrent file buffer.
 * @param  {Object} parsed parsed torrent
 * @return {Buffer}
 */
function encodeTorrentFile (parsed) {
  var torrent = {
    info: parsed.info
  }

  torrent['announce-list'] = (parsed.announce || []).map(function (url) {
    if (!torrent.announce) torrent.announce = url
    url = new Buffer(url, 'utf8')
    return [ url ]
  })

  torrent['url-list'] = parsed.urlList || []

  if (parsed.created) {
    torrent['creation date'] = (parsed.created.getTime() / 1000) | 0
  }

  if (parsed.createdBy) {
    torrent['created by'] = parsed.createdBy
  }

  if (parsed.comment) {
    torrent.comment = parsed.comment
  }

  return bencode.encode(torrent)
}

function sumLength (sum, file) {
  return sum + file.length
}

function splitPieces (buf) {
  var pieces = []
  for (var i = 0; i < buf.length; i += 20) {
    pieces.push(buf.slice(i, i + 20).toString('hex'))
  }
  return pieces
}

function ensure (bool, fieldName) {
  if (!bool) throw new Error('Torrent is missing required field: ' + fieldName)
}