How to use the torrent-piece.BLOCK_LENGTH function in torrent-piece

var randomIterate = require('random-iterate')
var Rusha = require('rusha')
var speedometer = require('speedometer')
var uniq = require('uniq')
var utMetadata = require('ut_metadata')
var utPex = require('ut_pex') // browser exclude

var File = require('./file')
var Peer = require('./peer')
var RarityMap = require('./rarity-map')
var Server = require('./server') // browser exclude

var MAX_BLOCK_LENGTH = 128 * 1024
var PIECE_TIMEOUT = 30000
var CHOKE_TIMEOUT = 5000
var SPEED_THRESHOLD = 3 * Piece.BLOCK_LENGTH

var PIPELINE_MIN_DURATION = 0.5
var PIPELINE_MAX_DURATION = 1

var RECHOKE_INTERVAL = 10000 // 10 seconds
var RECHOKE_OPTIMISTIC_DURATION = 2 // 30 seconds

var FILESYSTEM_CONCURRENCY = 2

var RECONNECT_WAIT = [ 1000, 5000, 15000 ]

var VERSION = require('../package.json').version
var USER_AGENT = 'WebTorrent/' + VERSION + ' (https://webtorrent.io)'

var TMP
try {

const sha1 = require('simple-sha1')
const speedometer = require('speedometer')
const uniq = require('uniq')
const utMetadata = require('ut_metadata')
const utPex = require('ut_pex') // browser exclude
const parseRange = require('parse-numeric-range')

const File = require('./file')
const Peer = require('./peer')
const RarityMap = require('./rarity-map')
const Server = require('./server') // browser exclude

const MAX_BLOCK_LENGTH = 128 * 1024
const PIECE_TIMEOUT = 30000
const CHOKE_TIMEOUT = 5000
const SPEED_THRESHOLD = 3 * Piece.BLOCK_LENGTH

const PIPELINE_MIN_DURATION = 0.5
const PIPELINE_MAX_DURATION = 1

const RECHOKE_INTERVAL = 10000 // 10 seconds
const RECHOKE_OPTIMISTIC_DURATION = 2 // 30 seconds

// IndexedDB chunk stores used in the browser benefit from maximum concurrency
const FILESYSTEM_CONCURRENCY = process.browser ? Infinity : 2

const RECONNECT_WAIT = [ 1000, 5000, 15000 ]

const VERSION = require('../package.json').version
const USER_AGENT = `WebTorrent/${VERSION} (https://webtorrent.io)`

let TMP

var eos = require('end-of-stream')
var piece = require('torrent-piece')
var rimraf = require('rimraf')
var FSChunkStore = require('fs-chunk-store')
var ImmediateChunkStore = require('immediate-chunk-store')
var peerDiscovery = require('torrent-discovery')
var bufferFrom = require('buffer-from')

var blocklist = require('ip-set')
var exchangeMetadata = require('./lib/exchange-metadata')
var fileStream = require('./lib/file-stream')

var MAX_REQUESTS = 5
var CHOKE_TIMEOUT = 5000
var REQUEST_TIMEOUT = 30000
var SPEED_THRESHOLD = 3 * piece.BLOCK_LENGTH
var DEFAULT_PORT = 6881

var BAD_PIECE_STRIKES_MAX = 3
var BAD_PIECE_STRIKES_DURATION = 120000 // 2 minutes

var RECHOKE_INTERVAL = 10000
var RECHOKE_OPTIMISTIC_DURATION = 2

var TMP = fs.existsSync('/tmp') ? '/tmp' : os.tmpDir()

var noop = function () {}

var sha1 = function (data) {
  return crypto.createHash('sha1').update(data).digest('hex')
}

function speedRanker () {
    var speed = wire.downloadSpeed() || 1
    if (speed > SPEED_THRESHOLD) return function () { return true }

    var secs = Math.max(1, wire.requests.length) * Piece.BLOCK_LENGTH / speed
    var tries = 10
    var ptr = 0

    return function (index) {
      if (!tries || self.bitfield.get(index)) return true

      var missing = self.pieces[index].missing

      for (; ptr < self.wires.length; ptr++) {
        var otherWire = self.wires[ptr]
        var otherSpeed = otherWire.downloadSpeed()

        if (otherSpeed < SPEED_THRESHOLD) continue
        if (otherSpeed <= speed) continue
        if (!otherWire.peerPieces.get(index)) continue
        if ((missing -= otherSpeed * secs) > 0) continue

var onhotswap = opts.hotswap === false ? falsy : function (wire, index) {
      var speed = wire.downloadSpeed()
      if (speed < piece.BLOCK_LENGTH) return
      if (!reservations[index] || !pieces[index]) return

      var r = reservations[index]
      var minSpeed = Infinity
      var min

      for (var i = 0; i < r.length; i++) {
        var other = r[i]
        if (!other || other === wire) continue

        var otherSpeed = other.downloadSpeed()
        if (otherSpeed >= SPEED_THRESHOLD) continue
        if (2 * otherSpeed > speed || otherSpeed > minSpeed) continue

        min = other
        minSpeed = otherSpeed

function getBlockPipelineLength (wire, duration) {
  return 2 + Math.ceil(duration * wire.downloadSpeed() / Piece.BLOCK_LENGTH)
}

_hotswap (wire, index) {
    const speed = wire.downloadSpeed()
    if (speed < Piece.BLOCK_LENGTH) return false
    if (!this._reservations[index]) return false

    const r = this._reservations[index]
    if (!r) {
      return false
    }

    let minSpeed = Infinity
    let minWire

    let i
    for (i = 0; i < r.length; i++) {
      const otherWire = r[i]
      if (!otherWire || otherWire === wire) continue

      const otherSpeed = otherWire.downloadSpeed()