Generate WebSocket frames in CoffeeScript

sample.coffee

hexToBuffer = (hex, padding) ->
  n = lpad hex.toString(16), '0', padding
  list = []

  while n.length > 0
    head = n.substr 0, n.length - 2
    tail = n.substr n.length - 2

    list.unshift parseInt tail, 16

    n = head

  new Buffer list

lpad = (str, padString, length) ->
  str = padString + str while str.length < length
  str

generateMask = (length = 8) ->
  buffer = new Buffer length
  max = Math.pow(16, length) - 1

  for i in [0..length]
    buffer[i] = Math.floor( Math.random() * max )

  buffer

generateFrame = (isFinal, kind, mask = null, length) ->
  firstByte = 0
  secondByte = 0

  firstTwoBytes = null
  lengthBytes = null
  maskBytes = null

  if isFinal
    firstByte += 0x80

  if kind == 'continuation'
    firstByte += 0x00
  else if kind == 'text'
    firstByte += 0x01
  else if kind == 'binary'
    firstByte += 0x02

  if mask
    secondByte += 0x80

  if mask
    maskBytes = mask
  else
    maskBytes = new Buffer []

  if length < 127
    initialLength = length
    lengthBytes = new Buffer []

    secondByte += initialLength
  else if length < 0xffff
    initialLength = 126
    lengthBytes = hexToBuffer length, 4

    secondByte += initialLength
  else if length <= 0xffffffffffffffff
    initialLength = 127
    lengthBytes = hexToBuffer length, 10

    secondByte += initialLength
  else
    throw new Error 'Length is too large.'

  firstTwoBytes = new Buffer 2
  firstTwoBytes[0] = firstByte
  firstTwoBytes[1] = secondByte

  frame = new Buffer(firstTwoBytes.length + lengthBytes.length + maskBytes.length)

  firstTwoBytes.copy frame
  lengthBytes.copy frame, firstTwoBytes.length
  maskBytes.copy frame, (firstTwoBytes.length + lengthBytes.length)

  frame

console.log 'one', generateFrame true, 'text', null, 120
console.log 'two', generateFrame true, 'text', generateMask(), 120