constructor (channel, bufferSize) {
    super(0)
    this._bufferSize = bufferSize || _DEFAULT_BUFFER_SIZE
    this._ch = channel
    this._buffer = alloc(this._bufferSize)
    this._currentChunkStart = 0
    this._chunkOpen = false
  }
Looks like a writable buffer, chunks output transparently into a channel below.
@access private