docs: function MongolianGridFileReadStream(file) {
      if (!file._id) throw new Error("Can only read files retrieved from the database")
      if (file.chunkSize instanceof Long) throw new Error("Long (64bit) chunkSize unsupported")
      if (file.chunkSize <= 0) throw new Error("File has invalid chunkSize: "+file.chunkSize)
  
      stream.Stream.call(this)
  
      this.file = file
      this.readable = true
      this._chunkCount = file.chunkCount()
      this._chunkIndex = 0
  
      process.nextTick(this._nextChunk.bind(this))
  }