code: func (s *BulkService) estimateSizeInBytes(r BulkableRequest) int64 {
  	lines, _ := r.Source()
  	size := 0
  	for _, line := range lines {
  		// +1 for the \n
  		size += len(line) + 1
  	}
  	return int64(size)
  }
docs: // estimateSizeInBytes returns the estimates size of the given
  // bulkable request, i.e. BulkIndexRequest, BulkUpdateRequest, and
  // BulkDeleteRequest.