code: def file_download_event_builder(event, sender_app, obj=None, **kwargs):
      
      event.update(dict(
          # When:
          timestamp=datetime.datetime.utcnow().isoformat(),
          # What:
          bucket_id=str(obj.bucket_id),
          file_id=str(obj.file_id),
          file_key=obj.key,
          size=obj.file.size,
          referrer=request.referrer,
          # Who:
          **get_user()
      ))
      return event
docs: Build a file-download event.