code: func (a *Archiver) PushFile(displayName, path string, priority int64) *PendingItem {
  	source := func() (io.ReadCloser, error) {
  		return os.Open(path)
  	}
  	return a.push(newItem(a, displayName, path, source, priority))
  }
docs: // PushFile schedules file upload to the isolate server. Smaller priority
  // value means earlier processing.