code: func shardItems(items []*Item, threshold int64) []*itemBundle {
  	// For deterministic isolated hashes, sort the items by path.
  	sort.Sort(itemByPath(items))
  
  	var bundles []*itemBundle
  	for len(items) > 0 {
  		var bundle *itemBundle
  		bundle, items = oneBundle(items, threshold)
  		bundles = append(bundles, bundle)
  	}
  	return bundles
  }
docs: // shardItems shards the provided items into itemBundles, using the provided
  // threshold as the maximum size the resultant tars should be.
  //
  // shardItems does not access the filesystem.