code: func extractBucket(id string) string {
  	if !strings.HasPrefix(id, "buildbucket/") {
  		return ""
  	}
  	toks := strings.SplitN(id, "/", 3)
  	if len(toks) != 3 {
  		return ""
  	}
  	return toks[1]
  }
docs: // extractBucket extracts bucket from a builder ID if possible.
  //
  // TODO(mknyszek): Get rid of this by either moving the logic above
  // or somehow getting access to BuilderID otherwise without an import
  // cycle.