code: func (s *Service) addBuildVersion(w http.ResponseWriter) {
  	// Add version header to every response, if available.
  	version := "unknown"
  	if v, ok := s.BuildInfo["version"].(string); ok {
  		version = v
  	}
  	w.Header().Add(VersionHTTPHeader, version)
  }
docs: // addBuildVersion adds the build version to the HTTP response.