code: func RegisterHandlerConstructor(typ string, ctor HandlerConstructor) {
  	mapLock.Lock()
  	defer mapLock.Unlock()
  	if _, ok := handlerConstructors[typ]; ok {
  		panic("blobserver: HandlerConstrutor already registered for type: " + typ)
  	}
  	handlerConstructors[typ] = ctor
  }
docs: // RegisterHandlerConstructor registers an http Handler constructor function
  // for a given handler type.
  //
  // It is an error to register the same handler type twice.