code: func (s *HTTPServer) preparedQueryUpdate(id string, resp http.ResponseWriter, req *http.Request) (interface{}, error) {
  	args := structs.PreparedQueryRequest{
  		Op: structs.PreparedQueryUpdate,
  	}
  	s.parseDC(req, &args.Datacenter)
  	s.parseToken(req, &args.Token)
  	if req.ContentLength > 0 {
  		if err := decodeBody(req, &args.Query, nil); err != nil {
  			resp.WriteHeader(http.StatusBadRequest)
  			fmt.Fprintf(resp, "Request decode failed: %v", err)
  			return nil, nil
  		}
  	}
  
  	if args.Query == nil {
  		args.Query = &structs.PreparedQuery{}
  	}
  
  	// Take the ID from the URL, not the embedded one.
  	args.Query.ID = id
  
  	var reply string
  	if err := s.agent.RPC("PreparedQuery.Apply", &args, &reply); err != nil {
  		return nil, err
  	}
  	return nil, nil
  }
docs: // preparedQueryUpdate updates a prepared query.