是否可以在快速中间件回调中修改 pug.js 参数 object

Question

Currently I'm on a legacy application using pug.js as view engine in a node.js express-app.

I want to implement a generic way to display feedback messages. I want to be able to display messages (successes, errors), even if the handler does reply with a redirect.

This is what I want:

handlePostRequest(req, res){
  // do stuff with the post request
  doStuff(req.body);

  //This should be done of course somewhere else.
  req.session.successes=req.session.successes|[];

  //save some success-message for the user
  req.session.successes.push("Your post has been saved. Thank you!");

  //but reply with a 302
  res.redirect(req.headers.referer);
}

//a get request. maybe the handler above redirected here
handleGetRequest(req,res){
  // we do NOT get the successes here. Just the 'pure' data.
  const renderData=getRenderData();
  res.render('fancy-pug-template', renderData);
}

fancyMiddlewareForMessages(req, res, next){
  //how to implement getRenderDataByBlackMagic()????
  const renderData = getRenderDataByBlackMagic();
  //set the messages
  renderData.successes = req.session.successes;
  //empty saved messages
  req.session.successes = [];
  next();
}

Obviously, I do not want to polute every handler which actually renders a template with some logic which retrieves the messages and adds them to the parameter object. I would like to move this cross-cutting concern in a middleware callback or something like that.

So, the question is: Can this be achieved? How? I'm fairly new to pug.js, maybe I'm overlooking something obvious.

Answer 1

Ok, I found a way. This is what I did:

const requestStorage = new AsyncLocalStorage<Request>();

function patchRenderFunction(req: Request, res: Response, next: NextFunction) {
  const render = res.render;
  res.render = function (view: string, options?: any, callback?: (err: Error, html: string) => void) {
    const messages = new MessageManager(req);

    //merge errorMessages
    options.errorMessages = mergeMessageArrays(options.errorMessages, messages.errors);
    //same for successMessages
    options.successMessages = mergeMessageArrays(options.successMessages, messages.successes);

    render.bind(this)(view, options, callback);
  };
  requestStorage.run(req, () => {
    next();
  });
}

export function applyAutomaticRenderAttributes(app: Express): void {
  app.use(patchRenderFunction);
}

export function successMessage(message: string, req?: Request) {
  if (!req) {
    req = requestStorage.getStore();
  }
  if (!req) {
    console.error('No request found in async storage. This should not happen. Please report this issue. (successMessage)');
    return;
  }
  new MessageManager(req).addSuccessMessage(message);
}

//export function errorMessage(...) omitted

The MessageManager uses the requests session to store messages. It also filters them in some respect. I'm using the session because the application runs clustered (thank you, pm2). Since the session is stored in the db via express-mysql-session , I avoid problems with non-sticky sessions.