Caching of node/express GET request on server side with JSON body

Question

I am trying to get a simple server-side cache up-and-running within node/express with a GET request. Managed to get this working when dealing with simple URL parameters, but not sure how to approach it with a JSON body.

This is what I have thus far for the URL parameter version:

const mcache = require('memory-cache');
app.set('view engine', 'jade');

const cache = (duration) => {
  return (req, res, next) => {
    let key = '__express__' + req.originalUrl || req.url;
    let cachedBody = mcache.get(key);
    if (cachedBody) {
      res.send(cachedBody);
      return;
    } else {
      res.sendResponse = res.send;
      res.send = (body) => {
        mcache.put(key, body, duration * 1000);
        res.sendResponse(body);
      };
      next();
    }
  };
};

app.get('/user/:id', cache(10), (req, res) => {
  setTimeout(() => {
    if (req.params.id == 1) {
      res.json({ id: 1, name: 'John' });
    } else if (req.params.id == 2) {
      res.json({ id: 2, name: 'Bob' });
    } else if (req.params.id == 3) {
      res.json({ id: 3, name: 'Stuart' });
    }
  }, 3000); //setTimeout was used to simulate a slow processing request
});

Any pointers?

Answer 1

For sure in your cache middleware you shouldn't be using res.send because you can only perform one response per request. So before you get to res.json in your app.get , res is already send.

I assume that you want to pass the data with that res.send to the app.get ? If so you can either pass it inside next() or use res.locals like res.locals.varName = catchedBody and then you can use that inside your app.get function because it will be available during entire http request