How to get around previously declared json body-parser in Nodebb?

Question

I am writing a private plugin for nodebb (open forum software). In the nodebb's webserver.js file there is a line that seems to be hogging all incoming json data.

app.use(bodyParser.json(jsonOpts));

I am trying to convert all incoming json data for one of my end-points into raw data. However the challenge is I cannot remove or modify the line above.

The following code works ONLY if I temporarily remove the line above.

    var rawBodySaver = function (req, res, buf, encoding) {
      if (buf && buf.length) {
        req.rawBody = buf.toString(encoding || 'utf8');
      }
    }

    app.use(bodyParser.json({ verify: rawBodySaver }));

However as soon as I put the app.use(bodyParser.json(jsonOpts)); middleware back into the webserver.js file it stops working. So it seems like body-parser only processes the first parser that matches the incoming data type and then skips all the rest?

How can I get around that? I could not find any information in their official documentation.

Any help is greatly appreciated.

** Update **

The problem I am trying to solve is to correctly handle an incoming stripe webhook event. In the official stripe documentation they suggested I do the following:

  // Match the raw body to content type application/json
  app.post('/webhook', bodyParser.raw({type: 'application/json'}), 
  (request, response) => {
    const sig = request.headers['stripe-signature'];

    let event;

    try {
      event = stripe.webhooks.constructEvent(request.body, sig, 
  endpointSecret);
    } catch (err) {
      return response.status(400).send(Webhook Error: 
  ${err.message});
    }

Both methods, the original at the top of this post and the official stripe recommended way, construct the stripe event correctly but only if I remove the middleware in webserver. So my understanding now is that you cannot have multiple middleware to handle the same incoming data. I don't have much wiggle room when it comes to the first middleware except for being able to modify the argument (jsonOpts) that is being passed to it and comes from a .json file. I tried adding a verify field but I couldn't figure out how to add a function as its value. I hope this makes sense and sorry for not stating what problem I am trying to solve initially.

Answer 1

The only solution I can find without modifying the NodeBB code is to insert your middleware in a convenient hook (that will be later than you want) and then hack into the layer list in the app router to move that middleware earlier in the app layer list to get it in front of the things you want to be in front of.

This is a hack so if Express changes their internal implementation at some future time, then this could break. But, if they ever changed this part of the implementation, it would likely only be in a major revision (as in Express 4 ==> Express 5) and you could just adapt the code to fit the new scheme or perhaps NodeBB will have given you an appropriate hook by then.

The basic concept is as follows:

1. Get the router you need to modify. It appears it's the app router you want for NodeBB.
2. Insert your middleware/route as you normally would to allow Express to do all the normal setup for your middleware/route and insert it in the internal Layer list in the app router.
3. Then, reach into the list, take it off the end of the list (where it was just added) and insert it earlier in the list.
4. Figure out where to put it earlier in the list. You probably don't want it at the very start of the list because that would put it after some helpful system middleware that makes things like query parameter parsing work. So, the code looks for the first middleware that has a name we don't recognize from the built-in names we know and insert it right after that.

Here's the code for a function to insert your middleware.

function getAppRouter(app) {
    // History:
    //   Express 4.x throws when accessing app.router and the router is on app._router
    //      But, the router is lazy initialized with app.lazyrouter()
    //   Express 5.x again supports app.router 
    //      And, it handles the lazy construction of the router for you
    let router;
    try {
        router = app.router;      // Works for Express 5.x, Express 4.x will throw when accessing
    } catch(e) {}
    if (!router) {
        // Express 4.x
        if (typeof app.lazyrouter === "function") {
            // make sure router has been created
            app.lazyrouter();
        }
        router = app._router;
    }

    if (!router) {
        throw new Error("Couldn't find app router");
    }
    return router;
} 

// insert a method on the app router near the front of the list
function insertAppMethod(app, method, path, fn) {
    let router = getAppRouter(app);
    let stack = router.stack;

    // allow function to be called with no path
    // as insertAppMethod(app, metod, fn);
    if (typeof path === "function") {
        fn = path;
        path = null;
    }

    // add the handler to the end of the list
    if (path) {
        app[method](path, fn);
    } else {
        app[method](fn);
    }
    // now remove it from the stack
    let layerObj = stack.pop();
    // now insert it near the front of the stack, 
    // but after a couple pre-built middleware's installed by Express itself
    let skips = new Set(["query", "expressInit"]);
    for (let i = 0; i < stack.length; i++) {
        if (!skips.has(stack[i].name)) {
            // insert it here before this item
            stack.splice(i, 0, layerObj);
            break;
        }
    }
}

You would then use this to insert your method like this from any NodeBB hook that provides you the app object sometime during startup. It will create your /webhook route handler and then insert it earlier in the layer list (before the other body-parser middleware).

let rawMiddleware = bodyParser.raw({type: 'application/json'});

insertAppMethod(app, 'post', '/webhook', (request, response, next) => {
    rawMiddleware(request, response, (err) => {
        if (err) {
            next(err);
            return;
        }
        const sig = request.headers['stripe-signature'];

        let event;

        try {
          event = stripe.webhooks.constructEvent(request.body, sig, endpointSecret);
          // you need to either call next() or send a response here
        } catch (err) {
          return response.status(400).send(`Webhook Error: ${err.message}`);
        }
    });
});

Answer 2

The bodyParser.json() middleware does the following:

1. Check the response type of an incoming request to see if it is application/json.
2. If it is that type, then read the body from the incoming stream to get all the data from the stream.
3. When it has all the data from the stream, parse it as JSON and put the result into req.body so follow-on request handlers can access the already-read and already-parsed data there.

Because it reads the data from the stream, there is no longer any more data in the stream. Unless it saves the raw data somewhere (I haven't looked to see if it does), then the original RAW data is gone - it's been read from the stream already. This is why you can't have multiple different middleware all trying to process the same request body. Whichever one goes first reads the data from the incoming stream and then the original data is no longer there in the stream.

To help you find a solution, we need to know what end-problem you're really trying to solve? You will not be able to have two middlewares both looking for the same content-type and both reading the request body. You could replace bodyParser.json() that does both what it does now and does something else for your purpose in the same middleware, but not in separate middleware.