example.js

import express from 'express';
import request from 'request';

const app = express();
export default app;

const preRequestRouter = new express.Router();
const postRequestRouter = new express.Router();

// middleware is run in order
// when next() is called, the next one is run
// if one doesn't call next(), the process stops
app.use(preRequestRouter);
app.use(scRequest);
app.use(postRequestRouter);
app.use(scOutput);

function scRequest(req, res, next) {
	req.headers.host = void 0;

	const options = {
		method: req.method,
		url: `https://example.com${req.originalUrl}`,
		headers: req.headers,
		body: req.body,
		...req.scRequestOverride,
	};

	request(options, function (err, result) {
		if (err) {
			next(err);
			return;
		}

		req.scResult = result;
		next();
	});
}

function scOutput(req, res) {
	res.status(req.scResult.status);
	res.send(req.scResult.body);
}

// stops the request immediately, doesn't forward to snapchat
preRequestRouter.get('/blahblah', function (req, res) {
	res.status(500);
	res.json({ yeaahhh: '...no' });
});

// changes the method to post, then forwards to snapchat
preRequestRouter.get('/asdf', function (req, res, next) {
	req.scRequestOverride = {
		method: 'POST',
	};

	next();
});

// logs the snapchat output, outputs something else, and stops the request
postRequestRouter.get('/foo', function (req, res) {
	console.log(req.scResult);
	res.sendStatus(204);
});

// overrides part of the snapchat response, then continues
postRequestRouter.get('/bar', function (req, res, next) {
	res.scResult.message = 'insert very offensive joke here';
	next();
});