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Middleware

The "middleware" app maintains a library of express middleware for easy insertion into routes. It also defines some standard middleware you can easily plug in.

The Middleware Service

When the "middleware" service loads, it connects to the MongoDB (for session) and defines some standard middleware. It also reads the file middleware.js from each installed app to add more middleware to its library.

The middleware library works similar to the app library, in that middleware functions are tracked by a name, but aliases can be applied to easily reference groups of middleware. The existing middleware and middleware group aliases are documented a little further below.

Getting Middleware

The method middleware(...names) will return a list of middleware functions, for easy insertion into a route. Note that in the root level of a router.js file (read by the "routes" app), the "middleware" service will have been loaded but not mounted, so you will have to access it via App.$('middleware') instead of App.$middleware.

// apps/my_custom_app/routes.js

const express = require('express');
const App = require('@carolina/core');

const router = express.Router();

// use standard and CSRF (csurf) middleware for this router
router.use(App.$('middleware').middleware(':standard', 'csrf'));

module.exports = { router };

Getting a Session

The middleware service also allows you to access a session by ID via the getSession(sessionId) method. Generally, this is not necessary as the "session" middleware will extract the current session and add it to the incoming request, but sometimes you may need to access a different session somewhere.

async someMethod() {
  let sessionId = '12345';
  let sess = await App.$middleware.getSession(sessionId);
}

Predefined Middleware

The "middleware" service automatically includes the following named middleware (listed in a sane order):

  • json: An instance of express.json(), for parsing incoming JSON.
  • urlencoded: An instance of express.urlencoded with extended set to true, for parsing form data.
  • cookies: An instance of cookie-parser for parsing cookies.
  • mongoDbSession: An instance of connect-mongodb-session configured to work with express-session. It uses the same MongoDB configuration that is used by the "db" app, and it stores session in a collection called 'sessions'. It uses cookies and makes the session object available as req.session.
  • flash: An instance of express-flash for flash messages.
  • logRequests: Middleware that logs incoming requests using express-winston and the winston instance used by the "logger" app.
  • csrf: An instance of csurf set to use cookies.

The "middleware" service also includes two aliases:

  • :basics: Includes the json, urlencoded, cookies, and logRequests middleware.
  • :standard: Includes all of :basics, plus mongoDbSession and flash.

Defining Middleware and Middleware Aliases

You can define custom middleware and custom middleware aliases by writing a middleware.js file in your app. The "middleware" service looks for a map of middleware names to middleware functions as middleware and a map of middleware group aliases to lists of middleware names as aliases.

Here is an example:

// apps/my_custom_app/middleware.js

function myCustomMiddleware(req, res, next) {
  console.log("Custom middleware executed.");
  next();
}

module.exports = {
  middleware: { myCustomMiddleware },
  aliases: {
    ":custom": ['myCustomMiddleware']
  }
};

Under this setup, you could add your custom middleware to a route, along with some included middleware, like this:

router.use(App.$('middleware').middleware(":standard", ":custom"));

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