adamrenklint/asimovjs.org

title: Middleware
---
text:

As we've said before, at the heart of asimov.js is a simple express server. To extend or change the behavior of the request flow, you can add custom middleware.

## The request middleware flow

When a request comes in to the server, it first passes through the InvisibleUrl middleware that protects all folders with a name that starts with underscore. After that, the LanguageRedirector ensures that the default languageCode is not present in the url, and redirects if necessary to ensure a single url per page.

The request is then passed to the chain of whatever custom middleware you define in you content textfile.

The CacheRouter and DirectoryRouter manages access to resources that should be cached and resources that are allowed be accessed on the filesystem. If a response has not been sent after this, the NotFound middleware will return a 404.

## Implement custom middleware

To extend or modify the request flow, you can add your custom middleware in the <code>site/middleware</code> folder. A Middleware class must implement a <code>handle(req, res, next)</code> method, or an error is thrown.

Consider this example, the code from the frameworks LanguageRedirector used in the beginning of the request flow. Pretty simple - if the url starts with the default language code, redirect to the same url without the language code.

    define([

      'asimov/Middleware'

    ], function (Middleware) {

      return Middleware.extend({

        'handle': function (req, res, next) {

          var self = this;
          var langCode = self.options.localization.defaultLangCode;

          if (req.url.indexOf('/' + langCode + '/') === 0) {
            return res.redirect(req.url.replace('/' + langCode, ''));
          }

          next();
        }
      });
    });

Remember, if you don't send a response in your handler or call <code>next()</code>, the request will hang on and time out.

## Define global middleware

Edit the <code>middleware</code> array in <code>environments/common.json</code>.

    {
      "middleware": [
        "bannedIps"
      ]
    }

## Define environment middleware

For example, edit the <code>middleware</code> array in <code>environments/staging.json</code>.

    {
      "middleware": [
        "basicAuth"
      ]
    }

## Define page middleware

In this example, the url <code>/secret</code> should only be available if the user is authenticated and not a bot. Simply edit the <code>middleware</code> content section in <code>content/secret/page.txt</code>.

    ---
    middleware: NotABot, Authenticated
    ---