fortress-maximus

Despite his great power, size, and rank, Fortress Maximus is a weary and reluctant warrior. Fighting is against his pacifist nature and now spends his time validating.

fortress maximus

Despite his great power, size, and rank, Fortress Maximus is a weary and reluctant warrior. Fighting is against his pacifist nature and now spends his time validating.

Whether I am a hero or a coward is not the issue! I am weary! My joints creak from the corrosion of war without end! I... cannot break this ring of hate that surrounds us all -- but I can remove myself from it. No matter what you decide... I am leaving and joining Primus to innovate real-time.

Fortress Maximus validates every incoming message on your Primus server as all user input should be seen as a potential security risk.

This is a plugin for the Primus framework and can be installed using npm:

npm install --save fortress-maximus

The --save tells npm to automatically add the installed version to your package.json.

In order to work with emitted events we assume that you're using the primus-emit module as emit plugin. Any other plugin will simply be seen and validated as data event. See http://github.com/primus/emit for more information about this supported plugin.

As this a plugin for Primus we need to add it. This plugin only has a server component so it doesn't require you to re-compile your client. To add this plugin to your Primus server simply call the .use method on your Primus instance:

primus.use('fortress maximus', require('fortress-maximus'));

And you're server will now require validation for every single incoming message. If you want every single message to be validated make sure that you've added fortress-maximus as the first plugin you use:

primus.use('fortress maximus', require('fortress-maximus'))
      .use('emit', require('primus-emit'));

In the example code above we can successfully intercept emit messages and validate them before they are processed by the primus-emit plugin and emitted on the spark instance. The primus-emit module has two different modes which configure on where the events are emitted. On the spark or on the server. We need to know where so we can correctly validate that there are events registered for it. That's why it's possible to configure the fortress-maximus module directly through the Primus server constructor. The following options are available:

  • fortress: Where are the events emitted. Either spark or primus. Defaults to spark.

Just as a quick reminder, this is how you supply the options to your Primus server:

var primus = new Primus(httpsserver, {
  fortress: 'spark'
});

After you've added the plugin you can the newly introduced primus.validate method to add validators for any given event that is emitted on the spark. The validate method accepts 2 arguments:

  1. The name of the event you want to validate. If you are not using custom events this would only be the data event.
  2. The function that does the actual validation. The function should accept the same amount of arguments as the event listener + one extra callback function
primus.on('connection', function (spark) {
  spark.on('data', function (msg) {
    // msg will always be string here 
  });
});
 
primus.validate('data', function (msgnext) {
  if ('string' !=== typeof msg) return next(new Error('Invalid'));
 
  return next();
})

When we receive a new message on the server we first run some standard checks to see if we've received validate data and we:

  1. Prevent reserved events from being emitted.
  2. Only allow events to be emitted when there are listeners.
  3. Only allow events which are validated.
  4. Make sure the correct amount of arguments are received.

If all these checks pass we will call the supplied validator function with arguments.

primus.validate('custom event', function validate(foobarnext) {
  if (foo !== 'bar') return next(new Error('Foo should be bar'));
  if (bar !== 'foo') return next(new Error('Bar should be foo'));
 
  next();
});

The context of you validate function will be set to the spark so you could do some additional validation based on that:

primus.validate('admin', function validate(notificationnext) {
  isUserAdministrator(this.headers.cookie, function (erradmin) {
    if (err) return next(err);
    if (!admin) return next(new Error('Received admin event by non-admin'));
 
    next();
  }):
});

If you are to lazy to create new Error() objects for every single validation you can also call the validation function with a boolean true and false to indicate if the event is valid.

primus.validate('custom event', function validate(foobarnext) {
  next(foo !== 'bar' && bar !== 'foo');
});

When ever we fail to validate an incoming message we will prevent it from being emitted. And will emit an invalid event on your Primus server instance. This invalid event receives 2 arguments:

  1. err An error instance explaining why the given message was invalid
  2. args The arguments that we attempted to validate.
primus.on('invalid', function invalid(errargs) {
  // log things 
});

To figure out which event we've validated you can check the supplied error object. We add an event property on it with the name of the event we've failed to validate.

primus.on('invalid', function invalid(errargs) {
  console.log(err.event);
});

In addition to the invalid event, we also log the error with the diagnostics module. These debug messages can seen by setting the environment variable DEBUG:

DEBUG=primus:fortress node <your app.js>

MIT