Roundcube Next Shell
Updated 1,098 Days AgoPublic

WARNING: This is a wiki used as a scratch-book. The texts on this wiki are being worked on actively, and are considered to be drafts.

What is the Roundcube Shell?

The Roundcube Shell builds the basic environment for the Roundcube Next client. It's based on Ember.js and provides the following core functionality:

As an application:

  • Authentication UI
  • Top-level navigation between full-page apps
  • User settings page (for simple account tweaks, password changes, etc)

As an API:

  • Access to the data store via the JMAP library
  • UI Toolkit with reusable components
  • Routing system with hooks
  • Pub/sub system for inter-component communication

Design

JMAP data store

Server

Roundcube Next's persistence is intended to be chiefly JMAP-based. It ought to work with any server that speaks correct JMAP. At this point, the most complete server implementation is the jmap-proxy (written in perl). Promising upcoming implementations are within Apache James and Cyrus.
For development, we use the Kolab-maintained perl proxy docker image.

Client

Two client libraries have been evaluated, one being jmap-js, and the other being jmap-client. The former lays a strong emphasis on Overture-like code patterns, while the latter is a simple, well-tested ES6 library that works very well with Ember.
For development, we use jmap-client.

An instance of the API client should be made available as an Ember service, which can be accessed by embedded apps.

UI Toolkit

When working with Ember, most widgets are contained within Components. Components which are expected to be repeatedly used within the various applications that Roundcube Next shall come with, ought to be provided as a reusable set by Roundcube Shell. This would range from simple things like buttons and labels to more complex components like list-views and editor toolbars. See a list of planned UI components here.

Having all components in one place lets us keep them organized and allows for an easy way to customize the look of the entire application consistently, making it very smooth for designers and developers to work together. Every time a new reusable component is created, it should be added to a living styleguide. For realizing this, we shall use broccoli-livingstyleguide, which is designed for ember-cli backed toolchains.

Routing

Ember lets an application define a set of abstract routes, which map to /-delimited locations. Routes can be organized hierarchically. Suppose an plugin with the name mail has it's own special routes. It should be able to provide those in the following hypothetical manner:

var exports = {
  name: 'mail',
  routes: function () {
    this.route('index', { path: '/' });
    this.route('message', function () {
      this.route('compose', { path: '/compose' });
      this.route('detail', { path: '/:id' });
    });
  },
 //...
};

This produces the following plugin-specific routes:

  • index -> /
  • message.compose -> /message/compose
  • message.detail -> /message/:id

The shell could mount routes from plugins like this:

var plugins = loadSpecifiedPlugins();

Router.map(function() {
  this.route('index', { path: '/' });
  this.route('login', { path: '/login' });

  for (var plugin in plugins) {
    this.route(plugin.name, plugin.routes);
  }
});

This would result in the roundcube app gaining the following routes:

  • mail.index -> /mail
  • mail.message.compose -> /mail/message/compose
  • mail.message.detail -> /mail/message/:id

... which seems nice and modular. Activating a route will broadcast an event indicating the abstract route name as explained in the pub/sub section.

NOTE: Incidentally, Discourse also uses a similar routing technique for plugins.

Pub/sub system

The shell also provides a global event emitter system where all components and apps can use to publish notifications and subscribe to messages from other components. Each component shall emit events

  • whenever it reaches a point where the application state is changed
  • where it makes sense to inform others about a certain action
  • where feedback and/or additional/modified data is desired

This can begin with an shell.init event at application startup where apps can register themselves in the shell, define routes and push items to the main navigation.

The pub/sub is inspired by the Node.js events.EventEmitter component and primarily provides three methods for public use: on(), once() and emit(). Bonus points if the registration of event listeners with on() supports wildcard event names such as mail.message.*.

NOTE: Shall the App instance itself provide the pub/sub methods or shall we define a specific (singleton) module that can be imported? Any suggestions for existing libraries to use for this?
Aditya says: See below - the shell can provide a (singleton) Ember.Evented service that can be imported by plugins.
Thomas says: Perfect. Sold!

Works with Promises

Event listener should be able to work asynchronously and therefore return a Promise. The pub/sub system collects Promises returned by the registered listeners and returns a list of Promises to the emitter. Thus, whoever emits an event through the pub/sub system is responsible to handle returned promises and execute them. Example:

Promise.all(pubsub.emit('foo.bar')).then(function(results) { /* continue */ }).catch(...);
Aditya says: I am not entirely sold on this. This promise pattern might be nice when listening for data coming over the jmap adapter, but probably not when it comes to intra-app communication. Especially when we have Ember-provided ways of doing the latter.
Thomas says: It's not a hard requirement but I can see use-cases where asynchronous execution can be useful. For example an encrypted message can be decrypted by the according plugin before rendering it. That might be an async procedure as we see it in the Mailvelope extension.

Works with Ember.Evented

Ember.Evented is how you do custom events in Ember. It lets you build a global message bus in a straightforward manner.

It also has a very similar API to EventEmitter, providing the following important methods:

  • on() is like on(),
  • one() is like once(),
  • off() is like removeListener()
  • trigger() is like emit(),
NOTE: Again, Discourse seems to be successfully using it for application-wide communication.

Naming conventions

Since the proposed pub/sub system is one global message bus, it's important to use unique names for the events emitted to it. A few rules apply for composing event names:

  1. each component (or app) emitting an event, shall prefix the name with its own namespace (e.g. shell.*).
  2. the general classification of the emitting component and the entity name shall be reflected in the event name (e.g. model.message or view.contactlist).
  3. finally, choose sane names describing the action performed before the event is emitted.
  4. by default, events are emitted after a certain action was performed.
  5. if events are emitted before and after the according action, this shall be reflected in the event name with the before and after keywords.

Here are a few examples, illustrating the just listed conventions:

  • shell.init
  • shell.ui.load
  • mail.model.mailboxlist.load
  • mail.model.message.flags.set
  • mail.view.mailboxlist.render
  • shell.account.settings.beforesave
  • shell.account.settings.aftersave

Documentation

In order to publish a comprehensive list of events emitted throughout the application, each component shall describe the emitted events and the provided parameters in a jsdoc block according to the JSDuck spec:

/**
 * @event mail.model.message.flags.set
 * Emitted when message flags are updated
 * @param {Mail.Model.Message} message The message object receiving flag updates
 * @param {Object} flags Map of flag names and their new values
 */

Plugins

Plugins are sub-applications like mail, jabber, calendar.

They are written as Ember Addons; most of the business logic resides within the addon/ directory, and the parts of that which we want to be 'merged' into the main application tree of the shell are exposed in the app/ directory.

Every addon "registers" it's functionality into the app using an Ember *initializer*, which is run before the application starts responding to user interaction.

NOTE: An idea to allow writing literal sub-applications has surfaced and is being excitedly worked upon, called Ember Engines. Probably not something we will be able to use anytime soon.
Last Author
Adityab
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petersen, bruederli, Adityab