EventDance, a peer-to-peer inter-process communication library

EventDance is a library aiming to help developing secure and scalable peer-to-peer applications. It provides a set of easy-to-use APIs that developers can use in their programs in order to connect with other local or remote applications in a fast, secure and reliable fashion.

EventDance breaks from the idea that any system capable of running code and connect to some type of network, can be considered a “peer” and should be able to exchange data with other peers in the network under equal conditions. There is no high level concept of client or server in EventDance, but only peers that are equally important and always treated as such. For instance, a webpage running in a browser is considered a peer as much as a daemon process running in a server; and so is for software running in a mobile phone, a TV or a fridge connected to internet. This homogenized view of applications as potential creators and consumers of content and events, is a fundamental feature of EventDance and the reason behind its simplicity.

EventDance defines an abstract concept of Transport as a mean to move data between peers. Several types of transport exist and peers can choose one or more of them to communicate with another peer. Two peers can communicate as long as they have at least one transport in common. EventDance provides implementations for different types of transport (at the moment, only a Web transport). As protocols and technologies run obsolete and new ones appear, EventDance is ready to drop and embrace new types of transport; yet holding the same abstract concept. This concept is not new. Several other networking software like GNUnet have used a similar abstraction in a future-proof design.

EventDance also provides means for applications to communicate securely following the end-to-end principle. APIs are provided for programs to easily implement data privacy and peer authentication at a cryptographic level. An effort has been made to hide some of the complexity of dealing with cryto APIs as much as possible. The library uses GnuTLS as the backend for cryptography.

EventDance is written in C language using GLib/GObject. It automatically generates gobject-introspection information upon building, meaning it can be used in other languages like Javascript, Python, Lua, Vala or any other environment supporting G-I; without the need for specific bindings. The framework is designed to be lightweight, fast, scalable and energy efficient. For socket IO, it currently uses epoll exclusively, but it might support other similar mechanisms available for other platforms, in the future.

EventDance is completely event-driven, based on the GLib main loop. Applications using it are expected to be event-driven as well. All activity in the library is asynchronous and non-blocking. If some bocking operation needs to be performed, it should be moved to a thread to avoid hanging the main event loop. This is a fundamental design feature of EventDance to guarantee scalability and graceful service degradation.

EventDance is in an early stage of development. I started coding it from scratch during autumn 2009, after a first attempt written in Perl, back in 2007. I have devoted mostly my free time, and some hours sponsored by my employer, Igalia, through its hackfest initiative.

The current and only release so far is 0.1.2. Following is a list of the features currently available and others planned for the near future:

Features currently implemented:

  • Berkeley and Unix sockets powered by epoll (based on GIO GSocket).
  • Socket connection with built-in support for TLS upgrade and bandwidth/latency throttling.
  • Connection group for bulk management of streams (throttling, TLS, etc).
  • X.509 and PGP certificate objects, with support for trust validation (using GnuTLS).
  • Reverse proxy with load-balancing.
  • Web transport (with only long-polling at the moment).
  • Peer Manager for peer activity tracking.
  • Simple web server for static content.
  • Web selector for filtering HTTP requests.
  • JSON stream filter.

Features planned for next minor release (0.2):

  • WebSocket client and server support in the web transport.
  • Raw TCP transport.
  • UDP transport with optional PGP encryption and optional NAT traversal.
  • JSON-DBus bridge.
  • TLS agent to handle blocking cryptographic operations.
  • PrivateKey object.
  • Symmetric and asymmetric encryption/decryption.
  • Peer discovery mechanism.

Some of the many features planned for the long-term:

  • Bluetooth transport (added as an extension).
  • Tor transport.
  • Gstreamer plugin for using EventDance transports in a multimedia pipeline (added as an extension).
  • FastCGI web service.

EventDance is licensed under the terms of the GNU LGPL license version 3, and is hosted at Gitorious. There is neither mailing-list nor bug tracking tool at the moment, but I’m always and happily expecting feedback, criticism, suggestions and bug reports in my inbox at elima at igalia dot com. Contributions are of course very welcomed. Minimal documentation does exist, but is less than useful at the moment.

Vagalume port to Moblin2

During summer, I started to work on porting Vagalume UI to Moblin platform during my beloved hackfest hours. Vagalume is a Last.fm client for GNOME and Maemo, created by Alberto García (aka Berto). Moblin is an open source project impulsed by Intel, to create a GNU/Linux-based platform optimized for mobile devices (mainly, those powered by Intel’s Atom processor and graphics accelerator).

Vagalume’s UI is currently based on GTK+ for GNOME and Hildon for Maemo. However, Moblin user-experience is based on Nbtk and Clutter, yet it can run pure GTK+ applications. Taking a look at Nbtk toolkit was in my wishlist since it’s presentation at GCDS 2009, where some cool features of the project attracted my interest, like using CSS for styling widgets. About Clutter… well, it’s a project I personally like a lot and have been following since early versions. Motivation was ready and served.

The goal

The porting main goal is to get Vagalume running in Moblin2, sharing the platform’s look n’ feel. Revamping the UI was not just replacing widgets, but initially make Vagalume use the technologies present in a Moblin ecosystem, and “by-the-port”, perform a complete redesign of the UI, getting help from those talented designers at Moblin team.

So far…

After some weeks of hacking and festing, we have partially completed the toolkit migration, and developed a concept-proof UI redesign for the main window using Nbtk and custom Clutter widgets, except for the shell-menu which was not migrated yet . A screen-cast demo of the new UI is available. Notice that the target at this stage was not to align with Moblin’s look n’ feel, but just mixing differnt toolkits and get them to run together.

One of the new features we thought it would be interesting to include is to provide information of next and prevoius tracks, right in the main UI. The Last.fm API provides means to fetch playlist items in advance, so was not really difficult to implement that (with some core patches from Berto.. thanks).

The port’s source code is temporarily in a public repository at Gitorious.org in the moblin branch, but it will eventually get merged upstream when it gets mature enough. To build the branch, you will need a Moblin library-featured environment, like the SDK provided, or the Moblin platform itself installing the development tools and libraries. Alternatively, you can use my jhbuild moduleset.

There are some issues when building the project:

  • Running Nbtk in 64 bits platform drops a segfault due to a problem in libccss-0.3.1, so use 32 bits for hacking by now.
  • Moblin platform is not properly detected during autogen.sh stage, so you have to pass ‘–with-platform=moblin2’. This shall be fixed soon.

What’s next

Right now, we are trying to get support and feedback from Moblin UI designers, in order to plan a complete layout and style redesign. Making Vagalume UI consistent with Moblin environment is the current milestone. In the mean, we are doing several stability tests and improving toolkit integration.

Contributions are very appreciated, specially with design ideas, testing and project build integration. I can even review patches in my limited time.

Stay tuned.