July 14, 2020

What about design?

Who around here hasn’t heard about the tragic and inevitable death of XMPP (eXtensible Messaging and Presence Protocol)? It’s a pretty common topic in the community and around, often started by users of XMPP themselves missing a certain feature in one or multiple specific implementations, or users of alternative solutions. In a way this is my own version of why XMPP is or isn’t doomed.

To go down this rabbit hole, we first need to set a few definitions. Most of my readers would probably know what XMPP is, but I feel obligated to provide a short reminder as it will allow me to highlight specific points I want to talk about.

XMPP? Was ist Das?

XMPP is a communication protocol, that is “nerd” speak to say it’s a language for applications to use and talk together at a level that the end-user doesn’t see. An example would be a chat application: your desktop or smartphone app talking to a server that then talks to another app.

It is defined as a standard at the IETF (Internet Engineering Task Force) – a standard being the specification of a protocol (a document, in this case publicised and accessible by anyone), which allows multiple products implementing what it describes to be able to work together in an interoperable way.

Core specifications of XMPP are written so that it is easily extendible allowing any developer to use custom (XML) elements for their own use, and optionally write a specification for their new feature for everyone else to use.

XMPP also defines a client-server-server-client model, where a client can talk with a server that can then talk with multiple servers before reaching other clients, thus allowing for decentralization – anyone setting up their own server to be free from restrictions of other operators, and communicating with the world or part of it.

So there we have it: (IETF) Standard, Decentralized, and Extensible. These are, I believe, the 3 selling-points of XMPP.

From there tons of features can be implemented and then negotiated (as part of the extensibility) and many things can change to use newer extensions that weren’t considered in the core specifications. For example even the serialization format (words of the language applications talk, originally XML) can be changed (just as EXI is doing), and it’s also perfectly fine to have non-compliant behaviour as long as it has been negotiated by entities taking part in it. And so on…

The XSF (XMPP Standards Foundation, previously known as Jabber Software Foundation) is the entity that did the original work on the protocol and submitted it to the IETF. It now has a sheperding role. There is no requirement that XMPP extensions be brought to the XSF, but it aims to be the place where technical knowledge around XMPP is gathered, so people can get better feedback when submitting their new specification. Developers have already layed out lots of protocol bricks for others to reuse through the XSF.

How do applications speak the same language in an extensible world?

This is indeed the core of the problem. While extensibility is one of the strenghs of XMPP, it’s also its main weakness, one of the main points of its critics. That said, I believe it’s not as bad as they make it look like.

It is true that most applications are incompatible one way or another, with various degrees of significance, either because they don’t implement the same set of extensions, or because an author interprets extensions differently, or simply because of bugs.

For the rest of this article I will leave aside interpretation issues and bugs as I consider both of them bugs – of specifications and/or implementations – and bugs happen everywhere and can be fixed. Generally, determining what is a bug and what is a (unintended?) feature is where the issue lies.

While there have been attempts within the XSF at defining common sets of extensions in what is called “Compliance Suites” (currently updated on a yearly-basis: 2020, 2019, etc.), they have in my opinion had mild success for the effort it takes the author to gather feedback and come up with not-so-controversial changes for newer revisions.

What these Compliance Suites don’t take into account so well, despite recent efforts; and what critics don’t account for either when saying XMPP is missing X, or that all implementations should do Y, is that it’s not just about features and protocols.

The process of coming up with a common set of extensions for an implementation requires a lot more groundwork. This includes figuring out who the userbase is, and how the experience for it should be, i.e., design. This process should be applied across a set of implementations, using the same design guidelines and ensuring interoperability.

It is not enough if somebody using Conversations on mobile talks to somebody else using Dino on desktop, even if they both follow the Compliance Suites for a given year and can then interop on a “basic” level (which to be honest, is still pretty advanced), they have different design guidelines and there will inevitably be areas where they differ and some features won’t behave as expected on the other side. The issue is not that there is no design guidelines, it’s that they’re not the same.

And in practice?

Multiple solutions following this design process already exist, such as Xabber and Tigase. Snikket is a new addition in this domain. You can read about its goals in the introduction article or in a more detailed explanation from its author. At the time of writing it is composed of a rebranded Prosody (server) and Conversations (client), is entirely based on XMPP and federates with the XMPP network. But the important part – and also why it deserves a name other than “XMPP” – is its goal: to provide a server and a (set of) client(s) that interoperate properly and have common design guidelines that match the expected userbase.

Maybe you’re not part of Snikket’s target, in which case there might someday be a similar solution that’s more adapted to your use-case. For the more technical of us who understand the protocol and/or can deal with less unified designs, it may be ok to continue using our current applications and work around these issues ourselves. For the mass audiences I believe this is not an option.

So why (not) XMPP?

To the question I set to answer at the beginning I say this: Why does it matter? For whom? My goal is to bring standardization, decentralization, and extensibility to mass audiences. Not to bring XMPP to them. As explained above I believe we need product suites with common design guidelines, and they should include these properties. XMPP has good building blocks but lacks consorted design.

I want decentralization and standardization to prevent users from being locked in closed – often also proprietary – silos such as WhatsApp, Hangouts, Slack, MS Teams, Tik-Tok, or even Signal. And I want extensibility to prevent being stuck in the past and to adapt to the people’s needs.

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© Maxime “pep.” Buquet 2019. Licensed under CC-BY-SA 4.0 unless specified.

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