Mike Rooney (Awn Extras developer, among other things) posted an article on this "webhooks" idea. As I understand it, it's essentially a customizable, web-based version of the "Subscribe to future XYZ via email" features (e.g., blog comments) that are currently around. The key phrase in this sort of thinking is "push technology". Mike asks:
So will webhooks replace the current paradigm that I'm using here, or complement it?
I believe that it will complement the current paradigm. We need to have a transitional period (à la the old, rigid deadline for the US digital television transition) between the current "polling" techniques and the "new and shiny" (and arguably bandwidth-saving) push techniques. Take, for example, Twitter . Let's assume that they didn't shut down their XMPP service, and they built upon it an (XML-based) API so that a client (for the purposes of this thought experiment, let's say my currently-in-vaporware Status Aggregator Awn applet) could connect to a specific JID (AKA user name + domain + "resource", or specific client) and listen for any new tweets, responses to my tweets, etc., replacing those messy timeout callbacks with messy async socket callbacks. The main benefit that I see is a savings in bandwidth for both the consumer and the producer. It avoids sending network requests every X minutes, which would add up, given the number of services/feeds that a user subscribes to (including mail). This actually leads me to my answer to Mike's other question:
Are webhooks the next step of this evolution, or something else entirely?
As evidenced by my thought experiment, I'd like to see XMPP as the next step, or at minimum, the step after webhooks. While I love HTTP, and am a big fan of the whole REST concept, it's hard for me to see it used as a facilitator for pushing data, as opposed to pulling it. In fact, given the way that ETags and the like are designed, HTTP is inherently a pull technology. The Comet model feels like a big kludge to me for that reason. XMPP, on the other hand, is designed to be a push technology, and its supporters are actively marketing it as such. It's also scalable, as servers like ejabberd and services like Google Talk can attest. I suppose the bottleneck here is a catch-22: you need both services and apps to buy into this particular implementation. Maybe when I finish one of the myriad projects I have going at once, I'll take a crack at adding a push-based web service client. Ideally, for configuration, all a user would have to do is set their app-specific JID (e.g. firstname.lastname@example.org/bar_app) in both the web app and the client app, and it would "just work" (well, you would also have to set the JID password somehow as well, but that's beside the point).
Update (2009/02/18): It seems that I was subconsciously channelling a presentation on XMPP PubSub that I read over six months ago.
|||I'm focusing on the one I actually use. Yes, I should be using identi.ca, since I am a supporter of free and open services/protocols. It even has the hallowed XMPP interface to microblogging. One of these days, I'll do what all the cool kids™ are doing and post to both. It'll probably happen when I (continue) work on the vaporware  mentioned above.|
|||It's vaporware until I push the source code onto a public server.|