What’s All The Hubbub About?
It’s got a funny name, but PubSubHubbub, recently released to Google Code, may prove quite useful. PubSub is short for publish/subscribe, an asynchronous messaging paradigm. A publisher produces messages and subscribes consume those messages. PubSub is often used in distributed software systems as a way for pieces of the application to communicate with each other even though they reside on different computers.
PubSubHubbub defines a way to publish and receive updates when Atom feeds change. As mentioned in my previous post, Atom feeds syndicate items from places like news sites, blogs and various parts of chi.mp (like the activity stream and blogs). With PubSubHubbub chi.mp could select one or more hubs to publish notifications to each time one of your feeds changes and then subscribers would receive notification and content from the hub directly. The primary benefit of this is that subscribers would no longer need to poll Atom feeds to see if the feed has changed, rather they could simply be notified of the change.
One interesting aspect of PubSubHubbub is that it does not require a single centralized hub. On the contrary it is designed to allow publishers to select one or more hubs that they publish to, which are defined in the atom feed, and then subscribers that support PubSubHubbub subscriptions can listen for updates on those hubs. The hubs in turn are responsible for checking whether or not the feed has updated and then posting to each subscriber’s HTTP endpoint that they have provided when an update occurs.
After reading the protocol my conclusion is that this will probably be useful in the future, however right now it’s so early on in the process that the implementation is still a significant challenge, largely due to lack of documentation and test environments. To be fair, there is a test implementation running on Google’s App Engine, however when I tried it out it lacked decent explanation for the various required fields and their expected values.
The bottom line: PubSubHubbub is interesting but still needs some more time to bake.