PubSubHubbub, or PuSH, is now supported on all WordPress.com blogs. For those running sites using the WordPress.org software the PuSHPress plugin is available to do the same thing. The big difference in this plugin compared to the other PuSH WordPress plugins is that it includes a PuSH hub built in.
A little bit of PubSubHubbub background
Like rssCloud, PuSH adds a line to your feed to let clients know where they can send PuSH subscription requests. In the RSS2 feed this looks like:
<atom:link rel="hub" href="http://josephscott.org/?pushpress=hub">
and in Atom looks like:
<link rel="hub" href="http://josephscott.org/?pushpress=hub">
The href attribute contains the URL that subscribers can send requests to. Details on what that request looks like are in the PubSubHubbub Spec. The short version, it’s a simple HTTP POST call with some specific field names.
Here’s an example PHP subscription request asking that updates to http://example.com/feed/ be sent to http://example.com/push/ via the hub at http://example.com/?pushpress=hub
$curl = curl_init( );
curl_setopt( $curl, CURLOPT_URL, 'http://example.com/?pushpress=hub' );
curl_setopt( $curl, CURLOPT_POSTFIELDS, 'hub.callback=http://example.com/push/&hub.mode=subscribe&hub.secret=not-telling-you&hub.verify=sync&hub.topic=http://example.com/feed/&hub.verify_token=133t-$7r1n9' );
curl_setopt( $curl, CURLOPT_VERBOSE, 1 );
curl_setopt( $curl, CURLOPT_POST, 1 );
curl_exec( $curl );
print_r( curl_getinfo( $curl ) );
curl_close( $curl );
The hub at example.com will then send new content (in feed format) right after it’s published to URL provided in hub.callback.
Why the PuSHPress plugin?
I love that there are large, open PuSH hubs available for anyone to use. There’s a list at http://code.google.com/p/pubsubhubbub/wiki/Hubs. In PuSH since most of the hard work (figuring out what’s new in a feed and sending that out to subscribers) is done via the hub this is very handy and really great for testing.
I also think there’s a role for a readily available simple hub that anyone can put up and use, in this case built on top of WordPress. And by leveraging WordPress the hub part can be greatly simplified. The real bonus for users is choice, they can relay the updates through 3rd party hubs, or use the built in hub in PuSHPress.
It’s worth noting that PuSHPress has a WordPress filter on the array of hubs; pushpress_hubs. This allows other plugins to easily add to or replace the hubs mentioned in the feeds by PuSHPress.
To help keep things simple and limit potential abuse the PuSHPress plugin will only allow subscriptions for the RSS2 and Atom feeds of the WordPress blog that it is installed on.
My thanks to Brett Slatkin for helping test PuSHPress. His tests revealed a few bugs that were quickly addressed.
When talking about these realtime-ish update features this question often comes up. Fair enough, I’d want to know too :-)
The PuSHPress plugin schedules pings to go out right away via the wp_schedule_single_event function in WordPress. I suspect for most people this will be quite fast. If your server is under tremendous load and really slow, then this will be really slow too, just like the rest of the server ;-)
On WordPress.com the details are a bit different. Instead of scheduling pings to be sent out with wp_schedule_single_event it adds them to our asynchronous jobs system ( more info available at http://code.trac.wordpress.org/ ). The jobs system is setup to do exactly these kinds of tasks really, really fast. Don’t be surprised if the ping shows up before you get a chance to finish the first Mississippi.
So where is all this going? Who knows, but it is fun to watch! :-)
If you have an interest in this area there are plenty of resources:
The spec is a quick read and to the point, worth reading.
And there you have it, a little more in-depth discussion of PuSHPress.