Bear's Log

a journal writ one beer at a time

XMPP PubSub + XSLT

by bear

One of the niftier configuration items for a XMPP PubSub node (see Configuring a Node) is the ability to define an XSL template to allow the PubSub component to generate a message body to go along with the message payload - basically a human readable version of the payload. This is great because it allows you to have a single node service both bots and people. Without this you would have to define proxy bots that are subscribed to nodes and then they would send out chat messages for each incoming PubSub event for people in their roster. Not exactly a friendly model IMO. So to prepare for this I started working on a XSLT file to transform an Atom payload to HTML - but first I needed to either learn XSLT real fast or “borrow” from someone :)… After about an hour of googling I finally found one that a) worked and b) targeted the 1.0 version of Atom at the OpenSearch site - wow was that a gold-plated, kitchen-sink-included version! It handles Atom, RSS (all of them), RDF and some others - and after a rather great question from @metajack (aka Jack Moffitt):

Why bother with RSS at all?

I started pulling out all of the non-Atom bits. He also helped me grok a template scope problem that was leading me to curse XPath royally - thanks Jack! So after many, many rounds of edit/test/curse I boiled it down to a basic template (tho I did keep some of their snazzy person and url templates - very nice!) and then proceeded to tweak the HTML it generates. So if you pass in this Atom payload:

<entry xmlns=“http://www.w3.org/2005/Atom”>
    <title type=“html”>Test Atom</title>
    <link href=“http://seesmic.com/videos/FOO”/>
    <id>http://seesmic.com/videos/FOO</id>
    <author>
        <uri>http://seesmic.com/foobarbaz</uri>
    </author>
    <published>2009-01-03T20:46:19+00:00</published>
    <updated>2009-01-03T20:46:19+00:00</updated>
    <link href=“http://t.seesmic.com/thumbnail/FOO_th1.jpg” type=“image/jpeg” rel=“enclosure” title=“Test Atom”/>
    <link href=“http://v.seesmic.com/flv/FOO.flv” type=“video/x-flv” rel=“enclosure” title=“Test Atom”/>
    <source>
        <generator>SeesmicBot</generator>
        <id>http://feeds.seesmic.com/user.foobarbaz.atom</id>
        <updated>2009-01-03T20:46:19+00:00</updated>
        <title type=“html”>Test Atom</title>
        <rights>Creative Commons Attribution</rights>
    </source>
    <in-reply-to xmlns=“http://purl.org/syndication/thread/1.0” type=“application/xhtml+xml” href=“http://seesmic.com/video/FOO” ref=“FOO”/>
    <category term=“en”/>
    <rights>Creative Commons Attribution</rights>
    <link href=“http://creativecommons.org/licenses/by/3.0//us/rdf” type=“application/rdf+xml” rel=“license”/>
</entry>

You will get this:

<html xmlns=“http://www.w3.org/1999/xhtml” xmlns:xhtml=“http://www.w3.org/1999/xhtml”>
<body>
    <div>
        <a href=“http://seesmic.com/videos/FOO”><div class=“x-escape”>Test Atom</div></a> by 
        <a href=“http://seesmic.com/foobarbaz”>http://seesmic.com/foobarbaz</a>; 
        <p>categories: en; </p>
        <p><a href=“http://t.seesmic.com/thumbnail/FOO_th1.jpg”>Test Atom</a> (image/jpeg)</p>
        <p><a href=“http://v.seesmic.com/flv/FOO.flv”>Test Atom</a> (video/x-flv)</p>
        <p><a href=“http://creativecommons.org/licenses/by/3.0//us/rdf”>Creative Commons Attribution</a>
        </p>
    </div>
</body>
</html>

Right now we think there is a bug in how Tigase handles this (well, actually since it’s not generating the body there is a bug somewhere), so I can’t show you a live example :( but as soon as the dev guys fix it, or tell me what I did wrong, I’ll make another post. You can find the XSL template I’m using here Update: sure enough, Bart demostrated it working on his test server so I dug deeper and discovered that the Java XSLT processor is much more pickier than xsltproc about errors. One of the helper templates was missing but it was never called so xsltproc just gleefully went on it’s merry way where as Java’s tossed an error and just refused to do anything more. So now Tigase is generating and payload data!

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