RSS feed for OpenBSD stable packages repository (made with XSLT)

I am happy to announce there is now a RSS feed for getting news in case of new packages available on my repository https://stable.perso.pw/

The file is available at https://stable.perso.pw/rss.xml.

I take the occasion of this blog post to explain how the file is generated as I did not find easy tool for this task, so I ended up doing it myself.

I choosed to use XSLT, which is not quite common. Briefly, XSLT allows to use some kind of XML template on a XML data file, this allow loops, filtering etc… It requires only two parts: the template and the data.

Simple RSS template

The following file is a template for my RSS file, we can see a few tags starting by xsl like xsl:for-each or xsl:value-of.

It’s interesting to note that the xsl-for-each can use a condition like position < 10 in order to limit the loop to the 10 first items.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    
<xsl:template match="/">
    <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
        <channel>
            <description></description>
    
            <!-- BEGIN CONFIGURATION -->
            <title>OpenBSD unofficial stable packages repository</title>
            <link>https://stable.perso.pw/</link>
            <atom:link href="https://stable.perso.pw/rss.xml" rel="self" type="application/rss+xml" />
            <!-- END CONFIGURATION -->
    
            <!-- Generating items -->
            <xsl:for-each select="feed/news[position()&lt;10]">
            <item>
                <title>
                    <xsl:value-of select="title"/>
                </title>
                <description>
                    <xsl:value-of select="description"/>
                </description>
                <pubDate>
                    <xsl:value-of select="date"/>
                </pubDate>
            </item>
            </xsl:for-each>
    
        </channel>
    </rss>
</xsl:template>
</xsl:stylesheet>

Simple data file

Now, we need some data to use with the template. I’ve added a comment block so I can copy / paste it to add a new entry into the RSS easily. As the date is in a painful format to write for a human, I added to my Makefile starting the commands a call to a script replacing the string DATE by the current date with the correct format.

<feed>
<news>
    <title>www/mozilla-firefox</title>
    <description>Firefox 67.0.1</description>
    <date>Wed, 05 Jun 2019 06:00:00 GMT</date>
</news>
    
<!-- copy paste for a new item
<news>
    <title></title>
    <description></description>
    <date></date>
</news>
-->
</feed>

Makefile

I love makefiles, so I share it even if this one is really short.

all:
	sh replace_date.sh
	xsltproc template.xml news.xml | xmllint -format - | tee rss.xml
	scp rss.xml perso.pw:/home/stable/
    
clean:
	rm rss.xml

When I want to add an entry, I copy / paste the comment block in news.xml, add DATE, run make and it’s uploaded :)

The command xsltproc is available from the package libxslt on OpenBSD.

And then, after writing this, I realise that manually editing the result file rss.xml is as much work as editing the news.xml file and then process it with xslt… But I keep that blog post as this can be useful for more complicated cases. :)