VSzA techblog 2011-07-01T13:04:47+02:00 utterson v0.4 https://techblog.vsza.hu/ Org-mode to RSS and custom HTML 2011-07-01T13:04:47+02:00 https://techblog.vsza.hu/posts/Org-mode_to_RSS_and_custom_HTML.html dnet Org-mode is one of the many outliner solutions I've seen, and I prefer it because of its slogan "Your Life in Plain Text". It allows me to keep track of my life in form of notes, lists and plans using only a text editor, and as the name suggests, it has its origins in Emacs, and it's possible to export these files to a number of formats. My problem was that I found no easy way to customize the HTML output, and I wanted to create a solution that'd allow me to generate an HTML page and an RSS feed from an .org file of mine.

My first hack was a really rudimentary solution that used ugly regular expressions and sed tied together in a shell script. It had many problems: first of all, it depended heavily on the formatting of the document, even small deviations would've made it fail. Also, it was difficult (e.g. required less-readable constructs) to achieve things that are usually trivial using any XML-friendly environment, for instance closing tags if there are no remaining items, but before closing the whole document.

#!/bin/bash
INFILE="input.org"
OUTFILE="output.html"
rm -f $OUTFILE
cat <<HTML >$OUTFILE
... HTML header ...
HTML
N=1
while read LINE; do
    OUT=$(echo "$LINE" | sed \
        -e 's/^[^*].*$//' \
        -e 's/^\*\ \(.*\)$/<h2>\1<\/h2>/' \
        -e 's/^\*\*\ DONE\ \[\[\([^]]*\)\]\[\([^]]*\)\]\]/<li class="done"><a href="\1">\2<\/a><\/li>/' \
        -e 's/^\*\*\ \[\[\([^]]*\)\]\[\([^]]*\)\]\]/<li><a href="\1">\2<\/a><\/li>/')
    echo "$OUT" | grep -v '/h2' >/dev/null 2>&1 || [ $N -eq 1 ] || echo "</ul>" >>$OUTFILE
    N=$[$N + 1]
    echo "$OUT" >>$OUTFILE
    echo "$OUT" | grep -v '/h2' >/dev/null 2>&1 || echo "<ul>" >>$OUTFILE
done <$INFILE
echo "</ul></body></html>" >>$OUTFILE

I thought of playing around with third party org-mode parsers, such as the Python one I used and improved called Orgnode, but that would've been also a compromise between a clean solution that involves to external org parsing and the simple but rude shell script, having few pros, but the cons of both. In the end I took a look on the export options of org-mode and found that it's capable of creating DocBook output. I hadn't used DocBook before, only heard of it from vmiklos, but figured out that it's an XML-based document markup language.

The remaining task is transforming XML to XML, and XSLT is the most powerful tool for it. I created two stylesheets, one for XHTML output and one for RSS, they almost instantly worked and produced the same (or better) output as the shell script. I also found a bug/feature in the DocBook export as it converts URL quoted special characters to their literal equivalents (such as %C3%B6 to รถ), which may cause incompatibilities in some browsers and also makes the RSS invalid.

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:db="http://docbook.org/ns/docbook"
  xmlns:xlink="http://www.w3.org/1999/xlink">
  <xsl:output method="xml" />
  <xsl:template match="/">
    <rss version="2.0">
      <channel>
        <title>...</title>
        <description>...</description>
        <link>http://...</link>
        <lastBuildDate><xsl:value-of select="$lbd" /></lastBuildDate>
        <xsl:for-each select="db:article/db:section/db:section/db:title">
          <xsl:if test="not(contains(text(), 'DONE'))">
            <item>
              <link><xsl:value-of select="db:link/@xlink:href" /></link>
              <guid><xsl:value-of select="db:link/@xlink:href" /></guid>
              <description><xsl:value-of select="db:link" /></description>
              <title><xsl:value-of select="db:link" /></title>
            </item>
          </xsl:if>
        </xsl:for-each>
      </channel>
    </rss>
  </xsl:template>
</xsl:stylesheet>

RSS needs the build date to be passed in RFC 2822 format, which is much easier to do in shell rather than some weird XSLT way. I used xsltproc which allows parameters to be passed on the command line, and the date command is capable of printing the date just in the right format. This way the RSS can be published using the following command.

$ xsltproc --stringparam lbd "$(date --rfc-2822)" \
    rss.xsl docbook.xml >feed.rss
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