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How to generate an Atom feed

So, after ranting about how RSS and Atom feeds are disappearing from the web in my article The Woeful Web, I decided I ought to offer a feed for this humble site.

I settled on offering an Atom feed, as the situation around RSS feeds is complicated. Atom was designed to deal with various issues that were arising in RSS feeds. Most feed readers will support both RSS and Atom, so generating both formats for my site would be overkill. I decided on Atom which seemed clean and modern and did not suffer the legacy issues that seem to trouble RSS.

The Atom feed format is more correctly known as Atom Syndication Format. It is the Atom Syndication format I mean when I refer to an Atom feed.

Having looked initially at the Atom Syndication Format RFC, I was a bit worried about what I was getting myself into - the RFC is fairly impenetrable. The solution, for me, was to look at examples of Atom feeds and this clarified things. Once you get your bearings by looking at generated Atom feeds, the RFC makes a lot more sense.

One of the hardest aspects of this was retrofitting the correct metadata to my existing content. I had to work out what data would be required, and how this would be added to my content. In the end I settled on Published date, Updated date, Summary, and Title. In addition each article has a UUID. This is required by the Atom feed spec. A UUID can be generated easily enough on the command line (in Mac OS X), using the command uuidgen. This seemed to be sufficient for my purposes. I decided not to add the full content of the article to my feed, as the user can simply click on the article heading in a feed reader to read the content on my site. This has the advantage that it keeps the feed simpler and quicker to generate. The downside is the user will need to be able to access the web in order to read the content - if they were using a desktop feed reader the content would be saved for offline reading if I provided a full feed. In this case the advantages of speed of generation and simplicity outweighed this convenience for the user. However, in the future I could offer a full feed capability. This would be relatively simple to add to the existing code based on my investigations so far.

The other aspect I needed to determine was dates and how to format them. The Atom feed uses ISO-8601 date times. I have already described dates and the issues around them in my article dealing with dates, so I won't go into these again here.

The data extracted from each article is used to populate an entry in the Atom feed. The header and footer for the Atom feed are more or less static pieces of text. The only requirement here is that the header is patched with the date-time of the feed generation. Essentially the entries are appended to the header in the output file, and then the footer written before the feed file is closed.

Metadata can be extracted from either the Markdown source for each article, or the generated HTML, with simple regular expressions. I originally planned to extract the data from the generated HTML, but decided to use the Markdown source instead. No changes were required to the regular expressions. However, a little additional code needed to be added to deal with the fact that the links to the articles in the Atom feed should reference HTML files. The reason for using the Markdown article source was I only need to add articles, not pages, to the Atom feed. The articles are, for convenience, stored separately from the static pages in source/articles. I can find these easily enough with some Bash shell scripting: find ./source/articles -name "*.md". These are then fed to the Python code that generates the Atom feed. I find is extremely useful to use Python's fileinput facility. This is rather similar to Perl's diamond operator <>. This facility allows your Python code to accept a list of files to operate on from stdin:

for filename in fileinput.input():

    # chomp
    filename = filename.rstrip()

This reads files in from stdin and you'll notice I do a Perl-style chomp to remove any extraneous new lines on the end of the file name.

Typically you will use some Bash shell script to find the required files and then pipe these into your Python code:

find ./source/articles -name "*.md" | ./generate_atom_feed.py

This may not be the prettiest approach to solving the problem as you could write all code in Python and have no Shell script at all. This is something I will consider for the future, but for now this is an effective way of directing the Python code.

I will not go into the Python source code to generate the feed as it is available in my GitHub - the file to look at is generate_atom_feed.py. The code is called from the build_website.sh shell script. It takes milliseconds to build the feed right now. I expect that even if the site expanded to thousands of articles (which won't happen any time soon), the feed would take a few seconds to build.

I tested the feed with Inoreader, the web-based feed reader. Everything seems to work fine. One thing I did need to do was add automatic feed discovery to each page. This was a matter of simply adding a little bit of code to the header that is automatically used in the building of each web page. To allow auto-discovery of the feed you simply need to indicate to the web browser / feed reader that a feed is available by adding a link in the <head> ... </head> element. This addition to clean.py is shown here:

<link rel="alternate" type="application/atom+xml" title="Coffee and Code Atom Feed" href= "https://coffeeandcode.neocities.org/atom.xml">

Once the metadata was added to each article it was not too bad to generate the feed. It was mostly an exercise in regexes. I could perhaps have used an XML parser, but I think that would have been overkill in this case. If I was writing a general purpose generator, or perhaps a feed reader, I would almost certainly have needed to use an XML parser, and perhaps one of the feed parser/generator libraries out there. It was however quite fun to generate my Atom feed without any external libraries.

I hope you find the Atom feed useful. If you experience any issues please let me know via my Contact page.