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104 lines
3.3 KiB
Markdown
104 lines
3.3 KiB
Markdown
+++
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title = "Generate a JSON Feed for a Zola Website"
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date = 2024-09-28T20:50:30+10:00
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[extra]
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updated = 2024-09-30T09:08:57+10:00
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+++
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[JSON Feed] is a specification for representing an RSS-style feed in JSON. I
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wanted to add one as an alternative alongside the Atom feed on a new website
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I'm building. The website is built with [Zola], which unfortunately [doesn't
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support the format][zola-issue], so this is how I went about adding one.
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<!-- more -->
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My first idea was to add a Tera template `json.feed` and try to generate JSON
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in the template. This was foiled on multiple fronts:
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1. Zola only loads files matching `*.{*ml,md}` and `robots.txt` as templates,
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so it didn't render my `json.feed` template.
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2. Tera has a `json_encode` filter but [does not support object literals][tera-issue],
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which makes building well formed JSON tricky.
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My next thought was to write a tool to convert the Atom feed to JSON. Rust is
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my scripting language of choice these days (only a tiny bit joking) but I
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didn't feel like adding a Rust project and build step for this. I then wondered
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if it could be done with [jq], or in my case [jaq]—a `jq` implementation in
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Rust. Short answer it can. Here's what I came up with:
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I created `templates/dump.xml` with these contents:
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```tera
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{{ __tera_context }}
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```
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This dumps the whole Tera context as JSON when rendered into `public/dump.xml`.
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It's `.xml` so that Zola will render it as a template. I added it to
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`feed_filenames` in the Zola `config.toml`:
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```toml
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feed_filenames = [
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"atom.xml",
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"dump.xml", # HACK: This just dumps the Tera context as JSON
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]
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```
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Then I wrote this `jaq` filter (`json-feed.jaq`) to generate a JSON Feed
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`feed.json` from the rendered version of the template.
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```jq
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# vim: ft=jq
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# Generate a JSON feed from context of a Zola feed template
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{
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"version": "https://jsonfeed.org/version/1.1",
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"title": .config.title,
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"home_page_url": .config.base_url,
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"feed_url": .feed_url | sub("dump\\.xml$"; "feed.json"),
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"authors": [ { "name": .config.author } ],
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"language": "en-AU",
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"items": .pages | map({
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"id": .permalink,
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"url": .permalink,
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"title": .title,
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"content_html": .content,
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"date_published": .date,
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"tags": .taxonomies.tags,
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} + if .updated then {"date_modified": .updated} else {} end
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+ if .extra.link then {"external_url": .extra.link} else {} end)
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}
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```
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It turned out quite nice. The main challenge with the `jaq` filter was working
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out how to conditionally include a key only if the value was non-null. I ended
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up with the trailing [if-then-else-end] expressions. If there's a better way
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I'd be keen to hear about it.
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Finally, to coordinate all this I added a `Makefile` that deletes `dump.xml`
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afterwards:
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```make
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help:
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@echo "Available tasks:"
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@echo
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@echo "- build"
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@echo "- deploy"
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build:
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zola build
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jaq --from-file json-feed.jaq public/dump.xml > public/feed.json
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rm public/dump.xml
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deploy:
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@echo todo
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.PHONY: build depoly
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```
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[JSON Feed]: https://www.jsonfeed.org/
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[tera-issue]: https://github.com/Keats/tera/issues/898
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[zola-issue]: https://github.com/getzola/zola/issues/311
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[Zola]: https://www.getzola.org/
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[jq]: https://jqlang.github.io/jq/
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[jaq]: https://github.com/01mf02/jaq
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[if-then-else-end]: https://jqlang.github.io/jq/manual/#if-then-else-end
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