I built an online RSS reader with Rust and WebAssembly

huydotnet · on Sept 28, 2019

I built this as an experiment with Cloudflare's Worker Script.

Here's a bit behind this app.

- Frontend: Just few lines of code using Svelte

- Backend: a Worker Script using Rust, here's how I do the RSS to JSON stuff:

    #[wasm_bindgen]
    pub fn parse(content: &str) -> String {
        let feed: Option<rss::Channel> = match content.parse::<Feed>().unwrap() {
            Feed::RSS(rss_feed) => Some(rss_feed),
            _ => None
        };
        if feed.is_some() {
            let rss_feed = feed.unwrap();
            let items: Vec<serde_json::Value> = rss_feed.items.iter().map(|item: &rss::Item| {
                return json!({
                    "title": item.title.as_ref(),
                    "link": item.link.as_ref(),
                    "date": item.pub_date.as_ref(),
                });
            }).collect();
            return json!({ "feed": items }).to_string();
        }
        return "".to_string();
    }

The only overhead, I think, is the part that I have to actually write the code to fetch RSS content in JavaScript (worker.js), as fool as you can imagine:

    const url = request.url.match(/url=(.*)/);
    if (url && url.length > 1) {
      const feeds = url[1].split(',');
      let promises = feeds.map(async url => {
        const res = await fetch(url);
        const text = await res.text();
        const json = JSON.parse(parse(text));
        return json && json.feed || [];
      });
      let result = await Promise.all(promises);
      let combined = result.reduce((arr, feed) => {
        arr = arr.concat(feed);
        return arr;
      }, []);
      return new Response(JSON.stringify({ "items": combined }), {status: 200, headers: {
        'Content-Type': 'application/json'
      }});
    }

If network libraries such as `reqwest`, and some date parser libraries like `chrono` already supported WASM, I'd be able to skip this JS step for good.

Deployed on Cloudflare using Wrangler CLI, I'm still on my free plan, and I hope I won't hit a 100k requests/day limit anytime soon.

lostmsu · on Sept 29, 2019

It is cool, but it is not really an application in the expected sense. It is just a 2 stage RSS to HTML converter (e.g. RSS->JSON server, JSON->HTML client).

Not sure why not make just do RSS->HTML directly on the server.

Obviously, does not track read state or sync, or anything else basically.

rahuldottech · on Sept 28, 2019

This is neat! I'm definitely going to be making use of this :)

dplgk · on Sept 28, 2019

Do you have a current rss reader you use? Will you be moving all your feeds to this reader?

huydotnet · on Sept 28, 2019

thank you :D