Service worker adventures

With SoFee major work is done in background using celery, polling twitter for latest status, extract the links, fetch their content and eventually the segregation of content would also be done this way. I was looking for a way to keep things updated on user side and concepts of Progressive web app were really appealing.

What does it do?

Browsers(google chrome, firefox et all) are becoming more capable as new web standards are rolling out, like having offline cache, push notifications, accessing hardware(physical web). With these features now HTML based websites can also work as an native app working on your phone(android, iPhone) or desktop.

Stumbling Block #1: Scope and caching

I am using Django and with it all static content(css, JS, fonts) gets served from /static. And for service workers, if we do that, its scope gets limited to /static, that is, it would be able to handle requests getting served under /static. This limits access to API calls I am making. I Looked around and indeed there was a stack-overflow discussion around the same issue. Its a hacky solution and I added on to it by passing on some get PARAMS which I can use in template rendering for caching user specific URLs.

Beyond this I had a few head scratchers while getting cache to work. I struggled quite a bit to short the fetch request and return cached response but it just won't work. I Kept on tweaking the code, experimenting things until I used Jake's trained-to-thrill demo as base to setup things from scratch and then build on top.

Stumbling Block #2: Push Notifications

Service worker provides access to background Push notification. In earlier releases, browsers would register for this service and return a unique Endpoint for subscription, a unique capability URL which is used by server to push notification to. While this endpoint provided by Firefox works out of box, for chromium and google chrome browser, it still returned an obsolete GCM based URL. Now google has started using Firebase SDK and GCM is no longer supported. Beyond this on service side PyFCM library worked just fine to push notifications and it works with firefox too.