swiiifz: IIIF from a zip, served by a Service Worker

I have always been a bit obsessed with serving static web content that is portable, cheap, maintenance-free, and easy to distribute and mirror. My reasons are practical. I often work on non-profit projects in my spare time, with little or no budget. The web is also changing fast: hosting and server prices are rising, and crawlers are devouring resources, making it harder to keep dynamic applications running. There is a political side too. The governance of the web is fragile, and content can be blocked, taken down or lost for political reasons. Content that is easy to copy and mirror is much harder to make disappear. The idea of serving digitized documents as zipped packages came to me in 2014, with deepzoom-osd-server. I later wrote about it in IIIF, tropy, canopy and SZI. Earlier this year I built mkiiif for my own needs, but one question stayed open: how do you serve this packaged content? I knew Service Workers and HTTP range requests could be the answer, since Webrecorder uses…