iiif-worker: IIIF Service Worker to enhance resources on the client

[jbaiter]

I've recently experimented with adding OCR to Manifests using tesseract.js and then indexing the text in a SQLite database in a service worker, which then serves an "enhanced" version of the manifest to the viewer:

reenc.mp4

https://twitter.com/jbaiter_/status/1686452012009799690

This got me thinking: What if we were to create a general-purpose IIIF Service Worker, that enriches IIIF Resources on the client?

Here are some things that could be possible:

• Serve Content Search endpoints based on Annotations and OCR references in Manifests
• Enrich Manifests with references to Annotations from one or more external repositories (or IPFS?)
• Serve IIIF Image API Level 0 requests based on ZIP or GeoTIFF 'Images' referenced in the Manifest (see https://github.com/orgs/IIIF-Commons/discussions/4)
• Add virtual links to PDF renderings that get generated on the fly in the service worker with https://github.com/jbaiter/pdiiif

The neat thing about such a worker, and why I think it might be a good fit for iiif-commons, is that it's completely independent from any viewer app, since it's only exposed to the client via regular HTTP and standard IIIF APIs (except for some optional messages that could be sent to the worker, like for indexing newly created annotations).

I'm working on a prototype implementation for the search use case and would love to get some feedback as to which direction this could take.