Varbook - self-hosted EPUB library with KOReader <-> web reading-posi

[n2024]

Hi all,

I read on a Kobo running KOReader at home, but during the day I often only have
my phone with me. I wanted my reading position to follow me between the two
without fuss, while keeping my books on my own server. I couldn't find a setup
that synced both the position and the reading time between KOReader and a
browser reader, so I built one: Varbook.

What it is:

- A small self-hosted EPUB library (single Docker container, SQLite by default).
- An in-browser reader (epub.js) that also works as an offline-capable PWA:
books are cached locally, and the position syncs back to the server when
you're online.
- An OPDS catalogue, so any compatible reader can browse and download.
- A KOReader plugin ("Varbook Sync") that pushes/pulls your position and reading
time to the server in a single gesture. It's on the KOReader App Store (search
"Varbook Sync"), or you can install it manually.

The part that took the most work is cross-device position sync. KOReader's
CREngine tracks position with XPointers, while web readers (epub.js / Readium)
use EPUB CFI, and the two aren't interchangeable. Varbook uses a "pivot" format
based on the EPUB spine (spine item index + percentage within the chapter),
computed on both ends, so moving between KOReader and the browser lands you on
the right page instead of throwing you off by a chapter. It falls back to the
native format when both ends share an engine (CFI web-to-web, XPointer
KO-to-KO), and to a global percentage as a last resort.

My daily loop:

- Evening on the Kobo: tap a corner (a gesture I assigned) -> Wi-Fi on, pull
latest position, Wi-Fi off again to save battery. Read. Tap again -> push
position + reading time.
- Next day: I open the PWA on my phone, it drops me where I left off and syncs
on each page turn.
- Evening: back to the Kobo, which picks up the phone's position.

It's open source (MIT), built with Laravel + React. It's still young but I've
been using it daily for a few months and it's been stable for my use.

There's a free public instance if you want to try it without installing
anything: https://varbook.hophop.be

- Code: https://github.com/ndieschburg/varbook
- KOReader plugin: https://github.com/ndieschburg/varbook.koplugin

Feedback very welcome, especially from KOReader users. The plugin is where I'd
most like to hear what works and what doesn't.