Extracting and de-minifying JavaScript from the Boox Mira AppImage

Boox have written an Electron app for controlling their Boox Mira and Boox Mira Pro displays. As mentioned in a previous post, I’m not a huge fan and have been working on reproducing its behaviour in a simple Python script - miractl.

Both miractl and its inspiration mira-js are made possible because the JavaScript from the manufacturer’s app can be extracted and inspected. What follows is a quick summary of how to do the same for yourself.

Getting the Boox Mira app

First, download the AppImage via Boox’s website.

wget https://static.send2boox.com/monitor-pc/linux/Mira-latest.AppImage

Then make it executable.

chmod +x ./Mira-latest.AppImage

Extracting content from the AppImage

Before continuing, it’s probably worth creating a directory to keep all the extracted files. Once created, move the AppImage inside and use this as your working directory for the ./Mira-latest.AppImage --appimage-extract command.

mkdir ~/boox-mira
mv Mira-latest.AppImage ~/boox-mira
cd ~/boox-mira && ./Mira-latest.AppImage --appimage-extract

This will create the folder ~/boox-mira/squashfs-root. Inside the resources folder is an archive file called app.asar, which contains the concatenated, minified source files for the app.

Getting to the JavaScript

Install asar.

npm install asar -g

Again, it’ll keep things tidier if you create a destination folder before extracting the contents of app.asar.

mkdir ~/boox-mira/app

Then extract the file into your newly created directory.

asar extract squashfs-root/resources/app.asar app/

Almost there! All that remains is de-minifying the JS to make it readable for mere mortals.

De-minifying

Inside app/js is the minified JS and its source map - app.5a0cfb40.js.map.

I used a tool (creatively) called source-map-unpack, but there are multiple ways of unpacking source maps.

npm install source-map-unpack -g
unpack unpacked app/js/app.5a0cfb40.js.map

This creates a folder called unpacked in your working directory and unpacks the JS there. And that’s it!

Your sweet JS prize awaits in unpacked/src.