When generating the build files for macOS with electron-builder the two natural artifacts for the updates are:
- a compressed zip file with the app
- a blockmap file
Where blockmap file is leveraged for effective incremental downloads, or in other words downloading only the updated parts of the new version of the app.
While using incremental downloads reduces download size dramatically it behaves unoptimally with regards to the asar package that contains most app's source files. The reason for this is that in a zip archive all files are compressed individually, but after compression each file has a high entropy and looks like mostly different blob when comparing the blockmaps.
This CLI tool mitigates this by taking in account the asar file structure when compressing it. Instead of deflating whole file as a single blob, we split it into logical chunks (one for every sub-file) and flush zlib stream after each chunk. This means that the same sub-files in asar are likely to result in the same compressed binary chunks in the resultant optimized .zip file.
npm install -g @indutny/rezip-electronrezip-electron optimize app.zip -o app.opt.zipBefore optimization:
$ rezip-electron compare signal-desktop-mac-arm64-6.48.0.zip \
signal-desktop-mac-arm64-6.48.1.zip
# ...A lot of changed files...
Total Download Size: 10.00mbAfter optimization:
$ rezip-electron compare signal-desktop-mac-arm64-6.48.0.opt.zip \
signal-desktop-mac-arm64-6.48.1.opt.zip
# ...Way less changed files...
Total Download Size: 2.87mbThis software is licensed under the MIT License.