How is an electron-builder NSIS block map generated? Can it be controlled?

Question

I have a project packaged using electron-builder with NSIS target, producing as artifacts a 40 MB .exe file and a .exe.blockmap file (which is gzipped JSON, I know). The problem is that even if something as simple as version number changes, blockmaps start differing vastly (for example only 1756 chunks of 2032 matched) and each update ends up downloading multiple megabytes.

I understand it may not be easy to make a detailed file-by-file map of an NSIS .exe containing app-64.7z containing app.asar finally containing files, but does electron-builder even try? Can it be overridden to use some binary-diff as basis for the block splitting, to ensure minimum differences between consecutive versions? I can't seem to find any documentation on app-builder.exe 's routines for blockmap creation.

Answer 1

The largest part of the solution was introducing shortVersion and shortVersionWindows configuration strings in electron-updater v22.3.1 (20 Jan 2020), letting the 50 MB application not be re-stamped with full versioning at every single version update.

Also, space-padding all -bundle.js files (if present) helps to keep any app.asar file length fields to stay the same, again limiting the scope of changes in the final file.