Zsync: Differential file downloading over HTTP using the rsync algorithm (2010)

We are using this for addon synchronization in our community through Arma3Sync. On server side we need to "build" repository - it just generates .zsync files, then clients are downloading just diff. Update size came down from 10-15GB to <3GB.

I like zsync quite a bit. The chunking patcher we wrote for League of Legends is similar to zsync in some key ways. One of the things we did to improve the efficiency of the core rolling hash based chunking logic was to add file type aware chunking. Basically, we teach the patcher about the different archive formats that our games use (say, Unreal Engine PAKs) and the algorithm ensures that chunks stop at the file boundaries within the archive…

It looks like it's designed for a different use case than rsync, rather than being better. I'm not sure that the space it sees between rsync, plain http, and bittorrent is a niche it can fill, or a gap through which to fall into obscurity.