upload/download only differences

Hello,

I'm working in a desktop application, and I'm working directly with API calls (not using an SDK).

I have most of the RPC endpoints already implemented and working, and now started to work with the upload and download endpoints.

The problem arises when I find out that Dropbox in the Synch desktop utility seems to use (correct me if I'm wrong) delta comparing and it sends only the differences of two versions of a file: I mean, when a file changes, it doesn't upload or dowload the whole file, but only the differences.

Here there is information: https://www.dropbox.com/en/help/8

But I don't see any documented API for doing that in https://www.dropbox.com/developers/documentation/http/documentation

I found that there is a library for doing the file comparison: https://github.com/dropbox/librsync but I have no idea how to use it.

I can't believe that all the other applications besides the Synch desktop utility provided by Dropbox are forced to upload or download the whole file every times a few bytes change.

Where can I find information about this?

Thanks in advance.