It would be a dud. rsync-style download needs to prepare and upload significant amount of data to describe what the client already has. Hashes don't compress, a

It would be a dud. rsync-style download needs to prepare and upload significant amount of data to describe what the client already has. Hashes don't compress, and you want granular ones to reuse as much as possible. Web is more sensitive to latency than bandwidth, and upload is more restricted than download. So rsync hits all the worst spots, for the least gain. The data that diffs nicely, like HTML, is already tiny and compresses very well. The large files, like videos, don't diff well at all. There is a way to make rsync-style differential download really quick to request: the client and server need to agree on diffing only from a specific shared dataset… like a dictionary! And you can replace hashes with smaller variable-length integers.