I agree; the XferCommand solution seems like an excellent way to prototype this and see if it is feasible. As Aaron and I have alluded to, we aren't real big on getting this done ourselves, but we will offer suggestions if asked.
Great. I'm asking for suggestions! I have verified that my makepkg patch works to create deltas of old versions placed by the packager in the build directory. The attached patch is for 2.9.8, as this is what I'm running on my system today. 3.0 just adds some $CARCH stuff, no big deal. I have verified that the download and patch from my own custom repo works using my custom XferCommand script. See attached. Where to from here? Some have suggested using another method rather than xdelta 1.1, bdiff/zsync/xdelta3 etc. I gave zsync a try but had to give up when it failed to download the files from my tomcat web server. Possibly it would work with apache, but it wasn't a good sign. I feel that there are quite a few more moving parts to the zsync solution which weigh against it. bdiff is reportedly a better xdelta - I personally think xdelta will do until proven otherwise. Dale