How to use rsync protocol with apt?

[Colin Watson]

On Sun, Oct 25, 2020 at 12:31:05AM +1100, Karl Auer wrote:
> On Sat, 2020-10-24 at 15:45 +0300, Lyubomir Parvanov wrote:
> > Hello, I tried changing http:// to rsync://, as my mirror supports
> > that protocol. However, running apt update errors with "The method
> > driver /usr/lib/apt/methods/rsync could not be found. Is the package
> > apt-transport-rsync installed?". I have installed "rsync" package,
> > but there is no "apt-transport-rsync" package in Ubuntu's repos.
> 
> There is one executable per actual real method in
> /usr/lib/apt/methods.If you stick any random string "blah" in front of
> your URIs, you will get an error about "apt-transport-blah" error.
> 
> There is no rsync transport method for apt by default. Read man
> sources.list(5) to get the lowdown on available transport methods.
> 
> People have written other transports. Maybe someone has written an
> rsync transport already, but a quick google didn't find one.

In addition to this, the point of rsync is really for mirror-to-mirror
communication: that is, it's a good protocol to use if you're trying to
maintain your own mirror based on a given upstream mirror.

For apt clients, the advantages of rsync (which is good at comparing
local and remote sets of files and transferring only the differences)
aren't really relevant, and it has some disadvantages in the general
client case (often less good at dealing with high-latency links, less
good at traversing firewalls, and server implementations don't tend to
cope with large numbers of clients very well), so it's not clear to me
why somebody would think it worth the effort to implement such an apt
transport.

-- 
Colin Watson (he/him)                              [cjwatson at ubuntu.com]