Speaking of x-to-x protocols; Eric had an idea that I found
interesting, namely to make to client-to-client protocol more-or-less
pure HTTP. After all, HTTP does almost exactly what the
client-to-client protocol is supposed to do. I would like people to
voice their opinions about that. In my mind, it is a very good
idea. Of course, it would have some DC-specific headers, but that
doesn't prevent anything at all. It would also make HTTPS quite
natural for encrypted transfers.

Yes, I totally agree with my own idea ;) and we clearly share the same point of view about specific headers (in both transfer query and reply).

Passive mode xfer will be the hardest problem to deal (using PUT instead of GET ?).

Eric