This question was asked about a week ago I think, the answer given was
that the limit for an XML node is 500k.
I would have thought sending anything over a few k would cause a big
problem for users with very slow connections (while it is being
received no other messages can get through)....
Yup. This obviously isn't an issue for buddy icons, which would be ~2kbytes.
For file xfers, at the time I suggested breaking the file into manageable chunks (32k?) and sending them as separate elements with sequence numbers, from which it would be really easy to reconstruct the file at the other end. Someone objected that this is an attempt to re-implement TCP, but it isn't since we already have a reliable channel and out-of-order delivery isn't a problem.
—Jens
