Quoting Justin Chapweske <justin@...> from ml.gnutella.dev-forum:
:I doubt you really need to put something like this explicitly in a
:spec. If a client choose to advertise less available ranges to a
:certain requester, then that should be fine.

It's useful to know how much of a file each client has, even if the list of
available ranges is incomplete, and the burden of the extra header is small
enough to be worthwhile.

If it wasn't for the documentation of the extra header, I wouldn't have
mentionned it. Gtk-gnutella has been limiting the returned ranges for years!

However, I had also noticed that some clients mistakenly dealt with 4xx
errors as if they were fatal, not retrying as they should on a 416 (but
naturally changing their request to encompass one of the returned available
ranges).

Hence the need for updating the specs.

Raphael