[NNTP] [2502] Correct code for unimplemented mandatory commands

[Clive D.W. Feather]

Issue: what response code should be returned for IHAVE with a reader-only
server, or reader commands (e.g. ARTICLE) with a transit-only server?

Ken Murchison said:
> 2502:  Per 3.2.1 paragraph 2, it would seem that 500 is the correct 
> response for "fails to implement.  I definitely don't think we want to 
> use 502 since it has permanent failure connotations (i.e. the closing of 
> the connection business).  I'd be happy with 503 however.

I'm deliberately trying to distinguish "IHAVE on a reader-only server" from
"unimplemented command". In previous drafts, IHAVE was a mandatory command
- though you shouldn't use it after MODE READER - and so 500 was
inappropriate. I feel that that hasn't changed.

I believe we all have the mental model of a "server site". Some connections
are transit ones and others are reader ones, but they're all connections to
the same site and, in principle, both are available at every site. Therefore
if you have a reader connection and want to do IHAVE, it's not that the
command isn't available but, rather, that you have the wrong connection. The
502 response code means "you can't do this without appropriate authority,
and you can't get that authority on this connection" and I think this is
the right one.

I accept, though, that it does to some extent come down to how we see
things structured. As with 2501, is this one protocol used in two different
ways, or is it two protocols that happen to have some things in common?

-- 
Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:    +44 20 8495 6138
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