ietf-nntp Mandatory and optional commands

[Russ Allbery]

Clive D W Feather <clive at demon.net> writes:

> I am under the impression that all commands in draft15, except those in
> the extensions (section 9.5) are mandatory. Is that correct ?

No.  Many of the LIST commands need not be implemented; in particular, all
of LIST {ACTIVE.TIMES,DISTRIBUTIONS,NEWSGROUPS,DISTRIB.PATS} are optional
and can return 501.

> LIST EXTENSIONS has a 500 response listed. That is surely wrong, even if
> the command isn't provided. Or is it intended ?

500 is incorrect.  The correct error response if LIST EXTENSIONS isn't
provided is 501.  The following changes should be made to 8.1.1:

Remove "500  Unknown command" from the table of responses.

Remove "a 500 (unknown command) or" from the text of that paragraph.

> Some LIST sub-commands, such as LIST ACTIVE.TIMES, need not return valid
> data if the server doesn't maintain it. This is what the 403 and 503
> responses are for, right ? Or do we really intend to allow 501 for this ?

501 is existing practice.  It's actually a form of extension mechanism,
albeit not a very good one, but it's been in NNTP for a while.  Basically,
you can tack on additional LIST FOO commands all you want and let clients
just try them, and your error if they don't work is 501.  This works
fairly well with existing servers that don't understand your commands.

INN supports a number of additional LIST commands not mentioned in the
base standard (LIST SUBSCRIPTIONS, LIST MODERATORS, and LIST MOTD).

> My problem is that I can't find anything that actually says that all
> commands are mandatory, or that some are optional. LIST ACTIVE.TIMES
> mentions that the information might not be available, though not in the
> clearest way. Do we need new wording for this ?

The only mandatory list command is LIST.

It's not clear to me if a server advertising the OVER extension is
permitted to respond 501 to LIST OVERVIEW.FMT, but I'm also not sure it
matters.

-- 
Russ Allbery (rra at stanford.edu)             <http://www.eyrie.org/~eagle/>