[NNTP] Article Numbers Becoming Invalid (RFC 3977)

[Russ Allbery]

Julien ÉLIE <julien at trigofacile.com> writes:

> If it is really what a news server is supposed to do, then RFC 3977 needs
> to be amended.  Only one additional word is needed:  "the current article
> number MUST be set to the first *valid* article in the group".
> Because the first article is currently defined as the reported low water
> mark -- which is also what INN implements.

Hm, while that wording change may be useful for clarity, I think that's
what RFC 3977 already says.  See:

   The successful selection response will return the article numbers of
   the first and last articles in the group at the moment of selection
   (these numbers are referred to as the "reported low water mark" and
   the "reported high water mark") and an estimate of the number of
   articles in the group currently available.

To me, the "at the moment of selection" pretty clearly implies that GROUP
should be checking and those numbers should really be valid.

Also, in general it doesn't seem right that one should have to say that it
must be set to the first valid article in the group.  I think that should
be implied by saying that it's set to the first article.  A number that
doesn't correspond to an article isn't really an article.

I think the implication of RFC 3977 is that the server can handwave the
article estimate, but the low and high water marks should really be
correct.

(In practice, this will slow down INN a little bit.)

> I see that RFC 977 defines two forms for ARTICLE:

>   When the ARTICLE command is followed by a message-id in angle brackets
>   ("<" and ">"), the first form of the command is used; when a numeric
>   parameter or no parameter is supplied, the second form is invoked.

> whereas RFC 3977 separates the form with an article number and without it:

>   Second form (article number specified)
>     223 n message-id      Article exists
>     412                   No newsgroup selected
>     423                   No article with that number

>   Third form (current article number used)
>     223 n message-id      Article exists
>     412                   No newsgroup selected
>     420                   Current article number is invalid

> The NNTP reference implementation, and also INN, cas use 420 and 423 for
> what is now called the third form.  It appears that the concept of
> "invalid" is not the same as it used to be.

In retrospect, it looks like we unfortunately introduced two separate
concepts of invalid and used the same terminology for both: the invalid
article number that results from entering an empty group, and an article
that's gone missing.  We probably should have reserved 420 for the former
case and continued to use 423 for the latter case.

> Well, I agree it is not a big deal.  I just hope readers cope with it,
> and were not expecting 423.

I suspect that NNTP clients that use ACTIVE without a number, or NEXT and
LAST, are fairly thin on the ground.  It's not a very natural way of
interacting with the server once you have overview information.

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