ietf-nntp Empty list on specific group / GROUP response

[Russ Allbery]

Joao Prado Maia <jpm at papercut.org> writes:

>              If the group is empty, one of the following three situations 
>              will occur. Clients MUST accept all three cases; servers MUST 
>              NOT represent an empty group in any other way. 
              
>              The high water mark will be one less than the low water mark, 
>              and the estimated article count will be zero. Servers SHOULD 
>              use this method to show an empty group. This is the only time 
>              that the high water mark can be less than the low water mark. 
>              All three numbers will be zero.

> Now what exactly does the last paragraph mean ? Maybe it is my english 
> failing on me, but it first says that on the case that the group is empty, 
> the response should be three zeros.

No, that's supposed to be another bullet item.  Let me propose some
alternate wording.  Let me know if this is cleaner.

I propose that the 4th, 5th, and 6th paragraphs of the description of
GROUP in 9.1.1.1 be replaced with the following:

    If the group is empty, one of the following three situations will
    occur.  Clients MUST accept all three cases; servers MUST NOT
    represent an empty group in any other way than one of these three:

     * The high water mark will be one less than the low water mark,
       and the estimated article count will be zero.  This is the
       preferred method of indicating an empty group.  Servers SHOULD
       use this method.  This is the only time that the high water mark
       is allowed to be less than the low water mark.

     * All three numbers will be zero.

     * The high water mark is greater than or equal to the low water mark
       and the estimated article count may be zero or non-zero.  If the
       estimated article count is non-zero, the same requirements apply as
       for a non-empty group.

    This last case may occur if the group is actually empty but the server
    doesn't realize this (if, for example, the only article in the group
    was just cancelled and the server databases have not yet been
    updated).

> Also, it would be very nice to have specific examples of the behavior of 
> the NNTP server on these cases, as the wording is not the clearest one.

I propose that the following examples be added to 9.1.1.1.2:

    Example of an empty group using the preferred server response:

        [C] GROUP misc.test
        [S] 211 0 45534 45533 misc.test

    Example of an empty group using another acceptable response:

        [C] GROUP misc.test
        [S] 211 0 0 0 misc.test

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