ietf-nntp New wording on article numbers

["Clive D.W. Feather" <[e-mail]>]

As promised. Comments welcome.


Proposed wording for RFC 977bis concerning article numbering.
=============================================================

New section:

    News is divided into named groups. Within each group exist articles.
    Each article has three relevant properties:
      - A Message-ID, which is unique over all articles in all groups; if
        an article occurs in more than one group, it has the same Message-ID
        in all groups.
      - An arrival timestamp, giving the time it arrived at the server.
      - An article number, which is unique only within the group; different
        articles in different groups may have the same number, and an
        article that occurs in more than one group may have different
        numbers in each group.

    The server MUST ensure that article numbers are issued in order of
    arrival timestamp; that is, later arriving articles MUST have higher
    numbers than earlier arriving ones. The server SHOULD allocate the first
    unused number to each new article.

    Article numbers MUST lie between 1 and 999999999 inclusive [this allows
    one article per second for 31 years]. The client and server SHOULD NOT
    use leading zeroes in specifying article numbers. If the server loses
    record of the most recent article number in a group, it MUST reset to a
    higher article number.


3.2.  The GROUP command
3.2.1.  GROUP

Replace the paragraph:

   The successful selection response will return the article numbers of
   the first and last articles in the group, and an estimate of the
   number of articles on file in the group.  It is not necessary that
   the estimate be correct, although that is helpful; it must only be
   equal to or larger than the actual number of articles on file.  (Some
   implementations will actually count the number of articles on file.
   Others will just subtract first article number from last to get an
   estimate.)

by the following paragraphs:

    The successful selection response will return the article numbers of the
    first and last articles in the group at the moment of selection, and an
    estimate of the number of articles on file in the group. The estimate
    MUST be at least the actual number of articles available. (Some
    implementations will actually count the number of articles on file.
    Others will just subtract first article number from last to get an
    estimate.)

    The last article number MIGHT be less than the first article number. In
    this case, there are no articles in the group and the estimated count
    MUST be zero.

    The set of articles in a group may change after the GROUP command is
    carried out. That is:
    * articles may be removed from the group;
    * articles may be reinstated in the group with the same article number,
      but those articles MUST have numbers no less than the first article
      number in the response;
    * new articles may be added with article numbers greater than the last
      article number returned in the response.

    When a subsequent GROUP command for the same newsgroup is issued, either
    by the same client or a different client, the first and last article
    numbers MUST be no less than those in the previous response for that
    newsgroup.


3.1.2.  ARTICLE (selection by number)

Add the paragraph:

    A previously valid article number might not remain valid if the article
    has been removed. A previously invalid article number might become valid
    if the article has been reinstated, but such an article number MUST be
    no less than the "first" article number specified in the most recent
    response to a GROUP command for that group.


3.5.  The LAST command
3.5.1.  LAST

Add the paragraphs:

    There might be no previous article in the group, even though the current
    article number is not the first one according to the last GROUP command.

    Because articles can be removed and added, the results of multiple LAST
    and NEXT commands might not be consistent over time.


3.9.  The NEXT command
3.9.1.  NEXT

Add the paragraphs:

    There might be no subsequent article in the group, even though the
    current article number is not the last one according to the last GROUP
    command. Similarly (and unlike the LAST command) there might be a
    subsequent article in the group even though the article number *is* the
    last one; in this case, another GROUP command will return a higher
    "last" value.

    Because articles can be removed and added, the results of multiple LAST
    and NEXT commands might not be consistent over time.

-- 
Clive D.W. Feather    | Associate Director  | Director
Tel: [phone] | Demon Internet Ltd. | CityScape Internet Services Ltd.
Fax: [phone] | <[e-mail]  | <[e-mail]>