[NNTP] Snapshot 6

[Clive D.W. Feather]

Charles Lindsey said:
> I mean that if the OVER command is merely an "optional" command, and the
> LIST OVERVIEW.FMT is also an "optional" command (or an "optional"
> parameter to LIST, which comes to the same thing), then there is nothing
> to prevent a server offerring either, neither, or both (and at least one
> of those 4 possibilities is a nonsense).
> 
> In the days when OVER was an extension, then those commands were never
> "optional" (they were obligatory if you implemented the extension).
> 
> I just want to be sure that the nonsense case(s) does not arise.

This is not possible.

Under the old regime, nothing stopped a server creating an XOVER extension
that did OVER but not LIST OVERVIEW.FMT. Or an XOVERFMT extension that did
LIST OVERVIEW.FMT but not OVER. However, if it advertised the OVER
extension in LIST EXTENSIONS, then it had to provide both commands.

Under the new regime, the same applies mutans mutandis.

Here's the actual situation:

  If server provides               then it

  * Neither                        MUST NOT advertise OVER capability
                                   MUST NOT advertise OVERVIEW.FMT ... [1]
  * Only LIST OVERVIEW.FMT         MUST NOT advertise OVER capability
                                   MUST advertise OVERVIEW.FMT argument
  * Only OVER                      MUST NOT advertise OVER capability
                                   MUST NOT advertise OVERVIEW.FMT argument
  * Both                           SHOULD [2] advertise OVER capability
                                   MUST advertise OVERVIEW.FMT argument

  If server advertises             then it

  * OVERVIEW.FMT argument          MUST provide LIST OVERVIEW.FMT

  * OVER capability                MUST provide both commands
                                   MUST advertise OVERVIEW.FMT argument.

  If server does not advertise     then it

  * OVERVIEW.FMT argument          MUST NOT provide LIST OVERVIEW.FMT
                                   MUST NOT advertise OVER capability

  * OVER capability                MAY provide either command
                                   SHOULD NOT provide both commands

[1] ... argument to the LIST capability (omitted to keep text on one line).

[2] "The server MUST ensure that the capability list accurately reflects
the capabilities (including extensions) currently available." but this
wording was written in the context of including and excluding a capability
as the extension becomes available or not during a session. Later on we
say "If the label is not included, the server MAY support none or some of
the commands, but SHOULD NOT support all of them."


Okay?

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