[NNTP] Extension snapshots 2

[Russ Allbery]

Ken Murchison <ken at oceana.com> writes:
> Clive D.W. Feather wrote:

>> 3.4.2 now says:
>>    A mode-switching server has three modes:
>>    o Initial mode, after the initial connection:
>>       * it MUST advertise the MODE-READER capability;
>>       * it MUST advertise the IHAVE capability;
>>       * it MUST advertise the READER capability with the -MODE-READER
>>         modifier;

> Since you state elsewhere that capability modifiers aren't required to be
> used by a server, I object to the MUST above.  Either change the MUST to
> SHOULD, or rewrite it to something like:

> "* the READER capability MUST NOT be advertised unless prefixed with the
> -MODE-READER modifier;"

Agreed.

>> and MODE READER now has added:

>>     The server MAY cease to advertise the MODE-READER capability once
>>     the client is no longer permitted to use the command, and SHOULD do
>>     so if the command would have unexpected effects.

>> I can easily be convinced to change the last two SHOULDs to MUST.

> I'd in favor of MUST unless there is good reason not to.

I would just say that the server MUST NOT advertise the MODE-READER
capability after MODE READER has been used *or* when the server is in
reader mode already.  Remember, a client that doesn't support modifiers
can be expected to key off the presence of that capability to decide
whether to issue the command, and a naive implementation could loop if the
capability isn't dropped.

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