[NNTP] [2501] Reader commands in transit servers and vice-versa

[Clive D.W. Feather]

Issue: if a server advertises itself as transit-only, should it be allowed
to implement some of the reader-only commands or not?

Ken Murchison said:
> 2501:  I personally don't care if an implementation supports more than 
> the relevant minimal commands.  However, if this does occur, then we're 
> back to a situation of not knowing what commands a server supports. 
> Perhaps if a transit-only server also supports NEWNEWS, then it 
> advertises "_TRANSIT NEWNEWS".  Likewise if a reader-only server also 
> supports IHAVE, then it advertises "_READER IHAVE".

One problem is that, as you say, we're back to a situation of not knowing
what commands a server supports.

Another problem is that we're creating lots and lots of different subsets
of NNTP. There's a reasonable amount of logic in separating transit and
reader functionality, but do we really want to go beyond that? Do we want
to have lots of different subsets so that you can never be sure what is and
isn't available.

One thing to note is the distinct asymmetry between transit-only and
reader-only. There is only one transit command in the core: IHAVE. On the
other hand, there are 12 different reader commands, giving 4095 possible
combinations. And it's worse than that: could a server implement everything
except GROUP, say? And then only implement the message-ID versions of
ARTICLE etc? This way, I think, lies madness.

Thinking it through, I think we need to decide exactly what subsets we
allow and forbid anything else. Currently we have five cases:
    transit-only:            general commands plus IHAVE
    reader-only no posting:  all commands except IHAVE and POST
    reader-only:             all commands except IHAVE
    general-use no posting:  all commands except POST
    general-use:             all commands
Is this sufficient?

If not, what further subsets do we really need?

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