ietf-nntp HDR parameter proposal

[Clive D.W. Feather]

Russ Allbery said:
> Accordingly, here's the proposal:
> 
> The HDR extension is indicated by one of the following extension strings:
> 
>     HDR
>     HDR BASE
>     HDR BASE EXTRA
>     HDR ALL
> 
> HDR BASE indicates that HDR is supported for the base overview headers
> Subject, From, Date, Message-ID, and References and the metadata items
> :bytes and :lines.  HDR ALL indicates that HDR is supported for all
> headers.  HDR BASE EXTRA indicates that HDR is supported for all of the
> headers included in HDR BASE plus some additional headers (not specified),
> but not for all headers.
> 
> If neither BASE nor ALL are given, HDR is supported on some other set of
> headers, and the exact set of headers isn't specified.
[...]
> One problem is that HDR BASE indicates that Xref is *not* in the HDR
> database, when it's nearly universally included in overview and therefore
> probably is.

I quite like the idea. Here's a possible way to both solve the Xref problem
and make it extensible.

The HDR extension can have zero or more parameters. Each parameter is a
"header package name" indicating some set of headers and metadata items
that are available through HDR.

    BASE   the 7 items mentioned above
    XREF   the Xref header

(we could perhaps add:

    BASEX  = BASE + XREF
)

Other package names may be defined in revisions to this specification or in
other RFCs. Private package names may be defined, prefixed with "-"
(e.g. "-INNUSUAL"). The package name "+" SHOULD be last on the list, and
means that the server also provides other headers and metadata items, but
not all (it's equivalent to a private package name specific to that server
and with a meaning that can change without warning).

I would lean towards saying that "HDR" with no parameters means "will
accept any header name or metadata item it knows about". I'm assuming
there's no backwards-compatibility issue here; if there is, then use
"HDR *" for this case and make "HDR" equivalent to "HDR +".

If people like this idea I'll craft words.

-- 
Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:  +44 20 8371 1138
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