From: Charles Lindsey (chl@clw.cs.man.ac.uk)
Date: Tue Apr 24 2001 - 10:39:22 CDT
In <yl4rvf55c0.fsf@windlord.stanford.edu> Russ Allbery <rra@stanford.edu> writes:
>Charles Lindsey <chl@clw.cs.man.ac.uk> writes:
>> I think the proper way for new headers is for IANA to keep a definitive
>> list of defined headers for mail, news and HTTP (there is much, but not
>> total, commonality between them).
>That would certainly be one direction in which this could go. Someone who
>wanted to do us all a favor could take that on as an action item and at
>least figure out what procedures would be involved in setting such a thing
>up. I think it's been tried for mail before, unsuccessfully, and there
>are some informational RFCs with informal lists.
OK, is there someone willing to take this on?
>My personal opinion is (1) that generic local headers should be removed
>entirely ...
Be careful. There are a lot of "local" headers used in mail (Status,
Content-Length, ...) and I think it likely that sites may well develop their
own for various reasons. So I think we should leave the concept there,
since it allows a way for us to say that they MAY/SHOULD/MUST be removed
under various circumstances. Otherwise, they will fall foul of our rule
that says "propagate everything you received regardless" (which is a Good
Thing most of the time).
>> But bear in mind that there are two levels of defence here.
>> 1. Serving agents SHOULD (was MUST) remove it on arrival, to avoid
>> confusions.
>To clarify, I think this SHOULD is fine.
>> 2. Serving agents whose clients expect it to be meaningful SHOULD have
>> replaced with their own version before letting clients see it.
>This SHOULD, however, should be a MUST. And *all* clients should be able
>to expect meaningful Xref headers; it's part of the article format now,
>and it's how crossposted articles are handled.
My only problem with a MUST there is that Xref is an optional header. So
sites can choose not to add it at all if they (and their clients) have
invented some alternative mechanism. What we actually say (6.16) is:
An agent inserting an Xref header into an article MUST delete any
previous Xref header(s). A relaying agent MAY delete it before
relaying, but otherwise it SHOULD be ignored (and usually replaced)
by any relying or serving agent receiving it.
That seems about right (though it says nothing about removing old ones if
you do not intend to generate a new one - but the generic SHOULD for local
headers covers that well enough, I think).
But the "Duties of a serving agent" wording needs to be consistent with
that, so I now have:
7. It SHOULD remove any local headers (4.2.2.3) from each article
and MAY (and usually will) generate a fresh Xref header (6.16),
in which case any existing Xref header MUST be removed.
Will that do?
>Any other local header I would argue should just be stripped before
>sending the article off the server. You can't do that in all cases with
>Xref because of replication.
Yes, but you can't say that (and I feel it needs to be said) unless there
exists the concept of a "local header" to say it about.
>Furthermore, the right place to handle local headers is in overview, not
>in the actual article, and putting into the standard language that seems
>to encourage people to modify the articles is in my opinion a bad idea.
>Again, this would also be the right way to handle Xref except for
>replication and historical behavior.
I think you have to leave it to implementors which mechanism to use.
Overview might well be the sensible option, but the concept of overview
does not exist in our document.
>The advantage of doing this is that we can move closer to fully
>enumerating all headers that a transit server is permitted to change
>without including this nebulous class of "all local headers."
We can only enmumerate such headers as exist at the time our standard is
written. If more such headers get invented in the future (officially or
otherwise) then a more general mechanism that enumeration is required.
-- Charles H. Lindsey ---------At Home, doing my own thing------------------------ Tel: +44 161 436 6131 Fax: +44 161 436 6133 Web: http://www.cs.man.ac.uk/~chl Email: chl@clw.cs.man.ac.uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K. PGP: 2C15F1A9 Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5