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Re: Sticky headers and pipelining (was: Sticky header draft -- as an attachment)

From: Roy T. Fielding <fielding@liege.ICS.UCI.EDU>
Date: Wed, 07 Aug 1996 21:49:45 -0700
To: Paul Leach <paulle@microsoft.com>
Cc: 'http-wg' <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
Message-Id: <9608072149.aa05462@paris.ics.uci.edu>
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/1240
> The mechanism for that in the draft is that the client sends the header
> name and an empty value, which means that, even though there was a value
> for that header in the last message, this message should be interpreted
> as if the header with that field-name is not present in the message.

Ummm, I guess this is one of those things that should have been said
in the section on message field parsing....

An empty header field value has a meaning which is distinct from
a nonexistant header field.  An analogy is a variable in Perl --
no header field is equivalent to a value of undefined (a null pointer),
whereas a header field with an empty or whitespace-only value is equivalent
to an empty value (a pointer to a zero-length data segment).  Whether or
not those two have equivalent semantics is dependent on the definition
of the header field, just as


means accept nothing (if no other Accept headers are in the message)
and no Accept header field means accept anything.

> There must be some mechanism like this, independent of the semantics of
> any request header, in order for sticky headers to work at all.

Time to look for another mechanism...

  Connection: sticky
  Sticky: reset="Accept"

and assorted other yucky ideas come to mind.

BTW, while we are on the topic, I would prefer that the two unrelated
concepts of sticky headers and short header names be in two separate
drafts.  They should be evaluated independently.

 ...Roy T. Fielding
    Department of Information & Computer Science    (fielding@ics.uci.edu)
    University of California, Irvine, CA 92697-3425    fax:+1(714)824-4056
Received on Wednesday, 7 August 1996 22:02:24 UTC

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