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

From: Daniel DuBois <dan@spyglass.com>
Date: Wed, 07 Aug 1996 15:11:34 -0700
Message-Id: <2.2.32.19960807221134.00ae0458@rafiki.spyglass.com>
To: Paul Leach <paulle@microsoft.com>, 'Jeffrey Mogul' <mogul@pa.dec.com>
Cc: 'http-wg' <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
At 02:35 PM 8/7/96 -0700, Paul Leach wrote:
>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.
>
>There must be some mechanism like this, independent of the semantics of
>any request header, in order for sticky headers to work at all.
>[...]
>One could invent a header with the property that (say)
>	Foo:<CRLF>
>meant one thing, and
>	Foo: Yes
>meant another. I don't believe that are currently any examples of this,
>however. Certainly, either we would either have to outlaw adding any
>such headers to HTTP, or outlaw their participation in the sticky header
>mechanism.

Uh.. The semantics of an empty Accept-Encoding are mentioned in the 11-06
draft.  And I think the semantics of "Accept:<CRLF>" are both self-evident,
and clearly not the same as a lack of the header.  Certainly the BNF allows
numerous headers to be NULL.

I was presuming (not having read the draft, can I admit that in a discussion
on the draft?) that your intentions were that a sticking client would
indicate turning off individual headers on subsequent requests by sending
the explicit format that was semantically equivalent to the default of those
individual headers.  As in, sending "Accept-Encoding:<CRLF>" since empty and
non-existant have the same meaning, or "Accept: */*" since that has the same
meaning as non-existant.  This would mean that all stick-able headers must
have a explict default-equivalent format (User-Agent:<CRLF> ??), or a that
you need a global way to wipe off all the stickyness (Here's where I propose
the Towel: header.), or, finally, that you have a
"Stuck-Headers-That-Slipped-Off:" header.

-----
Daniel DuBois, Traveling Coderman      http://www.spyglass.com/~ddubois/

  The difference between cats and dogs:
  1) Dogs look at their owners, and say:  "Hmmm . . . they feed me, and
     shelter me, and take care of me . . . THEY MUST BE GOD!!!!!!!!!!"
  2) Cats look at their owners, and say:  "Hmmm . . . they feed me, and
     shelter me, and take care of me . . . I MUST BE GOD!!!!!!!!"
Received on Wednesday, 7 August 1996 15:24:17 EDT

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