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Re: Header Table and Static Table Indicies Switched

From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Date: Sun, 3 Aug 2014 10:12:55 +0300
To: Jeff Pinner <jpinner@twitter.com>
Cc: Greg Wilkins <gregw@intalio.com>, HTTP Working Group <ietf-http-wg@w3.org>
Message-ID: <20140803071255.GA17434@LK-Perkele-VII>
On Sat, Aug 02, 2014 at 06:55:08PM -0700, Jeff Pinner wrote:
> 
> The order of the tables has no impact on the difficulty of
> implementation, it's basically a swap of the length checks and which
> table you offset. Why would we give up 8% in compression for free?

There is a trick to quickly extract individual headers (or small groups
of headers) out of compressed header block. It works if static table
comes before header table, but not vice versa (the reasons for this
involve interaction between eviction and Huffman).

But that trick would be mostly useless if Host is removed[1][2] given
that :headers are on front anyway and the trick can't deal well with
multi-valued headers (e.g. Cookie).


[1] The current spec seems to mix and match Host with :authority
with little pattern that I can figure out (or perhaps just EPARSE).

If both :authority and Host are route headers, that would cause
the following problems:
- What if the two disagree?
- Host seems much more expensive to process than :authority, due
  to being potentially near end of large header block (:authority
  is always near the begining).


[2] Or made to compress like :headers.


-Ilari
Received on Sunday, 3 August 2014 07:13:25 UTC

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