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Re: hpack static table question?

From: Greg Wilkins <gregw@intalio.com>
Date: Mon, 2 Jun 2014 17:45:12 +0200
Message-ID: <CAH_y2NHdHb-7SHuW6jD_fSbU7tyqYUcfCE-wFTSn6YzOPbbQog@mail.gmail.com>
To: Tatsuhiro Tsujikawa <tatsuhiro.t@gmail.com>
Cc: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>, HTTP Working Group <ietf-http-wg@w3.org>
Tatsuhiro,

sorry but I'm still not understanding.   If you want to clear the reference
set, there is a 1 byte code to send for that.   It makes little sense to
set the header table size to 0 just to clear the reference set.

This also raises another slight concern.  When the copied static entry in
the dynamic table is eventually evicted, then that field is also evicted
from the reference set.  Chances are that it will then be put straight back
in there.  Seams pointless?

So I'm still not getting why?

cheers



On 2 June 2014 17:22, Tatsuhiro Tsujikawa <tatsuhiro.t@gmail.com> wrote:

>
>
>
> On Tue, Jun 3, 2014 at 12:07 AM, Ilari Liusvaara <
> ilari.liusvaara@elisanet.fi> wrote:
>
>> On Mon, Jun 02, 2014 at 04:45:28PM +0200, Greg Wilkins wrote:
>> > The hpack draft 7 says in 3.2.1 : "The referenced static entry is
>> inserted
>> > at the beginning of the header table".
>> >
>> > I can't understand why this copy of a static entry to the dynamic table
>> is
>> > needed?   Doesn't this mean that the static entry will now be known by
>> two
>> > indexes?     Why is this copy needed?
>>
>> AFAIK, to avoid needing having to keep state bits (2 per entry[1]) for the
>> static table.
>>
>> Yeah, the static table is 61 entries, thus the amount of state needed
>> would
>> be just 16 bytes.
>>
>>
>> [1] In set and emitted bits.
>>
>>
> ​Another reason is that we can clear reference set when ​setting
> SETTINGS_HEADER_TABLE_SIZE to 0 if we static entry is copied int dynamic
> header table when it is referenced.
>
> Best regards,
> Tatsuhiro Tsujikawa
>
>
>
>>
>> -Ilari
>>
>>
>


-- 
Greg Wilkins <gregw@intalio.com>
http://eclipse.org/jetty HTTP, SPDY, Websocket server and client that scales
http://www.webtide.com  advice and support for jetty and cometd.
Received on Monday, 2 June 2014 15:45:41 UTC

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