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RE: hpack static table question?

From: RUELLAN Herve <Herve.Ruellan@crf.canon.fr>
Date: Mon, 2 Jun 2014 16:48:37 +0000
To: Cory Benfield <cory@lukasa.co.uk>, Tatsuhiro Tsujikawa <tatsuhiro.t@gmail.com>
CC: Greg Wilkins <gregw@intalio.com>, Ilari Liusvaara <ilari.liusvaara@elisanet.fi>, HTTP Working Group <ietf-http-wg@w3.org>
Message-ID: <6C71876BDCCD01488E70A2399529D5E532D61EB1@ADELE.crf.canon.fr>
The goal is to allow a receiver to limit the quantity of memory allocated for a given sender.

The size of the header table is limited by the SETTINGS_HEADER_TABLE_SIZE value. The computation of the size of the header table includes the length of the strings and 32 octets for the table structure overhead.

The memory allocated to the static table is fixed and can even be shared amongst all the senders.

However, there is no direct control over the memory used by the reference set. For items of the reference set belonging to the header table, there is an indirect control through the SETTINGS_HEADER_TABLE_SIZE value. To extent this indirect control to items belonging to the static table, it was decided to copy these items to the header table: in this way the memory used by the reference set is fully controlled by the SETTINGS_HEADER_TABLE_SIZE value.

Hervé.

PS: I will add this explanation to the spec.

> -----Original Message-----
> From: Cory Benfield [mailto:cory@lukasa.co.uk]
> Sent: lundi 2 juin 2014 18:21
> To: Tatsuhiro Tsujikawa
> Cc: Greg Wilkins; Ilari Liusvaara; HTTP Working Group
> Subject: Re: hpack static table question?
> 
> On 2 June 2014 17:05, Tatsuhiro Tsujikawa <tatsuhiro.t@gmail.com> wrote:
> > Sorry, I don't understand.  What is the problem here exactly?
> 
> Let's get everyone on the same page.
> 
> Greg is concerned that he has to copy a header out of the static table
> into the header table in order to add it to the reference set. He has
> to do this because the spec states that references may only be to
> headers in the header set without being clear of _why_ that's the
> case.
> 
> Tatsuhiro has provided the most compelling reason so far, which is
> that it enables the clearing of the reference set by the slightly
> obscure means of setting the header table size to zero via HTTP/2
> SETTINGS. I don't think anyone actually wants to do this.
> 
> I think the real question here is: why can't we have references to the
> static table? What is the architectural reason that ruled it out?

Received on Monday, 2 June 2014 16:49:42 UTC

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