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RE: Frame Length Restrictions

From: <K.Morgan@iaea.org>
Date: Sat, 19 Apr 2014 19:08:29 +0000
To: <mnot@mnot.net>, <jpinner@twitter.com>
CC: <ietf-http-wg@w3.org>
Message-ID: <0356EBBE092D394F9291DA01E8D28EC2011293E9E7@sem001pd.sg.iaea.org>
Regarding this part of the pull request...

The application data in DATA frames ... MUST NOT exceed 2^14-1 (16,383) octets in length. An endpoint MUST treat the receipt of a larger frame as a FRAME_SIZE_ERROR error ...

...and the pending pending re-introduction of gzip compression at the frame layer [1].



Is the size limit for application data _before_ or _after_ compression (specifically transfer layer compression)?



If the size limit is _before_ compression, it would kill the compression factor.  The only way to get a reasonable compression factor with frame-by-frame compression is to fill each frame with as much compressed data as possible (see [2]).



On a related note, if you're adding back the two bits, why not let application data use at least 32K?  Using at least 15 bits has advantages for the frame-by-frame compression factor - the max gzip "window bits" is 15 and so is better suited to 32K frames.

-keith

[1] See the thread "Transfer-codings, mandatory content-coding support and intermediaries"

[2] http://lists.w3.org/Archives/Public/ietf-http-wg/2014AprJun/0156.html





________________________________________
From: mnot@mnot.net [mnot@mnot.net]
Sent: 19 April 2014 08:36
To: Jeff Pinner
Cc: HTTP Working Group
Subject: Re: Frame Length Restrictions

Hi Jeff,

We need to show strong consensus on-list to overturn that, despite being a coin toss. If we want to get this into the next implementation draft, it needs to be demonstrated in the next ~2 days.

I.e., if there's a number of folks who feel this is a no-brainer, great; otherwise, probably not.

Who supports this, and does anyone have a problem with doing it?

Cheers,



On 17 Apr 2014, at 10:34 am, Jeff Pinner <jpinner@twitter.com> wrote:

> I put together a pull request to replace the frame length restriction with an HTTP application layer restriction that I would like the working group to consider.
>
> https://github.com/http2/http2-spec/pull/456
>
> Of particular note is that this is in contrast to a previous decision made by the working group (albeit by coin toss in Seattle) which can be found
>
> https://github.com/http2/http2-spec/issues/260
>
> With the addition of padding to the framing layer, I believe it is preferable to implement the frame length requirement at the HTTP layer to allow intermediaries to pad frames without running into frame length restrictions.
>
> Thanks!
> - Jeff

--
Mark Nottingham   http://www.mnot.net/

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