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Fwd: HPACK

From: Mark Nottingham <mnot@mnot.net>
Date: Tue, 17 Jun 2014 10:55:36 +1000
To: HTTP Working Group <ietf-http-wg@w3.org>
Message-Id: <280F6644-AB3C-42DE-AAC4-A0D8994DC71E@mnot.net>
More feedback from PHK, forwarded with permission.

See:
  <https://github.com/http2/http2-spec/issues/532>

Begin forwarded message:

> Page 8, appending static table
> ------------------------------
> 
> Lacking documentation, I find it somewhat dubious that
> assigning higher indicies to the static tables very common
> entries makes sense performance wise.
> 
> Forcing "GET" to have an index >30 causing it to encode into two
> bytes (or likely even three bytes) rather than one seems very
> counter inuitive.
> 
> The dynmic and shifting indicies for the static table also robs
> high-performance load balancers an important optimization opportunity
> (ie: screening out non-GETs and similar).
> 
> The optimal case is probably to have a small static table
> at the front and another one with less used entries at the
> tail, but I doubt that complexity is warranted.  I would just
> put the static table at the front.
> 
> 
> Page 25, just before the table
> ------------------------------
> 
>   As an example, the Huffman code for the symbol 48 (corresponding to
>   the ASCII character "0") consists in the 5 bits "0", "0", "1", "0",
>   "1".  This corresponds to the value 5 encoded on 5 bits.
> 
> This does not match the table.
> 
> Page 25, the table(s)
> ---------------------
> 
> The RFC should document for the future where these tables came from,
> people are (rightfully) quite paranoid about "magic numbers appearing
> out of nowhere" these days.
> 
> It might be wise to reserve a couple of bits somewhere to allow the
> tables to be revised if experience shows them to be too suboptimal.
> 
> Why does it make sense to assign huffman codes to characters which
> are illegal in HTTP headers, such as 0x01-0x31 and which should cause
> errors if encountered ?
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk@FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.

--
Mark Nottingham   https://www.mnot.net/
Received on Tuesday, 17 June 2014 00:56:04 UTC

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