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Re-work of op-code patterns

From: RUELLAN Herve <Herve.Ruellan@crf.canon.fr>
Date: Mon, 27 Jan 2014 16:19:28 +0000
To: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-ID: <6C71876BDCCD01488E70A2399529D5E532CCE052@ADELE.crf.canon.fr>
I created a new issue for better handling all the recent additions to HPACK, allowing for in-band signaling of changes in the encoding context: https://github.com/http2/http2-spec/issues/365.

With these recent additions, I think a re-working of the patterns used for the different op-code could be more efficient.
Current, we have 3 op-ocodes:
- 1 - Indexed Header
- 01 - Literal Header without Indexing
- 00 - Literal Header with Indexing

I would propose to add a 4th op-code, which would be used for signalling changes to the encoding context:
- Empty reference set
- Change maximum header table size
- Empty header table
- Padding

The new op-codes would be:
- 1 - Indexed Header
- 010 - Literal Header without Indexing
- 011 - Encoding context change
- 00 - Literal Header with Indexing

I did some quick testing, and changing the op-code for Literal Header without Indexing has only a very small impact on the compaction size.
- For the mnot test-set: going from 29.62% of HTTP/1.1 size to 29.64.
- For the hruellan test-set: going from 21.65% to 21.68%.

I think this is a cleaner approach with a negligible compression cost.

Received on Monday, 27 January 2014 16:20:00 UTC

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