Re: Straw Poll: Restore Header Table and Static Table Indices

[Willy Tarreau <[e-mail]>]

On Tue, Oct 21, 2014 at 11:25:05AM +0200, Willy Tarreau wrote:
> Hi Roberto,
> 
> On Tue, Oct 21, 2014 at 12:01:19AM -0700, Roberto Peon wrote:
> > While I prefer the indexing scheme of the previous draft, this proposal
> > would be better than what is currently drafted.
> 
> Thanks. Do you know how the following representations are ordered in
> terms of frequency/probability ?
> 
>   - Indexed Header Field Representation
>   - Literal Header Field with Incremental Indexing
>   - Literal Header Field without Indexing
>   - Literal Header Field never Indexed
> 
> I would guess they should appear in the order above, though that's not
> obvious to me. And I'm still sad at the idea of leaving many encoding
> values unused (eg: static header values above 16). Thus, we'll typically
> have 48 possible values out of 256 for the first byte that will never be
> emitted just for the indexed headers alone, that's a 20% waste, and I
> really think we can do better without making anything more complex. I
> just need to ensure I don't propose something stupid.

For example something like this (CCing Greg who also has concerns about
all this), which supports a single-byte encoding for :
   - 14 or the 16 static headers with values
   - all 62 static headers for literals
   - 62 dynamic headers for literals

   +---+---+----------------------+
   | 1 | D |  index 6+            |      literal with incremetal indexing
   +---+---+----------------------+

   +---+---+----------------------+
   | 0 | 1 |  index 6+            |      indexed dynamic header
   +---+---+----------------------+

   +---+---+---+---+--------------+
   | 0 | 0 | 1 | 1 |  index 4+    |      indexed static header
   +---+---+---+---+--------------+

   +---+---+---+---+--------------+
   | 0 | 0 | 1 | 0 |  size 4+     |      max dynamic table size change
   +---+---+---+---+--------------+

   +---+---+---+---+---+----------+
   | 0 | 0 | 0 | 0 | D | index 3+ |      literal without indexing 
   +---+---+---+---+---+----------+

   +---+---+---+---+---+----------+
   | 0 | 0 | 0 | 1 | D | index 3+ |      literal never indexed
   +---+---+---+---+---+----------+

Willy