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Re: First cut of Huffman encoding in compression document.

From: Fred Akalin <akalin@google.com>
Date: Thu, 17 Oct 2013 14:45:47 -0700
Message-ID: <CANUYc_QFpMxOzOMaWQNCDp_Myov8Sqz+gpo6ynbU0YVwB9WBvQ@mail.gmail.com>
To: Roberto Peon <grmocg@gmail.com>
Cc: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>, HTTP Working Group <ietf-http-wg@w3.org>
Thanks, makes sense. Your replies address all my concerns.

On Thu, Oct 17, 2013 at 2:32 PM, Roberto Peon <grmocg@gmail.com> wrote:

>
> I've closed the issue, though we can reopen. Please check the literal
> encoding section in the header compression document (in github). I hope
> this clarifies things quite a bit.
>
>
> On Thu, Oct 17, 2013 at 2:15 PM, Fred Akalin <akalin@google.com> wrote:
>
>> Initial comments:
>>
>> - I may be missing something, but I'm not sure why we need a string
>> literal to be both length-delimited and have an end marker. I'd prefer just
>> having the length and assigning the short encoding for EOS to something
>> else.
>>
>
> Since length is in bytes instead of bits, but huffman encoded things are
> bit based, you need either to represent length in bits (which makes the
> lengths bigger), or you need to ensure that the padding used to get to the
> next byte boundary at the end of the string cannot be interpreted as a
> valid huffman-code. What is in the document now is essentially what you've
> requested. EOS is a code which is guaranteed to be 7 bits long or greater
> and have no semantic meaning.
>
>
>
>> - Do we gain that much by having separate tables for request and
>> response? I was looking forward to not having to make a distinction between
>> request/response contexts since we now have a single static table, but this
>> separation blocks that again.
>>
>
> The tables are fairly different. You may want to experiment to see if it
> is worth removing one. I still wonder if it is worthwhile to have a
> separate one for cookies and the other for everything else (never did get
> around to testing that).
>
>
>> - I can see it being useful to encode both the Huffman-encoded length and
>> the original length of the string (or the delta between them), so that
>> buffers can be sized just once.
>>
>
> That would bloat the on-the-wire format a fair bit. I'm hoping that we end
> up storing the huffman-encoded values instead of the actual bytes in many
> cases in the future.
>
> -=R
>
>
Received on Thursday, 17 October 2013 21:46:14 UTC

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