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Re: #466 segment compression

From: Roberto Peon <grmocg@gmail.com>
Date: Tue, 29 Apr 2014 12:57:54 -0700
Message-ID: <CAP+FsNdiwq0n0w-SBDacGJen=0pb=QAuYQOzu-Us=z3NjcVjkQ@mail.gmail.com>
To: K.Morgan@iaea.org
Cc: Matthew Kerwin <matthew@kerwin.net.au>, HTTP Working Group <ietf-http-wg@w3.org>, Martin Thomson <martin.thomson@gmail.com>
If compression is per-segment as opposed to per-frame
   AND we wish to restrict the amount of state the server must keep around
   AND the sender wishes to have all the data in the segment compressed
  THEN then the segment being compressed must be sent in its entirety in a
contiguous series of frames with no muxing of other streams in the middle.

If one doesn't do this, then the server is forced to retain this state
indefinitely, though the client is allowed to make progress on other
streams. This likely masks the consumption of server-state from the user,
and also denies the user(and client) the ability to do compression for any
other stream.

If one does this, then one effectively loses the multiplexing feature of
the protocol.

Arguably, this is worse than simply doing per-frame compression, especially
when on considers that with relatively decent frame sizes, the marginal
benefit of continuing the compression context across frames is likely small.


Now, lets assume the part above is wrong because I've misinterpreted
something. :)

I'm still worried: There is an assumption here that the originator of the
stream actually knows the provenance of the various data within. This is
often a hard problem especially given that servers and services are not
currently architected to keep track of provenance. IMHO, if a segment/frame
wasn't compressed it should never be compressed. That leads to safety.


If the proposal is simply that if any frame in a segment is compressed all
of something in a segment can be compressed, sure. I'm on board with that.

-=R



On Tue, Apr 29, 2014 at 1:41 AM, <K.Morgan@iaea.org> wrote:

>  I think the simplest idea is to require the origin to separate
> attacker-controlled data and private/confidential data by segments.  All of
> the rest of the intermediary problems go away since an intermediary already
> can’t re-frame across segment boundaries, plus it allows an intermediary to
> do whatever it wants within a segment
> (compress/uncompress/concatenate/de-compress+re-compress).
>
>
>
> The thing I like about Martin’s idea to switch to one compression context
> per segment is that it provides greater compatibility between HTTP/1.x T-E
> and HTTP/2 transfer codings.  Per-frame compression as we have it now is
> compatible with T-E when going from 2 -> 1.x, but it’s not compatible from
> 1.x -> 2.  The added complexity and the “vast increase in DoS surface area”
> [1] is a big deal though.
>
>
>
> [1] https://github.com/http2/http2-spec/issues/466#issuecomment-41361711
>
>
>
>
>
>
>
> --
>
> Keith S. Morgan
>
> Remote Monitoring Unit
>
> Safeguards, International Atomic Energy Agency (IAEA)
>
> Vienna, Austria
>
> Office: +43 1 2600 26672
>
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>
>
> *From:* phluid61@gmail.com [mailto:phluid61@gmail.com] *On Behalf Of *
> matthew@kerwin.net.au
> *Sent:* Tuesday,29 April 2014 08:53
> *To:* ietf-http-wg@w3.org
> *Cc:* Martin Thomson
> *Subject:* Re: #466 segment compression
>
>
>
> Sorry for replying to myself.
>
>
>
> On 29 April 2014 16:26, Matthew Kerwin <matthew@kerwin.net.au> wrote:
>
> All three operations (determining frame length, compressing frames, and
> padding) are hop-by-hop operations, and any intermediary can second-guess
> or obstinately undo the previous hop's choices if it wants.
>
>
>
>
>
> ​I just noticed the ​bit in 10.6 that says that intermediaries can't add
> compression. Is that the delineation to which you referred in #466 Martin?
>  That text introduces complexity I hadn't imagined when proposing per-frame
> compression. I'll think about it some more.
>
>
>
>
>
> --
>
>   Matthew Kerwin
>   http://matthew.kerwin.net.au/
>
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Received on Tuesday, 29 April 2014 19:58:22 UTC

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