On Tue, Jul 7, 2015 at 1:02 AM, Robert Sparks
<rjsparks(_at_)nostrum(_dot_)com>
wrote:
(adding the hybi list)
Hi Robert,
Sorry for delay.
It seems to me that this effectively adding an actor (the intermediary) ,
and defining (not as explicitly as I think it needs to be) protocol
mechanics for that actor in ways that the base specification did not
anticipate.
Done more archaeology...
This text originates from the intermediaries section introduced on update
between
draft-tyoshino-hybi-websocket-perframe-deflate-06 and
draft-ietf-hybi-websocket-perframe-compression-00
I couldn't find the original proposal which led to this text from my mail
box. I thought someone made one on HyBi, but only found my comment on
publish of -00.
As far as I remember, we initially didn't intend to add any requirement,
expectation, etc. to the main (RFC 6455) spec by this spec. The text now
looks like an additional requirements to complement the main spec just
unexpectedly (unexpectedly at least for me). I added this text just to note
a fact that when one wants to change compression, handshake should be also
altered appropriately, otherwise, it doesn't work. Maybe the following
texts in RFC 6455 have a similar role.
o As control frames cannot be fragmented, an intermediary MUST NOT ...
o An intermediary MUST NOT change the fragmentation of a message if ...
o An intermediary MUST NOT change the fragmentation of any message ...
I'm not comfortable that the consequences of these new mechanics
(specifically - that the intermediary can directly participate in the
extension negotiations, and change the results) are well understood.
Did you mean "not well understood"?
The additions to the text you propose will certainly help point out that
there might be some, and the message that the endpoint won't have insight
into how its messages are handled beyond the intermediary needs to be
prominent.
Yeah. But now I'm wondering if it's in the scope of protocol
standardization or not. Seems the text should be changed to look like a
warning (don't do this or your stack won't work) as discussed above.
But I wonder if the mechanics of an intermediary _changing the protocol
signalling_ is something the working group should explicitly work on
writing down?
I've been viewing the PMCE from the view point of a browser developer.
Like fragmentation, permessage-deflate is also just a transport-level thing
which is invisible/transparent to the final user of the communication (e.g.
JavaScript using the WebSocket API). My comments are based on this idea.
But with your comment, I just noticed that it's not trivial.
Actually, the extensions under use is exposed to the user of the protocol
via _Extensions in Use_. We should have been aware of that.
RjS
On 6/30/15 3:42 AM, Takeshi Yoshino wrote:
Thank you for review, Robert.
On Thu, Jun 25, 2015 at 6:18 AM, Robert Sparks
<rjsparks(_at_)nostrum(_dot_)com>
wrote:
I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG. These comments were written primarily for the benefit of the
security area directors. Document editors and WG chairs should treat
these comments just like any other last call comments.
Summary: Ready with issues
(fwiw, I also reviewed up through version -24).
Section 7 (Intermediaries) should be more explicit that it's talking about
an intermediary doing compression on one side and not (or doing different
compression) on the other.
(If that's not what it's trying to set up, please clarify).
OK. So, I'd like to change the text as follows:
When an intermediary proxies ... Per-message Compression of messages
received from one peer, and then forward the messages to the other peer, if
the intermediary ...
It's not clear from reading RFC6455 that the idea of intermediaries
changing the contents of the websocket extension negotiation mechanism was
considered - have I missed the text in that RFC that discusses that?
Are there other extensions that suggest similar behavior? It's not
immediately clear that the protocol mechanics do the right thing when the
different negotiations on each side of the proxy fail differently.
It's not well discussed in RFC6455. Right. AFAIK, there's no such
extension defined, yet.
I understand that this text (intermediary section in the I-D) works
just not to disallow change of compression but there's nothing in RFC6455
that guarantees that such transformation doesn't cause any issue with other
infrastructure of the WebSocket protocol.
I believe that unless any extension that interferes with the other
negotiated extensions (e.g. counting the number of negotiated extensions,
relying on PMCE, etc.), the core WebSocket protocol (things defined in
RFC6455) should work. If such an extension is introduced, it would be just
considered to be incompatible with PMCEs, or that extension should describe
how to coordinate with change on PMCE in the intermediaries section of its
RFC.
I think this is more reasonable than prohibiting change on Per-message
Compression by intermediaries.
This also seems to put an endpoint in a position where it has no say on
what an intermediary does with the traffic on the other side of it. Is that
worth discussing in the document?
Ah, right. Maybe some text like:
"It's not guaranteed that the PMCE which an endpoint has negotiated in
the opening handshake is preserved in the whole path to the peer endpoint."
It would be good to point to, or provide, a discussion of how the
extension negotiation mechanism in WebSockets is meant to be protected.
As a general discussion to cover other extensions (if they want. by
referring to this to-be-RFC) like the section defining terms to complement
RFC6455 [1]?
[1]
https://tools.ietf.org/html/draft-ietf-hybi-permessage-compression-24#section-3