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Re: Stephen Farrell's Discuss on draft-ietf-httpbis-http2-16: (with DISCUSS and COMMENT)

From: Martin Thomson <martin.thomson@gmail.com>
Date: Mon, 26 Jan 2015 11:12:14 -0800
Message-ID: <CABkgnnVhAdCFjQ846-S-NWTjwP7nTpjBQ-mo9rSN+j-fQQMgAQ@mail.gmail.com>
To: Stephen Farrell <stephen.farrell@cs.tcd.ie>
Cc: The IESG <iesg@ietf.org>, Mark Nottingham <mnot@mnot.net>, httpbis-chairs@tools.ietf.org, HTTP Working Group <ietf-http-wg@w3.org>, draft-ietf-httpbis-http2.all@tools.ietf.org
Hi Stephen,

I've collected the edits I've made into a pull request that you can
review at your leisure:

https://github.com/http2/http2-spec/pull/707

On 22 January 2015 at 04:45, Stephen Farrell <stephen.farrell@cs.tcd.ie> wrote:
> 8.2.2 says that clients MUST validate that a proxy is
> configured for the correspondsing request. Since you say
> MUST, don't you need to say what exacftly is meant there?

The text in question:
Clients receiving a pushed response MUST validate that either the
server is authoritative (see Section 10.1), or the proxy that provided
the pushed response is configured for the corresponding request.

I'm not against adding additional clarification here:

"In other words, the client would be willing to send a request for the
identified resource to the server or proxy."

> If that is somewhere here, I'm not seeing it.

>From RFC 7230, from which we reference for this definition explicitly:
   A "<x:dfn>proxy</x:dfn>" is a message-forwarding agent that is
selected by the
   client, usually via local configuration rules, to receive requests
   for some type(s) of absolute URI and attempt to satisfy those
   requests via translation through the HTTP interface.

> (Putting this one first as I'd really like an answer
> but will not be blocking on it no matter how much I
> dislike the answer:-)
>
> - 6.1, and elsewhere, I just want to check that the 256
> octet limit on padding isn't too restrictive a design. Is it
> still possible to say arrange that every response from a
> server has the same size? (Say from a server that is only
> used for serving images and where there could be a 2KB
> variation in file size or something.) I think that can work
> via HEADERS and CONTINUATIONs but wanted to check the limits
> of flexibility here. I'm similarly interested in the limits
> within which a client can add padding to a request, but I
> think the same trick works if it works at all.

We talked to a couple of people who really are doing padding.  It
turns out that no one pads that much.  That 2KB variation, even if it
weren't addressed by the below, is more often broken into sets.

And the padding isn't as limited as it seems: For DATA, padding is
effectively unlimited, because you can just make more padded DATA
frames as you need.  For HEADERS and PUSH_PROMISE, additional padding
can be obtained other ways too.  (A new, dummy header field, for
example.)

> - 3.1: a question on the text to be removed about
> draft-specific identifiers - did the WG consider how to
> handle drafts produced from now until the RFC issues?  I've
> not yet looked to see if there are normative dependencies
> that might lengthen that process, but if there might be it
> could be useful to discuss in the WG if it turns out there
> are a bunch of discusses that might take a while and a few
> versions to sort out. If the IESG eval is clean enough and
> there are no delaying normative refs then that's probably
> not needed.

Well... we discussed it. I believe that the plan was to fight the IESG
tooth and nail if they want to change things.

In practice, that text will remain until the RFC editors gets the
draft.  At that point, if we're making breaking changes, we're not
going to publish.

We have no unresolved normative dependencies.

> - 3.2, the last para before 3.2.1 is hard to read, maybe it
> was added late but it seems to use concepts not yet
> explained at that point (e.g. half-closed) Maybe a forward
> ref to Figure 2 would be enough to fix.

I'll add some forward references.

> - 5.3.4, "can be moved" in 1st sentence - I don't get why
> it's ok to not say MUST or SHOULD there, iff the change is
> as a result of a peer's action. Shouldn't a 404 for a
> dependecy have a predictable impact on the overall page
> load?

Ahh, yes, priorities are advisory.  And removal of old or dead nodes
is largely at the discretion of the implementation.  In an ideal
world, implementations would have infinite state for the
prioritization graph and we wouldn't have to worry about this, but
they don't.

If a node has to be removed, then prioritization information might be
lost, so there isn't much point in being all normative about how to do
it properly.  That is what the remainder of the section is all about:
what the implications of various choices are regarding removal.

> - 6.10, odd that there's no padding here

See above answer.  This is entirely deliberate.

> - 8.1, a bit of abnf here might have helped, ah well

It was suggested.  Didn't happen.  Probably because the whole mess was
less complex at that time.  I blame Julian for insisting we continue
to support 1xx.

> - 8.1.2.3, I assume the underscors in "_:authority_" are a
> typo, if not they are possibly confusing

Yep, a mistake in use of <spanx>.

> - end of p57, does the last para mean that a header field
> value can be split betwee a HEADERS frame and the subsequent
> CONTINUATION frame (with possible padding in between when
> looked at on-the-wire)? If so, then I think you might want
> to be clearer about that since I could see it leading to
> interop issues.

http://http2.github.io/http2-spec/#HeaderBlock explains this already.
I've expanded on this a little.

> - p64, DNS-ID is what (dNSName?)? And "Common Name" might be
> better as commonName, but both probably need a reference.
> (I don't care about nitty capitalisations, but wouldn't some
> coders need to reference?)

Ahh, I used to have a 6125 reference.  Restored.  "Common Name" is now
correctly "CN-ID".

> - 9.1, which TLS library allows a client to know that it'll
> shortly be time to re-key? Doing so is doable, as e.g. NTP
> has a mechanism like that for pre-announcing leap seconds
> I'm told. Buti I'm not sure anyone actually does it at all
> today.

Since we prohibit renegotiation, rekeying won't happen until we get TLS 1.3.

I'm sure that what will happen in practice is that the connection will
suddenly drop.  Until someone happens to get annoyed about that.

In any case, I haven't run the numbers, but I believe that we will run
out of streams first, unless there are large resources (or a
disproportionately large number of TLS records).

> - 9.2.1 - the renegotiation text is confusing. First para on
> that starts with "MUST be disable" next one says "MAY use"
> for client cert confid. I think adding something like "Other
> than as noted below" before the start of  the 1st renego
> para (the 3rd para of 9.2.1) might fix this, but could be
> some more editing would be better.

Fair point.  I've had a bash at making it more appropriately
conditional than that.

> - 9.2.2 - Isn't it sad that there are so many undesirable
> TLS ciphersuites. Sorry about that;-)

Don't apologize.  Help in fixing it would be appreciated though :)

> - 10.1 - I think this could be a lot clearer about which
> pushed things are to be thrown away and I think being
> clearer about that might avoid some future problems.

I think that I'm going to take Richard's expansion here.  Check on his
DISCUSS responses for the outcome of that.

> - 10.5.1 has a few typos, no harm being nice to the RFC
> editor and fixing those if you're pushing out a -17

Yep, a little cleanup always helps.

> - 10.7 - what general purpose padding does TLS1.2 provide?
> I'm sad that this section is so negative - does that
> indicate that people haven't really tried this out so much?
> While it is clear there can be failed attempts at using
> padding to thwart traffic analysis I think having this
> mechanism defined so we can in future learn how to better
> mitigate traffic analysis is a good thing and we ought not
> be so down on that.

TLS 1.2 only pads to block boundaries, for some ciphers.  However,
this is an optimistic forward reference based on a thin hope that TLS
might provide a generic record padding mechanism, like
draft-pironti-....  I still hope for that to come about.

> - For the record, I'm also sad that this isn't all and only
> over TLS with the option of opportunistic security for http:
> schemed URIs but I accept that the wg debated that and
> decided for this.

You are not alone in being sad.  You can take consolation in the fact
that it's not being implemented by some.
Received on Monday, 26 January 2015 19:12:41 UTC

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