Return-Path: X-Original-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com Delivered-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id C80C421F8A0C for ; Sat, 25 May 2013 12:02:00 -0700 (PDT) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -9.976 X-Spam-Level: X-Spam-Status: No, score=-9.976 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_HI=-8] Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id h19V8zQuaod5 for ; Sat, 25 May 2013 12:01:55 -0700 (PDT) Received: from frink.w3.org (frink.w3.org [128.30.52.56]) by ietfa.amsl.com (Postfix) with ESMTP id 6825121F89D5 for ; Sat, 25 May 2013 12:01:52 -0700 (PDT) Received: from lists by frink.w3.org with local (Exim 4.72) (envelope-from ) id 1UgJgl-00087C-HR for ietf-http-wg-dist@listhub.w3.org; Sat, 25 May 2013 18:59:35 +0000 Resent-Date: Sat, 25 May 2013 18:59:35 +0000 Resent-Message-Id: Received: from lisa.w3.org ([128.30.52.41]) by frink.w3.org with esmtp (Exim 4.72) (envelope-from ) id 1UgJgS-00086P-Qo for ietf-http-wg@listhub.w3.org; Sat, 25 May 2013 18:59:16 +0000 Received: from mail-oa0-f46.google.com ([209.85.219.46]) by lisa.w3.org with esmtps (TLS1.0:RSA_ARCFOUR_SHA1:16) (Exim 4.72) (envelope-from ) id 1UgJgM-0001yU-Mh for ietf-http-wg@w3.org; Sat, 25 May 2013 18:59:16 +0000 Received: by mail-oa0-f46.google.com with SMTP id h2so7440067oag.5 for ; Sat, 25 May 2013 11:58:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=twitter.com; s=google; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=4wLw5vlyQhIl+RPp5O56rXIYSNUvh1PmL8I6/Y5CIFs=; b=An8aVOciJMm8djVgFbngi/w3zn2drxjJa8hSCSfbs0PfyWy1ia0fTU7xWJqA/VRAxG wqk3RBUOajcWWX7xWZPZB4TS0bMl+L9Uy+lONQrusnNXwAJeUzTMdrBPpDjkLKZeitzw vcKWdmi1ncHzRmCL8ZG7Zt4/zCOyFJ1LujylI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:x-gm-message-state; bh=4wLw5vlyQhIl+RPp5O56rXIYSNUvh1PmL8I6/Y5CIFs=; b=TeC15iFQC1PP8BFDtxGkR+xNPMSUmiDy8jRV4PY2HWjWDTP5jYKNV7B1kyIRtTKx0t +GrdCmhYPv31Ak2yk/RvKAryQJCPnQRKXn/ZULmD0gxKTkpFb0FsKeQcOc9KWAA89Maf Pp2B2rlxbHZotFbZLmtHE1pV69m2WkHJGyqt66Y5neMnw7N1ImGSw5b1Dleu9F0Vu6RS gJgOnJ42uzqkVlidP56NbKUsq7znYm7WxCz5T7dXNfusnGZUjYULRGLyGiTBzr7lnYJU lg1EUeCM8BWmfpIoFYAJT9ttS4uluNUDg5v4LWF5toBR82FGrl+LtTzIzejVkNMA/znw c0rQ== MIME-Version: 1.0 X-Received: by 10.60.85.74 with SMTP id f10mr15083029oez.32.1369508324353; Sat, 25 May 2013 11:58:44 -0700 (PDT) Received: by 10.182.39.36 with HTTP; Sat, 25 May 2013 11:58:44 -0700 (PDT) In-Reply-To: References: Date: Sat, 25 May 2013 11:58:44 -0700 Message-ID: From: Jeff Pinner To: James M Snell Cc: Roberto Peon , =?UTF-8?B?V2lsbGlhbSBDaGFuICjpmYjmmbrmmIwp?= , Patrick McManus , "ietf-http-wg@w3.org" Content-Type: multipart/alternative; boundary=089e0111b71c30b9f004dd8f81ff X-Gm-Message-State: ALoCoQnkelj5zEl+RGEmFjQa3hQxBWl7UIoFE9GewvD+64f/62oghnpp2BVmnfzexFF3LquPD656 Received-SPF: pass client-ip=209.85.219.46; envelope-from=jpinner@twitter.com; helo=mail-oa0-f46.google.com X-W3C-Hub-Spam-Status: No, score=-3.9 X-W3C-Hub-Spam-Report: AWL=-3.100, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001 X-W3C-Scan-Sig: lisa.w3.org 1UgJgM-0001yU-Mh 50127025a99e679d044e240f22d477c2 X-Original-To: ietf-http-wg@w3.org Subject: Re: Design Issue: Separate HEADERS and PRIORITY Frames, Eliminate HEADERS+PRIORITY Archived-At: Resent-From: ietf-http-wg@w3.org X-Mailing-List: archive/latest/18089 X-Loop: ietf-http-wg@w3.org Resent-Sender: ietf-http-wg-request@w3.org Precedence: list List-Id: List-Help: List-Post: List-Unsubscribe: --089e0111b71c30b9f004dd8f81ff Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable The color of my shed: I would like to see us remove HEADERS+PRIORITY entirely and add a separate PRIORITY frame. I don't agree that separating them will simply cause an additional 4 bytes to be sent on every request. While it might be true that most browsers will set the priority of a request, I don't think that all clients necessarily will (I have a mobile client that uses HTTP for API requests and have not found the priority mechanism necessary -- at least not yet). I could imagine that it would be acceptable to send the PRIORITY frame before the HEADERS frame and still mandate that HEADERS frames (and now only HEADERS frames) initiate streams. While this does cause some extra state allocation, we already have to do something similar with PUSH_PROMISE where we must track that the "stream identifier MUST be a valid choice for the next stream sent" and then initiate the stream later. This would also give us a mechanism to send priority changes for outstanding requests at the framing layer, and could allow priorities to be set for pushed responses should it prove useful. - Jeff On Tue, May 21, 2013 at 2:55 PM, James M Snell wrote: > On Tue, May 21, 2013 at 2:43 PM, Roberto Peon wrote: > > Sending the PRIORITY frame *MUST* cause state allocation at the receive= r, > > else it was useless to send before the HEADERS frame. As you point out, > at > > minimum it must allocate a stream ID and priority field, and for most > > implementations it will also need to include so mechanism of pointing o= ut > > that the headers don't exist, so, probably between 16 to 24 bytes worth > of > > allocation on a 64 bit machine. > > > > Sorry, I wasn't clear in my initial response. Yes, there is some state > that would need to be allocated but not the same as that when the > initial HEADERS frame is received, for instance. > > > If the PRIORITY frame was renamed to CHANGE_PRIORITY, would that clarif= y > > anything? Priority changing is the current intent of that frame type. > > > > Not particularly, because we'd still have the question of when to use > HEADERS+PRIORITY vs. the combination of HEADERS and a CHANGE_PRIORITY. > Can HEADERS+PRIORITY be used any time? For instance, could I send an > initial HEADERS frame on a stream then later send a HEADERS+PRIORITY > on the same stream? I honestly don't care how it ultimately ends up so > long as (a) It's the simplest thing that could possibly work and (b) > Is easy to explain in the spec and easy for a developer to implement. > > > btw, I am not particularly partial to the "any frame opening up a strea= m" > > thing. I'm not completely against it though :) > > My reason for slightly preferring that streams must begin with HEADERS = or > > HEADERS+PRIORITY is that it is an explicit statement of intent, and thu= s > > off-by-one, uninitialized var, etc. errors are more likely to be > detectable > > in a world where such is required. > > > > I would very much like to see us mandate that streams always initiate > with a HEADERS / HEADERS+PRIORITY frame. > > - James > > > > > > > -=3DR > > > > > > On Tue, May 21, 2013 at 2:19 PM, James M Snell > wrote: > >> > >> On Tue, May 21, 2013 at 10:30 AM, William Chan (=E9=99=88=E6=99=BA=E6= =98=8C) > >> wrote: > >> > Thanks for describing these cases now. I had not thought of them. > >> > > >> > If everyone's sold on reprioritization, then let's go ahead and do > this > >> > and > >> > have the debate about ditching HEADERS+PRIORITY or not. I want to ke= ep > >> > it. I > >> > don't like the idea of sending a PRIORITY frame first. Is sending a > >> > PRIORITY > >> > frame going to trigger stream state allocation at the receiver? What= 's > >> > the > >> > expectation? And if you don't have a priority for the HEADERS, then > you > >> > have > >> > the race that Roberto described. > >> > > >> > >> There is no reason to assume that sending a PRIORITY frame first would > >> trigger stream state allocation at the receiver. At most, it would > >> reserve the stream ID and store the priority value. The full state > >> allocation would not occur until the HEADERS frame is received. That > >> said, I'm not 100% dead set on removing HEADERS+PRIORITY, I would just > >> like to simplify the protocol where it makes sense to, and even then > >> only after it's been proven out in implementation. Having separate > >> HEADERS, HEADERS+PRIORITY and PRIORITY frames is confusing, if we can > >> do without separating them, we ought to do so. > >> > >> - James > >> > >> > > >> > On Tue, May 21, 2013 at 2:09 PM, Patrick McManus < > pmcmanus@mozilla.com> > >> > wrote: > >> >> > >> >> > >> >> On Tue, May 21, 2013 at 12:32 PM, William Chan (=E9=99=88=E6=99=BA= =E6=98=8C) > >> >> wrote: > >> >>> > >> >>> > >> >>> I support adding a new additional PRIORITY frame for stream > >> >>> reprioritization. > >> >> > >> >> > >> >> me too. Specifically I support this as a mechanism for the client t= o > be > >> >> able to explicitly prioritize an open pushed stream. I can wait for > >> >> more > >> >> evidence about re-prioritizing, but in cases where the client hasn'= t > >> >> ever > >> >> explicitly set the stream's priority I think we have evidence that > its > >> >> time > >> >> to do something. > >> >>> > >> >>> > >> >>> Unless there's a reason this needs to be in the current http/2 dra= ft > >> >>> sooner rather than later, I'd rather punt on this discussion until > we > >> >>> have > >> >>> implementation experience that can guide this debate. > >> >> > >> >> > >> >> I think there is experience here specifically related to push. > >> >> > >> >> e.g. You can easily configure mod_spdy to push images when html is > >> >> pulled. > >> >> but you can't effectively dictate the relative priorities of those > two > >> >> things. > >> >> > >> >> Sure, you can define an explicit priority for those images but > priority > >> >> implementations are all about relative levels and the client set th= e > >> >> priority of the html. > >> >> > >> >> You can argue that mod_spdy should have defined relative priorities > >> >> (+/- > >> >> the associated stream) instead of constants.. that would be better > but > >> >> the > >> >> client still has no way to make sure those streams are at a higher > >> >> priority > >> >> than a "save as" background stream (I've seen this one happen as > >> >> mod_spdy > >> >> defaults to lowest priority when pushing), or a lower priority than= a > >> >> real-time video stream.. > >> >> > >> >> plus there is no scale for the server to work with.. it might set a > +2 > >> >> priority for pushed images but the client might be using +3 for > pulled > >> >> images causing a mismatch in something that was intended to be > equally > >> >> weighted. > >> >> > >> >> at least with a priority frame the client can make those adjustment= s > in > >> >> a > >> >> RTT. > >> >> > >> >> Cheefully, > >> >> -Patrick > >> >> > >> >> > >> > > >> > > >> > > > > --089e0111b71c30b9f004dd8f81ff Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
The color of my shed:

I would like to s= ee us remove HEADERS+PRIORITY entirely and add a separate PRIORITY frame.

I don't agree that separating them = will simply cause an additional 4 bytes to be sent on every request. While = it might be true that most browsers will set the priority of a request, I d= on't think that all clients necessarily will (I have a mobile client th= at uses HTTP for API requests and have not found the priority mechanism nec= essary -- at least not yet).

I could imagine that it would be acceptable= to send the PRIORITY frame before the HEADERS frame and still mandate that= HEADERS frames (and now only HEADERS frames) initiate streams. While this = does cause some extra state allocation, we already have to do something sim= ilar with PUSH_PROMISE where we must track that the "stream identifier= MUST be a valid choice for the next stream sent" and then initiate th= e stream later.

This would also give us a mechanism to send= priority changes for outstanding requests at the framing layer, and could = allow priorities to be set for pushed responses should it prove useful.

- Jeff


On Tue, May 21, 2013 at 2:55 PM, James= M Snell <jasnell@gmail.com> wrote:
On Tue, May 21, 2013 at 2:= 43 PM, Roberto Peon <grmocg@gmail.co= m> wrote:
> Sending the PRIORITY frame *MUST* cause state allocation at the receiv= er,
> else it was useless to send before the HEADERS frame. As you point out= , at
> minimum it must allocate a stream ID and priority field, and for most<= br> > implementations it will also need to include so mechanism of pointing = out
> that the headers don't exist, so, probably between 16 to 24 bytes = worth of
> allocation on a 64 bit machine.
>

Sorry, I wasn't clear in my initial response. Yes, there is some = state
that would need to be allocated but not the same as that when the
initial HEADERS frame is received, for instance.

> If the PRIORITY frame was renamed to CHANGE_PRIORITY, would that clari= fy
> anything? Priority changing is the current intent of that frame type.<= br> >

Not particularly, because we'd still have the question of when to= use
HEADERS+PRIORITY vs. the combination of HEADERS and a CHANGE_PRIORITY.
Can HEADERS+PRIORITY be used any time? For instance, could I send an
initial HEADERS frame on a stream then later send a HEADERS+PRIORITY
on the same stream? I honestly don't care how it ultimately ends up so<= br> long as (a) It's the simplest thing that could possibly work and (b) Is easy to explain in the spec and easy for a developer to implement.

> btw, I am not particularly partial to the "any frame opening up a= stream"
> thing. I'm not completely against it though :)
> My reason for slightly preferring that streams must begin with HEADERS= or
> HEADERS+PRIORITY is that it is an explicit statement of intent, and th= us
> off-by-one, uninitialized var, etc. errors are more likely to be detec= table
> in a world where such is required.
>

I would very much like to see us mandate that streams always initiate=
with a HEADERS / HEADERS+PRIORITY frame.

- James

>
>
> -=3DR
>
>
> On Tue, May 21, 2013 at 2:19 PM, James M Snell <jasnell@gmail.com> wrote:
>>
>> On Tue, May 21, 2013 at 10:30 AM, William Chan (=E9=99=88=E6=99=BA= =E6=98=8C)
>> <willchan@chromium.org= > wrote:
>> > Thanks for describing these cases now. I had not thought of t= hem.
>> >
>> > If everyone's sold on reprioritization, then let's go= ahead and do this
>> > and
>> > have the debate about ditching HEADERS+PRIORITY or not. I wan= t to keep
>> > it. I
>> > don't like the idea of sending a PRIORITY frame first. Is= sending a
>> > PRIORITY
>> > frame going to trigger stream state allocation at the receive= r? What's
>> > the
>> > expectation? And if you don't have a priority for the HEA= DERS, then you
>> > have
>> > the race that Roberto described.
>> >
>>
>> There is no reason to assume that sending a PRIORITY frame first w= ould
>> trigger stream state allocation at the receiver. At most, it would=
>> reserve the stream ID and store the priority value. The full state=
>> allocation would not occur until the HEADERS frame is received. Th= at
>> said, I'm not 100% dead set on removing HEADERS+PRIORITY, I wo= uld just
>> like to simplify the protocol where it makes sense to, and even th= en
>> only after it's been proven out in implementation. Having sepa= rate
>> HEADERS, HEADERS+PRIORITY and PRIORITY frames is confusing, if we = can
>> do without separating them, we ought to do so.
>>
>> - James
>>
>> >
>> > On Tue, May 21, 2013 at 2:09 PM, Patrick McManus <pmcmanus@mozilla.com>
>> > wrote:
>> >>
>> >>
>> >> On Tue, May 21, 2013 at 12:32 PM, William Chan (=E9=99=88= =E6=99=BA=E6=98=8C)
>> >> <willchan@chr= omium.org> wrote:
>> >>>
>> >>>
>> >>> I support adding a new additional PRIORITY frame for = stream
>> >>> reprioritization.
>> >>
>> >>
>> >> me too. Specifically I support this as a mechanism for th= e client to be
>> >> able to explicitly prioritize an open pushed stream. I ca= n wait for
>> >> more
>> >> evidence about re-prioritizing, but in cases where the cl= ient hasn't
>> >> ever
>> >> explicitly set the stream's priority I think we have = evidence that its
>> >> time
>> >> to do something.
>> >>>
>> >>>
>> >>> Unless there's a reason this needs to be in the c= urrent http/2 draft
>> >>> sooner rather than later, I'd rather punt on this= discussion until we
>> >>> have
>> >>> implementation experience that can guide this debate.=
>> >>
>> >>
>> >> I think there is experience here specifically related to = push.
>> >>
>> >> e.g. You can easily configure mod_spdy to push images whe= n html is
>> >> pulled.
>> >> but you can't effectively dictate the relative priori= ties of those two
>> >> things.
>> >>
>> >> Sure, you can define an explicit priority for those image= s but priority
>> >> implementations are all about relative levels and the cli= ent set the
>> >> priority of the html.
>> >>
>> >> You can argue that mod_spdy should have defined relative = priorities
>> >> (+/-
>> >> the associated stream) instead of constants.. that would = be better but
>> >> the
>> >> client still has no way to make sure those streams are at= a higher
>> >> priority
>> >> than a "save as" background stream (I've se= en this one happen as
>> >> mod_spdy
>> >> defaults to lowest priority when pushing), or a lower pri= ority than a
>> >> real-time video stream..
>> >>
>> >> plus there is no scale for the server to work with.. it m= ight set a +2
>> >> priority for pushed images but the client might be using = +3 for pulled
>> >> images causing a mismatch in something that was intended = to be equally
>> >> weighted.
>> >>
>> >> at least with a priority frame the client can make those = adjustments in
>> >> a
>> >> RTT.
>> >>
>> >> Cheefully,
>> >> -Patrick
>> >>
>> >>
>> >
>> >
>>
>


--089e0111b71c30b9f004dd8f81ff--