Re: Design: Adding ASSOCIATED_ONLY
Jeff Pinner <jpinner@twitter.com> Wed, 19 June 2013 19:57 UTC
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Date: Wed, 19 Jun 2013 12:55:55 -0700
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From: Jeff Pinner <jpinner@twitter.com>
To: James M Snell <jasnell@gmail.com>
Cc: Mike Belshe <mike@belshe.com>, "William Chan (陈智昌)" <willchan@chromium.org>, Martin Thomson <martin.thomson@gmail.com>, "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
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Subject: Re: Design: Adding ASSOCIATED_ONLY
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Thanks for finding that in the SPDY spec! You're right, I totally missed reading that line. I'm happy to wait on adding the flag but I would like to drop the requirement that a server close all associated resources. In the SPDY spec the life-cycles of the pushed resources were much more tightly coupled with the original stream because there was no PUSH_PROMISE so all streams had to be created while the original stream was still open. With PUSH_PROMISE, the opening of the new streams can occur well after the original stream closes so this behavior no longer makes and sense. On Wed, Jun 19, 2013 at 12:50 PM, James M Snell <jasnell@gmail.com> wrote: > In the short term (for the implementer's draft) I'm perfectly fine > deferring this particular item, I just wanted to make sure the issue > was documented and available for discussion. The pull request has been > submitted and can easily sit there for a bit while we figure the other > items out :-) ... > > On Wed, Jun 19, 2013 at 12:46 PM, Mike Belshe <mike@belshe.com> wrote: > > > > > > > > On Wed, Jun 19, 2013 at 12:41 PM, William Chan (陈智昌) < > willchan@chromium.org> > > wrote: > >> > >> It's vague in the SPDY 3 spec but is definitely there, just not in the > >> RST_STREAM section. See > >> > http://dev.chromium.org/spdy/spdy-protocol/spdy-protocol-draft3#TOC-3.3.2-Client-implementation > : > >> > >> "To cancel all server push streams related to a request, the client may > >> issue a stream error (Section 2.4.2) with error code CANCEL on the > >> associated-stream-id. By cancelling that stream, the server MUST > immediately > >> stop sending frames for any streams with in-association-to for the > original > >> stream." > >> > >> Patrick's right and no implementation of server push has read that > >> section. I raised this point at least twice at the interim meeting. > >> Roberto's counterpoint (from the meeting) is that adding a flag for this > >> makes it explicit, so it won't be as easily forgotten. > > > > > > And so it seems that even people that wrote that spec have forgotten! :-) > > > > But, given what we know now, I still think that sending RST_STREAM for > each > > stream is sufficient and simplest. > > > > Mike > > > > > >> > >> > >> I'm personally lukewarm on this and would rather be explicit and send > all > >> the RST_STREAMs. But I don't have a strong opinion here. > >> > >> > >> > >> On Wed, Jun 19, 2013 at 11:43 AM, Jeff Pinner <jpinner@twitter.com> > wrote: > >>> > >>> I'm going to put the PRIORITY discussion aside for a second and only > >>> comment on RST_STREAMs. > >>> > >>> I believe Patrick is correct -- I don't think anyone who implemented > SPDY > >>> implemented RST_STREAM as closing all associated streams. But IIRC > that's > >>> because that isn't how it is specified in the SPDY/3 spec. SPDY/3 > Section > >>> 3.3 mentions Push and RST_STREAM but only talks about issuing a RST on > the > >>> pushed Stream-ID. > >>> > >>> I think the requirement was added for HTTP/2 and isn't desirable. This > >>> was the reason we considered adding the ASSOCIATED flag in the first > place. > >>> We wanted to clarify this issue and provide a mechanism while dropping > the > >>> new requirement. > >>> > >>> > >>> > >>> > >>> > >>> > >>> On Wed, Jun 19, 2013 at 11:26 AM, James M Snell <jasnell@gmail.com> > >>> wrote: > >>>> > >>>> Not very contrived use case: Switching away from one browser tab with > >>>> N-active push streams. Without this, we would need to send PRIORITY > >>>> frames for each individual pushed stream, which is bad. > >>>> > >>>> At the interim, as part of the updated lifecycle discussions, we all > >>>> seemed to agree that the lifecycle of push streams was independent of > >>>> the originating stream, given that, if I close a browser tab with > >>>> N-active push streams, I would have to send a separate RST_STREAM for > >>>> every push stream in addition to the originating stream. This > >>>> eliminates that need. > >>>> > >>>> You're right that this would be unnecessary if push was disabled, but > >>>> we are building push into the base protocol so we have to be able to > >>>> efficiently handle the case where push is not disabled. There's no way > >>>> around that. > >>>> > >>>> While I am quite sympathetic to the "let's not add stuff we really > >>>> don't need" point of view, ASSOCIATED_ONLY makes a lot of sense in my > >>>> opinion, and would make it easier and more efficient to implement the > >>>> "independent stream lifecycle" notion. > >>>> > >>>> On Wed, Jun 19, 2013 at 11:13 AM, Mike Belshe <mike@belshe.com> > wrote: > >>>> > Is there a specific use case that needs this? > >>>> > > >>>> > I suspect there are two camps of browsers: > >>>> > - those that disable push > >>>> > - those that don't disable push > >>>> > > >>>> > If you disabled push, then these aren't needed. > >>>> > > >>>> > If you didn't disable push, do you really need to be able to deal > with > >>>> > batch > >>>> > operations on associated streams? (I know we can contrive a > use-case > >>>> > on the > >>>> > fly right now - that is always possible. But if we don't *really* > >>>> > need it, > >>>> > its just more stuff in the protocol I'd rather omit until we really > >>>> > know > >>>> > that it is needed.) > >>>> > > >>>> > Thanks, > >>>> > Mike > >>>> > > >>>> > > >>>> > > >>>> > On Wed, Jun 19, 2013 at 11:07 AM, Martin Thomson > >>>> > <martin.thomson@gmail.com> > >>>> > wrote: > >>>> >> > >>>> >> On 19 June 2013 10:56, James M Snell <jasnell@gmail.com> wrote: > >>>> >> > https://github.com/http2/http2-spec/pull/144 > >>>> >> > > >>>> >> > This was a technical change brought up and discussed as part of > the > >>>> >> > "layering taskforce" breakout but was never discussed in the > larger > >>>> >> > interim discussions. > >>>> >> > > >>>> >> > Essentially, this PR would add an "ASSOCIATED_ONLY" flag to > >>>> >> > PRIORITY > >>>> >> > and RST_STREAM frames that would allow terminating and > >>>> >> > reprioritizing > >>>> >> > promised streams as a group. > >>>> >> > > >>>> >> > Sending PRIORITY(ASSOCIATED_ONLY) would ONLY set the priority for > >>>> >> > associated streams, not the referenced stream. > >>>> >> > > >>>> >> > Sending RST_STREAM(ASSOCIATED_ONLY) would terminate ONLY the > >>>> >> > associated streams, not the referenced stream. > >>>> >> > > >>>> >> > Without this, we would have to send PRIORITY and RST_STREAM for > >>>> >> > each > >>>> >> > individual associated stream, which is obviously quite > inefficient. > >>>> >> > >>>> >> What James omits is: > >>>> >> > >>>> >> RST_STREAM is currently specified to terminate all associated > streams > >>>> >> in addition to the parent stream. This would remove this coupling, > >>>> >> which is considered by some to be problematic. > >>>> >> > >>>> >> It's not possible to reprioritise associated streams as a group. > We > >>>> >> did agree that associated streams would inherit a priority that is > >>>> >> lower (by one) than the parent stream. As it stands, changing all > of > >>>> >> them requires first discovering the stream ID that will be used, > then > >>>> >> sending individual PRIORITY frames for each. > >>>> >> > >>>> >> There's not a lot of experience with this area of the > specification. > >>>> >> > >>>> > > >>>> > >>> > >> > > >
- Re: Design: Adding ASSOCIATED_ONLY Jeff Pinner
- Design: Adding ASSOCIATED_ONLY James M Snell
- Re: Design: Adding ASSOCIATED_ONLY Martin Thomson
- Re: Design: Adding ASSOCIATED_ONLY Mike Belshe
- Re: Design: Adding ASSOCIATED_ONLY Patrick McManus
- Re: Design: Adding ASSOCIATED_ONLY James M Snell
- Re: Design: Adding ASSOCIATED_ONLY Mike Belshe
- Re: Design: Adding ASSOCIATED_ONLY William Chan (陈智昌)
- Re: Design: Adding ASSOCIATED_ONLY Mike Belshe
- Re: Design: Adding ASSOCIATED_ONLY Mike Belshe
- Re: Design: Adding ASSOCIATED_ONLY James M Snell
- Re: Design: Adding ASSOCIATED_ONLY Jeff Pinner
- Re: Design: Adding ASSOCIATED_ONLY Patrick McManus
- Re: Design: Adding ASSOCIATED_ONLY Martin Thomson
- Re: Design: Adding ASSOCIATED_ONLY Mike Belshe
- Re: Design: Adding ASSOCIATED_ONLY Amos Jeffries
- Re: Design: Adding ASSOCIATED_ONLY James M Snell
- Re: Design: Adding ASSOCIATED_ONLY Amos Jeffries