Re: Design: Adding ASSOCIATED_ONLY
Mike Belshe <mike@belshe.com> Wed, 19 June 2013 19:46 UTC
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Date: Wed, 19 Jun 2013 12:45:18 -0700
Message-ID: <CABaLYCubcMg6xKUftgw_fNL9ufUApLqBFf6TSZZ0B-ex3LVm7w@mail.gmail.com>
From: Mike Belshe <mike@belshe.com>
To: "William Chan (陈智昌)" <willchan@chromium.org>
Cc: Jeff Pinner <jpinner@twitter.com>, James M Snell <jasnell@gmail.com>, 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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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. > > 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