Re: Design: Adding ASSOCIATED_ONLY
James M Snell <jasnell@gmail.com> Wed, 19 June 2013 19:51 UTC
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From: James M Snell <jasnell@gmail.com>
Date: Wed, 19 Jun 2013 12:50:01 -0700
Message-ID: <CABP7RbdR6XXP4oS5sK1HBkrz04NBJ7KV0wdymmfSYmWRnJVHGQ@mail.gmail.com>
To: Mike Belshe <mike@belshe.com>
Cc: "William Chan (陈智昌)" <willchan@chromium.org>, Jeff Pinner <jpinner@twitter.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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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