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Re: Design: Adding ASSOCIATED_ONLY

From: Martin Thomson <martin.thomson@gmail.com>
Date: Wed, 19 Jun 2013 11:07:35 -0700
Message-ID: <CABkgnnUKnborWAtuxwEvWx7wR=JYdOTvWHbpPd6NJ5kXK0Sw9A@mail.gmail.com>
To: James M Snell <jasnell@gmail.com>
Cc: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
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.
Received on Wednesday, 19 June 2013 18:08:03 UTC

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