[quicwg/base-drafts] Stream correlation in Transport (#672)

[Mike Bishop <[e-mail]>]

This is an augmentation of @martinthomson's PR to add stream correlation, as promised.

# Major changes

Leveraging @igorlord's insight that OO=00 only occurs on the first STREAM frame of a stream, I used that as the trigger for a Stream Properties byte.  Two bits of that byte describe the directionality of the stream:

- Unidirectional (no response expected)
- Initial bidirectional (one response expected)
- Initial multi-response (one or more responses expected; needs a better name)
- Response

If the type is Response, there's an Associated Stream ID field, length given by two more bits following the same pattern as the SS bits in the STREAM frame ID.

# Personal Opinion

On the plus side, these stream types seem to cover the abstractions I can envision for most applications.  You can unilaterally send something (unidirectional), do request/response (bidirectional), or pub/sub (single subscription stream, series of update streams).

I don't care for the fact that I still need the stream type header in HTTP after putting this in the transport.  That will be ameliorated if we go back to one stream per request, since all unidirectional streams will be push streams.  (As a side-note, I considered using the multiple-response option in the HTTP mapping, but then I need a stream header again to indicate which is the response and which the pushes.)

I particularly don't like that you now have to look at the frame type header to find out whether a field exists which tells you the length of something else in the header.  I'd like to simplify that.  I went with this model over a CREATE_STREAM frame because of @mikkelfj's use-case of very small messages -- this adds only one byte to the first frame on a stream in one direction and 2-5 bytes to the first frame of response streams.  A separate frame type would be somewhat larger, but could be cleaner in that respect.
You can view, comment on, or merge this pull request online at:

  https://github.com/quicwg/base-drafts/pull/672

-- Commit Summary --

  * Add stream correlation at the transport layer
  * Merge remote-tracking branch 'origin/unidirectional_mt' into multidirectional

-- File Changes --

    M draft-ietf-quic-http.md (144)
    M draft-ietf-quic-transport.md (63)

-- Patch Links --

https://github.com/quicwg/base-drafts/pull/672.patch
https://github.com/quicwg/base-drafts/pull/672.diff

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