Re: [quicwg/base-drafts] Don't use bitmap frames to describe varint structures (#3115)

Lucas Pardue <notifications@github.com> Mon, 28 October 2019 00:05 UTC

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Date: Sun, 27 Oct 2019 17:05:46 -0700
From: Lucas Pardue <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Don't use bitmap frames to describe varint structures (#3115)
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As the person that created many of the HTTP/3 frame diagrams I apologise for raising your ire :)

As someone that mainly came into IETF via HTTP/2, my main motivation for diagramming the frames in HTTP/3 was for consistency when switching back and forth between drafts. For example, single variable frames are diagrammed in RFC 7540 so it did seem inconsistent to skip them (to @MikeBishop's point). I'd experienced several occasions (myself and others) where the lack of a diagram had led to some oversight when implementing the specification - even if that is not their intended purpose because they are duplicatory of text.

That said, I do see the point you are making. For instance, I opened https://github.com/quicwg/base-drafts/issues/2338 to point out the problem with the diagram in section 6.2.2. I think the diagram is a problem but Mike closed it as no-one seemed to care at the time.

However, I'd like to highlight that RFC 7540 has, in part, the problem you are describing where fields of unknown length are represented by the `*` character.

https://tools.ietf.org/html/rfc7540#section-6.2
```
    +---------------+
    |Pad Length? (8)|
    +-+-------------+-----------------------------------------------+
    |E|                 Stream Dependency? (31)                     |
    +-+-------------+-----------------------------------------------+
    |  Weight? (8)  |
    +-+-------------+-----------------------------------------------+
    |                   Header Block Fragment (*)                 ...
    +---------------------------------------------------------------+
    |                           Padding (*)                       ...
    +---------------------------------------------------------------+

                      Figure 7: HEADERS Frame Payload
```

Is your complaint about the QUIC specs caused by the top line of each diagram that show the 32-bit space, or do you think we got it wrong with H2 also?

FWIW I think there could be merit in defining a more structured syntax for Frames and Streams - especially as we look forward to new versions and extensions of QUIC because we should make it pretty straightforward for new contributors to pick up and go. However, I see a change at this stage being a bunch of editorial work.
2) 

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