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

"Roy T. Fielding" <notifications@github.com> Fri, 25 October 2019 20:08 UTC

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Subject: Re: [quicwg/base-drafts] Don't use bitmap frames to describe varint structures (#3115)
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Honestly, I think people are responding based on "I don't want to change my imagination of what the diagrams show" versus any sensible understanding of the examples in use:

https://quicwg.org/base-drafts/draft-ietf-quic-http.html#rfc.section.6.2

```
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Stream Type (i)                      ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

```
https://quicwg.org/base-drafts/draft-ietf-quic-http.html#rfc.section.6.2.2

```
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           0x01 (i)                          ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Push ID (i)                        ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

```
https://quicwg.org/base-drafts/draft-ietf-quic-http.html#rfc.section.7.2

```
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Type (i)                          ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Length (i)                         ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Frame Payload (*)                     ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```

There is absolutely no value to these diagrams as a "mental model", in any way shape or form. They are simply misleading because they look like they contain information when they actually contain a list of ordered names of unknown length. The prose already contains that.

These are not the only ones -- there are eight more useless diagrams in that draft alone. There are some good diagrams of the same thing in other QUIC drafts, basically the ones containing bitfields, but even those lose sensibility as soon as a varint appears.

They would ALL be fine if they illustrated actual examples values and how their 0/1 bits were laid out. But they don't. They don't even come close in that middle example above.

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