Re: [quicwg/base-drafts] Make transport parameter ID and length varint (#3294)

Kazuho Oku <notifications@github.com> Thu, 12 December 2019 00:31 UTC

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Date: Wed, 11 Dec 2019 16:31:18 -0800
From: Kazuho Oku <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] Make transport parameter ID and length varint (#3294)
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@nibanks 
> This is like a 15 minute code change.

I think that this comment illustrates the difference of pain among the parties.

For people having a type-length-value codec specific to QUIC, the pain of sticking uint16 here is as small as something that can be modified in 15 minutes.

Compared to that, the pain would be much bigger for people sharing the codec with TLS, if we decide to move to a varint-based design. This is because that move would enforce those people to have two codecs instead of one, even though the logic would be equivalent with the exception of the integer representations being used.

The requirements on the type-length-value codec is not trivial. The decoder is required to:
* parse IDs and block lengths
* check that the block lengths were consistent for parameters that have been parsed
* detect duplicate IDs

For those who can share the codec, it helps a lot if these logic can be *kept and maintained* in one place.

I see that some people are arguing that the encoding can be different based on the view that TP belongs to QUIC. I dispute that. We deliberately decided to mix crypto handshake and transport negotiation in QUIC. TP is a cross-layer thing that is exchanged during the TLS handshake.

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