[quicwg/base-drafts] Confusing SNI recommendation in the HTTP/3 spec (#3324)

Ryan Hamilton <notifications@github.com> Tue, 07 January 2020 22:26 UTC

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Date: Tue, 07 Jan 2020 14:26:46 -0800
From: Ryan Hamilton <notifications@github.com>
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Subject: [quicwg/base-drafts] Confusing SNI recommendation in the HTTP/3 spec (#3324)
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In reading PR#3323, I noticed that we have the text (unchanged by that PR):

 HTTP/3 clients MUST indicate the target domain name during the TLS handshake.
 This may be done using the Server Name Indication (SNI) {{!RFC6066}} extension
 to TLS or using some other mechanism.

I read this as saying that in the absence of "some other mechanism" the SNI extension must be present. But as I read 6066, it prohibits IP literals:

   Literal IPv4 and IPv6 addresses are not permitted in "HostName".

As such, I'm not quite sure how to interpret the HTTP/3 MUST when the browser is requesting a URL with an IP literal as the host of the URL's. I could imagine two interpretations:
1. When HTTP/3 says "target domain name" that implicitly excludes IP literals, so no SN extension is expected.
2. When HTTP/3 says "target domain name" that implicitly includes IP literals, so an SNI extension is expected.
(Or probably more likely, 3. I'm misunderstanding something more deeply)

If 1 is the intended behavior it might be worth some text clarifying that. However, it seems like it would be "good" if QUIC handshakes *always* included the client's understanding of the hostname so I'd love the interpretation to be 2 (though that seems to conflict with 6066 so perhaps that's hard.)

Thoughts?

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