Re: HTTP/3 Preface (PRI method)

[Matt Joras <[e-mail]>]

Hi Ben,

This issue in general, if I'm understanding you correctly, is solved via
the ALPN[1]. I.e., as part of the TLS handshake the server will be able to
know which application is being used. For example, "h2" corresponds to
HTTP/2 and "h3" corresponds to HTTP/3. Also note that there are no
standardized mappings of HTTP over QUIC except for the currently-pending
HTTP/3 specification. Future versions of HTTP over QUIC would also be
distinguished via ALPN, presumably.

Best,
Matt Joras

[1] https://datatracker.ietf.org/doc/html/rfc7301

On Tue, Jun 29, 2021 at 12:11 PM <ben=[e-mail]> wrote:

> Hello all,
>
> When reading about QUIC, it comes to me as a better alternative of TCP,
> build upon UDP.
> In this case, servers that run on TCP could easily also run on UDP/QUIC;
> think about DNS, SMTP, FTP.
>
> Now there is also a new version of HTTP. HTTP/3. This version will be
> transfered over QUIC by default.
> However, as I mentioned above, it could be possible to have "TCP
> protocols" that use QUIC too.
> That makes me think about also transfering some old HTTP versions, for
> example HTTP/0.9 (I came across a library that transfered HTTP/0.9 over
> QUIC).
> But also HTTP/1.0, HTTP/1.1 and HTTP/2 are possible.
>
> All older HTTP versions send the following request line: <METHOD> <PATH>
> [VERSION] \n
> If an endpoint is directly accessed (without some negotiation), it will
> find out the version directly by reading the first line.
> For 0.9 the version will be absent. For 2.0 this will be a preface with
> a PRI method and * as path.
>
> When I think about running a HTTP server, I think about this:
>
> TCP (80) or TCP/SSL (443):
>   - HTTP/0.9
>   - HTTP/1.0
>   - HTTP/1.1
>   - HTTP/2.0
>   - HTTP/3.0 (I think this is possible too)
>
> UDP/QUIC:
>   - HTTP/0.9 (HTTP/0.9 but over QUIC)
>   - HTTP/1.0 (HTTP/1.0 but over QUIC)
>   - HTTP/1.1 (HTTP/1.1 but over QUIC)
>   - HTTP/2.0 (HTTP/2.0 but over QUIC)
>   - HTTP/3.0 (Default)
>
> However, if I listen for all versions on my HTTP-QUIC server, how am I
> supposed to know that it is HTTP/3? Does HTTP/3 has a preface? And if
> not, why not?
> I think the preface of HTTP/2 is great and I think it would be great in
> HTTP/3 too: PRI * HTTP/3.0
>
> I would like to see a preface added to HTTP/3.0. It is only 18 extra
> bytes at the beginning of the request. It could be ignored by some
> servers if they want, but for servers that want to have backwards
> compatibility it would be a great feature. (Luckily HTTP/3 is not a
> released standard yet.)
>
> Ben
>
>