Re: POST+Upgrade, or unexpected limitation of RFC8441

>> In fact, ":protocol" only supports a subset of the registered Upgrade Tokens
>> (i.e. those that explicitly describe their use with Extended CONNECT), and
>> even if an Upgrade Token is defined for use in both HTTP/1.1 Upgrade and
>> Extended CONNECT, there is no generic process for converting between these
>> forms without detailed knowledge of the specific Upgrade Token.

> My perception was that this extension was meant to be more generic. Section
> 4 (The Extended CONNECT) doesn't put any reserve regarding the supported
> protocols. Section 5 applies it to WebSocket.

Section 5 _defines_ how to use Extended CONNECT with WebSocket.  Without Section 5, there would be no defined procedure for using Extended CONNECT with WebSocket.

All other Upgrade Tokens are _potentially_ compatible with Extended CONNECT, but only if an integration is specified for that Upgrade Token.  In the absence of a defined integration (like the one for WebSocket), an Upgrade Token cannot be used with Extended CONNECT.

>> Someone
>> should tell them that "tcp" is not a registered Upgrade Token ...

> I agree with that to some extents, because Upgrade is a cleaner CONNECT,
> actually one that can decide whether or not to upgrade based on path,
> query string, and/or header fields.

I don't object to the design, but registration is required.  The registry is First Come First Served, so claiming the token for their usage should be a matter of one email exchange.

>> As for haproxy, it needs to restrict its HTTP Version Conversion logic to
>> recognized Upgrade Tokens where the conversion logic is known to be correct.

> For H1 to H1 that's definitely not acceptable ...

By "Version Conversion" I mean "conversion of requests between different HTTP versions".

> For H1 to H2, we're indeed more limited in that we can't pass a POST
> to H2 since CONNECT doesn't permit to upload contents. ...

No, this is incorrect.  Extended CONNECT does not permit transparent conversion of a GET or HEAD or OPTION or FOO request either.  Conversion between Upgrade and Extended CONNECT is only permitted if the intermediary recognizes the Upgrade Token, and knows the token-specific rules for conversion between these request forms (if that conversion is even possible).

--Ben