On Thu, 21 Oct 2021, 23:35 Ryan Hamilton, <rch@google.com> wrote: > On Thu, Oct 21, 2021 at 11:10 AM Lucas Pardue <lucaspardue.24.7@gmail.com> > wrote: > >> On Thu, Oct 21, 2021 at 6:46 PM David Schinazi <dschinazi.ietf@gmail.com> >> wrote: >> >>> In theory, in terms of HTTP semantics, if someone mints wss:// >>> websocket.example.org and sends an h3 Alt-Svc for websocket.example.org, >>> then that means that the client can use WebSocket over HTTP/3. >>> >>> However, in practice, as Stefan points out, that might not always hold. >>> In the scenario where someone accidentally misconfigured their server by >>> not having enough communication between h1/h2/h3, they can rectify the >>> situation by replying with HTTP status code 421. That'll cause the client >>> to fallback to an earlier version of HTTP. >>> >> >> I don't think 421 is the right status here. The example I would actually >> use is a document loaded from https://example.com/index.html that >> includes wss://example.com/chat. If this is loaded via an H2 connection, >> which supports extended connect for :protocol connect-udp but not >> websocket, then the CONNECT request should fail but 421 is a status about >> authority (generally caused by coalescing, a whole additional ballgame), >> and there is no authority problem here. The client fallback to a fresh >> connection would have to be careful to use HTTP/1.1. >> > > For HTTP/2 I think instead of 421, we could use HTTP_1_1_REQUIRED. Does > that sound right? > In H3, the equivalent error code is H3_VERSION_FALLBACK. These might possibly work, but it makes a big assumption that HTTP/1.1 is the solution. Stream errors in direct reaction to a syntactically valid request are specced but can be a bit thorny to handle in implementations. It could just be that one server instance that is authoritative, is not able to serve the request at the time. As I said upthread, there seems to be an omission of a status code or error code that articulates this simply, and perhaps a header that could be used to carry the list of actual support protocols (like Upgrade can do, but I think is prohibited in H2 or H3).
Received on Thursday, 21 October 2021 22:58:48 UTC