HTTPS:// URLs

HTTP/3 will be performed using HTTPS:// URLs. The world is full of theseURLs and it has been deemed impractical and downright unreasonable tointroduce another URL scheme for the new protocol. Much like HTTP/2 did notneed a new scheme, neither will HTTP/3.

The added complexity in the HTTP/3 situation is however that where HTTP/2 wasa completely new way of transporting HTTP over the wire, it was still based onTLS and TCP like HTTP/1 was. The fact that HTTP/3 is done over QUIC changesthings in a few important aspects.

Legacy, clear-text, HTTP:// URLs will be left as-is and as we proceedfurther into a future with more secure transfers they will probably becomeless and less frequently used. Requests to such URLs will simply not beupgraded to use HTTP/3. In reality they rarely upgrade to HTTP/2 either, butfor other reasons.

Initial connection

The first connection to a fresh, not previously visited host for aHTTPS:// URL probably has to be done over TCP (possibly in addition to aparallel attempt to connect via QUIC). The host might be a legacy server withoutQUIC support or there might be a middle box in between setting up obstaclespreventing a QUIC connection from succeeding.

A modern client and server would presumably negotiate HTTP/2 in the firsthandshake. When the connection has been setup and the server responds to aclient HTTP request, the server can tell the client about its support of andpreference for HTTP/3.