How are the HTTP/1, H2 and H3 protocols switched?

[kolinfluence]

can u show the code part where http1.1 or http2 or http3 is switched by browser detection ... or how is it done?

i cant seem to find that part. it's fantastic work by the way.

[cipriancraciun]

(I've converted this into a discussion thread.)

The browser is the one that chooses if it uses HTTP/1 or H2. H3 is a special case and the browser must first contact the server, from which it obtains a special header indicating where the H3 endpoint is. Getting back to H2, it works only over TLS, and the server states in the ALPN TLS extension that it supports http/1 or h2, and the browser then chooses the protocol it wants.

All the Go server-side code related to this is inside the sources/cmd/server/server.go file, see the following range especially.

https://github.com/volution/kawipiko/blob/development/sources/cmd/server/server.go#L1703-L1932

[kolinfluence]

your code is not that easy to digest but thx!

[cipriancraciun]

I understand that the code is quite hard to understand. (Sometimes I myself have a hard time understanding the intricacies of old code.)

However, my recommendation pertaining to the protocol subject is this: just stick with the built-in Go net/http package and don't bother about the protocol details. Go's built-in HTTP server already handles all the important aspects of HTTP/1 and H2 signaling and switching. (My code is so complex because I rely on the fasthttp library for HTTP/1 and on Go's net/http for H2. Your code most likely won't need it.)

With regard to H3 my advice is simply "don't"! It's overly complex and I believe it's mainly meant for CDN providers.

(In fact, the de-facto H3 Go implementation, which isn't yet part of net/http, is quite underperforming even when compared to H2.)

For more details about HTTP/1 vs H2 (and vs H3) please see the extensive discussion on the following fasthttp issue; I've commented extensively there about the issues with H2 (and H3).

valyala/fasthttp#144