How to disable HTTP/2 using Server.TLSNextProto - go

Question

I have a Go server handling https requests:
package main
import (
"fmt"
"net/http"
"log"
)
const (
port = "5966"
cert = "/tmp/cert.pem"
key = "/tmp/key.pem"
)
func main() {
listen_at := ":" + port
fmt.Println("Listening at", listen_at)
go http.HandleFunc("/job_handler/", job_handler)
log.Fatal(http.ListenAndServeTLS(listen_at, cert, key, nil))
}
func job_handler(w http.ResponseWriter, r *http.Request) {
// do somework
}
Turns out in https mode, Go has transparent support for the HTTP/2 protocol. We've some clients that noticeably misbehave in HTTP/2, and hence we need to disable HTTP/2 on the server side.
Unfortunately, I can't use ENV variable GODEBUG=http2server=0 to disable HTTP/2. What's left is Server.TLSNextProto as documented here.
How can I use Server.TLSNextProto on my server code above to disable https/2?

Answer 1

The simplest setup that disables HTTP/2 is
package main
import (
"log"
"net/http"
"crypto/tls"
)
func main() {
m := http.NewServeMux()
srv := &http.Server{
Handler: m,
Addr: "127.0.0.1:8080",
TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler)),
}
log.Fatal(srv.ListenAndServe())
}
You can verify the support with
curl -v --http2-prior-knowledge http://localhost:8080