Allow disabling of HTTP/2.0 while using the optimal default configuration in Go

main.go

package main

import (
	"crypto/tls"
	"flag"
	"log/slog"
	"net/http"
	"os"
)

var disableHTTP2 = flag.Bool("disable-http2", false, "Disable HTTP/2.0")

func main() {
	flag.Parse()

	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{})))

	tr := http.DefaultTransport.(*http.Transport).Clone()

	if *disableHTTP2 {
		tr.ForceAttemptHTTP2 = false
		tr.TLSNextProto = make(map[string]func(authority string, c *tls.Conn) http.RoundTripper)
		// The default TLSClientConfig has h2 in NextProtos, so the negotiated TLS connection will assume h2 support.
		// see https://github.com/golang/go/issues/50571
		tr.TLSClientConfig = &tls.Config{}
	}

	client := http.Client{
		Transport: tr,
	}

	resp, err := client.Get("https://google.com")
	if err != nil {
		panic(err)
	}

	defer resp.Body.Close()

	// Print the HTTP Status Code
	slog.With("resp.Status", resp.Status, "resp.StatusCode", resp.StatusCode, "resp.Proto", resp.Proto).Info("HTTP Status Code")

}