http*-default-user-agent checks while fixing bug https://github.com/golang/go/issues/13685

client.go

package main

import (
	"crypto/tls"
	"io/ioutil"
	"log"
	"net/http"
)

func main() {
	url := "http://localhost:8080"
	client := http.DefaultClient
	if os.Getenv("http1") == "" {
		url = "https://localhost:8080"
		tr := &http.Transport{
			TLSClientConfig: &tls.Config{
				InsecureSkipVerify: true,
			},
		}

		client = &http.Client{Transport: tr}
	}
	res, err := client.Get(url)
	if err != nil {
		log.Printf("get: %v\n", err)
		return
	}

	data, _ := ioutil.ReadAll(res.Body)
	res.Body.Close()

	log.Printf("data %s\n", data)
}

server.go

package main
// sample run: 
// $ http1=1 go run server.go # To run in http1 mode
// $ go run server.go # Default in http2 mode

import (
	"fmt"
	"log"
	"net/http"
	"os"
	"time"
)

func timeNow(w http.ResponseWriter, r *http.Request) {
	log.Println("got a request from ", r)
	fmt.Fprintf(w, "the time now is: %q", time.Now())
	fmt.Fprintf(w, "User-Agent: %q", r.UserAgent())
}

func main() {
	var server http.Server
	server.Addr = ":8080"

	http.HandleFunc("/", timeNow)
	http.HandleFunc("/time", timeNow)

	var err error
	if os.Getenv("http1") != "" {
		log.Println("http1 mode running")
		err = server.ListenAndServe()
	} else {
		log.Println("http2 mode running")
		err = server.ListenAndServeTLS("rosedn.cert", "rosedn.key")
	}

	if err != nil {
		log.Printf("servingTLS: %v\n", err)
	}
}