simpleserver.go

package main

import (
	"fmt"
	"net"
	"net/http"
)

func headers(w http.ResponseWriter, req *http.Request) {
	for name, headers := range req.Header {
		for _, h := range headers {
			fmt.Fprintf(w, "%v: %v\n", name, h)
		}
	}

	fmt.Fprintf(w, "remote addr: %v\n", req.RemoteAddr)
	fmt.Fprintf(w, "host addr: %v\n", req.Host)
}

func main() {
	http.HandleFunc("/headers", headers)
	go http.ListenAndServe("127.0.0.1:8090", nil)

	ipv6 := ipv6OnlyHandler{
		headersFunc: headers,
	}
	ListenAndServe(":8090", ipv6)
}

type ipv6OnlyHandler struct {
	headersFunc func(w http.ResponseWriter, req *http.Request)
}

func (i ipv6OnlyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	i.headersFunc(w, r)
	fmt.Fprintf(w, "ipv6 only server\n")
}

func ListenAndServe(addr string, handler http.Handler) error {
	srv := &http.Server{Addr: addr, Handler: handler}
	ln, err := net.Listen("tcp6", addr) // <--- tcp6 here
	if err != nil {
		return err
	}
	// return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
	return srv.Serve(ln)
}