package main
import (
	"errors"
	"fmt"
	"net"
	"net/http"
	"syscall"
	"time"
)
func ModifiedTransport() {
	var MyTransport = &http.Transport{
		DialContext: (&net.Dialer{
			Timeout:   30 * time.Second,
			KeepAlive: 30 * time.Second,
			DualStack: false,
			Control: func(network, address string, c syscall.RawConn) error {
				if network == "ipv4" {
					// cancel connection here because the site could connect via IPv6  and client.Get("http://myexample.com") return a non-nil err.
					return errors.New("you should not use ipv4")
				}
				return nil
			},
		}).DialContext,
		MaxIdleConns:          100,
		IdleConnTimeout:       90 * time.Second,
		TLSHandshakeTimeout:   10 * time.Second,
		ExpectContinueTimeout: 1 * time.Second,
	}
	var myClient = http.Client{Transport: MyTransport}
	resp, myerr := myClient.Get("http://www.github.com")
	if myerr != nil {
		fmt.Println("request error")
		return 
	}
	var buffer = make([]byte, 1000)
	resp.Body.Read(buffer)
	fmt.Println(string(buffer))
}
func main(){
	ModifiedTransport();
}