golang http proxy server CONNECT method

http_proxy.go

package main

import (
	"bufio"
	"encoding/base64"
	"flag"
	"io"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"strings"
	"time"
)

func transfer(destination io.WriteCloser, source io.ReadCloser) {
	defer destination.Close()
	defer source.Close()
	io.Copy(destination, source)
}

func main() {
	host := flag.String("host", ":80", "host proxy server")
	auth := flag.String("auth", "", "authentication to for client to connect proxy, ex: username:password")

	flag.Parse()

	listener, err := net.Listen("tcp", *host)
	if err != nil {
		log.Fatal(err)
	}
	defer listener.Close()

	for {
		conn, err := listener.Accept()
		if err != nil {
			log.Fatal(err)
		}

		go func(c net.Conn) {
			br := bufio.NewReader(c)
			req, err := http.ReadRequest(br)
			if err != nil {
				log.Println("buffer: ", err)
				return
			}

			if req.Method == http.MethodConnect {
				if *auth != "" {
					clientAuth := req.Header.Get("Proxy-Authorization")
					if clientAuth == "" {
						response := &http.Response{
							StatusCode: http.StatusProxyAuthRequired,
							ProtoMajor: 1,
							ProtoMinor: 1,
						}
						response.Write(c)
						c.Close()
						return
					}

					serverAuth := "Basic " + base64.StdEncoding.EncodeToString([]byte(*auth))
					if clientAuth != serverAuth {
						response := &http.Response{
							StatusCode: http.StatusUnauthorized,
							ProtoMajor: 1,
							ProtoMinor: 1,
						}
						response.Write(c)
						c.Close()
						return
					}
				}

				response := &http.Response{
					StatusCode: 200,
					ProtoMajor: 1,
					ProtoMinor: 1,
				}
				response.Write(c)

				destConn, err := net.DialTimeout("tcp", req.URL.Host, 10*time.Second)
				if err != nil {
					response := &http.Response{
						StatusCode: http.StatusRequestTimeout,
						ProtoMajor: 1,
						ProtoMinor: 1,
					}
					response.Write(c)
					return
				}

				go transfer(destConn, c)
				go transfer(c, destConn)

			} else {
				response := &http.Response{
					StatusCode: http.StatusRequestTimeout,
					ProtoMajor: 1,
					ProtoMinor: 1,
					Body:       ioutil.NopCloser(strings.NewReader("hello world")),
				}
				response.Write(c)
				c.Close()
				return
			}
		}(conn)
	}
}

Your transfer function closes the input streams after it exits. You're calling the transfer function twice in separate goroutines. The faster goroutine will end up closing both streams, so the slower goroutine will fail, won't it?