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)
	}
}