Go 编写的简单代理

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)
    }
}