完整实现流程

启动一个服务

  1. ln, err := net.Listen("tcp", ":8888")
  2. if err != nil {
  3.     fmt.Println("Server listen fail")
  4.     return
  5. }
  6. for {
  7.     sc, err := ln.Accept()
  8.     if err != nil {
  9.         fmt.Println("Server accept fail")
  10.         continue
  11.     }
  12.     go handleServer(sc)
  13. }

解析请求流程

确认版本和认证方式

服务端会接收到三个字节依次表示 VER、NMETHODS、METHODS，在得到连接请求时，需要响应客户端 VER 和采用的 METHOD，此处响应 5、0 表示无需认证

  1. buf := make([]byte, 1024)
  2. // read VER, NMETHODS, METHODS
  3. if _, err := io.ReadFull(sc, buf[:2]); err != nil {
  4.     return
  5. }
  6. nMethods := buf[1]
  7. if _, err := io.ReadFull(sc, buf[:nMethods]); err != nil {
  8.     return
  9. }
  10. // write VER METHOD
  11. if _, err := sc.Write([]byte{5, 0}); err != nil {
  12.     return
  13. }

建立连接

客户端建立连接时会带上 VER、CMD、RSV、ATYP、DST.ADDR、DST.PORT（详见 socks5 协议原理），服务端需要响应客户端连接成功

  1. // read VER CMD RSV ATYP DST.ADDR DST.PORT
  2. if _, err := io.ReadFull(sc, buf[:3]); err != nil {
  3.     return
  4. }
  5. // reply success
  6. _, _ = sc.Write([]byte{5, 0, 0, 1, 0, 0, 0, 0, 0, 0})

转发请求

首先需要从请求里面解析出 remoteAddr，

  1. b := make(byte[], 1024)
  2. _, err := io.ReadFull(r, b[:1])
  3. if err != nil {
  4.     return "", err
  5. }
  7. host, port := "", ""
  8. switch b[0] {
  9. case 3:
  10.     _, err = io.ReadFull(r, b[1:2])
  11.     if err != nil {
  12.         return "", err
  13.     }
  14.     _, err = io.ReadFull(r, b[2:2+int(b[1])+2])
  15.     host = string(b[2 : 2+int(b[1])])
  16.     port = strconv.Itoa((int(b[2+int(b[1])]) << 8) | int(b[2+int(b[1])+1]))
  17. case 1:
  18.     _, err = io.ReadFull(r, b[1:1+net.IPv4len+2])
  19.     host = net.IP(b[1 : 1+net.IPv4len]).String()
  20.     port = strconv.Itoa((int(b[1+net.IPv4len]) << 8) | int(b[1+net.IPv4len+1]))
  21. case 4:
  22.     _, err = io.ReadFull(r, b[1:1+net.IPv6len+2])
  23.     host = net.IP(b[1 : 1+net.IPv6len]).String()
  24.     port = strconv.Itoa((int(b[1+net.IPv6len]) << 8) | int(b[1+net.IPv6len+1]))
  25. default:
  26.     return "", errors.New("invalid aType")
  27. }
  28. address := net.JoinHostPort(host, port)
  30. return address, nil

然后跟 remoteAddr 建立连接

  1. rc, err := net.Dial("tcp", addr)
  2. if err != nil {
  3.     fmt.Println("server dial fail")
  4.     return
  5. }
  6. defer rc.Close()

最后中转客户端和远端 remote 之间交互的字节流

  1. go func() {
  2.     io.Copy(right, left)
  3. }()
  4. io.Copy(left, right)

完整代码

  1. package main
  3. import (
  4.     "errors"
  5.     "fmt"
  6.     "io"
  7.     "net"
  8.     "strconv"
  9. )
  11. func main() {
  12.     ln, err := net.Listen("tcp", ":8888")
  13.     if err != nil {
  14.         fmt.Println("Server listen fail")
  15.         return
  16.     }
  17.     for {
  18.         sc, err := ln.Accept()
  19.         if err != nil {
  20.             fmt.Println("Server accept fail")
  21.             continue
  22.         }
  23.         go handleServer(sc)
  24.     }
  25. }
  27. func handleServer(sc net.Conn) {
  28.     defer sc.Close()
  30.     buf := make([]byte, 1024)
  31.     // read VER, NMETHODS, METHODS
  32.     if _, err := io.ReadFull(sc, buf[:2]); err != nil {
  33.         return
  34.     }
  35.     nmethods := buf[1]
  36.     if _, err := io.ReadFull(sc, buf[:nmethods]); err != nil {
  37.         return
  38.     }
  39.     // write VER METHOD
  40.     if _, err := sc.Write([]byte{5, 0}); err != nil {
  41.         return
  42.     }
  43.     // read VER CMD RSV ATYP DST.ADDR DST.PORT
  44.     if _, err := io.ReadFull(sc, buf[:3]); err != nil {
  45.         return
  46.     }
  47.     _, _ = sc.Write([]byte{5, 0, 0, 1, 0, 0, 0, 0, 0, 0})
  49.     b := make([]byte, 1024)
  50.     addr, err := ReadAddr(sc, b)
  51.     if err != nil {
  52.         return
  53.     }
  55.     rc, err := net.Dial("tcp", addr)
  56.     if err != nil {
  57.         fmt.Println("server dial fail")
  58.         return
  59.     }
  60.     defer rc.Close()
  62.     if err = relay(sc, rc); err != nil {
  63.         fmt.Printf("relay error: %v", err)
  64.         return
  65.     }
  66. }
  68. func ReadAddr(r io.Reader, b []byte) (string, error) {
  69.     _, err := io.ReadFull(r, b[:1])
  70.     if err != nil {
  71.         return "", err
  72.     }
  74.     host, port := "", ""
  75.     switch b[0] {
  76.     case 3:
  77.         _, err = io.ReadFull(r, b[1:2])
  78.         if err != nil {
  79.             return "", err
  80.         }
  81.         _, err = io.ReadFull(r, b[2:2+int(b[1])+2])
  82.         host = string(b[2 : 2+int(b[1])])
  83.         port = strconv.Itoa((int(b[2+int(b[1])]) << 8) | int(b[2+int(b[1])+1]))
  84.     case 1:
  85.         _, err = io.ReadFull(r, b[1:1+net.IPv4len+2])
  86.         host = net.IP(b[1 : 1+net.IPv4len]).String()
  87.         port = strconv.Itoa((int(b[1+net.IPv4len]) << 8) | int(b[1+net.IPv4len+1]))
  88.     case 4:
  89.         _, err = io.ReadFull(r, b[1:1+net.IPv6len+2])
  90.         host = net.IP(b[1 : 1+net.IPv6len]).String()
  91.         port = strconv.Itoa((int(b[1+net.IPv6len]) << 8) | int(b[1+net.IPv6len+1]))
  92.     default:
  93.         return "", errors.New("invalid aType")
  94.     }
  95.     address := net.JoinHostPort(host, port)
  97.     return address, nil
  98. }
  100. func relay(left, right net.Conn) error {
  101.     go func() {
  102.         io.Copy(right, left)
  103.     }()
  104.     io.Copy(left, right)
  106.     return nil
  107. }

上述代码运行成功之后，配合浏览器的插件 SwitchyOmega 即可实现代理