基于Golang徒手写个转发代理服务

type ProtocolVersion struct {
    VER uint8
    NMETHODS uint8
    METHODS []uint8
}


func (s *ProtocolVersion) handshake(conn net.Conn) error {
    b := make([]byte, 255)
    n, err := conn.Read(b)
    if err != nil {
        log.Println(err)
        return err
    }
    s.VER = b[0] //ReadByte reads and returns a single byte，第一个参数为socks的版本号
    s.NMETHODS = b[1] //nmethods是记录methods的长度的。nmethods的长度是1个字节
    if n != int(2+s.NMETHODS) {
        return errors.New("协议错误, sNMETHODS不对")
    }
    s.METHODS = b[2:2+s.NMETHODS] //读取指定长度信息，读取正好len(buf)长度的字节。如果字节数不是指定长度，则返回错误信息和正确的字节数

    if s.VER != 5 {
        return errors.New("该协议不是socks5协议")
    }

    //服务器回应客户端消息:
    //第一个参数表示版本号为5，即socks5协议，
    // 第二个参数表示服务端选中的认证方法，0即无需密码访问, 2表示需要用户名和密码进行验证。  
    resp :=[]byte{5, 0} 
    conn.Write(resp)
    return nil
}

type Socks5Auth struct {
    VER uint8
    ULEN uint8
    UNAME string
    PLEN uint8
    PASSWD string
}

func (s *Socks5Auth) authenticate(conn net.Conn) error {
    b := make([]byte, 128)
    n, err := conn.Read(b)
    if err != nil{
        log.Println(err)
        return err
    }

    s.VER = b[0]
    if s.VER != 5 {
        return errors.New("该协议不是socks5协议")
    }

    s.ULEN = b[1]
    s.UNAME = string(b[2:2+s.ULEN])
    s.PLEN = b[2+s.ULEN+1]
    s.PASSWD = string(b[n-int(s.PLEN):n])
    log.Println(s.UNAME, s.PASSWD)
    if username != s.UNAME || passwd != s.PASSWD {
        return errors.New("账号密码错误")
    }

    /**
    回应客户端,响应客户端连接成功
    The server verifies the supplied UNAME and PASSWD, and sends the
    following response:
                            +----+--------+
                            |VER | STATUS |
                            +----+--------+
                            | 1  |   1    |
                            +----+--------+
    A STATUS field of X'00' indicates success. If the server returns a
    `failure' (STATUS value other than X'00') status, it MUST close the
    connection.
    */
	resp := []byte{0x05, 0x00}
    conn.Write(resp) 

    return nil
}

type Socks5Resolution struct {
    VER uint8
    CMD uint8
    RSV uint8
    ATYP uint8
    DSTADDR []byte
    DSTPORT uint16
    DSTDOMAIN string
    RAWADDR *net.TCPAddr
}

func (s *Socks5Resolution) lstRequest(conn net.Conn) error {
    b := make([]byte, 128)
    n, err := conn.Read(b)
    if err != nil || n < 7 {
        log.Println(err)
        return errors.New("请求协议错误")
    }
    s.VER = b[0]
    if s.VER != 5 {
        return errors.New("该协议不是socks5协议")
    }

    s.CMD = b[1]
    if s.CMD != 1 { 
        return errors.New("客户端请求类型不为代理连接, 其他功能暂时不支持.")
    }
    s.RSV = b[2] //RSV保留字端，值长度为1个字节

    s.ATYP = b[3]

    switch s.ATYP {
    case 1:
        //	IP V4 address: X'01'
        s.DSTADDR = b[4 : 4+net.IPv4len]
    case 3:
        //	DOMAINNAME: X'03'
        s.DSTDOMAIN = string(b[5:n-2])
        ipAddr, err := net.ResolveIPAddr("ip", s.DSTDOMAIN)
		if err != nil {
			return err
		}
        s.DSTADDR = ipAddr.IP
    case 4:
        //	IP V6 address: X'04'
        s.DSTADDR = b[4 : 4+net.IPv6len]
	default:
		return errors.New("IP地址错误")
    }

    s.DSTPORT = binary.BigEndian.Uint16(b[n-2:n])
    // DSTADDR全部换成IP地址，可以防止DNS污染和封杀
    s.RAWADDR = &net.TCPAddr{
		IP:   s.DSTADDR,
		Port: int(s.DSTPORT),
    }
    
    /**
    回应客户端,响应客户端连接成功
        +----+-----+-------+------+----------+----------+
        |VER | REP |  RSV  | ATYP | BND.ADDR | BND.PORT |
        +----+-----+-------+------+----------+----------+
        | 1  |  1  | X'00' |  1   | Variable |    2     |
        +----+-----+-------+------+----------+----------+
    */
	resp := []byte{0x05, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}
    conn.Write(resp) 

    return nil


}

  wg := new(sync.WaitGroup)
  wg.Add(2)

  go func() {
defer wg.Done()
defer dstServer.Close()
      io.Copy(dstServer, client)
  }()

  go func() {
defer wg.Done()
      defer client.Close()
      io.Copy(client, dstServer)
  }()

  wg.Wait()