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前言

SOCKS是一种网络传输协议，主要用于客户端与外网服务器之间通讯的中间传递。协议在应用层和传输层之间。

本文使用先了解socks协议。然后实现一个socks5的tcp代理服务端。最后，进行抓包验证。

本文完整代码见仓库：laboratory/16-go-socks5

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socks协议简介

socks协议相对http和tcp协议，还是比较简单。当然，想要搞明白每个细节，也非一件容易的事情。

关于协议本身的介绍见：rfc1928、RFC 1928 - SOCKS 5 协议中文文档「译」

文档总是枯燥的，可以边看文档边看代码：实战：150行Go实现高性能socks5代理

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go实现一个简单的socks5代理

了解协议后，我们来实现一个tcp的socks5服务端代理。

网上有很多这样的示例，见：socks - Search Results - Go Packages

本节的代码参考自：实战：150行Go实现高性能socks5代理 、Subsocks: 用 Go 实现一个 Socks5 安全代理 - Luyu Huang's Blog

完整代码见仓库，下面是主要的代码。

package socks5import ("bufio""encoding/binary""errors""fmt""go-socks5-demo/config""go-socks5-demo/utils""io""net""strconv"log "github.com/sirupsen/logrus"
)const SOCKS5VERSION uint8 = 5const (MethodNoAuth uint8 = iotaMethodGSSAPIMethodUserPassMethodNoAcceptable uint8 = 0xFF
)const (RequestConnect uint8 = iota + 1RequestBindRequestUDP
)const (RequestAtypIPV4       uint8 = iotaRequestAtypDomainname uint8 = 3RequestAtypIPV6       uint8 = 4
)const (Succeeded uint8 = iotaFailureAllowedNetUnreachableHostUnreachableConnRefusedTTLExpiredCmdUnsupportedAddrUnsupported
)type Proxy struct {Inbound struct {reader *bufio.Readerwriter net.Conn}Request struct {atyp uint8addr string}OutBound struct {reader *bufio.Readerwriter net.Conn}
}func Start() error {// 读取配置文件中的监听地址和端口log.Debug("socks5 server start")listenPort := config.Conf.ListenPortlistenIp := config.Conf.ListenIpif listenPort <= 0 || listenPort > 65535 {log.Error("invalid listen port:", listenPort)return errors.New("invalid listen port")}//创建监听addr, _ := net.ResolveTCPAddr("tcp", listenIp+":"+strconv.Itoa(listenPort))listener, err := net.ListenTCP("tcp", addr)if err != nil {log.Error("fail in listen port:", listenPort, err)return errors.New("fail in listen port")}// 建立连接for {conn, _ := listener.Accept()go socks5Handle(conn)}
}func socks5Handle(conn net.Conn) {proxy := &Proxy{}proxy.Inbound.reader = bufio.NewReader(conn)proxy.Inbound.writer = connerr := handshake(proxy)if err != nil {log.Warn("fail in handshake", err)return}transport(proxy)
}func handshake(proxy *Proxy) error {err := auth(proxy)if err != nil {log.Warn(err)return err}err = readRequest(proxy)if err != nil {log.Warn(err)return err}err = replay(proxy)if err != nil {log.Warn(err)return err}return err
}func auth(proxy *Proxy) error {/*Read+----+----------+----------+|VER | NMETHODS | METHODS  |+----+----------+----------+| 1  |    1     | 1 to 255 |+----+----------+----------+*/buf := utils.SPool.Get().([]byte)defer utils.SPool.Put(buf)n, err := io.ReadFull(proxy.Inbound.reader, buf[:2])if n != 2 {return errors.New("fail to read socks5 request:" + err.Error())}ver, nmethods := uint8(buf[0]), int(buf[1])if ver != SOCKS5VERSION {return errors.New("only support socks5 version")}_, err = io.ReadFull(proxy.Inbound.reader, buf[:nmethods])if err != nil {return errors.New("fail to read methods" + err.Error())}supportNoAuth := falsefor _, m := range buf[:nmethods] {switch m {case MethodNoAuth:supportNoAuth = true}}if !supportNoAuth {return errors.New("no only support no auth")}/*replay+----+--------+|VER | METHOD |+----+--------+| 1  |   1    |+----+--------+*/n, err = proxy.Inbound.writer.Write([]byte{0x05, 0x00}) // 无需认证if n != 2 {return errors.New("fail to wirte socks method " + err.Error())}return nil
}func readRequest(proxy *Proxy) error {/*Read+----+-----+-------+------+----------+----------+|VER | CMD |  RSV  | ATYP | DST.ADDR | DST.PORT |+----+-----+-------+------+----------+----------+| 1  |  1  | X'00' |  1   | Variable |    2     |+----+-----+-------+------+----------+----------+*/buf := utils.SPool.Get().([]byte)defer utils.SPool.Put(buf)n, err := io.ReadFull(proxy.Inbound.reader, buf[:4])if n != 4 {return errors.New("fail to read request " + err.Error())}ver, cmd, _, atyp := uint8(buf[0]), uint8(buf[1]), uint8(buf[2]), uint8(buf[3])if ver != SOCKS5VERSION {return errors.New("only support socks5 version")}if cmd != RequestConnect {return errors.New("only support connect requests")}var addr stringswitch atyp {case RequestAtypIPV4:_, err = io.ReadFull(proxy.Inbound.reader, buf[:4])if err != nil {return errors.New("fail in read requests ipv4 " + err.Error())}addr = string(buf[:4])case RequestAtypDomainname:_, err = io.ReadFull(proxy.Inbound.reader, buf[:1])if err != nil {return errors.New("fail in read requests domain len" + err.Error())}domainLen := int(buf[0])_, err = io.ReadFull(proxy.Inbound.reader, buf[:domainLen])if err != nil {return errors.New("fail in read requests domain " + err.Error())}addr = string(buf[:domainLen])case RequestAtypIPV6:_, err = io.ReadFull(proxy.Inbound.reader, buf[:16])if err != nil {return errors.New("fail in read requests ipv4 " + err.Error())}addr = string(buf[:16])}_, err = io.ReadFull(proxy.Inbound.reader, buf[:2])if err != nil {return errors.New("fail in read requests port " + err.Error())}port := binary.BigEndian.Uint16(buf[:2])proxy.Request.atyp = atypproxy.Request.addr = fmt.Sprintf("%s:%d", addr, port)log.Debug("request is", proxy.Request)return nil
}func replay(proxy *Proxy) error {/*write+----+-----+-------+------+----------+----------+|VER | REP |  RSV  | ATYP | BND.ADDR | BND.PORT |+----+-----+-------+------+----------+----------+| 1  |  1  | X'00' |  1   | Variable |    2     |+----+-----+-------+------+----------+----------+*/conn, err := net.Dial("tcp", proxy.Request.addr)if err != nil {log.Warn("fail to connect ", proxy.Request.addr)_, rerr := proxy.Inbound.writer.Write([]byte{SOCKS5VERSION, HostUnreachable, 0x00, 0x01, 0, 0, 0, 0, 0, 0})if rerr != nil {return errors.New("fail in replay " + err.Error())}return errors.New("fail in connect addr " + proxy.Request.addr + err.Error())}_, err = proxy.Inbound.writer.Write([]byte{SOCKS5VERSION, Succeeded, 0x00, 0x01, 0, 0, 0, 0, 0, 0})if err != nil {return errors.New("fail in replay " + err.Error())}proxy.OutBound.reader = bufio.NewReader(conn)proxy.OutBound.writer = connreturn nil
}func transport(proxy *Proxy) {// 语义上是注释的动作;但是iobuf.reader中无法获取rd值// io.Copy(proxy.OutBound.writer, proxy.Inbound.reader)go io.Copy(proxy.OutBound.writer, proxy.Inbound.writer) // outbound <- inbound// io.Copy(proxy.Inbound.writer, proxy.OutBound.reader)go io.Copy(proxy.Inbound.writer, proxy.OutBound.writer) // inbound <- outbound
}

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运行与压测

运行测试：可以在浏览器中安装和配置下Proxy SwitchyOmega。插件将http流量转换成socks5，流量通过代理，浏览器可正常上网。访问百度，看B站都没问题。

压测：略。

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抓包验证

关于wireshare的使用，可见：wireshark入门指北

1. 客户端连接到 SOCKS 服务端，发送的协议版本与方法选择消息。

   +----+----------+----------+
   |VER | NMETHODS | METHODS  |
   +----+----------+----------+
   | 1  |    1     | 1 to 255 |
   +----+----------+----------+
   

   

   socks5–客户端只支持1种方法–不验证

2. 服务器从给出的方法进行选择，并且发送方法选择消息

   +----+--------+
   |VER | METHOD |
   +----+--------+
   | 1  |   1    |
   +----+--------+
   

   

   socks5–不验证

3. 客户端发送要请求的目标地址。

   +----+-----+-------+------+----------+----------+
   |VER | CMD |  RSV  | ATYP | DST.ADDR | DST.PORT |
   +----+-----+-------+------+----------+----------+
   | 1  |  1  | X'00' |  1   | Variable |    2     |
   +----+-----+-------+------+----------+----------+
   

   

   客户端，告诉服务端：要请求www.bing.com,目标端口是443。

4. 服务端根据请求信息，去建立连接。并返回连接情况。

   +----+-----+-------+------+----------+----------+
   |VER | REP |  RSV  | ATYP | BND.ADDR | BND.PORT |
   +----+-----+-------+------+----------+----------+
   | 1  |  1  | X'00' |  1   | Variable |    2     |
   +----+-----+-------+------+----------+----------+  
   

   

   服务单与目标地址连接成功。这里没有设置与目标建立连接的地址和端口。对于UDP而言，这里必须返回。因为客户端与服务端协商完之后，客户端需要将udp的流量发送到这个地址和端口。

5. socks协议到这里已经结束。后面则是数据转发。由于转发过程是在传输层。所以无论是http还是https，该代理程序都可以很好的运行。