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
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
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 socks5
import (
"bufio"
"encoding/binary"
"errors"
"fmt"
"go-socks5-demo/config"
"go-socks5-demo/utils"
"io"
"net"
"strconv"
log "github.com/sirupsen/logrus"
)
const SOCKS5VERSION uint8 = 5
const (
MethodNoAuth uint8 = iota
MethodGSSAPI
MethodUserPass
MethodNoAcceptable uint8 = 0xFF
)
const (
RequestConnect uint8 = iota + 1
RequestBind
RequestUDP
)
const (
RequestAtypIPV4 uint8 = iota
RequestAtypDomainname uint8 = 3
RequestAtypIPV6 uint8 = 4
)
const (
Succeeded uint8 = iota
Failure
Allowed
NetUnreachable
HostUnreachable
ConnRefused
TTLExpired
CmdUnsupported
AddrUnsupported
)
type Proxy struct {
Inbound struct {
reader *bufio.Reader
writer net.Conn
}
Request struct {
atyp uint8
addr string
}
OutBound struct {
reader *bufio.Reader
writer 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.ListenPort
listenIp := config.Conf.ListenIp
if 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 = conn
err := 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 := false
for _, 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 string
switch 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 = atyp
proxy.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 = conn
return 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
}
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。
抓包验证
关于wireshare的使用，可见：wireshark入门指北
-
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
-
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
-
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。 -
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。文章来源：https://www.toymoban.com/news/detail-767639.html
-
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。文章来源地址https://www.toymoban.com/news/detail-767639.html
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