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main.go
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main.go
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package main
import (
"encoding/binary"
"errors"
"flag"
"fmt"
"io"
"log"
"net"
"os"
"os/signal"
"strconv"
"syscall"
)
const (
socksVer5 = 0x05
cmdConnect = 0x01
typeIPv4 = 1
typeDomain = 3
typeIPv6 = 4
)
type Config struct {
LocalAddr string `json:"local_address"`
ServerAddr string `json:"server_address"`
Method string `json:"method"`
Password string `json:"password"`
}
var config Config
// https://tools.ietf.org/rfc/rfc1928.txt
func handsake(conn net.Conn) error {
var n int
var err error
buf := make([]byte, 258)
// 1.
// The client connects to the server, and sends a version
// identifier/method selection message:
//
// +----+----------+----------+
// |VER | NMETHODS | METHODS |
// +----+----------+----------+
// | 1 | 1 | 1 to 255 |
// +----+----------+----------+
if n, err = io.ReadAtLeast(conn, buf, 2); err != nil {
return err
}
if buf[0] != socksVer5 {
return fmt.Errorf("expect version 5, got: %d", buf[0])
}
nmethods := int(buf[1])
if n != nmethods+2 {
return errors.New("fail to parse socks request header")
}
// 2.
// The server selects from one of the methods given in METHODS, and
// sends a METHOD selection message:
//
// +----+--------+
// |VER | METHOD |
// +----+--------+
// | 1 | 1 |
// +----+--------+
// METHOD: X'00' NO AUTHENTICATION REQUIRED
if _, err = conn.Write([]byte{socksVer5, 0x00}); err != nil {
return err
}
return nil
}
func readRawAddr(conn net.Conn) (addr []byte, err error) {
var n int
buf := make([]byte, 262) // 4 + 1 + 255 + 2
// 3.
// The SOCKS request is formed as follows:
//
// +----+-----+-------+------+----------+----------+
// |VER | CMD | RSV | ATYP | DST.ADDR | DST.PORT |
// +----+-----+-------+------+----------+----------+
// | 1 | 1 | X'00' | 1 | Variable | 2 |
// +----+-----+-------+------+----------+----------+
if n, err = io.ReadAtLeast(conn, buf, 5); err != nil {
return
}
if buf[0] != socksVer5 {
err = fmt.Errorf("expect version 5, got: %d", buf[0])
return
}
if buf[1] != cmdConnect {
err = errors.New("not supported socks command")
return
}
reqLen := -1
switch buf[3] {
case typeIPv4:
reqLen = 4 + net.IPv4len + 2 // 4(ver+cmd+rsv+atype) + ipv4 + 2port
case typeIPv6:
reqLen = 4 + net.IPv6len + 2
case typeDomain:
reqLen = 4 + 1 + 2 + int(buf[4]) // 4(ver+cmd+rsv+atype) + 1addrLen + 2port + addrLen
default:
err = errors.New("not supported address type")
return
}
if n != reqLen {
err = errors.New("fail to parse socks request header")
return
}
addr = buf[3:reqLen]
return
}
func handleLocal(conn net.Conn) {
defer conn.Close()
if err := handsake(conn); err != nil {
log.Println("handsake error: ", err)
return
}
tgtAddr, err := readRawAddr(conn)
if err != nil {
log.Println("fail to get target address from connection: ", err)
return
}
// 4.
// The server evaluates the request, and
// returns a reply formed as follows:
//
// +----+-----+-------+------+----------+----------+
// |VER | REP | RSV | ATYP | BND.ADDR | BND.PORT |
// +----+-----+-------+------+----------+----------+
// | 1 | 1 | X'00' | 1 | Variable | 2 |
// +----+-----+-------+------+----------+----------+
if _, err := conn.Write([]byte{socksVer5, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}); err != nil {
return
}
remote, err := net.Dial("tcp", config.ServerAddr)
if err != nil {
log.Printf("fail to dail server: %v\n", err)
return
}
defer remote.Close()
l := len(tgtAddr)
s := 1
if tgtAddr[0] == typeDomain {
s = 2
}
port := binary.BigEndian.Uint16(tgtAddr[l-2 : l])
host := net.JoinHostPort(string(tgtAddr[s:l-2]), strconv.Itoa(int(port)))
log.Printf("connecting %s <-> %s <-> %s\n", conn.RemoteAddr().String(), config.ServerAddr, host)
encRemote := &Conn{Conn: remote, cipher: NewCipher(config.Method, config.Password)}
// write {ATYP, BND.ADDR, BND.PORT} to server
if _, err = encRemote.Write(tgtAddr); err != nil {
log.Printf("fail to write target address: %v\n", err)
return
}
go transfer(conn, encRemote)
transfer(encRemote, conn)
}
func readTargetHost(conn *Conn) (host string, err error) {
buf := make([]byte, 269)
// read ATYP from client
if _, err = io.ReadFull(conn, buf[:1]); err != nil {
return
}
var reqStart, reqEnd int
addrType := buf[0]
switch addrType {
case typeIPv4:
reqStart, reqEnd = 1, 1+net.IPv4len+2 // 2 ports
case typeIPv6:
reqStart, reqEnd = 1, 1+net.IPv6len+2
case typeDomain:
if _, err = io.ReadFull(conn, buf[1:2]); err != nil {
return
}
reqStart, reqEnd = 2, 2+int(buf[1])+2
default:
err = errors.New("not supported address type")
return
}
if _, err = io.ReadFull(conn, buf[reqStart:reqEnd]); err != nil {
return
}
switch addrType {
case typeIPv4:
host = net.IP(buf[1 : 1+net.IPv4len]).String()
case typeIPv6:
host = net.IP(buf[1 : 1+net.IPv6len]).String()
case typeDomain:
host = string(buf[2 : 2+int(buf[1])])
}
port := binary.BigEndian.Uint16(buf[reqEnd-2 : reqEnd])
host = net.JoinHostPort(host, strconv.Itoa(int(port)))
return
}
func handleServer(c net.Conn) {
defer c.Close()
conn := &Conn{Conn: c, cipher: NewCipher(config.Method, config.Password)}
tgtHost, err := readTargetHost(conn)
if err != nil {
log.Printf("fail to get target host from connection: %v\n", err)
return
}
remote, err := net.Dial("tcp", tgtHost)
if err != nil {
log.Printf("fail to dail host %s, err: %v\n", tgtHost, err)
return
}
defer remote.Close()
log.Printf("connecting %s <-> %s\n", c.RemoteAddr().String(), tgtHost)
go transfer(conn, remote)
transfer(remote, conn)
}
func run(listenAddr string, handler func(conn net.Conn)) {
ln, err := net.Listen("tcp", listenAddr)
if err != nil {
log.Fatal("listen error: ", err)
}
log.Printf("listening at %v ...\n", listenAddr)
for {
conn, err := ln.Accept()
if err != nil {
log.Println("accept error: ", err)
continue
}
go handler(conn)
}
}
func main() {
flag.StringVar(&config.LocalAddr, "l", "", "local address")
flag.StringVar(&config.ServerAddr, "s", "", "server address")
flag.StringVar(&config.Method, "m", "aes-256-cfb", "encryption method")
flag.StringVar(&config.Password, "p", "", "password")
flag.Parse()
if config.LocalAddr != "" && config.ServerAddr != "" {
log.Println("starting local proxy")
go run(config.LocalAddr, handleLocal)
} else if config.ServerAddr != "" {
log.Println("starting server proxy")
go run(config.ServerAddr, handleServer)
} else {
flag.Usage()
return
}
sigs := make(chan os.Signal, 1)
signal.Notify(sigs, os.Interrupt, os.Kill, syscall.SIGINT, syscall.SIGTERM)
sig := <-sigs
log.Println("quit: ", sig)
}