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socks.go
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socks.go
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// Copyright 2012, Hailiang Wang. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
/*
Package socks implements a SOCKS (SOCKS4, SOCKS4A and SOCKS5) proxy client.
A complete example using this package:
package main
import (
"code.as/core/socks"
"fmt"
"net/http"
"io/ioutil"
)
func main() {
dialSocksProxy := socks.DialSocksProxy(socks.SOCKS5, "127.0.0.1:1080")
tr := &http.Transport{Dial: dialSocksProxy}
httpClient := &http.Client{Transport: tr}
bodyText, err := TestHttpsGet(httpClient, "https://h12.io/about")
if err != nil {
fmt.Println(err.Error())
}
fmt.Print(bodyText)
}
func TestHttpsGet(c *http.Client, url string) (bodyText string, err error) {
resp, err := c.Get(url)
if err != nil { return }
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil { return }
bodyText = string(body)
return
}
*/
package socks
import (
"errors"
"fmt"
"net"
"strconv"
)
// Constants to choose which version of SOCKS protocol to use.
const (
SOCKS4 = iota
SOCKS4A
SOCKS5
)
// DialSocksProxy returns the dial function to be used in http.Transport object.
// Argument socksType should be one of SOCKS4, SOCKS4A and SOCKS5.
// Argument proxy should be in this format "127.0.0.1:1080".
func DialSocksProxy(socksType int, proxy string) func(string, string) (net.Conn, error) {
if socksType == SOCKS5 {
return func(_, targetAddr string) (conn net.Conn, err error) {
return dialSocks5(proxy, targetAddr)
}
}
// SOCKS4, SOCKS4A
return func(_, targetAddr string) (conn net.Conn, err error) {
return dialSocks4(socksType, proxy, targetAddr)
}
}
func dialSocks5(proxy, targetAddr string) (conn net.Conn, err error) {
// dial TCP
conn, err = net.Dial("tcp", proxy)
if err != nil {
return
}
// version identifier/method selection request
req := []byte{
5, // version number
1, // number of methods
0, // method 0: no authentication (only anonymous access supported for now)
}
resp, err := sendReceive(conn, req)
if err != nil {
return
} else if len(resp) != 2 {
err = errors.New("Server does not respond properly.")
return
} else if resp[0] != 5 {
err = errors.New("Server does not support Socks 5.")
return
} else if resp[1] != 0 { // no auth
err = errors.New("socks method negotiation failed.")
return
}
// detail request
host, port, err := splitHostPort(targetAddr)
req = []byte{
5, // version number
1, // connect command
0, // reserved, must be zero
3, // address type, 3 means domain name
byte(len(host)), // address length
}
req = append(req, []byte(host)...)
req = append(req, []byte{
byte(port >> 8), // higher byte of destination port
byte(port), // lower byte of destination port (big endian)
}...)
resp, err = sendReceive(conn, req)
if err != nil {
return
} else if len(resp) != 10 {
err = errors.New("Server does not respond properly.")
} else if resp[1] != 0 {
err = errors.New("Can't complete SOCKS5 connection.")
}
return
}
func dialSocks4(socksType int, proxy, targetAddr string) (conn net.Conn, err error) {
// dial TCP
conn, err = net.Dial("tcp", proxy)
if err != nil {
return
}
// connection request
host, port, err := splitHostPort(targetAddr)
if err != nil {
return
}
ip := net.IPv4(0, 0, 0, 1).To4()
if socksType == SOCKS4 {
ip, err = lookupIP(host)
if err != nil {
return
}
}
req := []byte{
4, // version number
1, // command CONNECT
byte(port >> 8), // higher byte of destination port
byte(port), // lower byte of destination port (big endian)
ip[0], ip[1], ip[2], ip[3], // special invalid IP address to indicate the host name is provided
0, // user id is empty, anonymous proxy only
}
if socksType == SOCKS4A {
req = append(req, []byte(host+"\x00")...)
}
resp, err := sendReceive(conn, req)
if err != nil {
return
} else if len(resp) != 8 {
err = errors.New("Server does not respond properly.")
return
}
switch resp[1] {
case 90:
// request granted
case 91:
err = errors.New("Socks connection request rejected or failed.")
case 92:
err = errors.New("Socks connection request rejected becasue SOCKS server cannot connect to identd on the client.")
case 93:
err = errors.New("Socks connection request rejected because the client program and identd report different user-ids.")
default:
err = errors.New("Socks connection request failed, unknown error.")
}
return
}
func sendReceive(conn net.Conn, req []byte) (resp []byte, err error) {
_, err = conn.Write(req)
if err != nil {
return
}
resp, err = readAll(conn)
return
}
func readAll(conn net.Conn) (resp []byte, err error) {
resp = make([]byte, 1024)
n, err := conn.Read(resp)
resp = resp[:n]
return
}
func lookupIP(host string) (ip net.IP, err error) {
ips, err := net.LookupIP(host)
if err != nil {
return
}
if len(ips) == 0 {
err = errors.New(fmt.Sprintf("Cannot resolve host: %s.", host))
return
}
ip = ips[0].To4()
if len(ip) != net.IPv4len {
fmt.Println(len(ip), ip)
err = errors.New("IPv6 is not supported by SOCKS4.")
return
}
return
}
func splitHostPort(addr string) (host string, port uint16, err error) {
host, portStr, err := net.SplitHostPort(addr)
portInt, err := strconv.ParseUint(portStr, 10, 16)
port = uint16(portInt)
return
}

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