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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package proxy
import (
"errors"
"io"
"net"
"strconv"
)
// SOCKS5 returns a Dialer that makes SOCKSv5 connections to the given address
// with an optional username and password. See RFC 1928.
func SOCKS5(network, addr string, auth *Auth, forward Dialer) (Dialer, error) {
s := &socks5{
network: network,
addr: addr,
forward: forward,
}
if auth != nil {
s.user = auth.User
s.password = auth.Password
}
return s, nil
}
type socks5 struct {
user, password string
network, addr string
forward Dialer
}
const socks5Version = 5
const (
socks5AuthNone = 0
socks5AuthPassword = 2
)
const socks5Connect = 1
const (
socks5IP4 = 1
socks5Domain = 3
socks5IP6 = 4
)
var socks5Errors = []string{
"",
"general failure",
"connection forbidden",
"network unreachable",
"host unreachable",
"connection refused",
"TTL expired",
"command not supported",
"address type not supported",
}
// Dial connects to the address addr on the network net via the SOCKS5 proxy.
func (s *socks5) Dial(network, addr string) (net.Conn, error) {
switch network {
case "tcp", "tcp6", "tcp4":
default:
return nil, errors.New("proxy: no support for SOCKS5 proxy connections of type " + network)
}
conn, err := s.forward.Dial(s.network, s.addr)
if err != nil {
return nil, err
}
closeConn := &conn
defer func() {
if closeConn != nil {
(*closeConn).Close()
}
}()
host, portStr, err := net.SplitHostPort(addr)
if err != nil {
return nil, err
}
port, err := strconv.Atoi(portStr)
if err != nil {
return nil, errors.New("proxy: failed to parse port number: " + portStr)
}
if port < 1 || port > 0xffff {
return nil, errors.New("proxy: port number out of range: " + portStr)
}
// the size here is just an estimate
buf := make([]byte, 0, 6+len(host))
buf = append(buf, socks5Version)
if len(s.user) > 0 && len(s.user) < 256 && len(s.password) < 256 {
buf = append(buf, 2 /* num auth methods */, socks5AuthNone, socks5AuthPassword)
} else {
buf = append(buf, 1 /* num auth methods */, socks5AuthNone)
}
if _, err := conn.Write(buf); err != nil {
return nil, errors.New("proxy: failed to write greeting to SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
if _, err := io.ReadFull(conn, buf[:2]); err != nil {
return nil, errors.New("proxy: failed to read greeting from SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
if buf[0] != 5 {
return nil, errors.New("proxy: SOCKS5 proxy at " + s.addr + " has unexpected version " + strconv.Itoa(int(buf[0])))
}
if buf[1] == 0xff {
return nil, errors.New("proxy: SOCKS5 proxy at " + s.addr + " requires authentication")
}
if buf[1] == socks5AuthPassword {
buf = buf[:0]
buf = append(buf, 1 /* password protocol version */)
buf = append(buf, uint8(len(s.user)))
buf = append(buf, s.user...)
buf = append(buf, uint8(len(s.password)))
buf = append(buf, s.password...)
if _, err := conn.Write(buf); err != nil {
return nil, errors.New("proxy: failed to write authentication request to SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
if _, err := io.ReadFull(conn, buf[:2]); err != nil {
return nil, errors.New("proxy: failed to read authentication reply from SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
if buf[1] != 0 {
return nil, errors.New("proxy: SOCKS5 proxy at " + s.addr + " rejected username/password")
}
}
buf = buf[:0]
buf = append(buf, socks5Version, socks5Connect, 0 /* reserved */)
if ip := net.ParseIP(host); ip != nil {
if ip4 := ip.To4(); ip4 != nil {
buf = append(buf, socks5IP4)
ip = ip4
} else {
buf = append(buf, socks5IP6)
}
buf = append(buf, ip...)
} else {
if len(host) > 255 {
return nil, errors.New("proxy: destination hostname too long: " + host)
}
buf = append(buf, socks5Domain)
buf = append(buf, byte(len(host)))
buf = append(buf, host...)
}
buf = append(buf, byte(port>>8), byte(port))
if _, err := conn.Write(buf); err != nil {
return nil, errors.New("proxy: failed to write connect request to SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
if _, err := io.ReadFull(conn, buf[:4]); err != nil {
return nil, errors.New("proxy: failed to read connect reply from SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
failure := "unknown error"
if int(buf[1]) < len(socks5Errors) {
failure = socks5Errors[buf[1]]
}
if len(failure) > 0 {
return nil, errors.New("proxy: SOCKS5 proxy at " + s.addr + " failed to connect: " + failure)
}
bytesToDiscard := 0
switch buf[3] {
case socks5IP4:
bytesToDiscard = net.IPv4len
case socks5IP6:
bytesToDiscard = net.IPv6len
case socks5Domain:
_, err := io.ReadFull(conn, buf[:1])
if err != nil {
return nil, errors.New("proxy: failed to read domain length from SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
bytesToDiscard = int(buf[0])
default:
return nil, errors.New("proxy: got unknown address type " + strconv.Itoa(int(buf[3])) + " from SOCKS5 proxy at " + s.addr)
}
if cap(buf) < bytesToDiscard {
buf = make([]byte, bytesToDiscard)
} else {
buf = buf[:bytesToDiscard]
}
if _, err := io.ReadFull(conn, buf); err != nil {
return nil, errors.New("proxy: failed to read address from SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
// Also need to discard the port number
if _, err := io.ReadFull(conn, buf[:2]); err != nil {
return nil, errors.New("proxy: failed to read port from SOCKS5 proxy at " + s.addr + ": " + err.Error())
}
closeConn = nil
return conn, nil
}
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