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/*
* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* This is inspired by go.net/proxy/socks5.go:
*
* 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_socks4
import (
"errors"
"fmt"
"io"
"net"
"net/url"
"strconv"
"golang.org/x/net/proxy"
)
// socks4Proxy is a SOCKS4 proxy.
type socks4Proxy struct {
hostPort string
username string
forward proxy.Dialer
}
const (
socks4Version = 0x04
socks4CommandConnect = 0x01
socks4Null = 0x00
socks4ReplyVersion = 0x00
socks4Granted = 0x5a
socks4Rejected = 0x5b
socks4RejectedIdentdFailed = 0x5c
socks4RejectedIdentdMismatch = 0x5d
)
func newSOCKS4(uri *url.URL, forward proxy.Dialer) (proxy.Dialer, error) {
s := new(socks4Proxy)
s.hostPort = uri.Host
s.forward = forward
if uri.User != nil {
s.username = uri.User.Username()
}
return s, nil
}
func (s *socks4Proxy) Dial(network, addr string) (net.Conn, error) {
if network != "tcp" && network != "tcp4" {
return nil, errors.New("invalid network type")
}
// Deal with the destination address/string.
ipStr, portStr, err := net.SplitHostPort(addr)
if err != nil {
return nil, err
}
ip := net.ParseIP(ipStr)
if ip == nil {
return nil, errors.New("failed to parse destination IP")
}
ip4 := ip.To4()
if ip4 == nil {
return nil, errors.New("destination address is not IPv4")
}
port, err := strconv.ParseUint(portStr, 10, 16)
if err != nil {
return nil, err
}
// Connect to the proxy.
c, err := s.forward.Dial("tcp", s.hostPort)
if err != nil {
return nil, err
}
// Make/write the request:
// +----+----+----+----+----+----+----+----+----+----+....+----+
// | VN | CD | DSTPORT | DSTIP | USERID |NULL|
// +----+----+----+----+----+----+----+----+----+----+....+----+
req := make([]byte, 0, 9+len(s.username))
req = append(req, socks4Version)
req = append(req, socks4CommandConnect)
req = append(req, byte(port>>8), byte(port))
req = append(req, ip4...)
if s.username != "" {
req = append(req, s.username...)
}
req = append(req, socks4Null)
_, err = c.Write(req)
if err != nil {
c.Close()
return nil, err
}
// Read the response:
// +----+----+----+----+----+----+----+----+
// | VN | CD | DSTPORT | DSTIP |
// +----+----+----+----+----+----+----+----+
var resp [8]byte
_, err = io.ReadFull(c, resp[:])
if err != nil {
c.Close()
return nil, err
}
if resp[0] != socks4ReplyVersion {
c.Close()
return nil, errors.New("proxy returned invalid SOCKS4 version")
}
if resp[1] != socks4Granted {
c.Close()
return nil, fmt.Errorf("proxy error: %s", socks4ErrorToString(resp[1]))
}
return c, nil
}
func socks4ErrorToString(code byte) string {
switch code {
case socks4Rejected:
return "request rejected or failed"
case socks4RejectedIdentdFailed:
return "request rejected becasue SOCKS server cannot connect to identd on the client"
case socks4RejectedIdentdMismatch:
return "request rejected because the client program and identd report different user-ids"
default:
return fmt.Sprintf("unknown failure code %x", code)
}
}
func init() {
// Despite the scheme name, this really is SOCKS4.
proxy.RegisterDialerType("socks4a", newSOCKS4)
}
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