mirror of https://gitlab.com/yawning/obfs4
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/*
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* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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* This is inspired by go.net/proxy/socks5.go:
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*
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* Copyright 2011 The Go Authors. All rights reserved.
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* Use of this source code is governed by a BSD-style
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* license that can be found in the LICENSE file.
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*/
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package main
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import (
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"errors"
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"fmt"
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"io"
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"net"
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"net/url"
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"strconv"
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"code.google.com/p/go.net/proxy"
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)
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// socks4Proxy is a SOCKS4 proxy.
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type socks4Proxy struct {
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hostPort string
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username string
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forward proxy.Dialer
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}
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const (
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socks4Version = 0x04
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socks4CommandConnect = 0x01
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socks4Null = 0x00
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socks4ReplyVersion = 0x00
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socks4Granted = 0x5a
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socks4Rejected = 0x5b
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socks4RejectedIdentdFailed = 0x5c
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socks4RejectedIdentdMismatch = 0x5d
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)
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func newSOCKS4(uri *url.URL, forward proxy.Dialer) (proxy.Dialer, error) {
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s := new(socks4Proxy)
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s.hostPort = uri.Host
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s.forward = forward
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if uri.User != nil {
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s.username = uri.User.Username()
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}
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return s, nil
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}
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func (s *socks4Proxy) Dial(network, addr string) (net.Conn, error) {
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if network != "tcp" && network != "tcp4" {
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return nil, errors.New("invalid network type")
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}
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// Deal with the destination address/string.
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ipStr, portStr, err := net.SplitHostPort(addr)
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if err != nil {
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return nil, err
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}
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ip := net.ParseIP(ipStr)
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if ip == nil {
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return nil, errors.New("failed to parse destination IP")
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}
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ip4 := ip.To4()
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if ip4 == nil {
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return nil, errors.New("destination address is not IPv4")
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}
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port, err := strconv.ParseUint(portStr, 10, 16)
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if err != nil {
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return nil, err
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}
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// Connect to the proxy.
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c, err := s.forward.Dial("tcp", s.hostPort)
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if err != nil {
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return nil, err
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}
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// Make/write the request:
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// +----+----+----+----+----+----+----+----+----+----+....+----+
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// | VN | CD | DSTPORT | DSTIP | USERID |NULL|
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// +----+----+----+----+----+----+----+----+----+----+....+----+
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req := make([]byte, 0, 9+len(s.username))
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req = append(req, socks4Version)
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req = append(req, socks4CommandConnect)
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req = append(req, byte(port>>8), byte(port))
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req = append(req, ip4...)
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if s.username != "" {
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req = append(req, s.username...)
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}
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req = append(req, socks4Null)
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_, err = c.Write(req)
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if err != nil {
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c.Close()
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return nil, err
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}
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// Read the response:
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// +----+----+----+----+----+----+----+----+
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// | VN | CD | DSTPORT | DSTIP |
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// +----+----+----+----+----+----+----+----+
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var resp [8]byte
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_, err = io.ReadFull(c, resp[:])
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if err != nil {
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c.Close()
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return nil, err
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}
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if resp[0] != socks4ReplyVersion {
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c.Close()
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return nil, errors.New("proxy returned invalid SOCKS4 version")
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}
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if resp[1] != socks4Granted {
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c.Close()
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return nil, fmt.Errorf("proxy error: %s", socks4ErrorToString(resp[1]))
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}
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return c, nil
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}
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func socks4ErrorToString(code byte) string {
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switch code {
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case socks4Rejected:
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return "request rejected or failed"
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case socks4RejectedIdentdFailed:
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return "request rejected becasue SOCKS server cannot connect to identd on the client"
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case socks4RejectedIdentdMismatch:
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return "request rejected because the client program and identd report different user-ids"
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default:
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return fmt.Sprintf("unknown failure code %x", code)
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}
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}
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func init() {
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// Despite the scheme name, this really is SOCKS4.
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proxy.RegisterDialerType("socks4a", newSOCKS4)
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}
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