obfs4/obfs4-client/obfs4-client.go

/*
 * 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 file is based off goptlib's dummy-client.go file.
 */

// obfs4 pluggable transport client. Works only as a managed proxy.
//
// Usage (in torrc):
// 	UseBridges 1
// 	Bridge obfs4 X.X.X.X:YYYY public-key=<Base64 Bridge public key> node-id=<Base64 Node ID>
// 	ClientTransportPlugin obfs4 exec obfs4-client
//
// Becuase the pluggable transport requires arguments, using obfs4-client 
// requires tor 0.2.5.x.
package main

import (
	"io"
	"net"
	"os"
	"os/signal"
	"sync"
	"syscall"

	"github.com/yawning/obfs4"
)

import "git.torproject.org/pluggable-transports/goptlib.git"

var ptInfo pt.ClientInfo

// When a connection handler starts, +1 is written to this channel; when it
// ends, -1 is written.
var handlerChan = make(chan int)

func copyLoop(a, b net.Conn) {
	var wg sync.WaitGroup
	wg.Add(2)

	// TODO: Log errors.
	go func() {
		io.Copy(b, a)
		wg.Done()
	}()
	go func() {
		io.Copy(a, b)
		wg.Done()
	}()

	wg.Wait()
}

func handler(conn *pt.SocksConn) error {
	// Extract the peer's node ID and public key.
	nodeID, ok := conn.Req.Args.Get("node-id")
	if !ok {
		// TODO: Log something here.
		conn.Reject()
	}
	publicKey, ok := conn.Req.Args.Get("public-key")
	if !ok {
		// TODO: Log something here.
		conn.Reject()
	}

	handlerChan <- 1
	defer func() {
		handlerChan <- -1
	}()

	defer conn.Close()
	remote, err := obfs4.Dial("tcp", conn.Req.Target, nodeID, publicKey)
	if err != nil {
		conn.Reject()
		return err
	}
	defer remote.Close()
	err = conn.Grant(remote.RemoteAddr().(*net.TCPAddr))
	if err != nil {
		return err
	}

	copyLoop(conn, remote)

	return nil
}

func acceptLoop(ln *pt.SocksListener) error {
	defer ln.Close()
	for {
		conn, err := ln.AcceptSocks()
		if err != nil {
			if e, ok := err.(net.Error); ok && !e.Temporary() {
				return err
			}
			continue
		}
		go handler(conn)
	}
}

func main() {
	var err error

	ptInfo, err = pt.ClientSetup([]string{"obfs4"})
	if err != nil {
		os.Exit(1)
	}

	listeners := make([]net.Listener, 0)
	for _, methodName := range ptInfo.MethodNames {
		switch methodName {
		case "obfs4":
			ln, err := pt.ListenSocks("tcp", "127.0.0.1:0")
			if err != nil {
				pt.CmethodError(methodName, err.Error())
				break
			}
			go acceptLoop(ln)
			pt.Cmethod(methodName, ln.Version(), ln.Addr())
			listeners = append(listeners, ln)
		default:
			pt.CmethodError(methodName, "no such method")
		}
	}
	pt.CmethodsDone()

	var numHandlers int = 0
	var sig os.Signal
	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)

	// wait for first signal
	sig = nil
	for sig == nil {
		select {
		case n := <-handlerChan:
			numHandlers += n
		case sig = <-sigChan:
		}
	}
	for _, ln := range listeners {
		ln.Close()
	}

	if sig == syscall.SIGTERM {
		return
	}

	// wait for second signal or no more handlers
	sig = nil
	for sig == nil && numHandlers != 0 {
		select {
		case n := <-handlerChan:
			numHandlers += n
		case sig = <-sigChan:
		}
	}
}