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package shapeshifter // import "0xacab.org/leap/shapeshifter"
import (
"encoding/base64"
"fmt"
"io"
"log"
"net"
"strconv"
"sync"
pt "git.torproject.org/pluggable-transports/goptlib.git"
"gitlab.com/yawning/obfs4.git/common/ntor"
"gitlab.com/yawning/obfs4.git/transports/obfs4"
"golang.org/x/net/proxy"
)
const (
certLength = ntor.NodeIDLength + ntor.PublicKeyLength
)
func unpackCert(cert string) (*ntor.NodeID, *ntor.PublicKey, error) {
if l := base64.RawStdEncoding.DecodedLen(len(cert)); l != certLength {
return nil, nil, fmt.Errorf("cert length %d is invalid", l)
}
decoded, err := base64.RawStdEncoding.DecodeString(cert)
if err != nil {
return nil, nil, err
}
nodeID, _ := ntor.NewNodeID(decoded[:ntor.NodeIDLength])
pubKey, _ := ntor.NewPublicKey(decoded[ntor.NodeIDLength:])
return nodeID, pubKey, nil
}
type Logger interface {
Log(msg string)
}
type ShapeShifter struct {
Cert string
IatMode int
Target string // remote ip:port obfs4 server
SocksAddr string // -proxylistenaddr in shapeshifter-dispatcher
Logger Logger
ln net.Listener
errChan chan error
}
func (ss *ShapeShifter) Open() error {
err := ss.checkOptions()
if err != nil {
return err
}
ss.ln, err = net.Listen("tcp", ss.SocksAddr)
if err != nil {
return fmt.Errorf("failed to listen: %s", err.Error())
}
go ss.clientAcceptLoop()
return nil
}
func (ss *ShapeShifter) Close() error {
var err error
if ss.ln != nil {
err = ss.ln.Close()
}
if ss.errChan != nil {
close(ss.errChan)
}
return err
}
func (ss *ShapeShifter) GetErrorChannel() chan error {
if ss.errChan == nil {
ss.errChan = make(chan error, 2)
}
return ss.errChan
}
func (ss ShapeShifter) clientAcceptLoop() error {
for {
conn, err := ss.ln.Accept()
if err != nil {
if e, ok := err.(net.Error); ok && !e.Temporary() {
return err
}
ss.sendError("Error accepting connection: %v", err)
continue
}
go ss.clientHandler(conn)
}
}
func (ss ShapeShifter) clientHandler(conn net.Conn) {
defer conn.Close()
dialer := proxy.Direct
// The empty string is the StateDir argument which appears unused on the
// client side. I am unsure why the clientfactory requires it; possibly to
// satisfy an interface somewhere, but this is not documented.
//transport, err := obfs4.NewObfs4Client(ss.Cert, ss.IatMode, dialer)
transport, err := (&obfs4.Transport{}).ClientFactory("")
if err != nil {
ss.sendError("Can not create an obfs4 client (cert: %s, iat-mode: %d): %v", ss.Cert, ss.IatMode, err)
return
}
ptArgs := make(pt.Args)
nodeID, pubKey, err := unpackCert(ss.Cert)
if err != nil {
ss.sendError("Error unpacking cert: %v", err)
return
}
ptArgs.Add("node-id", nodeID.Hex())
ptArgs.Add("public-key", pubKey.Hex())
ptArgs.Add("iat-mode", strconv.Itoa(ss.IatMode))
args, err := transport.ParseArgs(&ptArgs)
if err != nil {
ss.sendError("Cannot parse arguments: %v", err)
return
}
remote, err := transport.Dial("tcp", ss.Target, dialer.Dial, args)
if err != nil {
ss.sendError("outgoing connection failed %s: %v", ss.Target, err)
return
}
if remote == nil {
ss.sendError("outgoing connection failed %s", ss.Target)
return
}
defer remote.Close()
err = copyLoop(conn, remote)
if err != nil {
ss.sendError("%s - closed connection: %v", ss.Target, err)
} else {
log.Printf("%s - closed connection", ss.Target)
}
return
}
func copyLoop(a net.Conn, b net.Conn) error {
// Note: b is always the pt connection. a is the SOCKS/ORPort connection.
errChan := make(chan error, 2)
var wg sync.WaitGroup
wg.Add(2)
go func() {
defer wg.Done()
defer b.Close()
defer a.Close()
_, err := io.Copy(b, a)
errChan <- err
}()
go func() {
defer wg.Done()
defer a.Close()
defer b.Close()
_, err := io.Copy(a, b)
errChan <- err
}()
// Wait for both upstream and downstream to close. Since one side
// terminating closes the other, the second error in the channel will be
// something like EINVAL (though io.Copy() will swallow EOF), so only the
// first error is returned.
wg.Wait()
if len(errChan) > 0 {
return <-errChan
}
return nil
}
func (ss *ShapeShifter) checkOptions() error {
if ss.SocksAddr == "" {
ss.SocksAddr = "127.0.0.1:0"
}
_, _, err := unpackCert(ss.Cert)
return err
}
func (ss *ShapeShifter) sendError(format string, a ...interface{}) {
if ss.Logger != nil {
ss.Logger.Log(fmt.Sprintf(format, a...))
return
}
if ss.errChan == nil {
ss.errChan = make(chan error, 2)
}
select {
case ss.errChan <- fmt.Errorf(format, a...):
default:
log.Printf(format, a...)
}
}
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