func (sshServer *sshServer) handleClient(tunnelProtocol string, clientConn net.Conn) {

	sshServer.registerAcceptedClient(tunnelProtocol)
	defer sshServer.unregisterAcceptedClient(tunnelProtocol)

	geoIPData := sshServer.support.GeoIPService.Lookup(
		common.IPAddressFromAddr(clientConn.RemoteAddr()))

	sshClient := newSshClient(sshServer, tunnelProtocol, geoIPData)

	// Set initial traffic rules, pre-handshake, based on currently known info.
	sshClient.setTrafficRules()

	// Wrap the base client connection with an ActivityMonitoredConn which will
	// terminate the connection if no data is received before the deadline. This
	// timeout is in effect for the entire duration of the SSH connection. Clients
	// must actively use the connection or send SSH keep alive requests to keep
	// the connection active. Writes are not considered reliable activity indicators
	// due to buffering.

	activityConn, err := common.NewActivityMonitoredConn(
		clientConn,
		SSH_CONNECTION_READ_DEADLINE,
		false,
		nil)
	if err != nil {
		clientConn.Close()
		log.WithContextFields(LogFields{"error": err}).Error("NewActivityMonitoredConn failed")
		return
	}
	clientConn = activityConn

	// Further wrap the connection in a rate limiting ThrottledConn.

	throttledConn := common.NewThrottledConn(clientConn, sshClient.rateLimits())
	clientConn = throttledConn

	// Run the initial [obfuscated] SSH handshake in a goroutine so we can both
	// respect shutdownBroadcast and implement a specific handshake timeout.
	// The timeout is to reclaim network resources in case the handshake takes
	// too long.

	type sshNewServerConnResult struct {
		conn     net.Conn
		sshConn  *ssh.ServerConn
		channels <-chan ssh.NewChannel
		requests <-chan *ssh.Request
		err      error
	}

	resultChannel := make(chan *sshNewServerConnResult, 2)

	if SSH_HANDSHAKE_TIMEOUT > 0 {
		time.AfterFunc(time.Duration(SSH_HANDSHAKE_TIMEOUT), func() {
			resultChannel <- &sshNewServerConnResult{err: errors.New("ssh handshake timeout")}
		})
	}

	go func(conn net.Conn) {
		sshServerConfig := &ssh.ServerConfig{
			PasswordCallback: sshClient.passwordCallback,
			AuthLogCallback:  sshClient.authLogCallback,
			ServerVersion:    sshServer.support.Config.SSHServerVersion,
		}
		sshServerConfig.AddHostKey(sshServer.sshHostKey)

		result := &sshNewServerConnResult{}

		// Wrap the connection in an SSH deobfuscator when required.

		if common.TunnelProtocolUsesObfuscatedSSH(tunnelProtocol) {
			// Note: NewObfuscatedSshConn blocks on network I/O
			// TODO: ensure this won't block shutdown
			conn, result.err = psiphon.NewObfuscatedSshConn(
				psiphon.OBFUSCATION_CONN_MODE_SERVER,
				conn,
				sshServer.support.Config.ObfuscatedSSHKey)
			if result.err != nil {
				result.err = common.ContextError(result.err)
			}
		}

		if result.err == nil {
			result.sshConn, result.channels, result.requests, result.err =
				ssh.NewServerConn(conn, sshServerConfig)
		}

		resultChannel <- result

	}(clientConn)

	var result *sshNewServerConnResult
	select {
	case result = <-resultChannel:
	case <-sshServer.shutdownBroadcast:
		// Close() will interrupt an ongoing handshake
		// TODO: wait for goroutine to exit before returning?
		clientConn.Close()
		return
	}

	if result.err != nil {
		clientConn.Close()
		// This is a Debug log due to noise. The handshake often fails due to I/O
		// errors as clients frequently interrupt connections in progress when
		// client-side load balancing completes a connection to a different server.
		log.WithContextFields(LogFields{"error": result.err}).Debug("handshake failed")
		return
	}

	sshClient.Lock()
	sshClient.sshConn = result.sshConn
	sshClient.activityConn = activityConn
	sshClient.throttledConn = throttledConn
	sshClient.Unlock()

	if !sshServer.registerEstablishedClient(sshClient) {
		clientConn.Close()
		log.WithContext().Warning("register failed")
		return
	}
	defer sshServer.unregisterEstablishedClient(sshClient.sessionID)

	sshClient.runClient(result.channels, result.requests)

	// Note: sshServer.unregisterClient calls sshClient.Close(),
	// which also closes underlying transport Conn.
}
func TestObfuscatedSSHConn(t *testing.T) {

	keyword, _ := MakeRandomStringHex(32)

	serverAddress := "127.0.0.1:2222"

	listener, err := net.Listen("tcp", serverAddress)
	if err != nil {
		t.Fatalf("Listen failed: %s", err)
	}

	rsaKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		t.Fatalf("GenerateKey failed: %s", err)
	}

	hostKey, err := ssh.NewSignerFromKey(rsaKey)
	if err != nil {
		t.Fatalf("NewSignerFromKey failed: %s", err)
	}

	sshCertChecker := &ssh.CertChecker{
		HostKeyFallback: func(addr string, remote net.Addr, publicKey ssh.PublicKey) error {
			if !bytes.Equal(hostKey.PublicKey().Marshal(), publicKey.Marshal()) {
				return errors.New("unexpected host public key")
			}
			return nil
		},
	}

	result := make(chan error, 1)

	go func() {

		conn, err := listener.Accept()

		if err == nil {
			conn, err = NewObfuscatedSshConn(
				OBFUSCATION_CONN_MODE_SERVER, conn, keyword)
		}

		if err == nil {
			config := &ssh.ServerConfig{
				NoClientAuth: true,
			}
			config.AddHostKey(hostKey)

			_, _, _, err = ssh.NewServerConn(conn, config)
		}

		if err != nil {
			select {
			case result <- err:
			default:
			}
		}
	}()

	go func() {

		conn, err := net.DialTimeout("tcp", serverAddress, 5*time.Second)

		if err == nil {
			conn, err = NewObfuscatedSshConn(
				OBFUSCATION_CONN_MODE_CLIENT, conn, keyword)
		}

		if err == nil {
			config := &ssh.ClientConfig{
				HostKeyCallback: sshCertChecker.CheckHostKey,
			}
			_, _, _, err = ssh.NewClientConn(conn, "", config)
		}

		// Sends nil on success
		select {
		case result <- err:
		default:
		}
	}()

	err = <-result
	if err != nil {
		t.Fatalf("obfuscated SSH handshake failed: %s", err)
	}
}