func performHandshakeAndValidation(conn *tls.Conn, uri *url.URL) error {
	if err := conn.Handshake(); err != nil {
		return err
	}

	cs := conn.ConnectionState()
	if !cs.NegotiatedProtocolIsMutual || cs.NegotiatedProtocol != protocol.ProtocolName {
		return fmt.Errorf("protocol negotiation error")
	}

	q := uri.Query()
	relayIDs := q.Get("id")
	if relayIDs != "" {
		relayID, err := syncthingprotocol.DeviceIDFromString(relayIDs)
		if err != nil {
			return fmt.Errorf("relay address contains invalid verification id: %s", err)
		}

		certs := cs.PeerCertificates
		if cl := len(certs); cl != 1 {
			return fmt.Errorf("unexpected certificate count: %d", cl)
		}

		remoteID := syncthingprotocol.NewDeviceID(certs[0].Raw)
		if remoteID != relayID {
			return fmt.Errorf("relay id does not match. Expected %v got %v", relayID, remoteID)
		}
	}

	return nil
}

// checkErr logs if an error occurs and closes the tlsConn.
func checkErr(err error, tlsConn *tls.Conn) {
	if err != nil {
		tlsConn.Close()
		log.Fatalf("GBNetworkTools: %s\n", err.Error())

	}
}

func (d *relayDialer) Dial(id protocol.DeviceID, uri *url.URL) (IntermediateConnection, error) {
	inv, err := client.GetInvitationFromRelay(uri, id, d.tlsCfg.Certificates, 10*time.Second)
	if err != nil {
		return IntermediateConnection{}, err
	}

	conn, err := client.JoinSession(inv)
	if err != nil {
		return IntermediateConnection{}, err
	}

	err = dialer.SetTCPOptions(conn)
	if err != nil {
		conn.Close()
		return IntermediateConnection{}, err
	}

	var tc *tls.Conn
	if inv.ServerSocket {
		tc = tls.Server(conn, d.tlsCfg)
	} else {
		tc = tls.Client(conn, d.tlsCfg)
	}

	err = tc.Handshake()
	if err != nil {
		tc.Close()
		return IntermediateConnection{}, err
	}

	return IntermediateConnection{tc, "Relay (Client)", relayPriority}, nil
}

func (c *connection) startTls() (err error) {
	if c.authOptions == nil {
		return nil
	}
	if c.authOptions.TlsConfig == nil {
		return ErrAuthMissingConfig
	}
	c.state = connTlsStarting
	startTlsCmd := &StartTlsCommand{}
	if err = c.execute(startTlsCmd); err != nil {
		return
	}
	var tlsConn *tls.Conn
	if tlsConn = tls.Client(c.conn, c.authOptions.TlsConfig); tlsConn == nil {
		err = ErrAuthTLSUpgradeFailed
		return
	}
	if err = tlsConn.Handshake(); err != nil {
		return
	}
	c.conn = tlsConn
	authCmd := &AuthCommand{
		User:     c.authOptions.User,
		Password: c.authOptions.Password,
	}
	err = c.execute(authCmd)
	return
}

func NewConnectingPeer(logger *util.Logger, server *TLSServer, connection *tls.Conn) *Peer {
	inst := NewPeer(logger, server, connection.RemoteAddr().String())
	inst.Connection = connection
	inst.State = PeerStateHandshake
	inst.Incoming = true
	return inst
}

// getChain returns chain of certificates retrieved from TLS session
// established at given addr (host:port) for hostname provided. If addr is
// empty, then hostname:443 is used.
func getChain(hostname, addr string) ([]*x509.Certificate, error) {
	if hostname == "" {
		return nil, errors.New("empty hostname")
	}
	var (
		conn *tls.Conn
		err  error
	)
	type tempErr interface {
		Temporary() bool
	}
	conf := &tls.Config{ServerName: hostname}
	if addr == "" {
		addr = hostname + ":443"
	}
	dialer := &net.Dialer{
		Timeout: 30 * time.Second,
	}
	for i := 0; i < 3; i++ {
		if i > 0 {
			time.Sleep(time.Duration(i) * time.Second)
		}
		conn, err = tls.DialWithDialer(dialer, "tcp", addr, conf)
		if e, ok := err.(tempErr); ok && e.Temporary() {
			continue
		}
		if err != nil {
			return nil, err
		}
		defer conn.Close()
		return conn.ConnectionState().PeerCertificates, nil
	}
	return nil, err
}

// SessionResumeScan tests that host is able to resume sessions across all addresses.
func sessionResumeScan(addr, hostname string) (grade Grade, output Output, err error) {
	config := defaultTLSConfig(hostname)
	config.ClientSessionCache = tls.NewLRUClientSessionCache(1)

	conn, err := tls.DialWithDialer(Dialer, Network, addr, config)
	if err != nil {
		return
	}
	if err = conn.Close(); err != nil {
		return
	}

	return multiscan(addr, func(addrport string) (g Grade, o Output, e error) {
		var conn *tls.Conn
		if conn, e = tls.DialWithDialer(Dialer, Network, addrport, config); e != nil {
			return
		}
		conn.Close()

		if o = conn.ConnectionState().DidResume; o.(bool) {
			g = Good
		}
		return
	})
}

// HandleStartTLS is the companion to StartTLS, and will do the connection upgrade.  It assumes
// that the TLS command byte has already been read.  Like StartTLS it returns the peer name, or
// an error
func (p *Protocol) HandleStartTLS(identity *security.Identity, caCertificate *security.Certificate) (string, error) {
	var (
		err     error
		tlsConn *tls.Conn
	)

	// Build the config
	config := new(tls.Config)
	config.ClientAuth = tls.RequireAndVerifyClientCert

	// Setup the tls connection
	if err := p.tlsSetup(config, identity, caCertificate); err != nil {
		return "", err
	}

	// Upgrade the connection to TLS
	// TODO: Add a deadline here?
	tlsConn = tls.Server(p.conn, config)
	if err = tlsConn.Handshake(); err != nil {
		return "", err
	}

	// Capture the connection state
	cs := tlsConn.ConnectionState()

	// And replace the original connection
	p.conn = net.Conn(tlsConn)
	p.setupBuffers()

	// Send an Ack
	p.Ack()

	return cs.PeerCertificates[0].Subject.CommonName, nil
}

func read(client *Client, conn *tls.Conn) {
	buffer := make([]byte, ERR_RESPONSE_LEN)

	if _, err := conn.Read(buffer); err != nil {
		log.Printf("read err %v, %v, %p\n", err, err == io.EOF, client)
		client.chConnectionErr <- conn
		return
	}

	errRsp := &errResponse{
		Command: uint8(buffer[0]),
		Status:  uint8(buffer[1]),
	}

	if err := binary.Read(bytes.NewBuffer(buffer[2:]), binary.BigEndian, &errRsp.Identifier); err != nil {
		log.Println("read identifier err", err)
		return
	}

	if errRsp.Command != ERR_RESPONSE_CMD {
		log.Println("unknown err response", buffer)
		return
	}

	errMsg, ok := ApplePushResponses[errRsp.Status]
	if !ok {
		log.Println("unknown err status", buffer)
		return
	}

	log.Printf("get err response : %##v, %s\n", errRsp, errMsg)

	client.chErrResponse <- errRsp
}

func HandleUserTimeout(UserCollection *mgo.Collection, username, RSA_Public_Key string, conn *tls.Conn, timeout_sec int) {
	log.Printf("Timeout:\tUser '%s' at %s\n", username, conn.RemoteAddr())
	err := GBServerDatabase.UpdateLastAccessedTime(UserCollection, username, string(RSA_Public_Key), 5)
	checkErr(err)
	err = GBServerDatabase.UpdateCurrentlyBeingUsed(UserCollection, username, string(RSA_Public_Key), false)
	checkErr(err)
}

func (c *connection) startTls() error {
	if c.authOptions == nil {
		return nil
	}
	if c.authOptions.TlsConfig == nil {
		return ErrAuthMissingConfig
	}
	c.setState(connTlsStarting)
	startTlsCmd := &startTlsCommand{}
	if err := c.execute(startTlsCmd); err != nil {
		return err
	}
	var tlsConn *tls.Conn
	if tlsConn = tls.Client(c.conn, c.authOptions.TlsConfig); tlsConn == nil {
		return ErrAuthTLSUpgradeFailed
	}
	if err := tlsConn.Handshake(); err != nil {
		return err
	}
	c.conn = tlsConn
	authCmd := &authCommand{
		user:     c.authOptions.User,
		password: c.authOptions.Password,
	}
	return c.execute(authCmd)
}

func connect(app string, keyFile string, certFile string, sandbox bool) {
	defer CapturePanic(fmt.Sprintf("connection to apns server error %s", app))
	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
	if err != nil {
		log.Printf("server : loadKeys: %s", err)
	}
	config := tls.Config{Certificates: []tls.Certificate{cert}, InsecureSkipVerify: true}
	endPoint := APNS_ENDPOINT
	if sandbox {
		endPoint = APNS_SANDBOX_ENDPOINT
	}
	var conn *tls.Conn
	for {
		conn, err = tls.Dial("tcp", endPoint, &config)
		if err != nil {
			log.Println("连接服务器有误, 2秒后将重连", err)
			time.Sleep(time.Second * 2)
		} else {
			break
		}
	}

	log.Println("client is connect to ", conn.RemoteAddr())
	state := conn.ConnectionState()

	log.Println("client: hand shake ", state.HandshakeComplete)
	log.Println("client: mutual", state.NegotiatedProtocolIsMutual)
	if sandbox {
		app = app + DEVELOP_SUBFIX
	}
	info := &ConnectInfo{Connection: conn, App: app, Sandbox: sandbox, lastActivity: time.Now().Unix()}
	socketCN <- info
}

func (t *TCP) startTLS() (el element.Element, err error) {
	var tlsConn *tls.Conn
	if t.mode == stream.Initiating {
		err = t.WriteElement(element.StartTLS)
		if err != nil {
			return
		}
		el, err = t.Next()
		if err != nil || el.Tag != element.TLSProceed.Tag {
			return
		}
		tlsConn = tls.Client(t.Conn, t.conf)
	} else {
		err = t.WriteElement(element.TLSProceed)
		if err != nil {
			return
		}
		tlsConn = tls.Server(t.Conn, t.conf)
	}

	err = tlsConn.Handshake()
	if err != nil {
		return
	}
	conn := net.Conn(tlsConn)
	t.Conn = conn
	t.Decoder = xml.NewDecoder(conn)
	el = element.Element{}
	err = stream.ErrRequireRestart
	t.secure = true
	log.Println("Done upgrading connection")
	return
}

func getPublicKey(tlsConn *tls.Conn) ([]byte, error) {
	state := tlsConn.ConnectionState()
	for _, v := range state.PeerCertificates {
		return x509.MarshalPKIXPublicKey(v.PublicKey)
	}
	return []byte{}, nil
}

// Start the simple voice app on the encrypted channel.
func startVoiceApp(tlsconn *tls.Conn, remoteCN string) {
	// start the speaker part and connect it to our socket
	spr := exec.Command("/usr/bin/aplay")
	spr.Stdin = tlsconn
	err := spr.Start() // start asynchronously
	check(err)

	// start the microphone too
	// defaults: 1 channel 8000 Hz sample rate, WAVE format
	mic := exec.Command("/usr/bin/arecord")
	mic.Stdout = tlsconn
	err = mic.Start() // start asynchronously
	check(err)

	// TODO: write a ping to signal connection
	// mess := text_to_speech("Connected to %s, chat away!\n", remoteCN)
	// spr.Write([]byte(mess))

	// wait for it to finish
	// TODO: find a way to hang up the connection, short of killall arecord/aplay
	err = mic.Wait()
	check(err)
	err = spr.Wait()
	check(err)

	tlsconn.Close()
}

func postVerifyTLSConnection(conn *tls.Conn, config *TLSConfig) error {
	st := conn.ConnectionState()

	if !st.HandshakeComplete {
		return errors.New("incomplete handshake")
	}

	// no more checks if no extra configs available
	if config == nil {
		return nil
	}

	versions := config.Versions
	if versions == nil {
		versions = tlsDefaultVersions
	}
	versionOK := false
	for _, version := range versions {
		versionOK = versionOK || st.Version == uint16(version)
	}
	if !versionOK {
		return fmt.Errorf("tls version %v not configured", TLSVersion(st.Version))
	}

	return nil
}

// StartTLS takes an identity and an authority certificate and upgrades the net.Conn on the protocol to TLS
// It returns the CommonName from the peer certitifcate, or an error
func (p *Protocol) StartTLS(identity *security.Identity, caCertificate *security.Certificate) (string, error) {
	var (
		err     error
		tlsConn *tls.Conn
	)

	if err = p.WriteBytesWithDeadline([]byte{TLS}); err != nil {
		return "", err
	}

	// Build the config
	config := new(tls.Config)
	config.ServerName = p.serverName

	// Setup the tls connection
	if err = p.tlsSetup(config, identity, caCertificate); err != nil {
		return "", err
	}

	// Upgrade the connection to TLS
	// TODO: Add a deadline here?
	tlsConn = tls.Client(p.conn, config)
	if err = tlsConn.Handshake(); err != nil {
		return "", err
	}

	// Capture the connection state
	cs := tlsConn.ConnectionState()

	// And replace the original connection
	p.conn = net.Conn(tlsConn)
	p.setupBuffers()

	return cs.PeerCertificates[0].Subject.CommonName, nil
}

func closeAndCountFDs(t *testing.T, conn *tls.Conn, err error, fdStart int) {
	if err == nil {
		conn.Close()
	}
	fdEnd := countTCPFiles()
	assert.Equal(t, fdStart, fdEnd, "Number of open TCP files should be the same after test as before")
}

func Connect(cert_filename string, key_filename string, server string) (*Apn, error) {
	rchan := make(chan NotificationError)

	cert, cert_err := tls.LoadX509KeyPair(cert_filename, key_filename)
	if cert_err != nil {
		return nil, cert_err
	}

	conn, err := net.Dial("tcp", server)
	if err != nil {
		return nil, err
	}

	certificate := []tls.Certificate{cert}
	conf := tls.Config{
		Certificates: certificate,
	}

	var client_conn *tls.Conn = tls.Client(conn, &conf)
	err = client_conn.Handshake()
	if err != nil {
		return nil, err
	}

	go readError(client_conn, rchan)

	return &Apn{cert, server, client_conn, rchan}, nil
}

// Start the simple chat app on the encrypted channel.
func startChatApp(tlsconn *tls.Conn, remoteCN string) {
	// Create listener socket for the simple chat
	socket, err := net.Listen("tcp", "[::1]:0")
	check(err)
	port := getPort(socket.Addr().String())

	// start the chat app and point it to our socket
	cmd := exec.Command("uxterm", "-e", "nc", "-6", "::1", port)

	err = cmd.Start() // start asynchronously
	check(err)

	// wait for it to connect
	app, err := socket.Accept()
	check(err)

	// show a welcome message
	mess := fmt.Sprintf("Connected to %s, chat away!\n", remoteCN)
	app.Write([]byte(mess))
	app.Write([]byte(fmt.Sprintf("%s\n", strings.Repeat("-", len(mess)-1))))

	// copy the TLS-connection to the chat app and back
	go io.Copy(app, tlsconn)
	go io.Copy(tlsconn, app)

	// wait for it to finish
	err = cmd.Wait()
	check(err)

	// Close all, including the socket and the TLS channel.
	// We run this only once.
	app.Close()
	socket.Close()
	tlsconn.Close()
}