Fix message for idle desktop connection

lib/srv/desktop/windows_server.go

@@ -902,10 +902,7 @@ func (s *WindowsService) connectRDP(ctx context.Context, log logrus.FieldLogger,
 		TeleportUser:          identity.Username,
 		ServerID:              s.cfg.Heartbeat.HostUUID,
 		IdleTimeoutMessage:    netConfig.GetClientIdleTimeoutMessage(),
-		MessageWriter: &monitorErrorSender{
-			log:     log,
-			tdpConn: tdpConn,
-		},
+		MessageWriter:         &monitorErrorSender{tdpConn: tdpConn},
 	}
 
 	// UpdateClientActivity before starting monitor to
@@ -1303,15 +1300,12 @@ func (s *WindowsService) trackSession(ctx context.Context, id *tlsca.Identity, w
 // monitor disconnect messages back to the frontend
 // over the tdp.Conn
 type monitorErrorSender struct {
-	log     logrus.FieldLogger
 	tdpConn *tdp.Conn
 }
 
 func (m *monitorErrorSender) WriteString(s string) (n int, err error) {
 	if err := m.tdpConn.SendNotification(s, tdp.SeverityError); err != nil {
-		errMsg := fmt.Sprintf("Failed to send TDP error message %v: %v", s, err)
-		m.log.Error(errMsg)
-		return 0, trace.Errorf(errMsg)
+		return 0, trace.Wrap(err, "sending TDP error message")
 	}
 
 	return len(s), nil

lib/srv/monitor.go

@@ -356,13 +356,16 @@ func (w *Monitor) start(lockWatch types.Watcher) {
 			clientLastActive := w.Tracker.GetClientLastActive()
 			since := w.Clock.Since(clientLastActive)
 			if since >= w.ClientIdleTimeout {
-				reason := "client reported no activity"
+				reason := "Client reported no activity"
 				if !clientLastActive.IsZero() {
-					reason = fmt.Sprintf("client is idle for %v, exceeded idle timeout of %v",
-						since, w.ClientIdleTimeout)
+					reason = fmt.Sprintf("Client exceeded idle timeout of %v", w.ClientIdleTimeout)
 				}
-				if w.MessageWriter != nil && w.IdleTimeoutMessage != "" {
-					if _, err := w.MessageWriter.WriteString(w.IdleTimeoutMessage); err != nil {
+				if w.MessageWriter != nil {
+					msg := w.IdleTimeoutMessage
+					if msg == "" {
+						msg = reason
+					}
+					if _, err := w.MessageWriter.WriteString(msg); err != nil {
 						w.Entry.WithError(err).Warn("Failed to send idle timeout message.")
 					}
 				}

lib/srv/monitor_test.go

@@ -22,6 +22,7 @@ import (
 	"context"
 	"io"
 	"net"
+	"strings"
 	"testing"
 	"time"
 
@@ -41,6 +42,9 @@ import (
 )
 
 func newTestMonitor(ctx context.Context, t *testing.T, asrv *auth.TestAuthServer, mut ...func(*MonitorConfig)) (*mockTrackingConn, *eventstest.ChannelEmitter, MonitorConfig) {
+	ctx, cancel := context.WithCancel(ctx)
+	t.Cleanup(cancel)
+
 	conn := &mockTrackingConn{closedC: make(chan struct{})}
 	emitter := eventstest.NewChannelEmitter(1)
 	cfg := MonitorConfig{
@@ -252,6 +256,29 @@ func TestMonitorStaleLocks(t *testing.T) {
 	require.Equal(t, services.StrictLockingModeAccessDenied.Error(), (<-emitter.C()).(*apievents.ClientDisconnect).Reason)
 }
 
+func TestWritesDisconnectMessage(t *testing.T) {
+	asrv, err := auth.NewTestAuthServer(auth.TestAuthServerConfig{
+		Dir:   t.TempDir(),
+		Clock: clockwork.NewFakeClock(),
+	})
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, asrv.Close()) })
+
+	var sw strings.Builder
+
+	ctx := context.Background()
+	clock := clockwork.NewFakeClock()
+	conn, _, _ := newTestMonitor(ctx, t, asrv, func(cfg *MonitorConfig) {
+		cfg.ClientIdleTimeout = 1 * time.Second
+		cfg.Clock = clock
+		cfg.MessageWriter = &sw
+	})
+	clock.BlockUntil(1)
+	clock.Advance(2 * time.Second)
+	<-conn.closedC
+	require.Contains(t, sw.String(), "exceeded idle timeout")
+}
+
 type mockTrackingConn struct {
 	net.Conn
 	closedC chan struct{}