Server: Time-limit pointer drag mutex by default

Closes #417

ChangeLog.md

@@ -12,6 +12,14 @@ number of simultaneously connected viewers.
 server. (These events can be generated with horizontal scroll gestures on a
 trackpad or, with certain mice, by side-clicking the scroll wheel.)
 
+3. By default, the TurboVNC Server now limits the amount of time that it will
+wait for a new pointer event from a connected viewer that is dragging the mouse
+(and thus has exclusive control over the pointer.) This prevents other viewers
+connected to the same session from being locked out of pointer control
+indefinitely if a viewer's network connection drops while it is dragging the
+mouse. A new Xvnc command-line option (`-pointerlocktimeout`) can be used to
+specify the time limit.
+
 
 3.1.1
 =====

unix/Xvnc/programs/Xserver/Xvnc.man.in

@@ -2,7 +2,7 @@
 .\" ** The above line should force tbl to be a preprocessor **
 .\" Man page for Xvnc
 .\"
-.\" Copyright (C) 2010, 2012, 2014-2022 D. R. Commander
+.\" Copyright (C) 2010, 2012, 2014-2022, 2024 D. R. Commander
 .\" Copyright (C) 2021 Steffen Kieß
 .\" Copyright (C) 2010 University Corporation for Atmospheric Research
 .\" Copyright (C) 2005-2008 Sun Microsystems, Inc.
@@ -14,7 +14,7 @@
 .\" License as specified in the file LICENCE.TXT that comes with the
 .\" TurboVNC distribution.
 .\"
-.TH Xvnc 1 "March 2021" "" "TurboVNC"
+.TH Xvnc 1 "July 2024" "" "TurboVNC"
 .SH NAME
 Xvnc \- the TurboVNC X server
 .SH SYNOPSIS
@@ -213,6 +213,17 @@ version of Xvnc by AT&T labs.
 \fB\-nocursor\fR
 Don't display a mouse pointer on the remote desktop.
 
+.TP
+\fB\-pointerlocktimeout \fItime\fR
+Maximum amount of time, in milliseconds, to wait for a new pointer event from a
+connected viewer that is dragging the mouse (moving the mouse with one or more
+mouse buttons held down) and thus has exclusive control over the pointer
+[default: 3000]. 0 = indefinitely.
+
+This prevents other viewers connected to the same session from being locked out
+of pointer control indefinitely if a viewer's network connection drops while it
+is dragging the mouse.
+
 .TP
 \fB\-viewonly\fR
 Don't accept keyboard and pointer events from viewers. All viewers will

unix/Xvnc/programs/Xserver/hw/vnc/init.c

@@ -417,6 +417,16 @@ int ddxProcessArgument(int argc, char *argv[], int i)
  return 1;
  }
 
+ if (strcasecmp(argv[i], "-pointerlocktimeout") == 0) {
+ REQUIRE_ARG();
+ rfbPointerLockTimeout = atoi(argv[i + 1]);
+ if (rfbPointerLockTimeout < 0) {
+ UseMsg();
+ exit(1);
+ }
+ return 2;
+ }
+
  /* Run server in view-only mode - Ehud Karni SW */
  if (strcasecmp(argv[i], "-viewonly") == 0) {
  rfbViewOnly = TRUE;
@@ -1627,6 +1637,7 @@ void ddxGiveUp(enum ExitCode error)
  rfbPAMEnd(cl);
 #endif
  ShutdownTightThreads();
+ TimerFree(pointerLockTimer);
  free(rfbFB.pfbMemory);
  if (initOutputCalled) {
  char unixSocketName[32];
@@ -1738,6 +1749,12 @@ void ddxUseMsg(void)
  ErrorF("======================\n");
  ErrorF("-compatiblekbd set META key = ALT key as in the original VNC\n");
  ErrorF("-nocursor don't display a cursor\n");
+ ErrorF("-pointerlocktimeout time\n");
+ ErrorF(" max time in ms (0 = indefinitely) to wait for a new\n");
+ ErrorF(" pointer event from a connected viewer that is dragging\n");
+ ErrorF(" the mouse (and thus has exclusive control over the\n");
+ ErrorF(" pointer) [default: %d]\n",
+ DEFAULT_POINTER_LOCK_TIMEOUT);
  ErrorF("-viewonly only let viewers view, not control, the remote desktop\n");
  ErrorF("-virtualtablet set up virtual stylus and eraser devices for this\n");
  ErrorF(" session, to emulate a Wacom tablet, and map all\n");

unix/Xvnc/programs/Xserver/hw/vnc/rfb.h

@@ -98,6 +98,8 @@
 
 #define DEFAULT_MAX_CLIENT_WAIT 20000
 
+#define DEFAULT_POINTER_LOCK_TIMEOUT 3000
+
 /* Constants for handling the UltraVNC Viewer's multitouch GII valuator event
  format */
 #define UVNCGII_MAX_TOUCHES 10
@@ -986,6 +988,9 @@ extern int rfbNumThreads;
 
 extern char *rfbCaptureFile;
 
+extern int rfbPointerLockTimeout;
+extern OsTimerPtr pointerLockTimer;
+
 #define debugregion(r, m) \
  rfbLog(m" %d, %d %d x %d\n", (r).extents.x1, (r).extents.y1, \
  (r).extents.x2 - (r).extents.x1, (r).extents.y2 - (r).extents.y1)

unix/Xvnc/programs/Xserver/hw/vnc/rfbserver.c

@@ -3,9 +3,9 @@
  */
 
 /* Copyright (C) 2009-2022, 2024 D. R. Commander. All Rights Reserved.
+ * Copyright (C) 2021, 2024 AnatoScope SA. All Rights Reserved.
  * Copyright (C) 2015-2017, 2020-2021 Pierre Ossman for Cendio AB.
  * All Rights Reserved.
- * Copyright (C) 2021 AnatoScope SA. All Rights Reserved.
  * Copyright (C) 2011 Joel Martin
  * Copyright (C) 2010 University Corporation for Atmospheric Research.
  * All Rights Reserved.
@@ -54,6 +54,13 @@ rfbClientPtr rfbClientHead = NULL;
 /* The client that is currently dragging the pointer
  This serves as a mutex for RFB pointer events. */
 rfbClientPtr pointerDragClient = NULL;
+/* Pointer lock timeout (in milliseconds)
+ Maximum amount of time, in milliseconds, to wait for a new pointer event
+ from a connected viewer that is dragging the mouse (and thus has exclusive
+ control over the pointer.) This prevents other viewers connected to the
+ same session from being locked out of pointer control indefinitely if a
+ viewer's network connection drops while it is dragging the mouse. */
+int rfbPointerLockTimeout = DEFAULT_POINTER_LOCK_TIMEOUT;
 /* The client that last moved the pointer
  Other clients will automatically receive cursor updates via the traditional
  mechanism of drawing the cursor into the framebuffer (AKA "server-side
@@ -124,6 +131,23 @@ void rfbWriteCapture(int captureFD, char *buf, int len)
 }
 
 
+/*
+ * Pointer lock timeout
+ */
+
+OsTimerPtr pointerLockTimer;
+
+static CARD32 PointerLockTimerCallback(OsTimerPtr timer, CARD32 time,
+ void *arg)
+{
+ if (pointerDragClient != NULL)
+ rfbLog("[%u] Timeout expired. Releasing pointer lock\n",
+ pointerDragClient->id);
+ pointerDragClient = NULL;
+ return 0;
+}
+
+
 /*
  * Idle timeout
  */
@@ -570,8 +594,11 @@ void rfbClientConnectionGone(rfbClientPtr cl)
  deflateEnd(&cl->zsStruct[i]);
  }
 
- if (pointerDragClient == cl)
+ if (pointerDragClient == cl) {
+ RFBLOGID("Releasing pointer lock\n");
  pointerDragClient = NULL;
+ TimerCancel(pointerLockTimer);
+ }
 
  if (pointerOwner == cl)
  pointerOwner = NULL;
@@ -1282,10 +1309,18 @@ static void rfbProcessClientNormalMessage(rfbClientPtr cl)
  if (pointerDragClient && (pointerDragClient != cl))
  return;
 
- if (msg.pe.buttonMask == 0)
- pointerDragClient = NULL;
- else
+ if (msg.pe.buttonMask == 0) {
+ if (pointerDragClient != NULL) {
+ pointerDragClient = NULL;
+ TimerCancel(pointerLockTimer);
+ }
+ } else {
  pointerDragClient = cl;
+ if (rfbPointerLockTimeout)
+ pointerLockTimer = TimerSet(pointerLockTimer, 0,
+ rfbPointerLockTimeout,
+ PointerLockTimerCallback, NULL);
+ }
 
  if (!rfbViewOnly && !cl->viewOnly) {
  cl->cursorX = (int)Swap16IfLE(msg.pe.x);