Re: [PATCH 7/9] vnc: force initial resize message

[Marc-André Lureau]

Hi

On Thu, Dec 3, 2020 at 3:12 PM Gerd Hoffmann <kraxel@redhat.com> wrote:

The vnc server should send desktop resize notifications unconditionally
on a new client connect, for feature negotiation reasons.  Add a bool
flag to vnc_desktop_resize() to force sending the message even in case
there is no size change.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

In principle, this looks harmless. But the spec says:

"The server should only send a DesktopSize pseudo-rectangle when an actual change of the framebuffer dimensions has occurred. Some clients respond to a DesktopSize pseudo-rectangle in a way that could send the system into an infinite loop if the server sent out the pseudo-rectangle for anything other than an actual change."

(https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#server-semantics)

I can't say if sending desktop resize during the initial SetEncoding phase is really compliant with the specification. Also, it's unclear to me if the client is allowed to SetEncoding multiple times (in which there would be no dimension change occurring).

What did you fix with this? Is it worth a clarification in the specification?

thanks

---
 ui/vnc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/ui/vnc.c b/ui/vnc.c
index 247e80d8f5c8..bdaf384f71a4 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -664,13 +664,14 @@ void vnc_framebuffer_update(VncState *vs, int x, int y, int w, int h,
 }


-static void vnc_desktop_resize(VncState *vs)
+static void vnc_desktop_resize(VncState *vs, bool force)
 {
     if (vs->ioc == NULL || !vnc_has_feature(vs, VNC_FEATURE_RESIZE)) {
         return;
     }
     if (vs->client_width == pixman_image_get_width(vs->vd->server) &&
-        vs->client_height == pixman_image_get_height(vs->vd->server)) {
+        vs->client_height == pixman_image_get_height(vs->vd->server) &&
+        !force) {
         return;
     }

@@ -800,7 +801,7 @@ static void vnc_dpy_switch(DisplayChangeListener *dcl,

     QTAILQ_FOREACH(vs, &vd->clients, next) {
         vnc_colordepth(vs);
-        vnc_desktop_resize(vs);
+        vnc_desktop_resize(vs, false);
         if (vs->vd->cursor) {
             vnc_cursor_define(vs);
         }
@@ -2143,7 +2144,7 @@ static void set_encodings(VncState *vs, int32_t *encodings, size_t n_encodings)
             break;
         }
     }
-    vnc_desktop_resize(vs);
+    vnc_desktop_resize(vs, true);
     check_pointer_type_change(&vs->mouse_mode_notifier, NULL);
     vnc_led_state_change(vs);
     if (vs->vd->cursor) {
--
2.27.0

--

Marc-André Lureau