[Spice-devel] [spice-gtk v2] gtk-session: clipboard request: notify agent on failure

[Victor Toso]

From: Victor Toso <me at victortoso.com>

Similar to 172c521271a3d - if we don't, the agent might be waiting for
data till some timeout happens in the system, blocking copy-paste
feature and possibly freezing applications.

A way to reproduce is copy-paste big clipboard data between two spice
clients.

Also add some documentation to the checks, in order to quickly
understand what they are about.

Related: https://gitlab.freedesktop.org/spice/win32/vd_agent/issues/6
Related: https://gitlab.freedesktop.org/spice/linux/vd_agent/issues/9
Related: https://bugzilla.redhat.com/show_bug.cgi?id=1594876

v1 -> v2:
- Fixed comment on s->clipboard_by_guest[selection] check (Marc-André)
- Removed the reply on read only. (Marc-André)

Signed-off-by: Victor Toso <victortoso at redhat.com>
---
 src/spice-gtk-session.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/spice-gtk-session.c b/src/spice-gtk-session.c
index 1a19bca..82a5b35 100644
--- a/src/spice-gtk-session.c
+++ b/src/spice-gtk-session.c
@@ -1015,12 +1015,29 @@ static gboolean clipboard_request(SpiceMainChannel *main, guint selection,
     int m;
 
     cb = get_clipboard_from_selection(s, selection);
-    g_return_val_if_fail(cb != NULL, FALSE);
-    g_return_val_if_fail(s->clipboard_by_guest[selection] == FALSE, FALSE);
-    g_return_val_if_fail(s->clip_grabbed[selection], FALSE);
+    if (cb == NULL) {
+        goto notify_agent;
+    }
+
+    /* As we are holding clipboard data sent by selection-grab from guest, the
+     * selection-request of clipboard data from guest must fail. We either sent
+     * a bad selection-grab to the guest or the agent is buggy. */
+    if (s->clipboard_by_guest[selection]) {
+        SPICE_DEBUG("clipboard: agent request: grab on hold by agent, possible race");
+        goto notify_agent;
+    }
 
-    if (read_only(self))
+    /* The selection-request by agent should happen only if the clipboard data is set
+     * by client */
+    if (!s->clip_grabbed[selection]) {
+        SPICE_DEBUG("clipboard: agent request: data set by agent, possible race");
+        goto notify_agent;
+    }
+
+    /* On read only, should not reply to the agent. */
+    if (read_only(self)) {
         return FALSE;
+    }
 
     if (type == VD_AGENT_CLIPBOARD_UTF8_TEXT) {
         gtk_clipboard_request_text(cb, clipboard_received_text_cb,
@@ -1039,6 +1056,10 @@ static gboolean clipboard_request(SpiceMainChannel *main, guint selection,
     }
 
     return TRUE;
+
+notify_agent:
+    spice_main_channel_clipboard_selection_notify(s->main, selection, type, NULL, 0);
+    return FALSE;
 }
 
 static void clipboard_release(SpiceMainChannel *main, guint selection,
-- 
2.20.1