Prefer online resize over reconnect resizes

We had a case on Windows 2012R2 where any early resizes would be
handled by a reconnect rather than an online resize, which led to a
bunch of follow-up problems with the session startup.

To solve this, we gave the RDPEDISP channel more time to become
established.

Co-authored-by: Henrik Andersson <hean01@cendio.com>
Co-authored-by: Karl Mikaelsson <derfian@cendio.se>

2 files changed, 24 insertions, 3 deletions

diff --git a/rdpedisp.c b/rdpedisp.c
index 43903ae..d1f27b8 100644
--- a/rdpedisp.c
+++ b/rdpedisp.c
@@ -28,6 +28,7 @@
 
 extern int g_dpi;
 extern RD_BOOL g_pending_resize_defer;
+extern struct timeval g_pending_resize_defer_timer;
 
 static void rdpedisp_send(STREAM s);
 static void rdpedisp_init_packet(STREAM s, uint32 type, uint32 length);
@@ -45,8 +46,15 @@ rdpedisp_process_caps_pdu(STREAM s)
 	       "rdpedisp_process_caps_pdu(), Max supported monitor area (square pixels) is %d",
 	       tmp[0] * tmp[1] * tmp[2]);
 
-	/* Start allowing session resizes */
+	/* When the RDPEDISP channel is established, we allow dynamic
+	   session resize straight away by clearing the defer flag and
+	   the defer timer. This lets process_pending_resize() start
+	   processing pending resizes immediately. We expect that
+	   process_pending_resize will prefer RDPEDISP resizes over
+	   disconnect/reconnect resizes. */
 	g_pending_resize_defer = False;
+	g_pending_resize_defer_timer.tv_sec = 0;
+	g_pending_resize_defer_timer.tv_usec = 0;
 }
 
 static void
diff --git a/xwin.c b/xwin.c
index 6fa4343..5fcd99d 100644
--- a/xwin.c
+++ b/xwin.c
@@ -3065,9 +3065,22 @@ process_pending_resize ()
 	/* There is a race problem when using disconnect / reconnect
 	   sequence were one sometimes would be presented with
 	   unexpected login window. Waiting a little bit extra after
-	   getting the reconnect cookie solves this problem. */
+	   getting the reconnect cookie solves this problem.
+
+	   In addition to that delay, we also want to wait for
+	   RDPEDISP to become available. In scenarios where we can use
+	   both online and reconnect-based resizes, we prefer
+	   online. Our brief investigation shows that RDPEDISP support
+	   is established about 100-300 ms after the login info packet
+	   was received. Thus, we want to wait a bit so we can avoid
+	   resizes using reconnect. Once RDPEDISP is established, the
+	   defer timer is cleared, so there will be no delay before
+	   the first resize for servers that support RDPEDISP. Other
+	   servers will get the initial resize delayed with 2 seconds.
+	*/
+
 	if (timeval_is_set(&g_pending_resize_defer_timer) &&
-	    time_difference_in_ms(g_pending_resize_defer_timer, now) >= 100)
+	    time_difference_in_ms(g_pending_resize_defer_timer, now) >= 2000)
 	{
 		g_pending_resize_defer_timer.tv_sec = g_pending_resize_defer_timer.tv_usec = 0;
 		g_pending_resize_defer = False;