[vino] Fix reading of TLS data to account for cached data

[David King <davidk src gnome org>]

commit 3b38cf49321924ff2ec657a6e4db8a1932245ef9
Author: Daniel P. Berrange <berrange redhat com>
Date:   Mon Sep 16 16:44:30 2013 +0100

    Fix reading of TLS data to account for cached data
    
    When you ask GnuTLS to read 'n' bytes of data it is free to read many
    more than just 'n' bytes, since there is no 1-1 mapping between
    encrypted and unencrypted byte counts.
    
    The Vino I/O handle triggered when POLLIN reads one single RFB message,
    then checks if POLLIN is still set. This is broken if gnutls has
    previously read more than one RFB message worth of data.
    
    A symptom of this brokeness is that when connecting to a Vino server
    with gtk-vnc, the screen will be initially black until the user moves
    the mouse or presses a key.  Even then there will be periodic delays in
    updates if the pending data condition arises again.
    
    Fortunately GnuTLS has a function gnutls_record_check_pending which lets
    apps determine if there is any cached data read off the wire.
    
    Signed-off-by: Daniel P. Berrange <berrange redhat com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=703326

 server/libvncserver/rfb/rfb.h |    1 +
 server/libvncserver/sockets.c |   15 +++++++++++++++
 server/vino-server.c          |    9 ++++++---
 3 files changed, 22 insertions(+), 3 deletions(-)
---
diff --git a/server/libvncserver/rfb/rfb.h b/server/libvncserver/rfb/rfb.h
index 368a4cf..0de79a4 100644
--- a/server/libvncserver/rfb/rfb.h
+++ b/server/libvncserver/rfb/rfb.h
@@ -397,6 +397,7 @@ extern void rfbSetLocalOnly(rfbScreenInfoPtr rfbScreen, rfbBool localOnly);
 extern void rfbCloseClient(rfbClientPtr cl);
 extern int ReadExact(rfbClientPtr cl, char *buf, int len);
 extern int ReadExactTimeout(rfbClientPtr cl, char *buf, int len,int timeout);
+extern int ReadPending(rfbClientPtr cl);
 extern int WriteExact(rfbClientPtr cl, const char *buf, int len);
 extern void rfbProcessNewConnection(rfbScreenInfoPtr rfbScreen, int insock);
 extern void rfbCheckFds(rfbScreenInfoPtr rfbScreen,long usec);
diff --git a/server/libvncserver/sockets.c b/server/libvncserver/sockets.c
index bbdaf3d..746a3e5 100644
--- a/server/libvncserver/sockets.c
+++ b/server/libvncserver/sockets.c
@@ -457,6 +457,21 @@ int ReadExact(rfbClientPtr cl,char* buf,int len)
 }
 
 #ifdef VINO_HAVE_GNUTLS
+extern int ReadPending(rfbClientPtr cl)
+{
+    if (cl->useTLS && cl->tlsSession)
+        return gnutls_record_check_pending(cl->tlsSession);
+    else
+        return 0;
+}
+#else
+extern int ReadPending(rfbClientPtr cl)
+{
+    return 0;
+}
+#endif
+
+#ifdef VINO_HAVE_GNUTLS
 static int
 WriteExactOverTLS(rfbClientPtr cl, const char* buf, int len)
 {
diff --git a/server/vino-server.c b/server/vino-server.c
index fc70e68..a3edf9d 100644
--- a/server/vino-server.c
+++ b/server/vino-server.c
@@ -445,9 +445,12 @@ vino_server_update_client_timeout (rfbClientPtr rfb_client)
 }
 
 static inline gboolean
-more_data_pending (int fd)
+more_data_pending (rfbClientPtr rfb_client)
 {
-  struct pollfd pollfd = { fd, POLLIN|POLLPRI, 0 };
+  struct pollfd pollfd = { rfb_client->sock, POLLIN|POLLPRI, 0 };
+
+  if (ReadPending(rfb_client) > 0)
+      return TRUE;
 
   return poll (&pollfd, 1, 0) == 1;
 }
@@ -462,7 +465,7 @@ vino_server_client_data_pending (GIOChannel   *source,
 
   do {
     rfbProcessClientMessage (rfb_client);
-  } while (more_data_pending (rfb_client->sock));
+  } while (more_data_pending (rfb_client));
   
   return vino_server_update_client (rfb_client);
 }