Fixes bugs in 4.7 preview engine. Work items: 30208, 30288

umbraco/presentation/UmbracoContext.cs

@@ -90,11 +90,11 @@ namespace umbraco.presentation
             get
             {
                 string currentUrl = Request.Url.AbsolutePath;
-				// zb-00004 #29956 : refactor cookies names & handling
-				return
-					StateHelper.Cookies.Preview.HasValue // has preview cookie
-					&& UmbracoUser != null // has user
-					&& !currentUrl.StartsWith(IO.IOHelper.ResolveUrl(IO.SystemDirectories.Umbraco)); // is not in admin UI
+                // zb-00004 #29956 : refactor cookies names & handling
+                return
+                    StateHelper.Cookies.Preview.HasValue // has preview cookie
+                    && UmbracoUser != null // has user
+                    && !currentUrl.StartsWith(IO.IOHelper.ResolveUrl(IO.SystemDirectories.Umbraco)); // is not in admin UI
             }
         }
 
@@ -105,14 +105,14 @@ namespace umbraco.presentation
                 if (_previewContent == null)
                 {
                     _previewContent = new PreviewContent(new Guid(StateHelper.Cookies.Preview.GetValue()));
-                    _previewContent.LoadPreviewset();
+                    if (_previewContent.ValidPreviewSet)
+                        _previewContent.LoadPreviewset();
                 }
-                return _previewContent.XmlContent;
-            }
-            else
-            {
-                return content.Instance.XmlContent;
+                if (_previewContent.ValidPreviewSet)
+                    return _previewContent.XmlContent;
             }
+            return content.Instance.XmlContent;
+
         }
 
         /// <summary>

umbraco/presentation/umbraco/preview/Preview.cs

@@ -24,6 +24,9 @@ namespace umbraco.presentation.preview
         public XmlDocument XmlContent { get; set; }
         public Guid PreviewSet { get; set; }
         public string PreviewsetPath { get; set; }
+
+        public bool ValidPreviewSet { get; set; }
+        
         private int m_userId = 0;
 
         public PreviewContent(User user)
@@ -54,16 +57,44 @@ namespace umbraco.presentation.preview
 
         public PreviewContent(Guid previewSet)
         {
-            updatePreviewPaths(previewSet);
+            ValidPreviewSet = updatePreviewPaths(previewSet);
         }
 
-        private void updatePreviewPaths(Guid previewSet)
+        private bool updatePreviewPaths(Guid previewSet)
         {
             PreviewSet = previewSet;
             PreviewsetPath = IO.IOHelper.MapPath(
                 Path.Combine(IO.SystemDirectories.Preview, m_userId.ToString() + "_" + PreviewSet + ".config"));
+
+            if (!ValidatePreviewPath())
+            {
+                // preview cookie failed so we'll log the error and clear the cookie
+                Log.Add(LogTypes.Error, User.GetUser(m_userId), -1, string.Format("Preview failed for preview set {0}", previewSet));
+                PreviewSet = Guid.Empty;
+                PreviewsetPath = String.Empty;
+
+                ClearPreviewCookie();
+
+                return false;
+            }
+
+            return true;
         }
 
+        /// <summary>
+        /// Checks a preview file exist based on preview cookie
+        /// </summary>
+        /// <returns></returns>
+        public bool ValidatePreviewPath()
+        {
+            if (!File.Exists(PreviewsetPath))
+                return false;
+
+            return true;
+        }
+
+
+
         public void LoadPreviewset()
         {
             XmlContent = new XmlDocument();