Add info bar if blocked elements present in Svg (#1620)

* Added logic to check for blocked elements

* Added unit tests

* Fix warnings from msi solution

src/modules/previewpane/SvgPreviewHandler/SvgPreviewControl.cs

@@ -15,6 +15,7 @@ using System.Xml.Linq;
 using Common;
 using Common.Utilities;
 using PreviewHandlerCommon;
+using SvgPreviewHandler.Utilities;
 
 namespace SvgPreviewHandler
 {
@@ -58,6 +59,13 @@ namespace SvgPreviewHandler
                         }
                     }
 
+                    // Add a info bar on top of the Preview if any blocked element is present.
+                    if (SvgPreviewHandlerHelper.CheckBlockedElements(svgData))
+                    {
+                        this.infoBarAdded = true;
+                        this.AddTextBoxControl(Resource.BlockedElementInfoText);
+                    }
+
                     this.AddBrowserControl(svgData);
                     this.Resize += this.FormResized;
                     base.DoPreview(dataSource);

src/modules/previewpane/SvgPreviewHandler/SvgPreviewHandler.csproj

@@ -107,6 +107,7 @@
     </Compile>
     <Compile Include="SvgPreviewHandler.cs" />
     <Compile Include="SvgTelemetry.cs" />
+    <Compile Include="Utilities\SvgPreviewHandlerHelper.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\common\PreviewHandlerCommon.csproj">

src/modules/previewpane/SvgPreviewHandler/Utilities/SvgPreviewHandlerHelper.cs

@@ -0,0 +1,66 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Xml.Linq;
+
+namespace SvgPreviewHandler.Utilities
+{
+    /// <summary>
+    /// Helper utilities for Svg Preview Handler.
+    /// </summary>
+    public class SvgPreviewHandlerHelper
+    {
+        /// <summary>
+        /// Dictionary of elements in lower case that are blocked from Svg for preview pane.
+        /// Reference for list of Svg Elements: https://developer.mozilla.org/en-US/docs/Web/SVG/Element.
+        /// </summary>
+        private static Dictionary<string, bool> blockedElementsName = new Dictionary<string, bool>
+        {
+            { "script", true },
+            { "image", true },
+            { "feimage", true },
+        };
+
+        /// <summary>
+        /// Check if any of the blocked elements present in Svg.
+        /// </summary>
+        /// <param name="svgData">Input Svg.</param>
+        /// <returns>Returns true in case any of the blocked element is present otherwise false.</returns>
+        public static bool CheckBlockedElements(string svgData)
+        {
+            bool foundBlockedElement = false;
+            if (string.IsNullOrWhiteSpace(svgData))
+            {
+                return foundBlockedElement;
+            }
+
+            // Check if any of the blocked element is present. If failed to parse or iterate over Svg return default false.
+            // No need to throw because all the external content and script are blocked on the Web Browser Control itself.
+            try
+            {
+                var doc = XDocument.Parse(svgData);
+                var elements = doc.Descendants().ToList();
+                foreach (XElement element in elements)
+                {
+                    var elementName = element?.Name?.LocalName?.ToLower();
+                    if (elementName != null && blockedElementsName.ContainsKey(elementName))
+                    {
+                        foundBlockedElement = true;
+
+                        // No need to iterate further since we are displaying info bar with condition of atleast one occurrence of blocked element is present.
+                        break;
+                    }
+                }
+            }
+            catch (Exception)
+            {
+            }
+
+            return foundBlockedElement;
+        }
+    }
+}