Added provider icons (#934)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/SvgIcon.cs

@@ -0,0 +1,113 @@
+using System.Text;
+using System.Xml;
+using System.Xml.Linq;
+
+namespace AIStudio.Tools;
+
+/// <summary>
+/// Turns an SVG icon which came from outside the app into a data URL we can put into an img tag.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Icons from plugins are never rendered inline. They go into an img element instead, where the
+/// browser treats the SVG as a standalone document: it runs no script, fires no event handlers, and
+/// loads nothing from the network. That is what makes a plugin-supplied icon harmless, so this
+/// class does not try to filter active content out of the markup.
+/// </para>
+/// <para>
+/// What is left to do is a size limit and the question of whether the icon is an SVG at all. The
+/// latter is a diagnostic rather than a defense: it turns a broken icon into a log message and a
+/// fallback instead of a broken image in the UI.
+/// </para>
+/// </remarks>
+internal static class SvgIcon
+{
+    /// <summary>
+    /// The largest icon we accept.
+    /// </summary>
+    /// <remarks>
+    /// Provider icons are persisted into the settings file as a data URL, so an oversized icon
+    /// would be written and parsed again on every single settings store. A logo needs far less.
+    /// </remarks>
+    public const int MAX_ICON_SIZE_BYTES = 32 * 1024;
+
+    private const string SVG_NAMESPACE = "http://www.w3.org/2000/svg";
+    private const string DATA_URL_PREFIX = "data:image/svg+xml;base64,";
+
+    private static readonly XNamespace SVG = SVG_NAMESPACE;
+
+    /// <summary>
+    /// Validates the given SVG and converts it into a data URL.
+    /// </summary>
+    /// <param name="svg">The SVG markup to convert.</param>
+    /// <param name="dataUrl">The resulting data URL, or an empty string when the icon was rejected.</param>
+    /// <param name="issue">The reason why the icon was rejected, or an empty string on success.</param>
+    /// <returns>True, when the icon could be converted.</returns>
+    public static bool TryCreateDataUrl(string svg, out string dataUrl, out string issue) => TryCreateDataUrl(Encoding.UTF8.GetBytes(svg), out dataUrl, out issue);
+
+    /// <inheritdoc cref="TryCreateDataUrl(string,out string,out string)"/>
+    public static bool TryCreateDataUrl(byte[] svg, out string dataUrl, out string issue)
+    {
+        dataUrl = string.Empty;
+        issue = string.Empty;
+
+        if (svg.Length is <= 0 or > MAX_ICON_SIZE_BYTES)
+        {
+            issue = $"The icon must be between 1 byte and {MAX_ICON_SIZE_BYTES / 1024} KiB.";
+            return false;
+        }
+
+        XDocument document;
+        try
+        {
+            var settings = new XmlReaderSettings
+            {
+                DtdProcessing = DtdProcessing.Prohibit,
+                MaxCharactersInDocument = MAX_ICON_SIZE_BYTES,
+                XmlResolver = null,
+            };
+
+            using var stream = new MemoryStream(svg, writable: false);
+            using var xmlReader = XmlReader.Create(stream, settings);
+            document = XDocument.Load(xmlReader, LoadOptions.None);
+        }
+        catch (Exception e)
+        {
+            issue = $"The icon is not valid SVG XML: {e.Message}";
+            return false;
+        }
+
+        if (document.Root is null || !string.Equals(document.Root.Name.LocalName, "svg", StringComparison.OrdinalIgnoreCase))
+        {
+            issue = "The icon does not have an SVG root element.";
+            return false;
+        }
+
+        //
+        // An SVG which is meant to be pasted into HTML often omits the namespace, because the HTML
+        // parser supplies it. A standalone document inside an img tag has no such help and would
+        // not render at all, so we add the namespace instead of rejecting such an icon:
+        //
+        if (document.Root.Name.Namespace == XNamespace.None)
+        {
+            // Materialize before renaming: we are about to change the very tree we walk.
+            foreach (var element in document.Root.DescendantsAndSelf().ToList())
+                if (element.Name.Namespace == XNamespace.None)
+                    element.Name = SVG + element.Name.LocalName;
+
+            dataUrl = ToDataUrl(Encoding.UTF8.GetBytes(document.ToString(SaveOptions.DisableFormatting)));
+            return true;
+        }
+
+        if (document.Root.Name.Namespace != SVG)
+        {
+            issue = "The icon root element is not in the SVG namespace.";
+            return false;
+        }
+
+        dataUrl = ToDataUrl(svg);
+        return true;
+    }
+
+    private static string ToDataUrl(byte[] svg) => $"{DATA_URL_PREFIX}{Convert.ToBase64String(svg)}";
+}