Fix preview crash on UNC and malformed paths

QuickLook.Common/Helpers/PathHelper.cs

@@ -0,0 +1,149 @@
+// Copyright © 2017-2026 QL-Win Contributors
+//
+// This file is part of QuickLook program.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System;
+using System.IO;
+
+namespace QuickLook.Common.Helpers;
+
+public static class PathHelper
+{
+    private static readonly char[] TrimmableExtensionChars = ['"', ' ', '\t', '\r', '\n'];
+
+    public static string GetExtension(string path)
+    {
+        if (string.IsNullOrEmpty(path))
+            return string.Empty;
+
+        var normalized = Normalize(path);
+
+        // Path.GetExtension validates the whole path through Path.CheckInvalidPathChars
+        // and can throw for shell-provided paths. Parse UNC paths directly so they
+        // always reach the preview pipeline.
+        if (IsUncPath(normalized))
+            return GetExtensionFallback(normalized);
+
+        try
+        {
+            return Path.GetExtension(normalized);
+        }
+        catch (ArgumentException)
+        {
+            return GetExtensionFallback(normalized);
+        }
+    }
+
+    public static string GetFileName(string path)
+    {
+        if (string.IsNullOrEmpty(path))
+            return path;
+
+        var normalized = Normalize(path);
+
+        try
+        {
+            return Path.GetFileName(normalized);
+        }
+        catch (ArgumentException)
+        {
+            var separator = normalized.LastIndexOfAny([Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar]);
+            return separator < 0 ? normalized : normalized.Substring(separator + 1);
+        }
+    }
+
+    public static string GetPathRoot(string path)
+    {
+        if (string.IsNullOrEmpty(path))
+            return string.Empty;
+
+        var normalized = Normalize(path);
+
+        try
+        {
+            return Path.GetPathRoot(normalized);
+        }
+        catch (ArgumentException)
+        {
+            if (normalized.StartsWith(@"\\", StringComparison.Ordinal))
+            {
+                var parts = normalized.Substring(2).Split([Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar], 3);
+                return parts.Length switch
+                {
+                    0 => string.Empty,
+                    1 => @"\\" + parts[0],
+                    _ => @"\\" + parts[0] + @"\" + parts[1],
+                };
+            }
+
+            if (normalized.Length >= 2 && normalized[1] == Path.VolumeSeparatorChar)
+                return normalized.Substring(0, 2) + Path.DirectorySeparatorChar;
+
+            return string.Empty;
+        }
+    }
+
+    public static bool IsShortcut(string path)
+    {
+        return GetExtension(path).Equals(".lnk", StringComparison.OrdinalIgnoreCase);
+    }
+
+    public static bool IsUncPath(string path)
+    {
+        if (string.IsNullOrEmpty(path))
+            return false;
+
+        var normalized = Normalize(path);
+        return normalized.Length >= 2 &&
+               normalized[0] == Path.DirectorySeparatorChar &&
+               normalized[1] == Path.DirectorySeparatorChar;
+    }
+
+    private static string Normalize(string path)
+    {
+        path = path.Trim();
+
+        if (path.Length >= 2 && path[0] == '"' && path[path.Length - 1] == '"')
+            path = path.Substring(1, path.Length - 2).Trim();
+
+        return path;
+    }
+
+    private static string GetExtensionFallback(string path)
+    {
+        var end = path.Length - 1;
+
+        while (end >= 0 && char.IsWhiteSpace(path[end]))
+            end--;
+
+        for (var i = end; i >= 0; i--)
+        {
+            var c = path[i];
+
+            if (c == '.')
+                return i == end
+                    ? string.Empty
+                    : path.Substring(i, end - i + 1).TrimEnd(TrimmableExtensionChars);
+
+            if (c == Path.DirectorySeparatorChar ||
+                c == Path.AltDirectorySeparatorChar ||
+                c == Path.VolumeSeparatorChar)
+                break;
+        }
+
+        return string.Empty;
+    }
+}

QuickLook.Tests/PathHelperTests.cs

@@ -0,0 +1,96 @@
+// Copyright © 2017-2026 QL-Win Contributors
+//
+// This file is part of QuickLook program.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using QuickLook.Common.Helpers;
+
+namespace QuickLook.Tests;
+
+[TestClass]
+public sealed class PathHelperTests
+{
+    [TestMethod]
+    [DataRow(@"\\server\share\file.png", ".png")]
+    [DataRow(@"\\server.domain\share\folder\image.JPG", ".JPG")]
+    [DataRow(@"\\10.1.2.3\share\file.pdf", ".pdf")]
+    [DataRow(@"\\wsl$\Ubuntu\home\user\file.png", ".png")]
+    [DataRow(@"\\wsl.localhost\Ubuntu\home\user\file.png", ".png")]
+    [DataRow(@"\\server\share\folder", "")]
+    [DataRow(@"\\wsl$\Ubuntu\home\user", "")]
+    [DataRow(@"C:\local\folder\file.png", ".png")]
+    [DataRow(@"Z:\mapped\folder\file.png", ".png")]
+    [DataRow(@"C:\local\folder\file", "")]
+    [DataRow("", "")]
+    public void GetExtensionHandlesUncAndLocalPaths(string path, string expected)
+    {
+        Assert.AreEqual(expected, PathHelper.GetExtension(path));
+    }
+
+    [TestMethod]
+    [DataRow(@"\\server\share\file.png" + "\n")]
+    [DataRow(@"\\server\share\bad""name.png")]
+    [DataRow(@"""\\server\share\file.png""")]
+    public void GetExtensionDoesNotThrowOnMalformedUncPaths(string path)
+    {
+        Assert.AreEqual(".png", PathHelper.GetExtension(path));
+    }
+
+    [TestMethod]
+    [DataRow(@"\\server\share\file.lnk", true)]
+    [DataRow(@"\\server\share\file.LNK", true)]
+    [DataRow(@"\\wsl$\Ubuntu\home\file.png", false)]
+    [DataRow(@"C:\local\folder\file.lnk", true)]
+    [DataRow(@"C:\local\folder\file.png", false)]
+    [DataRow(@"\\wsl$\Ubuntu\home", false)]
+    public void IsShortcutHandlesUncAndLocalPaths(string path, bool expected)
+    {
+        Assert.AreEqual(expected, PathHelper.IsShortcut(path));
+    }
+
+    [TestMethod]
+    [DataRow(@"\\server\share\file.png", true)]
+    [DataRow(@"\\wsl$\Ubuntu\home\file.png", true)]
+    [DataRow(@"""\\server\share\file.png""", true)]
+    [DataRow(@"C:\local\folder\file.png", false)]
+    [DataRow(@"Z:\mapped\file.png", false)]
+    [DataRow(@"\server\share\file.png", false)]
+    [DataRow("", false)]
+    public void IsUncPathHandlesUncAndLocalPaths(string path, bool expected)
+    {
+        Assert.AreEqual(expected, PathHelper.IsUncPath(path));
+    }
+
+    [TestMethod]
+    [DataRow(@"\\server\share\folder\file.png", "file.png")]
+    [DataRow(@"\\wsl$\Ubuntu\home\user\file.png", "file.png")]
+    [DataRow(@"C:\local\folder\file.png", "file.png")]
+    [DataRow(@"\\server\share\bad""name.png", "bad\"name.png")]
+    public void GetFileNameHandlesUncAndMalformedPaths(string path, string expected)
+    {
+        Assert.AreEqual(expected, PathHelper.GetFileName(path));
+    }
+
+    [TestMethod]
+    [DataRow(@"\\server\share\folder\file.png", @"\\server\share")]
+    [DataRow(@"\\wsl$\Ubuntu\home\user\file.png", @"\\wsl$\Ubuntu")]
+    [DataRow(@"C:\local\folder\file.png", @"C:\")]
+    [DataRow(@"Z:\mapped\file.png", @"Z:\")]
+    public void GetPathRootHandlesUncAndLocalPaths(string path, string expected)
+    {
+        Assert.AreEqual(expected, PathHelper.GetPathRoot(path));
+    }
+}

QuickLook.Tests/QuickLook.Tests.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net462</TargetFramework>
+        <IsPackable>false</IsPackable>
+        <LangVersion>latest</LangVersion>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+        <PackageReference Include="MSTest.TestAdapter" Version="3.6.4" />
+        <PackageReference Include="MSTest.TestFramework" Version="3.6.4" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <Compile Include="..\QuickLook.Common\Helpers\PathHelper.cs" Link="PathHelper.cs" />
+    </ItemGroup>
+
+</Project>

QuickLook/Helpers/ExtensionFilterHelper.cs

@@ -147,7 +147,7 @@ public static bool IsExtensionAllowed(string path)
         if (string.IsNullOrEmpty(path))
             return true;
 
-        var extension = Path.GetExtension(path);
+        var extension = PathHelper.GetExtension(path);
 
         // Files without extensions are always allowed (includes directories)
         if (string.IsNullOrEmpty(extension))

QuickLook/NativeMethods/QuickLook.cs

@@ -15,6 +15,7 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+using QuickLook.Common.Helpers;
 using System;
 using System.Diagnostics;
 using System.IO;
@@ -133,14 +134,23 @@ private static string ResolveShortcut(string path)
     {
         if (string.IsNullOrEmpty(path)) return path;
 
-        if (Path.GetExtension(path).ToLower() != ".lnk") return path;
+        if (!PathHelper.IsShortcut(path)) return path;
 
-        var link = new ShellLink();
-        ((IPersistFile)link).Load(path, 0);
-        var sb = new StringBuilder(MaxPath);
-        ((IShellLinkW)link).GetPath(sb, sb.Capacity, out _, 0);
+        try
+        {
+            var link = new ShellLink();
+            ((IPersistFile)link).Load(path, 0);
+            var sb = new StringBuilder(MaxPath);
+            ((IShellLinkW)link).GetPath(sb, sb.Capacity, out _, 0);
 
-        return sb.Length == 0 ? path : sb.ToString();
+            return sb.Length == 0 ? path : sb.ToString();
+        }
+        catch (Exception e)
+        {
+            // An unreadable shortcut must not break the whole preview.
+            Debug.WriteLine(e);
+            return path;
+        }
     }
 
     internal enum FocusedWindowType