Sanity check ShPk mods, ban incompatible ones

Penumbra/Interop/Processing/ShpkPathPreProcessor.cs

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+using FFXIVClientStructs.FFXIV.Client.System.Resource;
+using Penumbra.Api.Enums;
+using Penumbra.Collections;
+using Penumbra.GameData.Files;
+using Penumbra.GameData.Files.Utility;
+using Penumbra.Interop.Hooks.ResourceLoading;
+using Penumbra.String;
+using Penumbra.String.Classes;
+using Penumbra.UI;
+
+namespace Penumbra.Interop.Processing;
+
+/// <summary>
+/// Path pre-processor for shader packages that reverts redirects to known invalid files, as bad ShPks can crash the game.
+/// </summary>
+public sealed class ShpkPathPreProcessor(ResourceManagerService resourceManager, ChatWarningService chatWarningService) : IPathPreProcessor
+{
+    public ResourceType Type
+        => ResourceType.Shpk;
+
+    public unsafe FullPath? PreProcess(ResolveData resolveData, CiByteString path, Utf8GamePath originalGamePath, bool nonDefault, FullPath? resolved)
+    {
+        chatWarningService.CleanLastFileWarnings(false);
+
+        if (!resolved.HasValue)
+            return null;
+
+        // Skip the sanity check for game files. We are not considering the case where the user has modified game file: it's at their own risk.
+        var resolvedPath = resolved.Value;
+        if (!resolvedPath.IsRooted)
+            return resolvedPath;
+
+        // If the ShPk is already loaded, it means that it already passed the sanity check.
+        var existingResource = resourceManager.FindResource(ResourceCategory.Shader, ResourceType.Shpk, unchecked((uint)resolvedPath.InternalName.Crc32));
+        if (existingResource != null)
+            return resolvedPath;
+
+        var checkResult = SanityCheck(resolvedPath.FullName);
+        if (checkResult == SanityCheckResult.Success)
+            return resolvedPath;
+
+        Penumbra.Log.Warning($"Refusing to honor file redirection because of failed sanity check (result: {checkResult}). Original path: {originalGamePath} Redirected path: {resolvedPath}");
+        chatWarningService.PrintFileWarning(resolvedPath.FullName, originalGamePath, WarningMessageComplement(checkResult));
+
+        return null;
+    }
+
+    private static SanityCheckResult SanityCheck(string path)
+    {
+        try
+        {
+            using var file = MmioMemoryManager.CreateFromFile(path);
+            var bytes = file.GetSpan();
+
+            return ShpkFile.FastIsLegacy(bytes)
+                ? SanityCheckResult.Legacy
+                : SanityCheckResult.Success;
+        }
+        catch (FileNotFoundException)
+        {
+            return SanityCheckResult.NotFound;
+        }
+        catch (IOException)
+        {
+            return SanityCheckResult.IoError;
+        }
+    }
+
+    private static string WarningMessageComplement(SanityCheckResult result)
+        => result switch
+        {
+            SanityCheckResult.IoError  => "cannot read the modded file.",
+            SanityCheckResult.NotFound => "the modded file does not exist.",
+            SanityCheckResult.Legacy   => "this mod is not compatible with Dawntrail. Get an updated version, if possible, or disable it.",
+            _                          => string.Empty,
+        };
+
+    private enum SanityCheckResult
+    {
+        Success,
+        IoError,
+        NotFound,
+        Legacy,
+    }
+}