Add Asar ContentLoader

Right now all it does it load and verifies in the content level if our Asar Archive is valid supported by the craftersmine.Asar.Net library, but in the future we might use the content-level verification for hash checking too

Signed-off-by: Ayane <ayane@vignetteapp.org>

Author: sr229

source/Vignette/Content/AsarLoader.cs

@@ -0,0 +1,26 @@
+// Copyright (c) Cosyne 
+// Licensed under GPL 3.0 with SDK Exception. See LICENSE for details.
+
+using craftersmine.Asar.Net;
+using System;
+using System.IO;
+
+namespace Vignette.Content;
+internal class AsarLoader : IContentLoader<AsarArchive>
+{
+    // while the library is capable of verifying if its a valid archive, we would like to do
+    // it in the content loader level too so we can catch masquerading malicious files as we
+    // load them.
+    // The first 4 bytes of an asar archive is 04 00 00 00.
+    private static readonly byte[] signature = new byte[] { 0x04, 0x00, 0x00, 0x00 };
+
+    public AsarArchive Load(ReadOnlySpan<byte> bytes)
+    {
+        if (!MemoryExtensions.SequenceEqual(bytes[0..4], signature))
+            throw new ArgumentException("Failed to find sequence \"04 00 00 00\" in byte sequence.", nameof(bytes));
+
+        // read the bytes into a stream
+        var stream = new MemoryStream(bytes.ToArray());
+        return new AsarArchive(stream);
+    }
+}

source/Vignette/Vignette.csproj

@@ -8,6 +8,7 @@
   <ItemGroup>
     <PackageReference Include="Sekai" Version="0.1.0-alpha.9" />
     <PackageReference Include="StbiSharp" Version="1.2.1" />
+    <PackageReference Include="craftersmine.Asar.Net" Version="1.0.4" />
   </ItemGroup>
 
 </Project>