fix: Wrong keyword encoding, bad buffer, update cache fix

Was using ASCII for keyword and was generating inconsistent CRC whoops

Dotnet/ScreenshotMetadata/PNGChunk.cs

@@ -7,7 +7,7 @@ using System.Text;
 
 namespace VRCX;
 
-public struct PNGChunk
+public class PNGChunk
 {
     public int Index;
     public int Length;
@@ -58,7 +58,7 @@ public struct PNGChunk
         */
 
         // Parse keyword as null-terminated string
-        var keywordEncoding = Encoding.GetEncoding("ISO-8859-1");
+        var keywordEncoding = Encoding.UTF8;
         int keywordLength = 0;
         for (int i = 0; i < chunkLength; i++)
         {
@@ -126,8 +126,9 @@ public struct PNGChunk
     public bool ExistsInFile(FileStream fileStream)
     {
         fileStream.Seek(Index, SeekOrigin.Begin);
-        byte[] buffer = new byte[Length];
+        
-        fileStream.ReadExactly(buffer, 0, Length);
+        byte[] buffer = new byte[4];
+        fileStream.ReadExactly(buffer, 0, 4);
         
         if (BitConverter.IsLittleEndian)
             Array.Reverse(buffer, 0, 4);
@@ -137,14 +138,15 @@ public struct PNGChunk
             return false;
 
         fileStream.Seek(4 + chunkLength, SeekOrigin.Current);
-        fileStream.ReadExactly(buffer, 0, Length);
+        fileStream.ReadExactly(buffer, 0, 4);
         
         if (BitConverter.IsLittleEndian)
             Array.Reverse(buffer, 0, 4);
         
         uint crc = BitConverter.ToUInt32(buffer, 0);
+        uint calculatedCRC = CalculateCRC();
         
-        return crc == CalculateCRC();
+        return crc == calculatedCRC;
     }
 
     /// <summary>
@@ -186,7 +188,7 @@ public struct PNGChunk
 
     public uint CalculateCRC()
     {
-        var chunkTypeBytes = Encoding.ASCII.GetBytes(ChunkType);
+        var chunkTypeBytes = Encoding.UTF8.GetBytes(ChunkType);
         return Crc32(Data, 0, Data.Length, Crc32(chunkTypeBytes, 0, chunkTypeBytes.Length, 0));
     }
 

Dotnet/ScreenshotMetadata/PNGFile.cs

@@ -60,7 +60,7 @@ public class PNGFile : IDisposable
     public PNGChunk? GetChunkReverse(PNGChunkTypeFilter chunkTypeFilter)
     {
         var chunk = ReadChunkReverse(chunkTypeFilter);
-        if (chunk.HasValue &&chunk.Value.IsZero())
+        if (chunk != null && chunk.IsZero())
             return null;
 
         return chunk;
@@ -147,10 +147,10 @@ public class PNGFile : IDisposable
         }
 
         fileStream.SetLength(fileStream.Length - deleteLength);
-        
+
         metadataChunkCache.Remove(chunk);
         
-        // update the index of all cached chunks
+        // Update the index of cached chunks
         for (int i = 0; i < metadataChunkCache.Count; i++)
         {
             var cachedChunk = metadataChunkCache[i];

Dotnet/ScreenshotMetadata/PNGHelper.cs

@@ -16,9 +16,9 @@ namespace VRCX
         public static string ReadResolution(PNGFile pngFile)
         {
             var ihdrChunk = pngFile.GetChunk(PNGChunkTypeFilter.IHDR);
-            if (ihdrChunk.HasValue)
+            if (ihdrChunk != null)
             {
-                var resolution = ihdrChunk.Value.ReadIHDRChunkResolution();
+                var resolution = ihdrChunk.ReadIHDRChunkResolution();
                 return resolution.Item1 + "x" + resolution.Item2;
             }
 
@@ -42,9 +42,9 @@ namespace VRCX
             if (legacySearch)
             {
                 var legacyTextChunk = pngFile.GetChunkReverse(PNGChunkTypeFilter.iTXt);
-                if (legacyTextChunk.HasValue)
+                if (legacyTextChunk != null)
                 {
-                    var data = legacyTextChunk.Value.ReadITXtChunk();
+                    var data = legacyTextChunk.ReadITXtChunk();
                     if (data.Item1 == keyword)
                         return data.Item2;
                 }
@@ -91,7 +91,7 @@ namespace VRCX
         public static PNGChunk GenerateTextChunk(string keyword, string text)
         {
             byte[] textBytes = Encoding.UTF8.GetBytes(text);
-            byte[] keywordBytes = Encoding.GetEncoding("ISO-8859-1").GetBytes(keyword);
+            byte[] keywordBytes = Encoding.UTF8.GetBytes(keyword);
 
             List<byte> constructedTextChunk = new List<byte>();
             constructedTextChunk.AddRange(keywordBytes);

Dotnet/ScreenshotMetadata/ScreenshotHelper.cs

@@ -209,7 +209,7 @@ namespace VRCX
 
             // Check for chunk only present in files created by older modded versions of vrchat. (LFS, screenshotmanager), which put their metadata at the end of the file (which is not in spec bro).
             // Searching from the end of the file is a slower bruteforce operation so only do it if we have to.
-            if (result.Count == 0 && pngFile.GetChunk(PNGChunkTypeFilter.sRGB).HasValue)
+            if (result.Count == 0 && pngFile.GetChunk(PNGChunkTypeFilter.sRGB) != null)
             {
                 var lfsMetadata = PNGHelper.ReadTextChunk("Description", pngFile, true);
                 
@@ -233,7 +233,11 @@ namespace VRCX
         {
             using var pngFile = new PNGFile(path);
             var chunk = PNGHelper.GenerateTextChunk("Description", text);
-            return pngFile.WriteChunk(chunk);
+            pngFile.WriteChunk(chunk);
+            
+            DeleteTextMetadata(path, true);
+
+            return true;
         }
 
         public static ScreenshotMetadata ParseVRCImage(string xmlString)