.

Author: SimonCropp

src/DeterministicIoPackaging/DeterministicIoPackaging.csproj

@@ -4,13 +4,13 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Polyfill" PrivateAssets="all" />
+    <PackageReference Include="System.IO.Hashing" />
     <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
     <PackageReference Include="Microsoft.Sbom.Targets" PrivateAssets="all" Condition="'$(CI)' == 'true'" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'net472' OR '$(TargetFramework)' == 'net48'">
     <PackageReference Include="System.Threading.Tasks.Extensions" />
     <PackageReference Include="System.Buffers" />
-    <PackageReference Include="System.IO.Hashing" />
     <PackageReference Include="System.IO.Compression" />
     <PackageReference Include="System.Memory" />
   </ItemGroup>

src/DeterministicIoPackaging/PngNormalizer.cs

@@ -72,7 +72,7 @@ static bool ProcessChunk(byte[] header, byte[] body, int chunkLength, Stream tar
             if (!flushedIdat && idatData.Length > 0)
             {
                 flushedIdat = true;
-                WriteNormalizedIdat(target, idatData);
+                WriteNormalizedIdat(target, idatData.GetBuffer(), (int) idatData.Length);
             }
 
             target.Write(header);
@@ -82,44 +82,31 @@ static bool ProcessChunk(byte[] header, byte[] body, int chunkLength, Stream tar
         return isIend;
     }
 
-    static void WriteNormalizedIdat(Stream target, MemoryStream idatData)
+    static void WriteNormalizedIdat(Stream target, byte[] zlibBytes, int zlibLength)
     {
-        var zlibBytes = idatData.ToArray();
-
-        byte[] decompressed;
-        using (var zlibInput = new MemoryStream(zlibBytes))
+        using var decompressedStream = new MemoryStream();
+        using (var zlibInput = new MemoryStream(zlibBytes, 0, zlibLength))
         using (var zlibStream = new ZLibStream(zlibInput, CompressionMode.Decompress))
-        using (var decompressedStream = new MemoryStream())
         {
             zlibStream.CopyTo(decompressedStream);
-            decompressed = decompressedStream.ToArray();
         }
 
-        byte[] newIdatData;
-        using (var compressOutput = new MemoryStream())
+        using var compressOutput = new MemoryStream();
+        using (var zlibStream = new ZLibStream(compressOutput, CompressionLevel.Optimal, leaveOpen: true))
         {
-            using (var zlibStream = new ZLibStream(compressOutput, CompressionLevel.Optimal, leaveOpen: true))
-            {
-                zlibStream.Write(decompressed);
-            }
-
-            newIdatData = compressOutput.ToArray();
+            zlibStream.Write(decompressedStream.GetBuffer(), 0, (int) decompressedStream.Length);
         }
 
-        WriteChunk(target, idatType, newIdatData);
-    }
-
-    static void WriteChunk(Stream target, byte[] type, byte[] data)
-    {
+        var length = (int) compressOutput.Length;
         var header = new byte[4];
-        BinaryPrimitives.WriteInt32BigEndian(header, data.Length);
+        BinaryPrimitives.WriteInt32BigEndian(header, length);
         target.Write(header);
-        target.Write(type);
-        target.Write(data);
+        target.Write(idatType);
+        target.Write(compressOutput.GetBuffer(), 0, length);
 
         var crc = new Crc32();
-        crc.Append(type);
-        crc.Append(data);
+        crc.Append(idatType);
+        crc.Append(compressOutput.GetBuffer().AsSpan(0, length));
         var crcBytes = new byte[4];
         BinaryPrimitives.WriteUInt32BigEndian(crcBytes, crc.GetCurrentHashAsUInt32());
         target.Write(crcBytes);

src/Tests/PngNormalizerTests.cs

@@ -179,39 +179,39 @@ static void AssertValidPng(byte[] data)
 
     static byte[] BuildPng(CompressionLevel level)
     {
-        using var ms = new MemoryStream();
-        ms.Write(pngSignature);
+        using var stream = new MemoryStream();
+        stream.Write(pngSignature);
 
         var ihdrData = new byte[13];
         BinaryPrimitives.WriteInt32BigEndian(ihdrData.AsSpan(0), 2); // width
         BinaryPrimitives.WriteInt32BigEndian(ihdrData.AsSpan(4), 2); // height
         ihdrData[8] = 8; // bit depth
         ihdrData[9] = 2; // color type: RGB
-        WriteChunk(ms, ihdrType, ihdrData);
+        WriteChunk(stream, ihdrType, ihdrData);
 
         byte[] rawPixels =
         [
             0, 255, 0, 0, 255, 0, 0, // row 1: filter=0, red, red
             0, 255, 0, 0, 255, 0, 0 // row 2: filter=0, red, red
         ];
 
-        WriteChunk(ms, idatType, ZlibCompress(rawPixels, level));
-        WriteChunk(ms, iendType, Array.Empty<byte>());
+        WriteChunk(stream, idatType, ZlibCompress(rawPixels, level));
+        WriteChunk(stream, iendType, Array.Empty<byte>());
 
-        return ms.ToArray();
+        return stream.ToArray();
     }
 
     static byte[] BuildPngWithSplitIdat()
     {
-        using var ms = new MemoryStream();
-        ms.Write(pngSignature);
+        using var stream = new MemoryStream();
+        stream.Write(pngSignature);
 
         var ihdrData = new byte[13];
         BinaryPrimitives.WriteInt32BigEndian(ihdrData.AsSpan(0), 2);
         BinaryPrimitives.WriteInt32BigEndian(ihdrData.AsSpan(4), 2);
         ihdrData[8] = 8;
         ihdrData[9] = 2;
-        WriteChunk(ms, ihdrType, ihdrData);
+        WriteChunk(stream, ihdrType, ihdrData);
 
         byte[] rawPixels =
         [
@@ -221,37 +221,37 @@ static byte[] BuildPngWithSplitIdat()
 
         var zlibData = ZlibCompress(rawPixels, CompressionLevel.Fastest);
         var mid = zlibData.Length / 2;
-        WriteChunk(ms, idatType, zlibData.AsSpan(0, mid).ToArray());
-        WriteChunk(ms, idatType, zlibData.AsSpan(mid).ToArray());
-        WriteChunk(ms, iendType, Array.Empty<byte>());
+        WriteChunk(stream, idatType, zlibData.AsSpan(0, mid).ToArray());
+        WriteChunk(stream, idatType, zlibData.AsSpan(mid).ToArray());
+        WriteChunk(stream, iendType, Array.Empty<byte>());
 
-        return ms.ToArray();
+        return stream.ToArray();
     }
 
     static byte[] BuildPngWithTextChunk(string keyword, string text)
     {
-        using var ms = new MemoryStream();
-        ms.Write(pngSignature);
+        using var stream = new MemoryStream();
+        stream.Write(pngSignature);
 
         var ihdrData = new byte[13];
         BinaryPrimitives.WriteInt32BigEndian(ihdrData.AsSpan(0), 1);
         BinaryPrimitives.WriteInt32BigEndian(ihdrData.AsSpan(4), 1);
         ihdrData[8] = 8;
         ihdrData[9] = 2;
-        WriteChunk(ms, ihdrType, ihdrData);
+        WriteChunk(stream, ihdrType, ihdrData);
 
         var keywordBytes = Encoding.Latin1.GetBytes(keyword);
         var textBytes = Encoding.Latin1.GetBytes(text);
         var textChunkData = new byte[keywordBytes.Length + 1 + textBytes.Length];
         keywordBytes.CopyTo(textChunkData, 0);
         textChunkData[keywordBytes.Length] = 0;
         textBytes.CopyTo(textChunkData, keywordBytes.Length + 1);
-        WriteChunk(ms, textType, textChunkData);
+        WriteChunk(stream, textType, textChunkData);
 
-        WriteChunk(ms, idatType, ZlibCompress([0, 255, 0, 0], CompressionLevel.Fastest));
-        WriteChunk(ms, iendType, []);
+        WriteChunk(stream, idatType, ZlibCompress([0, 255, 0, 0], CompressionLevel.Fastest));
+        WriteChunk(stream, iendType, []);
 
-        return ms.ToArray();
+        return stream.ToArray();
     }
 
     static byte[] ZlibCompress(byte[] data, CompressionLevel level)