refactor PngDecoder to SpecializedImageDecoder<PngDecoderOptions>

Author: Sven Claesson

src/ImageSharp/Formats/Png/PngDecoder.cs

@@ -8,7 +8,7 @@ namespace SixLabors.ImageSharp.Formats.Png;
 /// <summary>
 /// Decoder for generating an image out of a png encoded stream.
 /// </summary>
-public sealed class PngDecoder : ImageDecoder
+public sealed class PngDecoder : SpecializedImageDecoder<PngDecoderOptions>
 {
     private PngDecoder()
     {
@@ -25,31 +25,31 @@ protected override ImageInfo Identify(DecoderOptions options, Stream stream, Can
         Guard.NotNull(options, nameof(options));
         Guard.NotNull(stream, nameof(stream));
 
-        return new PngDecoderCore(options).Identify(options.Configuration, stream, cancellationToken);
+        return new PngDecoderCore(new PngDecoderOptions() { GeneralOptions = options }).Identify(options.Configuration, stream, cancellationToken);
     }
 
     /// <inheritdoc/>
-    protected override Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+    protected override Image<TPixel> Decode<TPixel>(PngDecoderOptions options, Stream stream, CancellationToken cancellationToken)
     {
         Guard.NotNull(options, nameof(options));
         Guard.NotNull(stream, nameof(stream));
 
         PngDecoderCore decoder = new(options);
-        Image<TPixel> image = decoder.Decode<TPixel>(options.Configuration, stream, cancellationToken);
+        Image<TPixel> image = decoder.Decode<TPixel>(options.GeneralOptions.Configuration, stream, cancellationToken);
 
-        ScaleToTargetSize(options, image);
+        ScaleToTargetSize(options.GeneralOptions, image);
 
         return image;
     }
 
     /// <inheritdoc/>
-    protected override Image Decode(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+    protected override Image Decode(PngDecoderOptions options, Stream stream, CancellationToken cancellationToken)
     {
         Guard.NotNull(options, nameof(options));
         Guard.NotNull(stream, nameof(stream));
 
         PngDecoderCore decoder = new(options, true);
-        ImageInfo info = decoder.Identify(options.Configuration, stream, cancellationToken);
+        ImageInfo info = decoder.Identify(options.GeneralOptions.Configuration, stream, cancellationToken);
         stream.Position = 0;
 
         PngMetadata meta = info.Metadata.GetPngMetadata();
@@ -99,4 +99,7 @@ protected override Image Decode(DecoderOptions options, Stream stream, Cancellat
                 return this.Decode<Rgba32>(options, stream, cancellationToken);
         }
     }
+
+    /// <inheritdoc/>
+    protected override PngDecoderOptions CreateDefaultSpecializedOptions(DecoderOptions options) => new PngDecoderOptions() { GeneralOptions = options };
 }

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -113,27 +113,34 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// </summary>
     private PngChunk? nextChunk;
 
+    /// <summary>
+    /// If true, ADLER32 checksum in the IDAT chunk as well as the chunk CRCs will be ignored.
+    /// </summary>
+    private bool ignoreCrcErrors;
+
     /// <summary>
     /// Initializes a new instance of the <see cref="PngDecoderCore"/> class.
     /// </summary>
     /// <param name="options">The decoder options.</param>
-    public PngDecoderCore(DecoderOptions options)
+    public PngDecoderCore(PngDecoderOptions options)
     {
-        this.Options = options;
-        this.configuration = options.Configuration;
-        this.maxFrames = options.MaxFrames;
-        this.skipMetadata = options.SkipMetadata;
+        this.Options = options.GeneralOptions;
+        this.configuration = options.GeneralOptions.Configuration;
+        this.maxFrames = options.GeneralOptions.MaxFrames;
+        this.skipMetadata = options.GeneralOptions.SkipMetadata;
         this.memoryAllocator = this.configuration.MemoryAllocator;
+        this.ignoreCrcErrors = options.IgnoreCrcCheck;
     }
 
-    internal PngDecoderCore(DecoderOptions options, bool colorMetadataOnly)
+    internal PngDecoderCore(PngDecoderOptions options, bool colorMetadataOnly)
     {
-        this.Options = options;
+        this.Options = options.GeneralOptions;
         this.colorMetadataOnly = colorMetadataOnly;
-        this.maxFrames = options.MaxFrames;
+        this.maxFrames = options.GeneralOptions.MaxFrames;
         this.skipMetadata = true;
-        this.configuration = options.Configuration;
+        this.configuration = options.GeneralOptions.Configuration;
         this.memoryAllocator = this.configuration.MemoryAllocator;
+        this.ignoreCrcErrors = options.IgnoreCrcCheck;
     }
 
     /// <inheritdoc/>
@@ -1789,8 +1796,11 @@ private bool TryReadChunk(Span<byte> buffer, out PngChunk chunk)
             type: type,
             data: this.ReadChunkData(length));
 
-        this.ValidateChunk(chunk, buffer);
-
+        if (!this.ignoreCrcErrors)
+        {
+            this.ValidateChunk(chunk, buffer);
+        }
+        
         // Restore the stream position for IDAT and fdAT chunks, because it will be decoded later and
         // was only read to verifying the CRC is correct.
         if (type is PngChunkType.Data or PngChunkType.FrameData)

src/ImageSharp/Formats/Png/PngDecoderOptions.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Configuration options for decoding png images.
+/// </summary>
+public sealed class PngDecoderOptions : ISpecializedDecoderOptions
+{
+    /// <inheritdoc/>
+    public DecoderOptions GeneralOptions { get; init; } = new DecoderOptions();
+
+    /// <summary>
+    /// If true, ADLER32 checksum in the IDAT chunk as well as the chunk CRCs will be ignored.
+    /// Similar to PNG_CRC_QUIET_USE in libpng.
+    /// </summary>
+    public bool IgnoreCrcCheck { get; init; }
+}

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs

@@ -470,6 +470,17 @@ public void Decode_InvalidDataChunkCrc_ThrowsException<TPixel>(TestImageProvider
         Assert.Contains("CRC Error. PNG IDAT chunk is corrupt!", ex.Message);
     }
 
+    [Theory]
+    [WithFile(TestImages.Png.Bad.WrongCrcDataChunk, PixelTypes.Rgba32)]
+    public void Decode_InvalidDataChunkCrc_IgnoreCrcErrors<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance, new PngDecoderOptions() { IgnoreCrcCheck = true });
+
+        image.DebugSave(provider);
+        image.CompareToOriginal(provider, new MagickReferenceDecoder(false));
+    }
+
     // https://github.com/SixLabors/ImageSharp/issues/1014
     [Theory]
     [WithFileCollection(nameof(TestImagesIssue1014), PixelTypes.Rgba32)]

tests/ImageSharp.Tests/TestUtilities/ReferenceCodecs/MagickReferenceDecoder.cs

@@ -31,12 +31,17 @@ protected override Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream s
         {
             IgnoreFileSize = !this.validate
         };
+        PngReadDefines pngReadDefines = new()
+        {
+            IgnoreCrc = !this.validate
+        };
 
         MagickReadSettings settings = new()
         {
             FrameCount = (int)options.MaxFrames
         };
         settings.SetDefines(bmpReadDefines);
+        settings.SetDefines(pngReadDefines);
 
         using MagickImageCollection magickImageCollection = new(stream, settings);
         List<ImageFrame<TPixel>> framesList = new();