Fix #2924

Author: JimBobSquarePants

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -125,6 +125,11 @@ internal sealed class PngDecoderCore : ImageDecoderCore
     /// </summary>
     private readonly int maxUncompressedLength;
 
+    /// <summary>
+    /// A value indicating whether the image data has been read.
+    /// </summary>
+    private bool hasImageData;
+
     /// <summary>
     /// Initializes a new instance of the <see cref="PngDecoderCore"/> class.
     /// </summary>
@@ -746,7 +751,11 @@ private void ReadScanlines<TPixel>(
         where TPixel : unmanaged, IPixel<TPixel>
     {
         using ZlibInflateStream inflateStream = new(this.currentStream, getData);
-        inflateStream.AllocateNewBytes(chunkLength, true);
+        if (!inflateStream.AllocateNewBytes(chunkLength, !this.hasImageData))
+        {
+            return;
+        }
+
         DeflateStream dataStream = inflateStream.CompressedStream!;
 
         if (this.header.InterlaceMethod is PngInterlaceMode.Adam7)
@@ -800,7 +809,7 @@ private void DecodePixelData<TPixel>(
                 int bytesRead = compressedStream.Read(scanSpan, currentRowBytesRead, bytesPerFrameScanline - currentRowBytesRead);
                 if (bytesRead <= 0)
                 {
-                    return;
+                    goto EXIT;
                 }
 
                 currentRowBytesRead += bytesRead;
@@ -845,6 +854,7 @@ private void DecodePixelData<TPixel>(
         }
 
         EXIT:
+        this.hasImageData = true;
         blendMemory?.Dispose();
     }
 
@@ -903,7 +913,7 @@ private void DecodeInterlacedPixelData<TPixel>(
                     int bytesRead = compressedStream.Read(this.scanline.GetSpan(), currentRowBytesRead, bytesPerInterlaceScanline - currentRowBytesRead);
                     if (bytesRead <= 0)
                     {
-                        return;
+                        goto EXIT;
                     }
 
                     currentRowBytesRead += bytesRead;
@@ -976,6 +986,7 @@ private void DecodeInterlacedPixelData<TPixel>(
         }
 
         EXIT:
+        this.hasImageData = true;
         blendMemory?.Dispose();
     }
 

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

@@ -705,10 +705,20 @@ public void Decode_BadPalette(string file)
     [Theory]
     [WithFile(TestImages.Png.Issue2752, PixelTypes.Rgba32)]
     public void CanDecodeJustOneFrame<TPixel>(TestImageProvider<TPixel> provider)
-    where TPixel : unmanaged, IPixel<TPixel>
+        where TPixel : unmanaged, IPixel<TPixel>
     {
         DecoderOptions options = new() { MaxFrames = 1 };
         using Image<TPixel> image = provider.GetImage(PngDecoder.Instance, options);
         Assert.Equal(1, image.Frames.Count);
     }
+
+    [Theory]
+    [WithFile(TestImages.Png.Issue2924, PixelTypes.Rgba32)]
+    public void CanDecode_Issue2924<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance);
+        image.DebugSave(provider);
+        image.CompareToReferenceOutput(provider);
+    }
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -160,6 +160,9 @@ public static class Png
         // Issue 2752: https://github.com/SixLabors/ImageSharp/issues/2752
         public const string Issue2752 = "Png/issues/Issue_2752.png";
 
+        // Issue 2924: https://github.com/SixLabors/ImageSharp/issues/2924
+        public const string Issue2924 = "Png/issues/Issue_2924.png";
+
         public static class Bad
         {
             public const string MissingDataChunk = "Png/xdtn0g01.png";