Merge pull request #2561 from SixLabors/js/faster-png-eof-handling

Png- Do not attempt to read data for chunks of length 0.

Author: JimBobSquarePants

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -15,6 +15,7 @@
 using SixLabors.ImageSharp.Formats.Png.Filters;
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Memory.Internals;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
@@ -1863,6 +1864,11 @@ private void SkipChunkDataAndCrc(in PngChunk chunk)
     [MethodImpl(InliningOptions.ShortMethod)]
     private IMemoryOwner<byte> ReadChunkData(int length)
     {
+        if (length == 0)
+        {
+            return new BasicArrayBuffer<byte>(Array.Empty<byte>());
+        }
+
         // We rent the buffer here to return it afterwards in Decode()
         IMemoryOwner<byte> buffer = this.configuration.MemoryAllocator.Allocate<byte>(length, AllocationOptions.Clean);
 

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

@@ -636,4 +636,13 @@ static void RunTest(string providerDump, string nonContiguousBuffersStr)
                 "Disco")
             .Dispose();
     }
+
+    [Fact]
+    public void Binary_PrematureEof()
+    {
+        using EofHitCounter eofHitCounter = EofHitCounter.RunDecoder(TestImages.Png.Bad.FlagOfGermany0000016446);
+
+        Assert.True(eofHitCounter.EofHitCount <= 2);
+        Assert.Equal(new Size(200, 120), eofHitCounter.Image.Size);
+    }
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -180,6 +180,8 @@ public static class Bad
             // Invalid color type.
             public const string ColorTypeOne = "Png/xc1n0g08.png";
             public const string ColorTypeNine = "Png/xc9n2c08.png";
+
+            public const string FlagOfGermany0000016446 = "Png/issues/flag_of_germany-0000016446.png";
         }
     }