Ignore chunk length of 1. Fix #103

TODO: Read libpng for matching behaviour

src/ImageSharp.Formats.Png/PngDecoderCore.cs

@@ -927,12 +927,12 @@ namespace ImageSharp.Formats
         private void ReadChunkLength(PngChunk chunk)
         {
             int numBytes = this.currentStream.Read(this.chunkLengthBuffer, 0, 4);
-            if (numBytes >= 1 && numBytes <= 3)
+            if (numBytes > 1 && numBytes <= 3)
             {
                 throw new ImageFormatException("Image stream is not valid!");
             }
 
-            if (numBytes <= 0)
+            if (numBytes <= 1)
             {
                 chunk.Length = -1;
                 return;

tests/ImageSharp.Tests/FileTestBase.cs

@@ -6,7 +6,6 @@
 namespace ImageSharp.Tests
 {
     using System.Collections.Generic;
-    using ImageSharp.Formats;
 
     /// <summary>
     /// The test base class for reading and writing to files.
@@ -18,8 +17,8 @@ namespace ImageSharp.Tests
         /// </summary>
         protected static readonly List<TestFile> Files = new List<TestFile>
         {
-            TestFile.Create(TestImages.Jpeg.Baseline.Calliphora),
+               TestFile.Create(TestImages.Jpeg.Baseline.Calliphora),
-            TestFile.Create(TestImages.Jpeg.Baseline.Turtle),
+            // TestFile.Create(TestImages.Jpeg.Baseline.Turtle), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Jpeg.Baseline.Ycck), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Jpeg.Baseline.Cmyk), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Jpeg.Baseline.Floorplan), // Perf: Enable for local testing only
@@ -28,10 +27,11 @@ namespace ImageSharp.Tests
             // TestFile.Create(TestImages.Jpeg.Progressive.Progress), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Jpeg.Baseline.GammaDalaiLamaGray), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Jpeg.Progressive.Bad.BadEOF), // Perf: Enable for local testing only
-            TestFile.Create(TestImages.Bmp.Car),
+               TestFile.Create(TestImages.Bmp.Car),
             // TestFile.Create(TestImages.Bmp.Neg_height), // Perf: Enable for local testing only
-            TestFile.Create(TestImages.Png.Splash),
+               TestFile.Create(TestImages.Png.Splash),
-            TestFile.Create(TestImages.Png.Powerpoint),
+            // TestFile.Create(TestImages.Png.ChunkLength), // Perf: Enable for local testing only
+            // TestFile.Create(TestImages.Png.Powerpoint), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Png.Blur), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Png.Indexed), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Png.SplashInterlaced), // Perf: Enable for local testing only
@@ -44,7 +44,7 @@ namespace ImageSharp.Tests
             // TestFile.Create(TestImages.Png.FilterVar), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Png.P1), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Png.Pd), // Perf: Enable for local testing only
-            TestFile.Create(TestImages.Gif.Rings), // Perf: Enable for local testing only
+               TestFile.Create(TestImages.Gif.Rings),
             // TestFile.Create(TestImages.Gif.Cheers), // Perf: Enable for local testing only
             // TestFile.Create(TestImages.Gif.Giphy) // Perf: Enable for local testing only
         };

tests/ImageSharp.Tests/TestImages.cs

@@ -34,6 +34,9 @@ namespace ImageSharp.Tests
 
             // filter changing per scanline
             public const string FilterVar = "Png/filterVar.png";
+
+            // Chunk length of 1 by end marker
+            public const string ChunkLength = "Png/chunklength1.png";
         }
 
         public static class Jpeg

tests/ImageSharp.Tests/TestImages/Formats/Png/chunklength1.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:7b9957a86738acc0b682618a6677c8d659614cd6be5728e85185aef314c21981
+size 149591