Fix #115

src/ImageSharp.Formats.Png/PngDecoderCore.cs

@@ -10,6 +10,7 @@ namespace ImageSharp.Formats
     using System.Collections.Generic;
     using System.IO;
     using System.Linq;
+    using System.Runtime.CompilerServices;
 
     using static ComparableExtensions;
 
@@ -945,12 +946,7 @@ namespace ImageSharp.Formats
         private void ReadChunkLength(PngChunk chunk)
         {
             int numBytes = this.currentStream.Read(this.chunkLengthBuffer, 0, 4);
-            if (numBytes > 1 && numBytes <= 3)
-            {
-                throw new ImageFormatException("Image stream is not valid!");
-            }
-
-            if (numBytes <= 1)
+            if (numBytes < 4)
             {
                 chunk.Length = -1;
                 return;
@@ -966,6 +962,7 @@ namespace ImageSharp.Formats
         /// </summary>
         /// <param name="pass">Th current pass index</param>
         /// <returns>The <see cref="int"/></returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private int ComputeColumnsAdam7(int pass)
         {
             int width = this.header.Width;

tests/ImageSharp.Tests/FileTestBase.cs

@@ -30,7 +30,8 @@ namespace ImageSharp.Tests
                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.ChunkLength), // Perf: Enable for local testing only
+            // TestFile.Create(TestImages.Png.ChunkLength1), // Perf: Enable for local testing only
+            // TestFile.Create(TestImages.Png.ChunkLength2), // 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

tests/ImageSharp.Tests/TestImages.cs

@@ -25,18 +25,19 @@ namespace ImageSharp.Tests
             public const string SplashInterlaced = "Png/splash-interlaced.png";
             public const string Interlaced = "Png/interlaced.png";
 
-            // filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
+            // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
             public const string Filter0 = "Png/filter0.png";
             public const string Filter1 = "Png/filter1.png";
             public const string Filter2 = "Png/filter2.png";
             public const string Filter3 = "Png/filter3.png";
             public const string Filter4 = "Png/filter4.png";
 
-            // filter changing per scanline
+            // 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";
+            // Odd chunk lengths
+            public const string ChunkLength1 = "Png/chunklength1.png";
+            public const string ChunkLength2 = "Png/chunklength2.png";
         }
 
         public static class Jpeg