Only exit JPEG scan decoding after multiple EOF hits

src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegBitReader.cs

@@ -22,6 +22,9 @@ internal struct JpegBitReader
     // Whether there is no more good data to pull from the stream for the current mcu.
     private bool badData;
 
+    // How many times have we hit the eof.
+    private int eofHitCount;
+
     public JpegBitReader(BufferedReadStream stream)
     {
         this.stream = stream;
@@ -31,6 +34,7 @@ public JpegBitReader(BufferedReadStream stream)
         this.MarkerPosition = 0;
         this.badData = false;
         this.NoData = false;
+        this.eofHitCount = 0;
     }
 
     /// <summary>
@@ -219,11 +223,16 @@ private int ReadStream()
         // we know we have hit the EOI and completed decoding the scan buffer.
         if (value == -1 || (this.badData && this.data == 0 && this.stream.Position >= this.stream.Length))
         {
-            // We've encountered the end of the file stream which means there's no EOI marker
+            // We've hit the end of the file stream more times than allowed which means there's no EOI marker
             // in the image or the SOS marker has the wrong dimensions set.
-            this.badData = true;
-            this.NoData = true;
-            value = 0;
+            if (this.eofHitCount > JpegConstants.Huffman.FetchLoop)
+            {
+                this.badData = true;
+                this.NoData = true;
+                value = 0;
+            }
+
+            this.eofHitCount++;
         }
 
         return value;

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.cs

@@ -364,4 +364,15 @@ public void Issue2517_DecodeWorks<TPixel>(TestImageProvider<TPixel> provider)
         image.DebugSave(provider);
         image.CompareToOriginal(provider);
     }
+
+    // https://github.com/SixLabors/ImageSharp/issues/2638
+    [Theory]
+    [WithFile(TestImages.Jpeg.Issues.Issue2638, PixelTypes.Rgba32)]
+    public void Issue2638_DecodeWorks<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(JpegDecoder.Instance);
+        image.DebugSave(provider);
+        image.CompareToOriginal(provider);
+    }
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -316,6 +316,7 @@ public static class Issues
             public const string HangBadScan = "Jpg/issues/Hang_C438A851.jpg";
             public const string Issue2517 = "Jpg/issues/issue2517-bad-d7.jpg";
             public const string Issue2067_CommentMarker = "Jpg/issues/issue-2067-comment.jpg";
+            public const string Issue2638 = "Jpg/issues/Issue2638.jpg";
 
             public static class Fuzz
             {