Decoupled mcu size from the decoder, fixed SOF component bytes length check

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

@@ -89,6 +89,11 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// </summary>
         public int McusPerColumn { get; set; }
 
+        /// <summary>
+        /// Gets the mcu size of the image.
+        /// </summary>
+        public Size McuSize => new Size(this.McusPerLine, this.McusPerColumn);
+
         /// <summary>
         /// Gets the color depth, in number of bits per pixel.
         /// </summary>

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -112,11 +112,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// <inheritdoc/>
         Size IImageDecoderInternals.Dimensions => this.Frame.PixelSize;
 
-        /// <summary>
-        /// Gets the number of MCU blocks in the image as <see cref="Size"/>.
-        /// </summary>
-        public Size ImageSizeInMCU { get; private set; }
-
         /// <summary>
         /// Gets a value indicating whether the metadata should be ignored when the image is being decoded.
         /// </summary>
@@ -834,6 +829,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             byte componentCount = this.temp[5];
             this.ColorSpace = this.DeduceJpegColorSpace(componentCount);
 
+            this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr;
+
             this.Frame = new JpegFrame
             {
                 Extended = frameMarker.Marker == JpegConstants.Markers.SOF1,
@@ -844,14 +841,12 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 ComponentCount = componentCount
             };
 
-            this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr;
-
             if (!metadataOnly)
             {
                 remaining -= length;
 
                 const int componentBytes = 3;
-                if (remaining > componentCount * componentBytes)
+                if (remaining != componentCount * componentBytes)
                 {
                     JpegThrowHelper.ThrowBadMarker("SOFn", remaining);
                 }
@@ -894,9 +889,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                 this.Frame.MaxVerticalFactor = maxV;
                 this.Frame.InitComponents();
 
-                this.ImageSizeInMCU = new Size(this.Frame.McusPerLine, this.Frame.McusPerColumn);
-
-                // This can be injected in SOF marker callback
                 this.scanDecoder.InjectFrameData(this.Frame, this);
             }
         }

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

@@ -48,7 +48,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
                 Size expectedSizeInBlocks = decoder.ImageSizeInPixels.DivideRoundUp(8);
 
-                Assert.Equal(expectedSizeInBlocks, decoder.ImageSizeInMCU);
+                Assert.Equal(expectedSizeInBlocks, decoder.Frame.McuSize);
 
                 var uniform1 = new Size(1, 1);
                 JpegComponent c0 = decoder.Components[0];
@@ -70,7 +70,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             using (JpegDecoderCore decoder = JpegFixture.ParseJpegStream(imageFile))
             {
                 sb.AppendLine(imageFile);
-                sb.AppendLine($"Size:{decoder.ImageSizeInPixels} MCU:{decoder.ImageSizeInMCU}");
+                sb.AppendLine($"Size:{decoder.ImageSizeInPixels} MCU:{decoder.Frame.McuSize}");
                 JpegComponent c0 = decoder.Components[0];
                 JpegComponent c1 = decoder.Components[1];
 
@@ -115,7 +115,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
 
                 var uniform1 = new Size(1, 1);
 
-                Size expectedLumaSizeInBlocks = decoder.ImageSizeInMCU.MultiplyBy(fLuma);
+                Size expectedLumaSizeInBlocks = decoder.Frame.McuSize.MultiplyBy(fLuma);
 
                 Size divisor = fLuma.DivideBy(fChroma);