Add JxlToJpegDecoder static methods

src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlDecoderCore.cs

@@ -363,11 +363,6 @@ internal sealed class JxlDecoderCore : ImageDecoderCore, IDisposable
     /// </summary>
     private readonly JxlBoxContentDecoder? boxContentDecoder;
 
-    /// <summary>
-    /// Decodes JPEG XL to JPEG.
-    /// </summary>
-    private JxlToJpegDecoder? jpegDecoder;
-
     private readonly JxlBoxContentDecoder? metadataDecoder;
 
     /// <summary>
@@ -2246,12 +2241,12 @@ internal sealed class JxlDecoderCore : ImageDecoderCore, IDisposable
 
                 if (this.reconstructionExifSize > 0)
                 {
-                    JxlToJpegDecoder.SetExif(this.exifMetadata!.Memory, jpegData);
+                    JxlToJpegDecoder.TrySetExif(this.exifMetadata!.Memory.Span, jpegData);
                 }
 
                 if (this.reconstructionXmpSize > 0)
                 {
-                    JxlToJpegDecoder.SetXmp(this.xmpMetadata!.Memory, jpegData);
+                    JxlToJpegDecoder.TrySetXmp(this.xmpMetadata!.Memory.Span, jpegData);
                 }
 
                 this.reconstructionOutputJpeg = JpegReconstructionStage.Output;
@@ -2592,7 +2587,7 @@ internal sealed class JxlDecoderCore : ImageDecoderCore, IDisposable
                             throw new InvalidOperationException("Only one EXIF marker for JPEG reconstruction can be present");
                         }
 
-                        if (JxlToJpegDecoder.ExifBoxContentSize(jpegData, ref this.reconstructionExifSize) != Success)
+                        if (!JxlToJpegDecoder.ExifBoxContentSize(jpegData, ref this.reconstructionExifSize))
                         {
                             throw new InvalidOperationException("Invalid jbrd EXIF size");
                         }
@@ -2605,7 +2600,7 @@ internal sealed class JxlDecoderCore : ImageDecoderCore, IDisposable
                             throw new InvalidOperationException("Only one XMP marker for JPEG reconstruction can be present");
                         }
 
-                        if (JxlToJpegDecoder.XmlBoxContentSize(jpegData, ref this.reconstructionXmpSize) != Success)
+                        if (!JxlToJpegDecoder.XmpBoxContentSize(jpegData, ref this.reconstructionXmpSize))
                         {
                             throw new InvalidOperationException("Invalid jbrd XMP size");
                         }

src/ImageSharp/Formats/Jxl/Processing/Decoder/JxlToJpegDecoder.cs

@@ -0,0 +1,150 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Formats.Jxl.IO.Jpeg.Data;
+
+namespace SixLabors.ImageSharp.Formats.Jxl.Processing.Decoder;
+
+internal class JxlToJpegDecoder
+{
+    /// <summary>
+    /// Returns the number of EXIF markers in the JPEG file.
+    /// </summary>
+    /// <param name="jpegData">Input parsed JPEG data</param>
+    /// <returns>Number of EXIFs in the JPEG</returns>
+    public static int NumExifMarkers(JpegData jpegData) => jpegData.AppMarkerTypes.Count(x => x == JpegAppMarkerType.Exif);
+
+    /// <summary>
+    /// Returns the number of XMP markers in the JPEG file.
+    /// </summary>
+    /// <param name="jpegData">Input parsed JPEG data</param>
+    /// <returns>Number of XMPs in the JPEG</returns>
+    public static int NumXmpMarkers(JpegData jpegData) => jpegData.AppMarkerTypes.Count(x => x == JpegAppMarkerType.Xmp);
+
+    /// <summary>
+    /// Attempts to set EXIF data in the JPEG file.
+    /// </summary>
+    /// <param name="data">EXIF data</param>
+    /// <param name="jpegData">JPEG file for EXIF data</param>
+    /// <returns>If EXIF data was set, true; returns false if no EXIF marker is present, or is present but not enough data</returns>
+    public static bool TrySetExif(Span<byte> data, JpegData jpegData)
+    {
+        int size = data.Length;
+        ReadOnlySpan<byte> exifTag = JpegDataConstants.ExifTag;
+        int exifTagSize = exifTag.Length;
+
+        for (int i = 0; i < jpegData.AppData.Count; ++i)
+        {
+            if (jpegData.AppMarkerTypes[i] == JpegAppMarkerType.Exif)
+            {
+                Span<byte> dataSpan = CollectionsMarshal.AsSpan(jpegData.AppData[i]);
+
+                if (dataSpan.Length != size + 3 + exifTagSize - 4)
+                {
+                    return false;
+                }
+
+                // The first 9 bytes are used for JPEG marker header.
+                dataSpan[0] = 0xE1;
+
+                // The second and third byte are already filled in correctly
+                exifTag.CopyTo(dataSpan[3..]);
+
+                // The first 4 bytes are the TIFF header from the box contents, and are
+                // not included in the JPEG
+                data[4..].CopyTo(dataSpan[(3 + exifTagSize)..]);
+
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /// <summary>
+    /// Attempts to set XMP data in the JPEG file.
+    /// </summary>
+    /// <param name="data">XMP data</param>
+    /// <param name="jpegData">JPEG file for XMP data</param>
+    /// <returns>If XMP data was set, true; returns false if no XMP marker is present, or is present but not enough data</returns>
+    public static bool TrySetXmp(Span<byte> data, JpegData jpegData)
+    {
+        int size = data.Length;
+        ReadOnlySpan<byte> xmpTag = JpegDataConstants.XmpTag;
+        int xmpTagSize = xmpTag.Length;
+
+        for (int i = 0; i < jpegData.AppData.Count; ++i)
+        {
+            if (jpegData.AppMarkerTypes[i] == JpegAppMarkerType.Xmp)
+            {
+                Span<byte> dataSpan = CollectionsMarshal.AsSpan(jpegData.AppData[i]);
+
+                if (dataSpan.Length != size + 3 + xmpTagSize)
+                {
+                    return false;
+                }
+
+                // The first 9 bytes are used for JPEG marker header.
+                dataSpan[0] = 0xE1;
+
+                // The second and third byte are already filled in correctly
+                xmpTag.CopyTo(dataSpan[3..]);
+
+                data.CopyTo(dataSpan[(3 + xmpTagSize)..]);
+
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public static bool ExifBoxContentSize(JpegData jpegData, ref long size)
+    {
+        size = 0;
+        int exifTagLength = JpegDataConstants.ExifTag.Length;
+
+        for (int i = 0; i < jpegData.AppData.Count; ++i)
+        {
+            if (jpegData.AppMarkerTypes[i] == JpegAppMarkerType.Exif)
+            {
+                if (jpegData.AppData[i].Count < 3 + exifTagLength)
+                {
+                    // too small for app marker header
+                    return false;
+                }
+
+                // The first 4 bytes are the TIFF header from the box contents, and are
+                // not included in the JPEG
+                size = jpegData.AppData[i].Count + 4 - 3 - exifTagLength;
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public static bool XmpBoxContentSize(JpegData jpegData, ref long size)
+    {
+        size = 0;
+        int xmpTagLength = JpegDataConstants.XmpTag.Length;
+
+        for (int i = 0; i < jpegData.AppData.Count; ++i)
+        {
+            if (jpegData.AppMarkerTypes[i] == JpegAppMarkerType.Xmp)
+            {
+                if (jpegData.AppData[i].Count < 3 + xmpTagLength)
+                {
+                    // too small for app marker header
+                    return false;
+                }
+
+                size = jpegData.AppData[i].Count - 3 - xmpTagLength;
+                return true;
+            }
+        }
+
+        return false;
+    }
+}