to make ExifProfile format agnostic again: passing ExifIdCode as ReadonlySpan to the ToByteArray method

src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs

@@ -6,6 +6,7 @@ using System.IO;
 using System.Runtime.CompilerServices;
 
 using SixLabors.ImageSharp.Formats.Jpeg.Components;
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
 using SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder;
 using SixLabors.ImageSharp.MetaData.Profiles.Exif;
 using SixLabors.ImageSharp.MetaData.Profiles.Icc;
@@ -608,7 +609,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         private void WriteExifProfile(ExifProfile exifProfile)
         {
             const int Max = 65533;
-            byte[] data = exifProfile?.ToByteArray();
+            byte[] data = exifProfile?.ToByteArray(ProfileResolver.ExifMarker);
             if (data == null || data.Length == 0)
             {
                 return;

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -536,7 +536,7 @@ namespace SixLabors.ImageSharp.Formats.Png
         {
             if (image.MetaData.ExifProfile?.Values.Count > 0)
             {
-                this.WriteChunk(stream, PngChunkType.Exif, image.MetaData.ExifProfile.ToByteArray(includeExifIdCode: false));
+                this.WriteChunk(stream, PngChunkType.Exif, image.MetaData.ExifProfile.ToByteArray());
             }
         }
 

src/ImageSharp/MetaData/Profiles/Exif/ExifProfile.cs

@@ -5,7 +5,6 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
-using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Primitives;
 
@@ -234,20 +233,13 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
         /// <summary>
         /// Converts this instance to a byte array.
         /// </summary>
-        /// <param name="includeExifIdCode">Indicates, if the Exif ID code should be included.
-        /// The Exif Id Code is part of the JPEG APP1 segment. This Exif ID code should not be included in case of PNG's.
-        /// Defaults to true.</param>
+        /// <param name="exifIdCode">The Exif Id Code is part of the JPEG APP1 segment (Exif00). Those bytes will be written at
+        /// the beginning of the array. This Exif ID code should not be included in case of PNG's.</param>
         /// <returns>The <see cref="T:byte[]"/></returns>
-        public byte[] ToByteArray(bool includeExifIdCode = true)
+        public byte[] ToByteArray(ReadOnlySpan<byte> exifIdCode = default)
         {
             if (this.values == null)
             {
-                if (!includeExifIdCode && this.StartsWithExifIdCode(this.data))
-                {
-                    // skip the first 6 bytes (the Exif Code)
-                    return this.data.Skip(6).ToArray();
-                }
-
                 return this.data;
             }
 
@@ -257,31 +249,7 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
             }
 
             var writer = new ExifWriter(this.values, this.Parts);
-            return writer.GetData(includeExifIdCode);
-        }
-
-        /// <summary>
-        /// Checks if a byte array start with the Exif Code: ASCII "Exif" followed by two zeros.
-        /// </summary>
-        /// <param name="exifBytes">The byte array to check for the Exif Code.</param>
-        /// <returns>True, if the byte array starts with the Exif Code</returns>
-        private bool StartsWithExifIdCode(byte[] exifBytes)
-        {
-            if (exifBytes.Length < 6)
-            {
-                return false;
-            }
-
-            int exifLength = ProfileResolver.ExifMarker.Length;
-            for (int i = 0; i < ProfileResolver.ExifMarker.Length; i++)
-            {
-                if (exifBytes[i] != ProfileResolver.ExifMarker[i])
-                {
-                    return false;
-                }
-            }
-
-            return true;
+            return writer.GetData(exifIdCode);
         }
 
         /// <summary>

src/ImageSharp/MetaData/Profiles/Exif/ExifWriter.cs

@@ -5,7 +5,6 @@ using System;
 using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.Text;
-using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
 using SixLabors.ImageSharp.Primitives;
 
 namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
@@ -42,15 +41,15 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
         /// <summary>
         /// Returns the EXIF data.
         /// </summary>
-        /// <param name="includeExifIdCode">Indicates, if the Exif ID code should be included.
-        /// The Exif Id Code is part of the JPEG APP1 segment. This Exif ID code should not be included in case of PNG's.
-        /// Defaults to true.</param>
+        /// <param name="exifIdCode">The Exif Id Code is part of the JPEG APP1 segment (Exif00). Those bytes will be written at
+        /// the beginning of the array. This Exif ID code should not be included in case of PNG's.</param>
         /// <returns>
         /// The <see cref="T:byte[]"/>.
         /// </returns>
-        public byte[] GetData(bool includeExifIdCode = true)
+        public byte[] GetData(ReadOnlySpan<byte> exifIdCode)
         {
-            uint startIndex = (uint)ProfileResolver.ExifMarker.Length;
+            uint exifIdCodeLength = exifIdCode.IsEmpty ? 0 : (uint)exifIdCode.Length;
+            uint startIndex = exifIdCodeLength;
             uint length;
             int exifIndex = -1;
             int gpsIndex = -1;
@@ -86,17 +85,7 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
                 return null;
             }
 
-            if (includeExifIdCode)
-            {
-                // Exif Id Code "Exif00" (6 bytes)
-                length += (uint)ProfileResolver.ExifMarker.Length;
-            }
-            else
-            {
-                // special case for PNG eXIf Chunk:
-                // if the Exif Code ("Exif00") is not included, the start index is 0 instead of 6
-                startIndex = 0;
-            }
+            length += exifIdCodeLength;
 
             // two bytes for the byte Order marker 'II', followed by the number 42 (0x2A) and a 0, making 4 bytes total
             length += (uint)ExifConstants.LittleEndianByteOrderMarker.Length;
@@ -106,10 +95,10 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Exif
             byte[] result = new byte[length];
 
             int i = 0;
-            if (includeExifIdCode)
+            if (!exifIdCode.IsEmpty)
             {
-                ProfileResolver.ExifMarker.AsSpan().CopyTo(result); // 0-5
-                i += ProfileResolver.ExifMarker.Length;
+                exifIdCode.CopyTo(result); // 0-5
+                i += exifIdCode.Length;
             }
 
             // the byte order marker for little-endian, followed by the number 42 and a 0

tests/ImageSharp.Tests/MetaData/ImageMetaDataTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
 using SixLabors.ImageSharp.MetaData;
 using SixLabors.ImageSharp.MetaData.Profiles.Exif;
 using SixLabors.ImageSharp.PixelFormats;
@@ -32,6 +33,7 @@ namespace SixLabors.ImageSharp.Tests
             ImageMetaData clone = metaData.Clone();
 
             Assert.Equal(exifProfile.ToByteArray(), clone.ExifProfile.ToByteArray());
+            Assert.Equal(exifProfile.ToByteArray(ProfileResolver.ExifMarker), clone.ExifProfile.ToByteArray(ProfileResolver.ExifMarker));
             Assert.Equal(4, clone.HorizontalResolution);
             Assert.Equal(2, clone.VerticalResolution);
             Assert.Equal(imageProperty, clone.Properties[0]);

tests/ImageSharp.Tests/MetaData/Profiles/Exif/ExifProfileTests.cs

@@ -324,7 +324,7 @@ namespace SixLabors.ImageSharp.Tests
             // Force parsing of the profile.
             Assert.Equal(24, profile.Values.Count);
 
-            byte[] bytes = profile.ToByteArray();
+            byte[] bytes = profile.ToByteArray(ProfileResolver.ExifMarker);
             Assert.Equal(495, bytes.Length);
         }
 
@@ -360,21 +360,21 @@ namespace SixLabors.ImageSharp.Tests
             // arrange
             byte[] exifBytesWithExifCode = ProfileResolver.ExifMarker.Concat(ExifConstants.LittleEndianByteOrderMarker).ToArray(); 
             byte[] exifBytesWithoutExifCode = ExifConstants.LittleEndianByteOrderMarker;
-            var profile = new ExifProfile(exifBytesWithExifCode);
+            ExifProfile profile = CreateExifProfile();
 
             // act
-            byte[] actual = profile.ToByteArray(includeExifIdCode);
+            byte[] actual = profile.ToByteArray(includeExifIdCode ? ProfileResolver.ExifMarker : default(ReadOnlySpan<byte>));
 
             // assert
             Assert.NotNull(actual);
             Assert.NotEmpty(actual);
             if (includeExifIdCode)
             {
-                Assert.Equal(exifBytesWithExifCode, actual);
+                Assert.Equal(exifBytesWithExifCode, actual.Take(exifBytesWithExifCode.Length).ToArray());
             }
             else
             {
-                Assert.Equal(exifBytesWithoutExifCode, actual);
+                Assert.Equal(exifBytesWithoutExifCode, actual.Take(exifBytesWithoutExifCode.Length).ToArray());
             }
         }
 

tests/ImageSharp.Tests/Processing/Processors/Transforms/AutoOrientTests.cs

@@ -9,6 +9,7 @@ using Xunit;
 
 namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
 {
+    using SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder;
     using SixLabors.ImageSharp.Processing.Transforms;
 
     public class AutoOrientTests : FileTestBase
@@ -65,7 +66,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
             var profile = new ExifProfile();
             profile.SetValue(ExifTag.JPEGTables, orientation);
 
-            byte[] bytes = profile.ToByteArray();
+            byte[] bytes = profile.ToByteArray(ProfileResolver.ExifMarker);
             // Change the tag into ExifTag.Orientation
             bytes[16] = 18;
             bytes[17] = 1;