Support for XMP metadata

src/ImageSharp/Formats/Gif/GifConstants.cs

@@ -121,5 +121,16 @@ internal static class GifConstants
             (byte)'P', (byte)'E',
             (byte)'2', (byte)'.', (byte)'0'
         };
+
+        /// <summary>
+        /// Gets the ASCII encoded application identification bytes.
+        /// </summary>
+        internal static ReadOnlySpan<byte> XmpApplicationIdentificationBytes => new[]
+        {
+            (byte)'X', (byte)'M', (byte)'P',
+            (byte)' ', (byte)'D', (byte)'a',
+            (byte)'t', (byte)'a',
+            (byte)'X', (byte)'M', (byte)'P'
+        };
     }
 }

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -11,6 +11,7 @@
 using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Gif
@@ -250,33 +251,45 @@ private void ReadLogicalScreenDescriptor()
         }
 
         /// <summary>
-        /// Reads the application extension block parsing any animation information
+        /// Reads the application extension block parsing any animation or XMP information
         /// if present.
         /// </summary>
         private void ReadApplicationExtension()
         {
             int appLength = this.stream.ReadByte();
 
             // If the length is 11 then it's a valid extension and most likely
-            // a NETSCAPE or ANIMEXTS extension. We want the loop count from this.
+            // a NETSCAPE, XMP or ANIMEXTS extension. We want the loop count from this.
             if (appLength == GifConstants.ApplicationBlockSize)
             {
-                this.stream.Skip(appLength);
-                int subBlockSize = this.stream.ReadByte();
+                this.stream.Read(this.buffer, 0, GifConstants.ApplicationBlockSize);
+                bool isXmp = this.buffer.AsSpan().StartsWith(GifConstants.XmpApplicationIdentificationBytes);
 
-                // TODO: There's also a NETSCAPE buffer extension.
-                // http://www.vurdalakov.net/misc/gif/netscape-buffering-application-extension
-                if (subBlockSize == GifConstants.NetscapeLoopingSubBlockSize)
+                if (isXmp)
                 {
-                    this.stream.Read(this.buffer, 0, GifConstants.NetscapeLoopingSubBlockSize);
-                    this.gifMetadata.RepeatCount = GifNetscapeLoopingApplicationExtension.Parse(this.buffer.AsSpan(1)).RepeatCount;
-                    this.stream.Skip(1); // Skip the terminator.
+                    var extension = GifXmpApplicationExtension.Read(this.stream);
+                    this.metadata.XmpProfile = new XmpProfile(extension.Data);
                     return;
                 }
+                else
+                {
+                    int subBlockSize = this.stream.ReadByte();
+
+                    // TODO: There's also a NETSCAPE buffer extension.
+                    // http://www.vurdalakov.net/misc/gif/netscape-buffering-application-extension
+                    if (subBlockSize == GifConstants.NetscapeLoopingSubBlockSize)
+                    {
+                        this.stream.Read(this.buffer, 0, GifConstants.NetscapeLoopingSubBlockSize);
+                        this.gifMetadata.RepeatCount = GifNetscapeLoopingApplicationExtension.Parse(this.buffer.AsSpan(1)).RepeatCount;
+                        this.stream.Skip(1); // Skip the terminator.
+                        return;
+                    }
+
+                    // Could be something else not supported yet.
+                    // Skip the subblock and terminator.
+                    this.SkipBlock(subBlockSize);
+                }
 
-                // Could be XMP or something else not supported yet.
-                // Skip the subblock and terminator.
-                this.SkipBlock(subBlockSize);
                 return;
             }
 

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -10,6 +10,7 @@
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
+using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
@@ -121,11 +122,8 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
             // Write the comments.
             this.WriteComments(gifMetadata, stream);
 
-            // Write application extension to allow additional frames.
-            if (image.Frames.Count > 1)
-            {
-                this.WriteApplicationExtension(stream, gifMetadata.RepeatCount);
-            }
+            // Write application extensions.
+            this.WriteApplicationExtensions(stream, gifMetadata.RepeatCount, metadata.XmpProfile);
 
             if (useGlobalTable)
             {
@@ -327,14 +325,23 @@ private void WriteLogicalScreenDescriptor(
         /// </summary>
         /// <param name="stream">The stream to write to.</param>
         /// <param name="repeatCount">The animated image repeat count.</param>
-        private void WriteApplicationExtension(Stream stream, ushort repeatCount)
+        /// <param name="xmpProfile">The XMP metadata profile. Null if profile is not to be written.</param>
+        private void WriteApplicationExtensions(Stream stream, ushort repeatCount, XmpProfile xmpProfile)
         {
-            // Application Extension Header
+            // Application Extension: Loop repeat count.
             if (repeatCount != 1)
             {
                 var loopingExtension = new GifNetscapeLoopingApplicationExtension(repeatCount);
                 this.WriteExtension(loopingExtension, stream);
             }
+
+            // Application Extension: XMP Profile.
+            if (xmpProfile != null)
+            {
+                xmpProfile.UpdateData();
+                var xmpExtension = new GifXmpApplicationExtension(xmpProfile.Data);
+                this.WriteExtension(xmpExtension, stream);
+            }
         }
 
         /// <summary>
@@ -420,14 +427,28 @@ private void WriteGraphicalControlExtension(GifFrameMetadata metadata, int trans
         private void WriteExtension<TGifExtension>(TGifExtension extension, Stream stream)
             where TGifExtension : struct, IGifExtension
         {
-            this.buffer[0] = GifConstants.ExtensionIntroducer;
-            this.buffer[1] = extension.Label;
+            IMemoryOwner<byte> owner = null;
+            Span<byte> buffer;
+            int extensionSize = extension.ContentLength;
+            if (extensionSize > this.buffer.Length - 3)
+            {
+                owner = this.memoryAllocator.Allocate<byte>(extensionSize + 3);
+                buffer = owner.GetSpan();
+            }
+            else
+            {
+                buffer = this.buffer;
+            }
+
+            buffer[0] = GifConstants.ExtensionIntroducer;
+            buffer[1] = extension.Label;
 
-            int extensionSize = extension.WriteTo(this.buffer.AsSpan(2));
+            extension.WriteTo(buffer.Slice(2));
 
-            this.buffer[extensionSize + 2] = GifConstants.Terminator;
+            buffer[extensionSize + 2] = GifConstants.Terminator;
 
-            stream.Write(this.buffer, 0, extensionSize + 3);
+            stream.Write(buffer, 0, extensionSize + 3);
+            owner?.Dispose();
         }
 
         /// <summary>

src/ImageSharp/Formats/Gif/Sections/GifGraphicControlExtension.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -63,6 +63,8 @@ public GifGraphicControlExtension(
 
         byte IGifExtension.Label => GifConstants.GraphicControlLabel;
 
+        int IGifExtension.ContentLength => 5;
+
         public int WriteTo(Span<byte> buffer)
         {
             ref GifGraphicControlExtension dest = ref Unsafe.As<byte, GifGraphicControlExtension>(ref MemoryMarshal.GetReference(buffer));

src/ImageSharp/Formats/Gif/Sections/GifNetscapeLoopingApplicationExtension.cs

@@ -12,6 +12,8 @@ namespace SixLabors.ImageSharp.Formats.Gif
 
         public byte Label => GifConstants.ApplicationExtensionLabel;
 
+        public int ContentLength => 16;
+
         /// <summary>
         /// Gets the repeat count.
         /// 0 means loop indefinitely. Count is set as play n + 1 times.

src/ImageSharp/Formats/Gif/Sections/GifXmpApplicationExtension.cs

@@ -0,0 +1,96 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace SixLabors.ImageSharp.Formats.Gif
+{
+    internal readonly struct GifXmpApplicationExtension : IGifExtension
+    {
+        public GifXmpApplicationExtension(byte[] data) => this.Data = data;
+
+        public byte Label => GifConstants.ApplicationExtensionLabel;
+
+        public int ContentLength => this.Data.Length + 269; // 12 + Data Length + 1 + 256
+
+        /// <summary>
+        /// Gets the raw Data.
+        /// </summary>
+        public byte[] Data { get; }
+
+        /// <summary>
+        /// Reads the XMP metadata from the specified stream.
+        /// </summary>
+        /// <param name="stream">The stream to read from.</param>
+        /// <returns>The XMP metadata</returns>
+        /// <exception cref="ImageFormatException">Thrown if the XMP block is not properly terminated.</exception>
+        public static GifXmpApplicationExtension Read(Stream stream)
+        {
+            // Read data in blocks, until an \0 character is encountered.
+            // We overshoot, indicated by the terminatorIndex variable.
+            const int bufferSize = 256;
+            var list = new List<byte[]>();
+            int terminationIndex = -1;
+            while (terminationIndex < 0)
+            {
+                byte[] temp = new byte[bufferSize];
+                int bytesRead = stream.Read(temp);
+                list.Add(temp);
+                terminationIndex = Array.IndexOf(temp, (byte)1);
+            }
+
+            // Pack all the blocks (except magic trailer) into one single array again.
+            int dataSize = ((list.Count - 1) * bufferSize) + terminationIndex;
+            byte[] buffer = new byte[dataSize];
+            Span<byte> bufferSpan = buffer;
+            int pos = 0;
+            for (int j = 0; j < list.Count - 1; j++)
+            {
+                list[j].CopyTo(bufferSpan.Slice(pos));
+                pos += bufferSize;
+            }
+
+            // Last one only needs the portion until terminationIndex copied over.
+            Span<byte> lastBytes = list[list.Count - 1];
+            lastBytes.Slice(0, terminationIndex).CopyTo(bufferSpan.Slice(pos));
+
+            // Skip the remainder of the magic trailer.
+            stream.Skip(258 - (bufferSize - terminationIndex));
+            return new GifXmpApplicationExtension(buffer);
+        }
+
+        public int WriteTo(Span<byte> buffer)
+        {
+            int totalSize = this.ContentLength;
+            if (buffer.Length < totalSize)
+            {
+                throw new InsufficientMemoryException("Unable to write XMP metadata to GIF image");
+            }
+
+            int bytesWritten = 0;
+            buffer[bytesWritten++] = GifConstants.ApplicationBlockSize;
+
+            // Write "XMP DataXMP"
+            ReadOnlySpan<byte> idBytes = GifConstants.XmpApplicationIdentificationBytes;
+            idBytes.CopyTo(buffer.Slice(bytesWritten));
+            bytesWritten += idBytes.Length;
+
+            // XMP Data itself
+            this.Data.CopyTo(buffer.Slice(bytesWritten));
+            bytesWritten += this.Data.Length;
+
+            // Write the Magic Trailer
+            buffer[bytesWritten++] = 0x01;
+            for (byte i = 255; i > 0; i--)
+            {
+                buffer[bytesWritten++] = i;
+            }
+
+            buffer[bytesWritten++] = 0x00;
+
+            return totalSize;
+        }
+    }
+}

src/ImageSharp/Formats/Gif/Sections/IGifExtension.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -15,6 +15,11 @@ public interface IGifExtension
         /// </summary>
         byte Label { get; }
 
+        /// <summary>
+        /// Gets the length of the contents of this extension.
+        /// </summary>
+        int ContentLength { get; }
+
         /// <summary>
         /// Writes the extension data to the buffer.
         /// </summary>

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

@@ -60,6 +60,18 @@ internal static class ProfileResolver
             (byte)'E', (byte)'x', (byte)'i', (byte)'f', (byte)'\0', (byte)'\0'
         };
 
+        /// <summary>
+        /// Gets the XMP specific markers.
+        /// </summary>
+        public static ReadOnlySpan<byte> XmpMarker => new[]
+        {
+            (byte)'h', (byte)'t', (byte)'t', (byte)'p', (byte)':', (byte)'/', (byte)'/',
+            (byte)'n', (byte)'s', (byte)'.', (byte)'a', (byte)'d', (byte)'o', (byte)'b',
+            (byte)'e', (byte)'.', (byte)'c', (byte)'o', (byte)'m', (byte)'/', (byte)'x',
+            (byte)'a', (byte)'p', (byte)'/', (byte)'1', (byte)'.', (byte)'0', (byte)'/',
+            (byte)0
+        };
+
         /// <summary>
         /// Gets the Adobe specific markers <see href="http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe"/>.
         /// </summary>