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@ -2,9 +2,9 @@ |
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// Licensed under the Apache License, Version 2.0.
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using System; |
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using System.Collections.Generic; |
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using System.IO; |
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using SixLabors.ImageSharp.Metadata.Profiles.Xmp; |
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using SixLabors.ImageSharp.IO; |
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using SixLabors.ImageSharp.Memory; |
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namespace SixLabors.ImageSharp.Formats.Gif |
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{ |
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@ -14,7 +14,10 @@ namespace SixLabors.ImageSharp.Formats.Gif |
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public byte Label => GifConstants.ApplicationExtensionLabel; |
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public int ContentLength => this.Data.Length + 269; // 12 + Data Length + 1 + 256
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// size : 1
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// identifier : 11
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// magic trailer : 257
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public int ContentLength => this.Data.Length + 269; |
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/// <summary>
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/// Gets the raw Data.
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@ -25,40 +28,23 @@ namespace SixLabors.ImageSharp.Formats.Gif |
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/// Reads the XMP metadata from the specified stream.
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/// </summary>
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/// <param name="stream">The stream to read from.</param>
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/// <param name="allocator">The memory allocator.</param>
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/// <returns>The XMP metadata</returns>
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/// <exception cref="ImageFormatException">Thrown if the XMP block is not properly terminated.</exception>
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public static GifXmpApplicationExtension Read(Stream stream) |
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public static GifXmpApplicationExtension Read(Stream stream, MemoryAllocator allocator) |
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{ |
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// Read data in blocks, until an \0 character is encountered.
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// We overshoot, indicated by the terminatorIndex variable.
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const int bufferSize = 256; |
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var list = new List<byte[]>(); |
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int terminationIndex = -1; |
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while (terminationIndex < 0) |
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{ |
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byte[] temp = new byte[bufferSize]; |
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int bytesRead = stream.Read(temp); |
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list.Add(temp); |
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terminationIndex = Array.IndexOf(temp, (byte)1); |
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} |
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byte[] xmpBytes = ReadXmpData(stream, allocator); |
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// Pack all the blocks (except magic trailer) into one single array again.
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int dataSize = ((list.Count - 1) * bufferSize) + terminationIndex; |
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byte[] buffer = new byte[dataSize]; |
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Span<byte> bufferSpan = buffer; |
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int pos = 0; |
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for (int j = 0; j < list.Count - 1; j++) |
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// Exclude the "magic trailer", see XMP Specification Part 3, 1.1.2 GIF
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int xmpLength = xmpBytes.Length - 256; // 257 - unread 0x0
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byte[] buffer = Array.Empty<byte>(); |
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if (xmpLength > 0) |
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{ |
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list[j].CopyTo(bufferSpan.Slice(pos)); |
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pos += bufferSize; |
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buffer = new byte[xmpLength]; |
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xmpBytes.AsSpan(0, xmpLength).CopyTo(buffer); |
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stream.Skip(1); // Skip the terminator.
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} |
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// Last one only needs the portion until terminationIndex copied over.
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Span<byte> lastBytes = list[list.Count - 1]; |
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lastBytes.Slice(0, terminationIndex).CopyTo(bufferSpan.Slice(pos)); |
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// Skip the remainder of the magic trailer.
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stream.Skip(258 - (bufferSize - terminationIndex)); |
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return new GifXmpApplicationExtension(buffer); |
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} |
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@ -67,7 +53,7 @@ namespace SixLabors.ImageSharp.Formats.Gif |
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int totalSize = this.ContentLength; |
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if (buffer.Length < totalSize) |
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{ |
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throw new InsufficientMemoryException("Unable to write XMP metadata to GIF image"); |
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ThrowInsufficientMemory(); |
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} |
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int bytesWritten = 0; |
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@ -93,5 +79,29 @@ namespace SixLabors.ImageSharp.Formats.Gif |
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return totalSize; |
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} |
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private static byte[] ReadXmpData(Stream stream, MemoryAllocator allocator) |
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{ |
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using ChunkedMemoryStream bytes = new(allocator); |
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// XMP data doesn't have a fixed length nor is there an indicator of the length.
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// So we simply read one byte at a time until we hit the 0x0 value at the end
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// of the magic trailer or the end of the stream.
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// Using ChunkedMemoryStream reduces the array resize allocation normally associated
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// with writing from a non fixed-size buffer.
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while (true) |
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{ |
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int b = stream.ReadByte(); |
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if (b <= 0) |
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{ |
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return bytes.ToArray(); |
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} |
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bytes.WriteByte((byte)b); |
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} |
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} |
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private static void ThrowInsufficientMemory() |
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=> throw new InsufficientMemoryException("Unable to write XMP metadata to GIF image"); |
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} |
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} |
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James Jackson-South
4 years ago
