Refactor determining chunk types

src/ImageSharp/Formats/WebP/Vp8LBitReader.cs

@@ -15,11 +15,13 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// <summary>
         /// Initializes a new instance of the <see cref="Vp8LBitReader"/> class.
         /// </summary>
-        /// <param name="stream">The stream to read from.</param>
-        public Vp8LBitReader(Stream stream)
+        /// <param name="inputStream">The input stream to read from.</param>
+        public Vp8LBitReader(Stream inputStream)
         {
             this.stream = new MemoryStream();
-            stream.CopyTo(this.stream);
+            long inputStreamPos = inputStream.Position;
+            inputStream.CopyTo(this.stream);
+            inputStream.Position = inputStreamPos;
             this.Offset = 0;
             this.Bit = 0;
         }
@@ -29,7 +31,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
         private int Bit { get; set; }
 
         /// <summary>
-        /// Gets a value indicating whether the offset is inside the stream length.
+        /// Gets a value indicating whether the offset is inside the inputStream length.
         /// </summary>
         private bool ValidPosition
         {
@@ -40,7 +42,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
         }
 
         /// <summary>
-        /// Reads a unsigned short value from the stream. The bits of each byte are read in least-significant-bit-first order.
+        /// Reads a unsigned short value from the inputStream. The bits of each byte are read in least-significant-bit-first order.
         /// </summary>
         /// <param name="count">The number of bits to read (should not exceed 16).</param>
         /// <returns>A ushort value.</returns>
@@ -67,7 +69,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
         {
             if (!this.ValidPosition)
             {
-                WebPThrowHelper.ThrowImageFormatException("The image stream does not contain enough data");
+                WebPThrowHelper.ThrowImageFormatException("The image inputStream does not contain enough data");
             }
 
             this.stream.Seek(this.Offset, SeekOrigin.Begin);
@@ -79,7 +81,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
         }
 
         /// <summary>
-        /// Advances the stream by one Bit.
+        /// Advances the inputStream by one Bit.
         /// </summary>
         public void AdvanceBit()
         {

src/ImageSharp/Formats/WebP/WebPChunkType.cs

@@ -0,0 +1,56 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    /// <summary>
+    /// Contains a list of different webp chunk types.
+    /// </summary>
+    internal enum WebPChunkType : uint
+    {
+        /// <summary>
+        /// Header signaling the use of VP8 video format.
+        /// </summary>
+        Vp8 = 0x56503820U,
+
+        /// <summary>
+        /// Header for a extended-VP8 chunk.
+        /// </summary>
+        Vp8L = 0x5650384CU,
+
+        /// <summary>
+        /// Header for a extended-VP8 chunk.
+        /// </summary>
+        Vp8X = 0x56503858U,
+
+        /// <summary>
+        /// Chunk contains information about the alpha channel.
+        /// </summary>
+        Alpha = 0x414C5048U,
+
+        /// <summary>
+        /// Chunk which contains a color profile.
+        /// </summary>
+        Iccp = 0x49434350U,
+
+        /// <summary>
+        /// Chunk which contains EXIF metadata about the image.
+        /// </summary>
+        Exif = 0x45584946U,
+
+        /// <summary>
+        /// Chunk contains XMP metadata about the image.
+        /// </summary>
+        Xmp = 0x584D5020U,
+
+        /// <summary>
+        /// For an animated image, this chunk contains the global parameters of the animation.
+        /// </summary>
+        AnimationParameter = 0x414E494D,
+
+        /// <summary>
+        /// For animated images, this chunk contains information about a single frame. If the Animation flag is not set, then this chunk SHOULD NOT be present.
+        /// </summary>
+        Animation = 0x414E4D46,
+    }
+}

src/ImageSharp/Formats/WebP/WebPConstants.cs

@@ -58,106 +58,5 @@ namespace SixLabors.ImageSharp.Formats.WebP
             0x42, // B
             0x50 // P
         };
-
-        /// <summary>
-        /// Header signaling the use of VP8 video format.
-        /// </summary>
-        public static readonly byte[] Vp8Header =
-        {
-            0x56, // V
-            0x50, // P
-            0x38, // 8
-            0x20, // Space
-        };
-
-        /// <summary>
-        /// Header for a extended-VP8 chunk.
-        /// </summary>
-        public static readonly byte[] Vp8XHeader =
-        {
-            0x56, // V
-            0x50, // P
-            0x38, // 8
-            0x58, // X
-        };
-
-        public static readonly byte LossLessFlag = 0x4C; // L
-
-        /// <summary>
-        /// VP8 header, signaling the use of VP8L lossless format.
-        /// </summary>
-        public static readonly byte[] Vp8LHeader =
-        {
-            0x56, // V
-            0x50, // P
-            0x38, // 8
-            LossLessFlag // L
-        };
-
-        /// <summary>
-        /// Chunk contains information about the alpha channel.
-        /// </summary>
-        public static readonly byte[] AlphaHeader =
-        {
-            0x41, // A
-            0x4C, // L
-            0x50, // P
-            0x48, // H
-        };
-
-        /// <summary>
-        /// Chunk which contains a color profile.
-        /// </summary>
-        public static readonly byte[] IccpHeader =
-        {
-            0x49, // I
-            0x43, // C
-            0x43, // C
-            0x50, // P
-        };
-
-        /// <summary>
-        /// Chunk which contains EXIF metadata about the image.
-        /// </summary>
-        public static readonly byte[] ExifHeader =
-        {
-            0x45, // E
-            0x58, // X
-            0x49, // I
-            0x46, // F
-        };
-
-        /// <summary>
-        /// Chunk contains XMP metadata about the image.
-        /// </summary>
-        public static readonly byte[] XmpHeader =
-        {
-            0x58, // X
-            0x4D, // M
-            0x50, // P
-            0x20, // Space
-        };
-
-        /// <summary>
-        /// For an animated image, this chunk contains the global parameters of the animation.
-        /// </summary>
-        public static readonly byte[] AnimationParameterHeader =
-        {
-            0x41, // A
-            0x4E, // N
-            0x49, // I
-            0x4D, // M
-        };
-
-        /// <summary>
-        /// For animated images, this chunk contains information about a single frame. If the Animation flag is not set, then this chunk SHOULD NOT be present.
-        /// </summary>
-        public static readonly byte[] AnimationHeader =
-        {
-            0x41, // A
-            0x4E, // N
-            0x4D, // M
-            0x46, // F
-        };
     }
 }

src/ImageSharp/Formats/WebP/WebPDecoderCore.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Buffers.Binary;
 using System.IO;
-using System.Linq;
 
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
@@ -74,14 +73,15 @@ namespace SixLabors.ImageSharp.Formats.WebP
             Buffer2D<TPixel> pixels = image.GetRootFramePixelBuffer();
             if (imageInfo.IsLossLess)
             {
-                ReadSimpleLossless(pixels, image.Width, image.Height);
+                ReadSimpleLossless(pixels, image.Width, image.Height, (int)imageInfo.DataSize);
             }
             else
             {
-                ReadSimpleLossy(pixels, image.Width, image.Height);
+                ReadSimpleLossy(pixels, image.Width, image.Height, (int)imageInfo.DataSize);
             }
 
             // TODO: there can be optional chunks after the image data, like EXIF, XMP etc.
+            this.ParseOptionalChunks();
 
             return image;
         }
@@ -123,22 +123,16 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
         private WebPImageInfo ReadVp8Info(int vpxWidth = 0, int vpxHeight = 0)
         {
-            // Read VP8 chunk header.
-            this.currentStream.Read(this.buffer, 0, 4);
-
-            if (this.buffer.AsSpan().SequenceEqual(WebPConstants.Vp8Header))
-            {
-                return this.ReadVp8Header(vpxWidth, vpxHeight);
-            }
+            WebPChunkType type = this.ReadChunkType();
 
-            if (this.buffer.AsSpan().SequenceEqual(WebPConstants.Vp8LHeader))
+            switch (type)
             {
-                return this.ReadVp8LHeader(vpxWidth, vpxHeight);
-            }
-
-            if (this.buffer.SequenceEqual(WebPConstants.Vp8XHeader))
-            {
-                return this.ReadVp8XHeader();
+                case WebPChunkType.Vp8:
+                    return this.ReadVp8Header(vpxWidth, vpxHeight);
+                case WebPChunkType.Vp8L:
+                    return this.ReadVp8LHeader(vpxWidth, vpxHeight);
+                case WebPChunkType.Vp8X:
+                    return this.ReadVp8XHeader();
             }
 
             WebPThrowHelper.ThrowImageFormatException("Unrecognized VP8 header");
@@ -185,6 +179,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
             int height = BinaryPrimitives.ReadInt32LittleEndian(this.buffer) + 1;
 
             // TODO: optional chunks ICCP and ANIM can follow here. Ignoring them for now.
+            this.ParseOptionalChunks();
 
             // A VP8 or VP8L chunk will follow here.
             return this.ReadVp8Info(width, height);
@@ -324,16 +319,24 @@ namespace SixLabors.ImageSharp.Formats.WebP
                    };
         }
 
-        private void ReadSimpleLossy<TPixel>(Buffer2D<TPixel> pixels, int width, int height)
+        private void ParseOptionalChunks()
+        {
+            // Read VP8 chunk header.
+            this.currentStream.Read(this.buffer, 0, 4);
+        }
+
+        private void ReadSimpleLossy<TPixel>(Buffer2D<TPixel> pixels, int width, int height, int chunkSize)
             where TPixel : struct, IPixel<TPixel>
         {
-            // TODO: implement decoding
+            // TODO: implement decoding, for simulating the decoding, skipping the chunk size bytes.
+            this.currentStream.Skip(chunkSize);
         }
 
-        private void ReadSimpleLossless<TPixel>(Buffer2D<TPixel> pixels, int width, int height)
+        private void ReadSimpleLossless<TPixel>(Buffer2D<TPixel> pixels, int width, int height, int chunkSize)
             where TPixel : struct, IPixel<TPixel>
         {
-            // TODO: implement decoding
+            // TODO: implement decoding, for simulating the decoding, skipping the chunk size bytes.
+            this.currentStream.Skip(chunkSize);
         }
 
         private void ReadExtended<TPixel>(Buffer2D<TPixel> pixels, int width, int height)
@@ -341,5 +344,18 @@ namespace SixLabors.ImageSharp.Formats.WebP
         {
             // TODO: implement decoding
         }
+
+        /// <summary>
+        /// Identifies the chunk type from the chunk.
+        /// </summary>
+        /// <exception cref="ImageFormatException">
+        /// Thrown if the input stream is not valid.
+        /// </exception>
+        private WebPChunkType ReadChunkType()
+        {
+            return this.currentStream.Read(this.buffer, 0, 4) == 4
+                       ? (WebPChunkType)BinaryPrimitives.ReadUInt32BigEndian(this.buffer)
+                       : throw new ImageFormatException("Invalid WebP data.");
+        }
     }
 }