From ea2c4fa5f892fed1aee7e228b618cd9d40f5fd9c Mon Sep 17 00:00:00 2001
From: Stefan Nikolei <stefan@nikolei.eu>
Date: Wed, 22 Feb 2023 15:04:46 +0100
Subject: [PATCH] Refactor BitReaderBase

---
 .../Formats/Webp/BitReader/BitReaderBase.cs    | 18 +++++++++++-------
 .../Formats/Webp/BitReader/Vp8BitReader.cs     |  8 ++++----
 .../Formats/Webp/BitReader/Vp8LBitReader.cs    |  5 ++---
 3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs b/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs
index fa121be4f..37997d3e2 100644
--- a/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs
+++ b/src/ImageSharp/Formats/Webp/BitReader/BitReaderBase.cs
@@ -2,7 +2,6 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers;
-using System.Diagnostics.CodeAnalysis;
 using SixLabors.ImageSharp.Memory;
 
 namespace SixLabors.ImageSharp.Formats.Webp.BitReader;
@@ -14,10 +13,14 @@ internal abstract class BitReaderBase : IDisposable
 {
     private bool isDisposed;
 
+    protected BitReaderBase(IMemoryOwner<byte> data) => this.Data = data;
+
+    protected BitReaderBase(Stream inputStream, int imageDataSize, MemoryAllocator memoryAllocator) => this.Data = ReadImageDataFromStream(inputStream, imageDataSize, memoryAllocator);
+
     /// <summary>
     /// Gets or sets the raw encoded image data.
     /// </summary>
-    public IMemoryOwner<byte>? Data { get; set; }
+    public IMemoryOwner<byte> Data { get; set; }
 
     /// <summary>
     /// Copies the raw encoded image data from the stream into a byte array.
@@ -25,12 +28,13 @@ internal abstract class BitReaderBase : IDisposable
     /// <param name="input">The input stream.</param>
     /// <param name="bytesToRead">Number of bytes to read as indicated from the chunk size.</param>
     /// <param name="memoryAllocator">Used for allocating memory during reading data from the stream.</param>
-    [MemberNotNull(nameof(Data))]
-    protected void ReadImageDataFromStream(Stream input, int bytesToRead, MemoryAllocator memoryAllocator)
+    protected static IMemoryOwner<byte> ReadImageDataFromStream(Stream input, int bytesToRead, MemoryAllocator memoryAllocator)
     {
-        this.Data = memoryAllocator.Allocate<byte>(bytesToRead);
-        Span<byte> dataSpan = this.Data.Memory.Span;
+        IMemoryOwner<byte> data = memoryAllocator.Allocate<byte>(bytesToRead);
+        Span<byte> dataSpan = data.Memory.Span;
         input.Read(dataSpan[..bytesToRead], 0, bytesToRead);
+
+        return data;
     }
 
     protected virtual void Dispose(bool disposing)
@@ -42,7 +46,7 @@ internal abstract class BitReaderBase : IDisposable
 
         if (disposing)
         {
-            this.Data?.Dispose();
+            this.Data.Dispose();
         }
 
         this.isDisposed = true;
diff --git a/src/ImageSharp/Formats/Webp/BitReader/Vp8BitReader.cs b/src/ImageSharp/Formats/Webp/BitReader/Vp8BitReader.cs
index 1fa4deda9..7b64d8329 100644
--- a/src/ImageSharp/Formats/Webp/BitReader/Vp8BitReader.cs
+++ b/src/ImageSharp/Formats/Webp/BitReader/Vp8BitReader.cs
@@ -57,12 +57,12 @@ internal class Vp8BitReader : BitReaderBase
     /// <param name="partitionLength">The partition length.</param>
     /// <param name="startPos">Start index in the data array. Defaults to 0.</param>
     public Vp8BitReader(Stream inputStream, uint imageDataSize, MemoryAllocator memoryAllocator, uint partitionLength, int startPos = 0)
+        : base(inputStream, (int)imageDataSize, memoryAllocator)
     {
         Guard.MustBeLessThan(imageDataSize, int.MaxValue, nameof(imageDataSize));
 
         this.ImageDataSize = imageDataSize;
         this.PartitionLength = partitionLength;
-        this.ReadImageDataFromStream(inputStream, (int)imageDataSize, memoryAllocator);
         this.InitBitreader(partitionLength, startPos);
     }
 
@@ -73,8 +73,8 @@ internal class Vp8BitReader : BitReaderBase
     /// <param name="partitionLength">The partition length.</param>
     /// <param name="startPos">Start index in the data array. Defaults to 0.</param>
     public Vp8BitReader(IMemoryOwner<byte> imageData, uint partitionLength, int startPos = 0)
+        : base(imageData)
     {
-        this.Data = imageData;
         this.ImageDataSize = (uint)imageData.Memory.Length;
         this.PartitionLength = partitionLength;
         this.InitBitreader(partitionLength, startPos);
@@ -186,7 +186,7 @@ internal class Vp8BitReader : BitReaderBase
     {
         if (this.pos < this.bufferMax)
         {
-            ulong inBits = BinaryPrimitives.ReadUInt64LittleEndian(this.Data!.Memory.Span.Slice((int)this.pos, 8));
+            ulong inBits = BinaryPrimitives.ReadUInt64LittleEndian(this.Data.Memory.Span.Slice((int)this.pos, 8));
             this.pos += BitsCount >> 3;
             ulong bits = ByteSwap64(inBits);
             bits >>= 64 - BitsCount;
@@ -205,7 +205,7 @@ internal class Vp8BitReader : BitReaderBase
         if (this.pos < this.bufferEnd)
         {
             this.bits += 8;
-            this.value = this.Data!.Memory.Span[(int)this.pos++] | (this.value << 8);
+            this.value = this.Data.Memory.Span[(int)this.pos++] | (this.value << 8);
         }
         else if (!this.eof)
         {
diff --git a/src/ImageSharp/Formats/Webp/BitReader/Vp8LBitReader.cs b/src/ImageSharp/Formats/Webp/BitReader/Vp8LBitReader.cs
index df95f01f4..8da717545 100644
--- a/src/ImageSharp/Formats/Webp/BitReader/Vp8LBitReader.cs
+++ b/src/ImageSharp/Formats/Webp/BitReader/Vp8LBitReader.cs
@@ -63,8 +63,8 @@ internal class Vp8LBitReader : BitReaderBase
     /// </summary>
     /// <param name="data">Lossless compressed image data.</param>
     public Vp8LBitReader(IMemoryOwner<byte> data)
+        : base(data)
     {
-        this.Data = data;
         this.len = data.Memory.Length;
         this.value = 0;
         this.bitPos = 0;
@@ -88,11 +88,10 @@ internal class Vp8LBitReader : BitReaderBase
     /// <param name="imageDataSize">The raw image data size in bytes.</param>
     /// <param name="memoryAllocator">Used for allocating memory during reading data from the stream.</param>
     public Vp8LBitReader(Stream inputStream, uint imageDataSize, MemoryAllocator memoryAllocator)
+        : base(inputStream, (int)imageDataSize, memoryAllocator)
     {
         long length = imageDataSize;
 
-        this.ReadImageDataFromStream(inputStream, (int)imageDataSize, memoryAllocator);
-
         this.len = length;
         this.value = 0;
         this.bitPos = 0;