ArrayBuffer.cs

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using System.Buffers;
using System.Runtime.InteropServices;
 
namespace System.Net;
 
[StructLayout(LayoutKind.Auto)]
internal struct ArrayBuffer : IDisposable
{
    private readonly bool _usePool;
 
    private byte[] _bytes;
 
    private int _activeStart;
 
    private int _availableStart;
 
    public int ActiveLength => _availableStart - _activeStart;
 
    public Span<byte> ActiveSpan => new Span<byte>(_bytes, _activeStart, _availableStart - _activeStart);
 
    public ReadOnlySpan<byte> ActiveReadOnlySpan => new ReadOnlySpan<byte>(_bytes, _activeStart, _availableStart - _activeStart);
 
    public int AvailableLength => _bytes.Length - _availableStart;
 
    public Memory<byte> AvailableMemory => _bytes.AsMemory(_availableStart);
 
    public ArrayBuffer(int initialSize, bool usePool = false)
    {
        _usePool = usePool;
        _bytes = (usePool ? ArrayPool<byte>.Shared.Rent(initialSize) : new byte[initialSize]);
        _activeStart = 0;
        _availableStart = 0;
    }
 
    public void Dispose()
    {
        _activeStart = 0;
        _availableStart = 0;
        byte[] bytes = _bytes;
        _bytes = null;
        if (_usePool && bytes != null)
        {
            ArrayPool<byte>.Shared.Return(bytes);
        }
    }
 
    public void Discard(int byteCount)
    {
        _activeStart += byteCount;
        if (_activeStart == _availableStart)
        {
            _activeStart = 0;
            _availableStart = 0;
        }
    }
 
    public void Commit(int byteCount)
    {
        _availableStart += byteCount;
    }
 
    public void EnsureAvailableSpace(int byteCount)
    {
        if (byteCount <= AvailableLength)
        {
            return;
        }
        int num = _activeStart + AvailableLength;
        if (byteCount <= num)
        {
            Buffer.BlockCopy(_bytes, _activeStart, _bytes, 0, ActiveLength);
            _availableStart = ActiveLength;
            _activeStart = 0;
            return;
        }
        int num2 = ActiveLength + byteCount;
        int num3 = _bytes.Length;
        do
        {
            num3 *= 2;
        }
        while (num3 < num2);
        byte[] array = (_usePool ? ArrayPool<byte>.Shared.Rent(num3) : new byte[num3]);
        byte[] bytes = _bytes;
        if (ActiveLength != 0)
        {
            Buffer.BlockCopy(bytes, _activeStart, array, 0, ActiveLength);
        }
        _availableStart = ActiveLength;
        _activeStart = 0;
        _bytes = array;
        if (_usePool)
        {
            ArrayPool<byte>.Shared.Return(bytes);
        }
    }
}