PooledByteBufferWriter.cs

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using System.Buffers;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
 
namespace System.Text.Json;
 
internal sealed class PooledByteBufferWriter : IBufferWriter<byte>, IDisposable
{
    private byte[] _rentedBuffer;
 
    private int _index;
 
    public ReadOnlyMemory<byte> WrittenMemory => _rentedBuffer.AsMemory(0, _index);
 
    public int Capacity => _rentedBuffer.Length;
 
    public PooledByteBufferWriter(int initialCapacity)
    {
        _rentedBuffer = ArrayPool<byte>.Shared.Rent(initialCapacity);
        _index = 0;
    }
 
    public void Clear()
    {
        ClearHelper();
    }
 
    private void ClearHelper()
    {
        _rentedBuffer.AsSpan(0, _index).Clear();
        _index = 0;
    }
 
    public void Dispose()
    {
        if (_rentedBuffer != null)
        {
            ClearHelper();
            byte[] rentedBuffer = _rentedBuffer;
            _rentedBuffer = null;
            ArrayPool<byte>.Shared.Return(rentedBuffer);
        }
    }
 
    public void Advance(int count)
    {
        _index += count;
    }
 
    public Memory<byte> GetMemory(int sizeHint = 0)
    {
        CheckAndResizeBuffer(sizeHint);
        return _rentedBuffer.AsMemory(_index);
    }
 
    public Span<byte> GetSpan(int sizeHint = 0)
    {
        CheckAndResizeBuffer(sizeHint);
        return _rentedBuffer.AsSpan(_index);
    }
 
    internal ValueTask WriteToStreamAsync(Stream destination, CancellationToken cancellationToken)
    {
        return destination.WriteAsync(WrittenMemory, cancellationToken);
    }
 
    internal void WriteToStream(Stream destination)
    {
        destination.Write(WrittenMemory.Span);
    }
 
    private void CheckAndResizeBuffer(int sizeHint)
    {
        if (sizeHint == 0)
        {
            sizeHint = 256;
        }
        int num = _rentedBuffer.Length - _index;
        if (sizeHint <= num)
        {
            return;
        }
        int num2 = _rentedBuffer.Length;
        int num3 = Math.Max(sizeHint, num2);
        int num4 = num2 + num3;
        if ((uint)num4 > 2147483647u)
        {
            num4 = num2 + sizeHint;
            if ((uint)num4 > 2147483647u)
            {
                ThrowHelper.ThrowOutOfMemoryException_BufferMaximumSizeExceeded((uint)num4);
            }
        }
        byte[] rentedBuffer = _rentedBuffer;
        _rentedBuffer = ArrayPool<byte>.Shared.Rent(num4);
        Span<byte> span = rentedBuffer.AsSpan(0, _index);
        span.CopyTo(_rentedBuffer);
        span.Clear();
        ArrayPool<byte>.Shared.Return(rentedBuffer);
    }
}