AsyncWindowsFileStreamStrategy.cs

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using System.Threading;
using System.Threading.Tasks;
using Microsoft.Win32.SafeHandles;
 
namespace System.IO.Strategies;
 
internal sealed class AsyncWindowsFileStreamStrategy : OSFileStreamStrategy
{
    internal override bool IsAsync => true;
 
    internal AsyncWindowsFileStreamStrategy(SafeFileHandle handle, FileAccess access)
        : base(handle, access)
    {
    }
 
    internal AsyncWindowsFileStreamStrategy(string path, FileMode mode, FileAccess access, FileShare share, FileOptions options, long preallocationSize)
        : base(path, mode, access, share, options, preallocationSize)
    {
    }
 
    public override Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
    {
        if (_fileHandle.IsClosed)
        {
            ThrowHelper.ThrowObjectDisposedException_FileClosed();
        }
        if (!CanRead)
        {
            ThrowHelper.ThrowNotSupportedException_UnreadableStream();
        }
        if (cancellationToken.IsCancellationRequested)
        {
            return Task.FromCanceled<int>(cancellationToken);
        }
        return AsyncModeCopyToAsync(destination, bufferSize, cancellationToken);
    }
 
    private async Task AsyncModeCopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
    {
        try
        {
            await FileStreamHelpers.AsyncModeCopyToAsync(_fileHandle, CanSeek, _filePosition, destination, bufferSize, cancellationToken).ConfigureAwait(continueOnCapturedContext: false);
        }
        finally
        {
            if (!_fileHandle.IsClosed && CanSeek)
            {
                _filePosition = Length;
            }
        }
    }
}