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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Buffers;
using System.Diagnostics;
namespace Microsoft.AspNetCore.Http;
// FYI: In most cases the source will be a FileStream and the destination will be to the network.
internal static class StreamCopyOperationInternal
{
private const int DefaultBufferSize = 4096;
/// <summary>Asynchronously reads the given number of bytes from the source stream and writes them to another stream.</summary>
/// <returns>A task that represents the asynchronous copy operation.</returns>
/// <param name="source">The stream from which the contents will be copied.</param>
/// <param name="destination">The stream to which the contents of the current stream will be copied.</param>
/// <param name="count">The count of bytes to be copied.</param>
/// <param name="cancel">The token to monitor for cancellation requests. The default value is <see cref="P:System.Threading.CancellationToken.None" />.</param>
public static Task CopyToAsync(Stream source, Stream destination, long? count, CancellationToken cancel)
{
return CopyToAsync(source, destination, count, DefaultBufferSize, cancel);
}
/// <summary>Asynchronously reads the given number of bytes from the source stream and writes them to another stream, using a specified buffer size.</summary>
/// <returns>A task that represents the asynchronous copy operation.</returns>
/// <param name="source">The stream from which the contents will be copied.</param>
/// <param name="destination">The stream to which the contents of the current stream will be copied.</param>
/// <param name="count">The count of bytes to be copied.</param>
/// <param name="bufferSize">The size, in bytes, of the buffer. This value must be greater than zero. The default size is 4096.</param>
/// <param name="cancel">The token to monitor for cancellation requests. The default value is <see cref="P:System.Threading.CancellationToken.None" />.</param>
public static async Task CopyToAsync(Stream source, Stream destination, long? count, int bufferSize, CancellationToken cancel)
{
var bytesRemaining = count;
var buffer = ArrayPool<byte>.Shared.Rent(bufferSize);
try
{
Debug.Assert(source != null);
Debug.Assert(destination != null);
Debug.Assert(!bytesRemaining.HasValue || bytesRemaining.GetValueOrDefault() >= 0);
Debug.Assert(buffer != null);
while (true)
{
// The natural end of the range.
if (bytesRemaining.HasValue && bytesRemaining.GetValueOrDefault() <= 0)
{
return;
}
cancel.ThrowIfCancellationRequested();
var readLength = buffer.Length;
if (bytesRemaining.HasValue)
{
readLength = (int)Math.Min(bytesRemaining.GetValueOrDefault(), (long)readLength);
}
var read = await source.ReadAsync(buffer.AsMemory(0, readLength), cancel);
if (bytesRemaining.HasValue)
{
bytesRemaining -= read;
}
// End of the source stream.
if (read == 0)
{
return;
}
cancel.ThrowIfCancellationRequested();
await destination.WriteAsync(buffer.AsMemory(0, read), cancel);
}
}
finally
{
ArrayPool<byte>.Shared.Return(buffer);
}
}
}
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