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FileBufferingReadStream.cs
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FileBufferingReadStream.cs
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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;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;
using Microsoft.AspNetCore.Internal;
namespace Microsoft.AspNetCore.WebUtilities;
/// <summary>
/// A Stream that wraps another stream and enables rewinding by buffering the content as it is read.
/// The content is buffered in memory up to a certain size and then spooled to a temp file on disk.
/// The temp file will be deleted on Dispose.
/// </summary>
public class FileBufferingReadStream : Stream
{
private const int _maxRentedBufferSize = 1024 * 1024; // 1MB
private readonly Stream _inner;
private readonly ArrayPool<byte> _bytePool;
private readonly int _memoryThreshold;
private readonly long? _bufferLimit;
private string? _tempFileDirectory;
private readonly Func<string>? _tempFileDirectoryAccessor;
private string? _tempFileName;
private Stream _buffer;
private byte[]? _rentedBuffer;
private bool _inMemory = true;
private bool _completelyBuffered;
private bool _disposed;
/// <summary>
/// Initializes a new instance of <see cref="FileBufferingReadStream" />.
/// </summary>
/// <param name="inner">The wrapping <see cref="Stream" />.</param>
/// <param name="memoryThreshold">The maximum size to buffer in memory.</param>
public FileBufferingReadStream(Stream inner, int memoryThreshold)
: this(inner, memoryThreshold, bufferLimit: null, tempFileDirectoryAccessor: AspNetCoreTempDirectory.TempDirectoryFactory)
{
}
/// <summary>
/// Initializes a new instance of <see cref="FileBufferingReadStream" />.
/// </summary>
/// <param name="inner">The wrapping <see cref="Stream" />.</param>
/// <param name="memoryThreshold">The maximum size to buffer in memory.</param>
/// <param name="bufferLimit">The maximum size that will be buffered before this <see cref="Stream"/> throws.</param>
/// <param name="tempFileDirectoryAccessor">Provides the temporary directory to which files are buffered to.</param>
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
Func<string> tempFileDirectoryAccessor)
: this(inner, memoryThreshold, bufferLimit, tempFileDirectoryAccessor, ArrayPool<byte>.Shared)
{
}
/// <summary>
/// Initializes a new instance of <see cref="FileBufferingReadStream" />.
/// </summary>
/// <param name="inner">The wrapping <see cref="Stream" />.</param>
/// <param name="memoryThreshold">The maximum size to buffer in memory.</param>
/// <param name="bufferLimit">The maximum size that will be buffered before this <see cref="Stream"/> throws.</param>
/// <param name="tempFileDirectoryAccessor">Provides the temporary directory to which files are buffered to.</param>
/// <param name="bytePool">The <see cref="ArrayPool{T}"/> to use.</param>
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
Func<string> tempFileDirectoryAccessor,
ArrayPool<byte> bytePool)
{
ArgumentNullException.ThrowIfNull(inner);
ArgumentNullException.ThrowIfNull(tempFileDirectoryAccessor);
_bytePool = bytePool;
if (memoryThreshold <= _maxRentedBufferSize)
{
_rentedBuffer = bytePool.Rent(memoryThreshold);
_buffer = new MemoryStream(_rentedBuffer);
_buffer.SetLength(0);
}
else
{
_buffer = new MemoryStream();
}
_inner = inner;
_memoryThreshold = memoryThreshold;
_bufferLimit = bufferLimit;
_tempFileDirectoryAccessor = tempFileDirectoryAccessor;
}
/// <summary>
/// Initializes a new instance of <see cref="FileBufferingReadStream" />.
/// </summary>
/// <param name="inner">The wrapping <see cref="Stream" />.</param>
/// <param name="memoryThreshold">The maximum size to buffer in memory.</param>
/// <param name="bufferLimit">The maximum size that will be buffered before this <see cref="Stream"/> throws.</param>
/// <param name="tempFileDirectory">The temporary directory to which files are buffered to.</param>
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
string tempFileDirectory)
: this(inner, memoryThreshold, bufferLimit, tempFileDirectory, ArrayPool<byte>.Shared)
{
}
/// <summary>
/// Initializes a new instance of <see cref="FileBufferingReadStream" />.
/// </summary>
/// <param name="inner">The wrapping <see cref="Stream" />.</param>
/// <param name="memoryThreshold">The maximum size to buffer in memory.</param>
/// <param name="bufferLimit">The maximum size that will be buffered before this <see cref="Stream"/> throws.</param>
/// <param name="tempFileDirectory">The temporary directory to which files are buffered to.</param>
/// <param name="bytePool">The <see cref="ArrayPool{T}"/> to use.</param>
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
string tempFileDirectory,
ArrayPool<byte> bytePool)
{
ArgumentNullException.ThrowIfNull(inner);
ArgumentNullException.ThrowIfNull(tempFileDirectory);
_bytePool = bytePool;
if (memoryThreshold <= _maxRentedBufferSize)
{
_rentedBuffer = bytePool.Rent(memoryThreshold);
_buffer = new MemoryStream(_rentedBuffer);
_buffer.SetLength(0);
}
else
{
_buffer = new MemoryStream();
}
_inner = inner;
_memoryThreshold = memoryThreshold;
_bufferLimit = bufferLimit;
_tempFileDirectory = tempFileDirectory;
}
/// <summary>
/// The maximum amount of memory in bytes to allocate before switching to a file on disk.
/// </summary>
/// <remarks>
/// Defaults to 32kb.
/// </remarks>
public int MemoryThreshold => _memoryThreshold;
/// <summary>
/// Gets a value that determines if the contents are buffered entirely in memory.
/// </summary>
public bool InMemory
{
get { return _inMemory; }
}
/// <summary>
/// Gets a value that determines where the contents are buffered on disk.
/// </summary>
public string? TempFileName
{
get { return _tempFileName; }
}
/// <inheritdoc/>
public override bool CanRead
{
get { return !_disposed; }
}
/// <inheritdoc/>
public override bool CanSeek
{
get { return !_disposed; }
}
/// <inheritdoc/>
public override bool CanWrite
{
get { return false; }
}
/// <summary>
/// The total bytes read from and buffered by the stream so far, it will not represent the full
/// data length until the stream is fully buffered. e.g. using <c>stream.DrainAsync()</c>.
/// </summary>
public override long Length
{
get { return _buffer.Length; }
}
/// <inheritdoc/>
public override long Position
{
get { return _buffer.Position; }
// Note this will not allow seeking forward beyond the end of the buffer.
set
{
ThrowIfDisposed();
_buffer.Position = value;
}
}
/// <inheritdoc/>
public override long Seek(long offset, SeekOrigin origin)
{
ThrowIfDisposed();
if (!_completelyBuffered && origin == SeekOrigin.End)
{
// Can't seek from the end until we've finished consuming the inner stream
throw new NotSupportedException("The content has not been fully buffered yet.");
}
else if (!_completelyBuffered && origin == SeekOrigin.Current && offset + Position > Length)
{
// Can't seek past the end of the buffer until we've finished consuming the inner stream
throw new NotSupportedException("The content has not been fully buffered yet.");
}
else if (!_completelyBuffered && origin == SeekOrigin.Begin && offset > Length)
{
// Can't seek past the end of the buffer until we've finished consuming the inner stream
throw new NotSupportedException("The content has not been fully buffered yet.");
}
return _buffer.Seek(offset, origin);
}
private Stream CreateTempFile()
{
if (_tempFileDirectory == null)
{
Debug.Assert(_tempFileDirectoryAccessor != null);
_tempFileDirectory = _tempFileDirectoryAccessor();
Debug.Assert(_tempFileDirectory != null);
}
_tempFileName = Path.Combine(_tempFileDirectory, "ASPNETCORE_" + Guid.NewGuid().ToString() + ".tmp");
// Create a temp file with the correct Unix file mode before moving it to the assigned _tempFileName in the _tempFileDirectory.
if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
{
var tempTempFileName = Path.GetTempFileName();
File.Move(tempTempFileName, _tempFileName);
}
return new FileStream(_tempFileName, FileMode.Create, FileAccess.ReadWrite, FileShare.Delete, 1024 * 16,
FileOptions.Asynchronous | FileOptions.DeleteOnClose | FileOptions.SequentialScan);
}
/// <inheritdoc/>
public override int Read(Span<byte> buffer)
{
ThrowIfDisposed();
if (_buffer.Position < _buffer.Length || _completelyBuffered)
{
// Just read from the buffer
return _buffer.Read(buffer);
}
var read = _inner.Read(buffer);
if (_bufferLimit.HasValue && _bufferLimit - read < _buffer.Length)
{
throw new IOException("Buffer limit exceeded.");
}
// We're about to go over the threshold, switch to a file
if (_inMemory && _memoryThreshold - read < _buffer.Length)
{
_inMemory = false;
var oldBuffer = _buffer;
_buffer = CreateTempFile();
if (_rentedBuffer == null)
{
// Copy data from the in memory buffer to the file stream using a pooled buffer
oldBuffer.Position = 0;
var rentedBuffer = _bytePool.Rent(Math.Min((int)oldBuffer.Length, _maxRentedBufferSize));
try
{
var copyRead = oldBuffer.Read(rentedBuffer);
while (copyRead > 0)
{
_buffer.Write(rentedBuffer.AsSpan(0, copyRead));
copyRead = oldBuffer.Read(rentedBuffer);
}
}
finally
{
_bytePool.Return(rentedBuffer);
}
}
else
{
_buffer.Write(_rentedBuffer.AsSpan(0, (int)oldBuffer.Length));
_bytePool.Return(_rentedBuffer);
_rentedBuffer = null;
}
}
if (read > 0)
{
_buffer.Write(buffer.Slice(0, read));
}
// Allow zero-byte reads
else if (buffer.Length > 0)
{
_completelyBuffered = true;
}
return read;
}
/// <inheritdoc/>
public override int Read(byte[] buffer, int offset, int count)
{
return Read(buffer.AsSpan(offset, count));
}
/// <inheritdoc/>
public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
return ReadAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
}
/// <inheritdoc/>
[SuppressMessage("ApiDesign", "RS0027:Public API with optional parameter(s) should have the most parameters amongst its public overloads.", Justification = "Required to maintain compatibility")]
public override async ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
{
ThrowIfDisposed();
if (_buffer.Position < _buffer.Length || _completelyBuffered)
{
// Just read from the buffer
return await _buffer.ReadAsync(buffer, cancellationToken);
}
var read = await _inner.ReadAsync(buffer, cancellationToken);
if (_bufferLimit.HasValue && _bufferLimit - read < _buffer.Length)
{
throw new IOException("Buffer limit exceeded.");
}
if (_inMemory && _memoryThreshold - read < _buffer.Length)
{
_inMemory = false;
var oldBuffer = _buffer;
_buffer = CreateTempFile();
if (_rentedBuffer == null)
{
oldBuffer.Position = 0;
var rentedBuffer = _bytePool.Rent(Math.Min((int)oldBuffer.Length, _maxRentedBufferSize));
try
{
// oldBuffer is a MemoryStream, no need to do async reads.
var copyRead = oldBuffer.Read(rentedBuffer);
while (copyRead > 0)
{
await _buffer.WriteAsync(rentedBuffer.AsMemory(0, copyRead), cancellationToken);
copyRead = oldBuffer.Read(rentedBuffer);
}
}
finally
{
_bytePool.Return(rentedBuffer);
}
}
else
{
await _buffer.WriteAsync(_rentedBuffer.AsMemory(0, (int)oldBuffer.Length), cancellationToken);
_bytePool.Return(_rentedBuffer);
_rentedBuffer = null;
}
}
if (read > 0)
{
await _buffer.WriteAsync(buffer.Slice(0, read), cancellationToken);
}
// Allow zero-byte reads
else if (buffer.Length > 0)
{
_completelyBuffered = true;
}
return read;
}
/// <inheritdoc/>
public override void Write(byte[] buffer, int offset, int count)
{
throw new NotSupportedException();
}
/// <inheritdoc/>
public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken)
{
throw new NotSupportedException();
}
/// <inheritdoc/>
public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
throw new NotSupportedException();
}
/// <inheritdoc/>
public override void SetLength(long value)
{
throw new NotSupportedException();
}
/// <inheritdoc/>
public override void Flush()
{
throw new NotSupportedException();
}
/// <inheritdoc/>
public override Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
{
// Set a minimum buffer size of 4K since the base Stream implementation has weird behavior when the stream is
// seekable *and* the length is 0 (it passes in a buffer size of 1).
// See https://github.com/dotnet/runtime/blob/222415c56c9ea73530444768c0e68413eb374f5d/src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs#L164-L184
bufferSize = Math.Max(4096, bufferSize);
// If we're completed buffered then copy from the underlying source
if (_completelyBuffered)
{
return _buffer.CopyToAsync(destination, bufferSize, cancellationToken);
}
async Task CopyToAsyncImpl()
{
// At least a 4K buffer
byte[] buffer = _bytePool.Rent(bufferSize);
try
{
while (true)
{
int bytesRead = await ReadAsync(buffer, cancellationToken);
if (bytesRead == 0)
{
break;
}
await destination.WriteAsync(buffer.AsMemory(0, bytesRead), cancellationToken);
}
}
finally
{
_bytePool.Return(buffer);
}
}
return CopyToAsyncImpl();
}
/// <inheritdoc/>
protected override void Dispose(bool disposing)
{
if (!_disposed)
{
_disposed = true;
if (_rentedBuffer != null)
{
_bytePool.Return(_rentedBuffer);
}
if (disposing)
{
_buffer.Dispose();
}
}
}
/// <inheritdoc/>
public override async ValueTask DisposeAsync()
{
if (!_disposed)
{
_disposed = true;
if (_rentedBuffer != null)
{
_bytePool.Return(_rentedBuffer);
}
await _buffer.DisposeAsync();
}
}
private void ThrowIfDisposed()
{
ObjectDisposedException.ThrowIf(_disposed, nameof(FileBufferingReadStream));
}
}