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FileBufferingReadStream.cs
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FileBufferingReadStream.cs
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// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Buffers;
using System.Diagnostics;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
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;
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
Func<string> tempFileDirectoryAccessor)
: this(inner, memoryThreshold, bufferLimit, tempFileDirectoryAccessor, ArrayPool<byte>.Shared)
{
}
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
Func<string> tempFileDirectoryAccessor,
ArrayPool<byte> bytePool)
{
if (inner == null)
{
throw new ArgumentNullException(nameof(inner));
}
if (tempFileDirectoryAccessor == null)
{
throw new ArgumentNullException(nameof(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;
}
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
string tempFileDirectory)
: this(inner, memoryThreshold, bufferLimit, tempFileDirectory, ArrayPool<byte>.Shared)
{
}
public FileBufferingReadStream(
Stream inner,
int memoryThreshold,
long? bufferLimit,
string tempFileDirectory,
ArrayPool<byte> bytePool)
{
if (inner == null)
{
throw new ArgumentNullException(nameof(inner));
}
if (tempFileDirectory == null)
{
throw new ArgumentNullException(nameof(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;
}
public bool InMemory
{
get { return _inMemory; }
}
public string TempFileName
{
get { return _tempFileName; }
}
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return true; }
}
public override bool CanWrite
{
get { return false; }
}
public override long Length
{
get { return _buffer.Length; }
}
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;
}
}
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");
return new FileStream(_tempFileName, FileMode.Create, FileAccess.ReadWrite, FileShare.Delete, 1024 * 16,
FileOptions.Asynchronous | FileOptions.DeleteOnClose | FileOptions.SequentialScan);
}
public override int Read(byte[] buffer, int offset, int count)
{
ThrowIfDisposed();
if (_buffer.Position < _buffer.Length || _completelyBuffered)
{
// Just read from the buffer
return _buffer.Read(buffer, offset, (int)Math.Min(count, _buffer.Length - _buffer.Position));
}
int read = _inner.Read(buffer, offset, count);
if (_bufferLimit.HasValue && _bufferLimit - read < _buffer.Length)
{
Dispose();
throw new IOException("Buffer limit exceeded.");
}
if (_inMemory && _buffer.Length + read > _memoryThreshold)
{
_inMemory = false;
var oldBuffer = _buffer;
_buffer = CreateTempFile();
if (_rentedBuffer == null)
{
oldBuffer.Position = 0;
var rentedBuffer = _bytePool.Rent(Math.Min((int)oldBuffer.Length, _maxRentedBufferSize));
var copyRead = oldBuffer.Read(rentedBuffer, 0, rentedBuffer.Length);
while (copyRead > 0)
{
_buffer.Write(rentedBuffer, 0, copyRead);
copyRead = oldBuffer.Read(rentedBuffer, 0, rentedBuffer.Length);
}
_bytePool.Return(rentedBuffer);
}
else
{
_buffer.Write(_rentedBuffer, 0, (int)oldBuffer.Length);
_bytePool.Return(_rentedBuffer);
_rentedBuffer = null;
}
}
if (read > 0)
{
_buffer.Write(buffer, offset, read);
}
else
{
_completelyBuffered = true;
}
return read;
}
public override async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
ThrowIfDisposed();
if (_buffer.Position < _buffer.Length || _completelyBuffered)
{
// Just read from the buffer
return await _buffer.ReadAsync(buffer, offset, (int)Math.Min(count, _buffer.Length - _buffer.Position), cancellationToken);
}
int read = await _inner.ReadAsync(buffer, offset, count, cancellationToken);
if (_bufferLimit.HasValue && _bufferLimit - read < _buffer.Length)
{
Dispose();
throw new IOException("Buffer limit exceeded.");
}
if (_inMemory && _buffer.Length + read > _memoryThreshold)
{
_inMemory = false;
var oldBuffer = _buffer;
_buffer = CreateTempFile();
if (_rentedBuffer == null)
{
oldBuffer.Position = 0;
var rentedBuffer = _bytePool.Rent(Math.Min((int)oldBuffer.Length, _maxRentedBufferSize));
// oldBuffer is a MemoryStream, no need to do async reads.
var copyRead = oldBuffer.Read(rentedBuffer, 0, rentedBuffer.Length);
while (copyRead > 0)
{
await _buffer.WriteAsync(rentedBuffer, 0, copyRead, cancellationToken);
copyRead = oldBuffer.Read(rentedBuffer, 0, rentedBuffer.Length);
}
_bytePool.Return(rentedBuffer);
}
else
{
await _buffer.WriteAsync(_rentedBuffer, 0, (int)oldBuffer.Length, cancellationToken);
_bytePool.Return(_rentedBuffer);
_rentedBuffer = null;
}
}
if (read > 0)
{
await _buffer.WriteAsync(buffer, offset, read, cancellationToken);
}
else
{
_completelyBuffered = true;
}
return read;
}
public override void Write(byte[] buffer, int offset, int count)
{
throw new NotSupportedException();
}
public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
throw new NotSupportedException();
}
public override void SetLength(long value)
{
throw new NotSupportedException();
}
public override void Flush()
{
throw new NotSupportedException();
}
protected override void Dispose(bool disposing)
{
if (!_disposed)
{
_disposed = true;
if (_rentedBuffer != null)
{
_bytePool.Return(_rentedBuffer);
}
if (disposing)
{
_buffer.Dispose();
}
}
}
private void ThrowIfDisposed()
{
if (_disposed)
{
throw new ObjectDisposedException(nameof(FileBufferingReadStream));
}
}
}
}