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[Prototype] Alternative shape: derive ReadOnlyMemoryStream / WritableMemoryStream from Stream #129913

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[Prototype] Alternative shape: derive ReadOnlyMemoryStream / WritableMemoryStream from Stream #129913

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10 changes: 5 additions & 5 deletions src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,17 +22,17 @@ public class MemoryStream : Stream
{
private byte[] _buffer; // Either allocated internally or externally.
private readonly int _origin; // For user-provided arrays, start at this origin
private protected int _position; // read/write head.
private protected int _length; // Number of bytes within the memory stream
private int _position; // read/write head.
private int _length; // Number of bytes within the memory stream
private int _capacity; // length of usable portion of buffer for stream
// Note that _capacity == _buffer.Length for non-user-provided byte[]'s

private bool _expandable; // User-provided buffers aren't expandable.
private protected bool _writable; // Can user write to this stream?
private bool _writable; // Can user write to this stream?
private readonly bool _exposable; // Whether the array can be returned to the user.
private protected bool _isOpen; // Is this stream open or closed?
private bool _isOpen; // Is this stream open or closed?

private protected CachedCompletedInt32Task _lastReadTask; // The last successful task returned from ReadAsync
private CachedCompletedInt32Task _lastReadTask; // The last successful task returned from ReadAsync

public MemoryStream()
: this(0)
Expand Down
126 changes: 110 additions & 16 deletions src/libraries/System.Private.CoreLib/src/System/IO/ReadOnlyMemoryStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,49 +7,140 @@
namespace System.IO
{
/// <summary>
/// Provides a seekable, read-only <see cref="MemoryStream"/> over a <see cref="ReadOnlyMemory{Byte}"/>.
/// Provides a seekable, read-only <see cref="Stream"/> over a <see cref="ReadOnlyMemory{Byte}"/>.
/// </summary>
/// <remarks>
/// <para>The stream cannot be written to. <see cref="MemoryStream.CanWrite"/> always returns <see langword="false"/>.</para>
/// <para><see cref="MemoryStream.GetBuffer"/> throws and <see cref="MemoryStream.TryGetBuffer"/> returns <see langword="false"/>.</para>
/// <para>The stream cannot be written to. <see cref="CanWrite"/> always returns <see langword="false"/>.</para>
/// <para><see cref="GetBuffer"/> throws and <see cref="TryGetBuffer"/> returns <see langword="false"/>.</para>
/// </remarks>
public sealed class ReadOnlyMemoryStream : MemoryStream
public sealed class ReadOnlyMemoryStream : Stream
{
private ReadOnlyMemory<byte> _memory;
private int _position;
private bool _isOpen;
private CachedCompletedInt32Task _lastReadTask;

/// <summary>
/// Initializes a new instance of the <see cref="ReadOnlyMemoryStream"/> class over the specified <see cref="ReadOnlyMemory{Byte}"/>.
/// </summary>
/// <param name="source">The <see cref="ReadOnlyMemory{Byte}"/> to wrap.</param>
public ReadOnlyMemoryStream(ReadOnlyMemory<byte> source) : base()
public ReadOnlyMemoryStream(ReadOnlyMemory<byte> source)
{
_writable = false;
_memory = source;
_length = source.Length;
_isOpen = true;
}

/// <inheritdoc/>
public override int Capacity
public override bool CanRead => _isOpen;

/// <inheritdoc/>
public override bool CanSeek => _isOpen;

/// <inheritdoc/>
public override bool CanWrite => false;

/// <inheritdoc/>
public override long Length
{
get
{
EnsureNotClosed();
return _memory.Length;
}
set => throw new NotSupportedException(SR.NotSupported_MemStreamNotExpandable);
}

/// <inheritdoc/>
public override byte[] GetBuffer() =>
throw new UnauthorizedAccessException(SR.UnauthorizedAccess_MemStreamBuffer);
public override long Position
{
get
{
EnsureNotClosed();
return _position;
}
set
{
ArgumentOutOfRangeException.ThrowIfNegative(value);
ArgumentOutOfRangeException.ThrowIfGreaterThan(value, int.MaxValue);
EnsureNotClosed();
_position = (int)value;
}
Comment on lines +60 to +66
}

/// <inheritdoc/>
public override long Seek(long offset, SeekOrigin loc)
{
EnsureNotClosed();

ArgumentOutOfRangeException.ThrowIfGreaterThan(offset, int.MaxValue);

long target = loc switch
{
SeekOrigin.Begin => offset,
SeekOrigin.Current => _position + offset,
SeekOrigin.End => _memory.Length + offset,
_ => throw new ArgumentException(SR.Argument_InvalidSeekOrigin, nameof(loc)),
};

if (target < 0)
throw new IOException(SR.IO_SeekBeforeBegin);
ArgumentOutOfRangeException.ThrowIfGreaterThan(target, int.MaxValue, nameof(offset));

_position = (int)target;
return _position;
}

/// <inheritdoc/>
public override void Flush() { }

/// <inheritdoc/>
public override Task FlushAsync(CancellationToken cancellationToken) =>
cancellationToken.IsCancellationRequested
? Task.FromCanceled(cancellationToken)
: Task.CompletedTask;

/// <inheritdoc/>
public override bool TryGetBuffer(out ArraySegment<byte> buffer)
public override void SetLength(long value) =>
throw new NotSupportedException(SR.NotSupported_UnwritableStream);
Comment on lines 101 to +103

/// <summary>Gets the size of the underlying buffer.</summary>
public int Capacity
{
get
{
EnsureNotClosed();
return _memory.Length;
}
}

/// <summary>Always throws; the underlying buffer is not exposed.</summary>
/// <exception cref="UnauthorizedAccessException">Always thrown.</exception>
public byte[] GetBuffer() =>
throw new UnauthorizedAccessException(SR.UnauthorizedAccess_MemStreamBuffer);

/// <summary>Always returns <see langword="false"/>; the underlying buffer is not exposed.</summary>
/// <param name="buffer">When this method returns, contains the default value of <see cref="ArraySegment{Byte}"/>.</param>
/// <returns><see langword="false"/>.</returns>
public bool TryGetBuffer(out ArraySegment<byte> buffer)
{
buffer = default;
return false;
}

/// <inheritdoc/>
public override void Write(byte[] buffer, int offset, int count)
{
ValidateBufferArguments(buffer, offset, count);
throw new NotSupportedException(SR.NotSupported_UnwritableStream);
}
Comment on lines +129 to +134

/// <inheritdoc/>
public override void Write(ReadOnlySpan<byte> buffer) =>
throw new NotSupportedException(SR.NotSupported_UnwritableStream);

/// <inheritdoc/>
public override void WriteByte(byte value) =>
throw new NotSupportedException(SR.NotSupported_UnwritableStream);
Comment on lines +137 to +142

/// <inheritdoc/>
public override int ReadByte()
{
Expand Down Expand Up @@ -156,8 +247,9 @@ public override Task CopyToAsync(Stream destination, int bufferSize, Cancellatio
return Task.CompletedTask;
}

/// <inheritdoc/>
public override byte[] ToArray()
/// <summary>Writes the stream contents to a byte array, regardless of the <see cref="Position"/>.</summary>
/// <returns>A new byte array containing a copy of the stream's contents.</returns>
public byte[] ToArray()
{
EnsureNotClosed();
if (_memory.Length == 0)
Expand All @@ -170,8 +262,9 @@ public override byte[] ToArray()
return copy;
}

/// <inheritdoc/>
public override void WriteTo(Stream stream)
/// <summary>Writes the entire contents of this stream to another stream.</summary>
/// <param name="stream">The destination stream.</param>
public void WriteTo(Stream stream)
{
ArgumentNullException.ThrowIfNull(stream);
EnsureNotClosed();
Expand All @@ -183,6 +276,7 @@ public override void WriteTo(Stream stream)
protected override void Dispose(bool disposing)
{
_memory = default;
_isOpen = false;
base.Dispose(disposing);
}

Expand Down
106 changes: 92 additions & 14 deletions src/libraries/System.Private.CoreLib/src/System/IO/WritableMemoryStream.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,42 +7,117 @@
namespace System.IO
{
/// <summary>
/// Provides a seekable, writable <see cref="MemoryStream"/> over a <see cref="Memory{Byte}"/> with fixed capacity.
/// Provides a seekable, writable <see cref="Stream"/> over a <see cref="Memory{Byte}"/> with fixed capacity.
/// </summary>
/// <remarks>
/// <para>The stream cannot expand beyond the initial memory capacity.</para>
/// <para><see cref="MemoryStream.GetBuffer"/> throws and <see cref="MemoryStream.TryGetBuffer"/> returns <see langword="false"/>.</para>
/// <para><see cref="GetBuffer"/> throws and <see cref="TryGetBuffer"/> returns <see langword="false"/>.</para>
/// </remarks>
public sealed class WritableMemoryStream : MemoryStream
public sealed class WritableMemoryStream : Stream
{
private Memory<byte> _memory;
private int _position;
private int _length;
private bool _isOpen;
private CachedCompletedInt32Task _lastReadTask;

/// <summary>
/// Initializes a new instance of the <see cref="WritableMemoryStream"/> class over the specified <see cref="Memory{Byte}"/>.
/// </summary>
/// <param name="buffer">The <see cref="Memory{Byte}"/> to wrap.</param>
public WritableMemoryStream(Memory<byte> buffer) : base()
public WritableMemoryStream(Memory<byte> buffer)
{
_memory = buffer;
_isOpen = true;
}

/// <inheritdoc/>
public override int Capacity
public override bool CanRead => _isOpen;

/// <inheritdoc/>
public override bool CanSeek => _isOpen;

/// <inheritdoc/>
public override bool CanWrite => _isOpen;

/// <inheritdoc/>
public override long Length
{
get
{
EnsureNotClosed();
return _memory.Length;
return _length;
}
set => throw new NotSupportedException(SR.NotSupported_MemStreamNotExpandable);
}

/// <inheritdoc/>
public override byte[] GetBuffer() =>
throw new UnauthorizedAccessException(SR.UnauthorizedAccess_MemStreamBuffer);
public override long Position
{
get
{
EnsureNotClosed();
return _position;
}
set
{
ArgumentOutOfRangeException.ThrowIfNegative(value);
ArgumentOutOfRangeException.ThrowIfGreaterThan(value, int.MaxValue);
EnsureNotClosed();
_position = (int)value;
}
Comment on lines +61 to +67
}

/// <inheritdoc/>
public override long Seek(long offset, SeekOrigin loc)
{
EnsureNotClosed();

ArgumentOutOfRangeException.ThrowIfGreaterThan(offset, int.MaxValue);

long target = loc switch
{
SeekOrigin.Begin => offset,
SeekOrigin.Current => _position + offset,
SeekOrigin.End => _length + offset,
_ => throw new ArgumentException(SR.Argument_InvalidSeekOrigin, nameof(loc)),
};

if (target < 0)
throw new IOException(SR.IO_SeekBeforeBegin);
ArgumentOutOfRangeException.ThrowIfGreaterThan(target, int.MaxValue, nameof(offset));

_position = (int)target;
return _position;
}

/// <inheritdoc/>
public override bool TryGetBuffer(out ArraySegment<byte> buffer)
public override void Flush() { }

/// <inheritdoc/>
public override Task FlushAsync(CancellationToken cancellationToken) =>
cancellationToken.IsCancellationRequested
? Task.FromCanceled(cancellationToken)
: Task.CompletedTask;

/// <summary>Gets the size of the underlying buffer.</summary>
public int Capacity
{
get
{
EnsureNotClosed();
return _memory.Length;
}
}

/// <summary>Always throws; the underlying buffer is not exposed.</summary>
/// <exception cref="UnauthorizedAccessException">Always thrown.</exception>
public byte[] GetBuffer() =>
throw new UnauthorizedAccessException(SR.UnauthorizedAccess_MemStreamBuffer);

/// <summary>Always returns <see langword="false"/>; the underlying buffer is not exposed.</summary>
/// <param name="buffer">When this method returns, contains the default value of <see cref="ArraySegment{Byte}"/>.</param>
/// <returns><see langword="false"/>.</returns>
public bool TryGetBuffer(out ArraySegment<byte> buffer)
{
buffer = default;
return false;
Expand Down Expand Up @@ -238,8 +313,9 @@ public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationTo
/// <inheritdoc/>
public override void SetLength(long value) => throw new NotSupportedException(SR.NotSupported_MemStreamNotExpandable);

/// <inheritdoc/>
public override byte[] ToArray()
/// <summary>Writes the stream contents to a byte array, regardless of the <see cref="Position"/>.</summary>
/// <returns>A new byte array containing a copy of the written contents.</returns>
public byte[] ToArray()
{
EnsureNotClosed();
if (_length == 0)
Expand All @@ -252,8 +328,9 @@ public override byte[] ToArray()
return copy;
}

/// <inheritdoc/>
public override void WriteTo(Stream stream)
/// <summary>Writes the stream contents to another stream.</summary>
/// <param name="stream">The destination stream.</param>
public void WriteTo(Stream stream)
{
ArgumentNullException.ThrowIfNull(stream);
EnsureNotClosed();
Expand All @@ -265,6 +342,7 @@ public override void WriteTo(Stream stream)
protected override void Dispose(bool disposing)
{
_memory = default;
_isOpen = false;
base.Dispose(disposing);
}

Expand Down
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