Add Stream wrappers for memory and text-based types

src/libraries/Common/src/System/IO/ReadOnlyMemoryStream.cs

@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+// On net11.0+, the public ReadOnlyMemoryStream in System.Runtime (CoreLib) supersedes this internal copy.
+#if !NET11_0_OR_GREATER
+
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -213,3 +216,5 @@ private static void ValidateBufferArguments(byte[] buffer, int offset, int count
 #endif
     }
 }
+
+#endif // !NET11_0_OR_GREATER

src/libraries/System.Memory/ref/System.Memory.cs

@@ -160,6 +160,33 @@ public void Rewind(long count) { }
         public bool TryReadExact(int count, out System.Buffers.ReadOnlySequence<T> sequence) { throw null; }
     }
 }
+namespace System.Buffers
+{
+    public sealed partial class ReadOnlySequenceStream : System.IO.Stream
+    {
+        public ReadOnlySequenceStream(System.Buffers.ReadOnlySequence<byte> source) { }
+        public override bool CanRead { get { throw null; } }
+        public override bool CanSeek { get { throw null; } }
+        public override bool CanWrite { get { throw null; } }
+        public override long Length { get { throw null; } }
+        public override long Position { get { throw null; } set { } }
+        public override void Flush() { }
+        public override System.Threading.Tasks.Task FlushAsync(System.Threading.CancellationToken cancellationToken) { throw null; }
+        public override int Read(byte[] buffer, int offset, int count) { throw null; }
+        public override int Read(System.Span<byte> buffer) { throw null; }
+        public override System.Threading.Tasks.Task<int> ReadAsync(byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken) { throw null; }
+        public override System.Threading.Tasks.ValueTask<int> ReadAsync(System.Memory<byte> buffer, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+        public override int ReadByte() { throw null; }
+        public override void CopyTo(System.IO.Stream destination, int bufferSize) { }
+        public override System.Threading.Tasks.Task CopyToAsync(System.IO.Stream destination, int bufferSize, System.Threading.CancellationToken cancellationToken) { throw null; }
+        public override long Seek(long offset, System.IO.SeekOrigin origin) { throw null; }
+        public override void SetLength(long value) { }
+        public override void Write(byte[] buffer, int offset, int count) { }
+        public override void Write(System.ReadOnlySpan<byte> buffer) { }
+        public override System.Threading.Tasks.Task WriteAsync(byte[] buffer, int offset, int count, System.Threading.CancellationToken cancellationToken) { throw null; }
+        public override System.Threading.Tasks.ValueTask WriteAsync(System.ReadOnlyMemory<byte> buffer, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
+    }
+}
 namespace System.Runtime.InteropServices
 {
     public static partial class SequenceMarshal

src/libraries/System.Memory/src/Resources/Strings.resx

@@ -147,4 +147,13 @@
   <data name="BufferMaximumSizeExceeded" xml:space="preserve">
     <value>Cannot allocate a buffer of size {0}.</value>
   </data>
+  <data name="NotSupported_UnwritableStream" xml:space="preserve">
+    <value>Stream does not support writing.</value>
+  </data>
+  <data name="IO_SeekBeforeBegin" xml:space="preserve">
+    <value>An attempt was made to move the position before the beginning of the stream.</value>
+  </data>
+  <data name="Argument_InvalidSeekOrigin" xml:space="preserve">
+    <value>Invalid seek origin.</value>
+  </data>
 </root>

src/libraries/System.Memory/src/System.Memory.csproj

@@ -28,6 +28,7 @@
     <Compile Include="System\Buffers\ReadOnlySequence.cs" />
     <Compile Include="System\Buffers\ReadOnlySequenceDebugView.cs" />
     <Compile Include="System\Buffers\ReadOnlySequenceSegment.cs" />
+    <Compile Include="System\Buffers\ReadOnlySequenceStream.cs" />
     <Compile Include="System\Buffers\ReadOnlySequence.Helpers.cs" />
     <Compile Include="System\Buffers\SequenceReader.cs" />
     <Compile Include="System\Buffers\SequenceReader.Search.cs" />
@@ -40,6 +41,8 @@
     <!-- Common or Common-branched source files -->
     <Compile Include="$(CommonPath)System\Buffers\ArrayBufferWriter.cs"
              Link="Common\System\Buffers\ArrayBufferWriter.cs" />
+    <Compile Include="$(CommonPath)System\Threading\Tasks\CachedCompletedInt32Task.cs"
+             Link="Common\System\Threading\Tasks\CachedCompletedInt32Task.cs" />
   </ItemGroup>
 
   <ItemGroup>

src/libraries/System.Memory/src/System/Buffers/ReadOnlySequenceStream.cs

@@ -0,0 +1,296 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Buffers
+{
+    /// <summary>
+    /// Provides a seekable, read-only <see cref="Stream"/> over a <see cref="ReadOnlySequence{Byte}"/>.
+    /// </summary>
+    /// <remarks>
+    /// <para>The underlying sequence is not copied; reads are served directly from its segments.</para>
+    /// <para>This type is not thread-safe. Synchronize access if the stream is used concurrently.</para>
+    /// <para>The stream cannot be written to. <see cref="CanWrite"/> always returns <see langword="false"/>.</para>
+    /// </remarks>
+    public sealed class ReadOnlySequenceStream : Stream
+    {
+        private ReadOnlySequence<byte> _sequence;
+        private SequencePosition _position;
+        private long _absolutePosition;
+        private bool _isDisposed;
+        private CachedCompletedInt32Task _lastReadTask;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ReadOnlySequenceStream"/> class over the specified <see cref="ReadOnlySequence{Byte}"/>.
+        /// </summary>
+        /// <param name="source">The <see cref="ReadOnlySequence{Byte}"/> to wrap.</param>
+        public ReadOnlySequenceStream(ReadOnlySequence<byte> source)
+        {
+            _sequence = source;
+            _position = source.Start;
+            _absolutePosition = 0;
+            _isDisposed = false;
+        }
+
+        /// <inheritdoc />
+        public override bool CanRead => !_isDisposed;
+
+        /// <inheritdoc />
+        public override bool CanSeek => !_isDisposed;
+
+        /// <inheritdoc />
+        public override bool CanWrite => false;
+
+        private void EnsureNotDisposed() => ObjectDisposedException.ThrowIf(_isDisposed, this);
+
+        /// <inheritdoc />
+        public override long Length
+        {
+            get
+            {
+                EnsureNotDisposed();
+                return _sequence.Length;
+            }
+        }
+
+        /// <inheritdoc />
+        public override long Position
+        {
+            get
+            {
+                EnsureNotDisposed();
+                return _absolutePosition;
+            }
+            set
+            {
+                EnsureNotDisposed();
+                ArgumentOutOfRangeException.ThrowIfNegative(value);
+
+                if (value >= _sequence.Length)
+                {
+                    _position = _sequence.End;
+                }
+                else if (value >= _absolutePosition)
+                {
+                    _position = _sequence.GetPosition(value - _absolutePosition, _position);
+                }
+                else
+                {
+                    _position = _sequence.GetPosition(value, _sequence.Start);
+                }
+
+                _absolutePosition = value;
+            }
+        }
+
+        /// <inheritdoc />
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            ValidateBufferArguments(buffer, offset, count);
+            return Read(buffer.AsSpan(offset, count));
+        }
+
+        /// <inheritdoc />
+        public override int Read(Span<byte> buffer)
+        {
+            EnsureNotDisposed();
+
+            if (_absolutePosition >= _sequence.Length)
+            {
+                return 0;
+            }
+
+            ReadOnlySequence<byte> remaining = _sequence.Slice(_position);
+            int n = (int)Math.Min(remaining.Length, buffer.Length);
+            if (n <= 0)
+            {
+                return 0;
+            }
+
+            remaining.Slice(0, n).CopyTo(buffer);
+            _position = _sequence.GetPosition(n, _position);
+            _absolutePosition += n;
+            return n;
+        }
+
+        /// <inheritdoc />
+        public override int ReadByte()
+        {
+            EnsureNotDisposed();
+
+            byte b = 0;
+            return Read(new Span<byte>(ref b)) > 0 ? b : -1;
+        }
+
+        /// <inheritdoc/>
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            ValidateBufferArguments(buffer, offset, count);
+            EnsureNotDisposed();
+
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Task.FromCanceled<int>(cancellationToken);
+            }
+
+            try
+            {
+                int n = Read(buffer, offset, count);
+                return _lastReadTask.GetTask(n);
+            }
+            catch (OperationCanceledException oce)
+            {
+                return Task.FromCanceled<int>(oce.CancellationToken);
+            }
+            catch (Exception ex)
+            {
+                return Task.FromException<int>(ex);
+            }
+        }
+
+        /// <inheritdoc/>
+        public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            EnsureNotDisposed();
+
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return ValueTask.FromCanceled<int>(cancellationToken);
+            }
+
+            try
+            {
+                int n = Read(buffer.Span);
+                return new ValueTask<int>(n);
+            }
+            catch (OperationCanceledException oce)
+            {
+                return ValueTask.FromCanceled<int>(oce.CancellationToken);
+            }
+            catch (Exception ex)
+            {
+                return ValueTask.FromException<int>(ex);
+            }
+        }
+
+        /// <inheritdoc />
+        public override void CopyTo(Stream destination, int bufferSize)
+        {
+            ValidateCopyToArguments(destination, bufferSize);
+            EnsureNotDisposed();
+
+            if (_absolutePosition >= _sequence.Length)
+            {
+                return;
+            }
+
+            ReadOnlySequence<byte> remaining = _sequence.Slice(_position);
+            foreach (ReadOnlyMemory<byte> segment in remaining)
+            {
+                destination.Write(segment.Span);
+            }
+
+            _position = _sequence.End;
+            _absolutePosition = _sequence.Length;
+        }
+
+        /// <inheritdoc />
+        public override Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
+        {
+            ValidateCopyToArguments(destination, bufferSize);
+            EnsureNotDisposed();
+
+            if (cancellationToken.IsCancellationRequested)
+            {
+                return Task.FromCanceled(cancellationToken);
+            }
+
+            if (_absolutePosition >= _sequence.Length)
+            {
+                return Task.CompletedTask;
+            }
+
+            return CopyToAsyncCore(destination, cancellationToken);
+        }
+
+        private async Task CopyToAsyncCore(Stream destination, CancellationToken cancellationToken)
+        {
+            ReadOnlySequence<byte> remaining = _sequence.Slice(_position);
+            foreach (ReadOnlyMemory<byte> segment in remaining)
+            {
+                await destination.WriteAsync(segment, cancellationToken).ConfigureAwait(false);
+            }
+
+            _position = _sequence.End;
+            _absolutePosition = _sequence.Length;
+        }
+
+        /// <inheritdoc />
+        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException(SR.NotSupported_UnwritableStream);
+
+        /// <inheritdoc/>
+        public override void Write(ReadOnlySpan<byte> buffer) => throw new NotSupportedException(SR.NotSupported_UnwritableStream);
+
+        /// <inheritdoc/>
+        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken) => throw new NotSupportedException(SR.NotSupported_UnwritableStream);
+
+        /// <inheritdoc/>
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default) => throw new NotSupportedException(SR.NotSupported_UnwritableStream);
+
+        /// <inheritdoc/>
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            EnsureNotDisposed();
+
+            long absolutePosition = origin switch
+            {
+                SeekOrigin.Begin => offset,
+                SeekOrigin.Current => _absolutePosition + offset,
+                SeekOrigin.End => _sequence.Length + offset,
+                _ => throw new ArgumentException(SR.Argument_InvalidSeekOrigin, nameof(origin))
+            };
+
+            if (absolutePosition < 0)
+            {
+                throw new IOException(SR.IO_SeekBeforeBegin);
+            }
+
+            if (absolutePosition >= _sequence.Length)
+            {
+                _position = _sequence.End;
+            }
+            else if (absolutePosition >= _absolutePosition)
+            {
+                _position = _sequence.GetPosition(absolutePosition - _absolutePosition, _position);
+            }
+            else
+            {
+                _position = _sequence.GetPosition(absolutePosition, _sequence.Start);
+            }
+
+            _absolutePosition = absolutePosition;
+            return absolutePosition;
+        }
+
+        /// <inheritdoc />
+        public override void Flush() { }
+
+        /// <inheritdoc />
+        public override Task FlushAsync(CancellationToken cancellationToken) =>
+            cancellationToken.IsCancellationRequested ? Task.FromCanceled(cancellationToken) : Task.CompletedTask;
+
+        /// <inheritdoc />
+        public override void SetLength(long value) => throw new NotSupportedException(SR.NotSupported_UnwritableStream);
+
+        /// <inheritdoc />
+        protected override void Dispose(bool disposing)
+        {
+            _isDisposed = true;
+            _sequence = default;
+            base.Dispose(disposing);
+        }
+    }
+}