Add PipeReader.Create from ReadOnlySequence<byte>

src/libraries/System.IO.Pipelines/ref/System.IO.Pipelines.cs

@@ -50,6 +50,7 @@ protected PipeReader() { }
         public virtual System.Threading.Tasks.Task CopyToAsync(System.IO.Pipelines.PipeWriter destination, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public virtual System.Threading.Tasks.Task CopyToAsync(System.IO.Stream destination, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
         public static System.IO.Pipelines.PipeReader Create(System.IO.Stream stream, System.IO.Pipelines.StreamPipeReaderOptions? readerOptions = null) { throw null; }
+        public static System.IO.Pipelines.PipeReader Create(System.Buffers.ReadOnlySequence<byte> sequence) { throw null; }
         [System.ObsoleteAttribute("OnWriterCompleted may not be invoked on all implementations of PipeReader. This will be removed in a future release.")]
         public virtual void OnWriterCompleted(System.Action<System.Exception?, object?> callback, object? state) { }
         public abstract System.Threading.Tasks.ValueTask<System.IO.Pipelines.ReadResult> ReadAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));

src/libraries/System.IO.Pipelines/src/System.IO.Pipelines.csproj

@@ -31,6 +31,7 @@
     <Compile Include="System\IO\Pipelines\PipeWriterStream.cs" />
     <Compile Include="System\IO\Pipelines\ReadResult.cs" />
     <Compile Include="System\IO\Pipelines\ResultFlags.cs" />
+    <Compile Include="System\IO\Pipelines\SequencePipeReader.cs" />
     <Compile Include="System\IO\Pipelines\StreamPipeExtensions.cs" />
     <Compile Include="System\IO\Pipelines\StreamPipeReader.cs" />
     <Compile Include="System\IO\Pipelines\StreamPipeReaderOptions.cs" />

src/libraries/System.IO.Pipelines/src/System/IO/Pipelines/PipeReader.cs

@@ -104,6 +104,16 @@ public static PipeReader Create(Stream stream, StreamPipeReaderOptions? readerOp
             return new StreamPipeReader(stream, readerOptions ?? StreamPipeReaderOptions.s_default);
         }
 
+        /// <summary>
+        /// Creates a <see cref="PipeReader"/> wrapping the specified <see cref="ReadOnlySequence{T}"/>.
+        /// </summary>
+        /// <param name="sequence">The sequence.</param>
+        /// <returns>A <see cref="PipeReader"/> that wraps the <see cref="ReadOnlySequence{T}"/>.</returns>
+        public static PipeReader Create(ReadOnlySequence<byte> sequence)
+        {
+            return new SequencePipeReader(sequence);
+        }
+
         /// <summary>Asynchronously reads the bytes from the <see cref="System.IO.Pipelines.PipeReader" /> and writes them to the specified <see cref="System.IO.Pipelines.PipeWriter" />, using a specified buffer size and cancellation token.</summary>
         /// <param name="destination">The pipe writer to which the contents of the current stream will be copied.</param>
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="System.Threading.CancellationToken.None" />.</param>

src/libraries/System.IO.Pipelines/src/System/IO/Pipelines/SequencePipeReader.cs

@@ -0,0 +1,97 @@
+// 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.Threading;
+using System.Threading.Tasks;
+
+namespace System.IO.Pipelines
+{
+    internal sealed class SequencePipeReader : PipeReader
+    {
+        private ReadOnlySequence<byte> _sequence;
+        private bool _isReaderCompleted;
+
+        private int _cancelNext;
+
+        public SequencePipeReader(ReadOnlySequence<byte> sequence)
+        {
+            _sequence = sequence;
+        }
+
+        /// <inheritdoc />
+        public override void AdvanceTo(SequencePosition consumed)
+        {
+            AdvanceTo(consumed, consumed);
+        }
+
+        /// <inheritdoc />
+        public override void AdvanceTo(SequencePosition consumed, SequencePosition examined)
+        {
+            ThrowIfCompleted();
+
+            // Fast path: did we consume everything?
+            if (consumed.Equals(_sequence.End))
+            {
+                _sequence = ReadOnlySequence<byte>.Empty;
+                return;
+            }
+
+            _sequence = _sequence.Slice(consumed);
+        }
+
+        /// <inheritdoc />
+        public override void CancelPendingRead()
+        {
+            Interlocked.Exchange(ref _cancelNext, 1);
+        }
+
+        /// <inheritdoc />
+        public override void Complete(Exception? exception = null)
+        {
+            if (_isReaderCompleted)
+            {
+                return;
+            }
+
+            _isReaderCompleted = true;
+            _sequence = ReadOnlySequence<byte>.Empty;
+        }
+
+        /// <inheritdoc />
+        public override ValueTask<ReadResult> ReadAsync(CancellationToken cancellationToken = default)
+        {
+            if (TryRead(out ReadResult result))
+            {
+                return new ValueTask<ReadResult>(result);
+            }
+
+            result = new ReadResult(ReadOnlySequence<byte>.Empty, isCanceled: false, isCompleted: true);
+            return new ValueTask<ReadResult>(result);
+        }
+
+        /// <inheritdoc />
+        public override bool TryRead(out ReadResult result)
+        {
+            ThrowIfCompleted();
+
+            bool isCancellationRequested = Interlocked.Exchange(ref _cancelNext, 0) == 1;
+            if (isCancellationRequested || _sequence.Length > 0)
+            {
+                result = new ReadResult(_sequence, isCancellationRequested, isCompleted: true);
+                return true;
+            }
+
+            result = default;
+            return false;
+        }
+
+        private void ThrowIfCompleted()
+        {
+            if (_isReaderCompleted)
+            {
+                ThrowHelper.ThrowInvalidOperationException_NoReadingAllowed();
+            }
+        }
+    }
+}

src/libraries/System.IO.Pipelines/tests/SequencePipeReaderTests.cs

@@ -0,0 +1,232 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace System.IO.Pipelines.Tests
+{
+    public class SequencePipeReaderTests
+    {
+        [Fact]
+        public async Task CanRead()
+        {
+            var sequence = new ReadOnlySequence<byte>(Encoding.ASCII.GetBytes("Hello World"));
+            var reader = PipeReader.Create(sequence);
+
+            ReadResult readResult = await reader.ReadAsync();
+            ReadOnlySequence<byte> buffer = readResult.Buffer;
+
+            Assert.Equal(11, buffer.Length);
+            Assert.True(buffer.IsSingleSegment);
+            Assert.Equal("Hello World", Encoding.ASCII.GetString(buffer.ToArray()));
+
+            reader.AdvanceTo(buffer.End);
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task TryReadReturnsTrueIfBufferedBytesAndNotExaminedEverything()
+        {
+            var sequence = new ReadOnlySequence<byte>(Encoding.ASCII.GetBytes("Hello World"));
+            var reader = PipeReader.Create(sequence);
+
+            ReadResult readResult = await reader.ReadAsync();
+            ReadOnlySequence<byte> buffer = readResult.Buffer;
+            Assert.Equal(11, buffer.Length);
+            Assert.True(buffer.IsSingleSegment);
+            reader.AdvanceTo(buffer.Start, buffer.GetPosition(5));
+
+            Assert.True(reader.TryRead(out readResult));
+            Assert.Equal(11, buffer.Length);
+            Assert.True(buffer.IsSingleSegment);
+            Assert.Equal("Hello World", Encoding.ASCII.GetString(buffer.ToArray()));
+
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task TryReadReturnsFalseIfBufferedBytesAndEverythingExamined()
+        {
+            var sequence = new ReadOnlySequence<byte>(Encoding.ASCII.GetBytes("Hello World"));
+            var reader = PipeReader.Create(sequence);
+
+            ReadResult readResult = await reader.ReadAsync();
+            ReadOnlySequence<byte> buffer = readResult.Buffer;
+            Assert.Equal(11, buffer.Length);
+            Assert.True(buffer.IsSingleSegment);
+            reader.AdvanceTo(buffer.End);
+
+            Assert.False(reader.TryRead(out readResult));
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task ReadAsyncAfterReceivingCompletedReadResultDoesNotThrow()
+        {
+            var sequence = ReadOnlySequence<byte>.Empty;
+            PipeReader reader = PipeReader.Create(sequence);
+            ReadResult readResult = await reader.ReadAsync();
+            Assert.True(readResult.Buffer.IsEmpty);
+            Assert.True(readResult.IsCompleted);
+            reader.AdvanceTo(readResult.Buffer.End);
+
+            readResult = await reader.ReadAsync();
+            Assert.True(readResult.Buffer.IsEmpty);
+            Assert.True(readResult.IsCompleted);
+            reader.AdvanceTo(readResult.Buffer.End);
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task DataCanBeReadMultipleTimes()
+        {
+            var helloBytes = Encoding.ASCII.GetBytes("Hello World");
+            var sequence = new ReadOnlySequence<byte>(helloBytes);
+            PipeReader reader = PipeReader.Create(sequence);
+
+
+            ReadResult readResult = await reader.ReadAsync();
+            ReadOnlySequence<byte> buffer = readResult.Buffer;
+            reader.AdvanceTo(buffer.Start, buffer.End);
+
+            // Make sure IsCompleted is true
+            readResult = await reader.ReadAsync();
+            buffer = readResult.Buffer;
+            reader.AdvanceTo(buffer.Start, buffer.End);
+            Assert.True(readResult.IsCompleted);
+
+            var value = await ReadFromPipeAsString(reader);
+            Assert.Equal("Hello World", value);
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task NextReadAfterPartiallyExaminedReturnsImmediately()
+        {
+            var sequence = new ReadOnlySequence<byte>(Encoding.ASCII.GetBytes(new string('a', 10000)));
+            PipeReader reader = PipeReader.Create(sequence);
+
+            ReadResult readResult = await reader.ReadAsync();
+            reader.AdvanceTo(readResult.Buffer.Start, readResult.Buffer.GetPosition(2048));
+
+            ValueTask<ReadResult> task = reader.ReadAsync();
+
+            // This should complete synchronously since
+            Assert.True(task.IsCompleted);
+
+            readResult = await task;
+            reader.AdvanceTo(readResult.Buffer.End);
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task CompleteReaderWithoutAdvanceDoesNotThrow()
+        {
+            PipeReader reader = PipeReader.Create(ReadOnlySequence<byte>.Empty);
+            await reader.ReadAsync();
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task AdvanceAfterCompleteThrows()
+        {
+            PipeReader reader = PipeReader.Create(new ReadOnlySequence<byte>(new byte[100]));
+            ReadOnlySequence<byte> buffer = (await reader.ReadAsync()).Buffer;
+
+            reader.Complete();
+
+            Assert.Throws<InvalidOperationException>(() => reader.AdvanceTo(buffer.End));
+        }
+
+        [Fact]
+        public async Task ThrowsOnReadAfterCompleteReader()
+        {
+            PipeReader reader = PipeReader.Create(ReadOnlySequence<byte>.Empty);
+
+            reader.Complete();
+            await Assert.ThrowsAsync<InvalidOperationException>(async () => await reader.ReadAsync());
+        }
+
+        [Fact]
+        public void TryReadAfterCancelPendingReadReturnsTrue()
+        {
+            PipeReader reader = PipeReader.Create(ReadOnlySequence<byte>.Empty);
+
+            reader.CancelPendingRead();
+
+            Assert.True(reader.TryRead(out ReadResult result));
+            Assert.True(result.IsCanceled);
+            reader.AdvanceTo(result.Buffer.End);
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task ReadAsyncReturnsCanceledIfCanceledBeforeRead()
+        {
+            var sequence = new ReadOnlySequence<byte>(new byte[10000]);
+            PipeReader reader = PipeReader.Create(sequence);
+
+            // Make sure state isn't used from before
+            for (var i = 0; i < 3; i++)
+            {
+                reader.CancelPendingRead();
+                ValueTask<ReadResult> readResultTask = reader.ReadAsync();
+                Assert.True(readResultTask.IsCompleted);
+                ReadResult readResult = readResultTask.GetAwaiter().GetResult();
+                Assert.True(readResult.IsCanceled);
+                readResult = await reader.ReadAsync();
+                reader.AdvanceTo(readResult.Buffer.End);
+            }
+
+            reader.Complete();
+        }
+
+        [Fact]
+        public async Task ReadAsyncReturnsCanceledInterleaved()
+        {
+            var sequence = new ReadOnlySequence<byte>(new byte[10000]);
+            PipeReader reader = PipeReader.Create(sequence);
+
+            // Cancel and Read interleaved to confirm cancellations are independent
+            for (var i = 0; i < 3; i++)
+            {
+                reader.CancelPendingRead();
+                ValueTask<ReadResult> readResultTask = reader.ReadAsync();
+                Assert.True(readResultTask.IsCompleted);
+                ReadResult readResult = readResultTask.GetAwaiter().GetResult();
+                Assert.True(readResult.IsCanceled);
+
+                readResult = await reader.ReadAsync();
+                Assert.False(readResult.IsCanceled);
+            }
+
+            reader.Complete();
+        }
+
+        [Fact]
+        public void OnWriterCompletedNoops()
+        {
+            bool fired = false;
+            PipeReader reader = PipeReader.Create(ReadOnlySequence<byte>.Empty);
+#pragma warning disable CS0618 // Type or member is obsolete
+            reader.OnWriterCompleted((_, __) => { fired = true; }, null);
+#pragma warning restore CS0618 // Type or member is obsolete
+            reader.Complete();
+            Assert.False(fired);
+        }
+
+        private static async Task<string> ReadFromPipeAsString(PipeReader reader)
+        {
+            ReadResult readResult = await reader.ReadAsync();
+            var result = Encoding.ASCII.GetString(readResult.Buffer.ToArray());
+            reader.AdvanceTo(readResult.Buffer.End);
+            return result;
+        }
+    }
+}

src/libraries/System.IO.Pipelines/tests/System.IO.Pipelines.Tests.csproj

@@ -30,6 +30,7 @@
     <Compile Include="ReadAsyncCompletionTests.cs" />
     <Compile Include="ReadResultTests.cs" />
     <Compile Include="SchedulerFacts.cs" />
+    <Compile Include="SequencePipeReaderTests.cs" />
     <Compile Include="StreamPipeReaderTests.cs" />
     <Compile Include="Infrastructure\TestMemoryPool.cs" />
     <Compile Include="StreamPipeWriterTests.cs" />