[release/3.1] Fix ReadOnlySequence created out of sliced Memory owned by MemoryManager

src/System.Memory/src/System/Buffers/ReadOnlySequence.cs

@@ -153,7 +153,7 @@ public ReadOnlySequence(ReadOnlyMemory<T> memory)
  _startObject = manager;
  _endObject = manager;
  _startInteger = ReadOnlySequence.MemoryManagerToSequenceStart(index);
- _endInteger = ReadOnlySequence.MemoryManagerToSequenceEnd(length);
+ _endInteger = ReadOnlySequence.MemoryManagerToSequenceEnd(index + length);
  }
  else if (MemoryMarshal.TryGetArray(memory, out ArraySegment<T> segment))
  {

src/System.Memory/tests/ReadOnlyBuffer/ReadOnlySequenceFactory.byte.cs

@@ -5,13 +5,16 @@
 using System.Buffers;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 
 namespace System.Memory.Tests
 {
  public abstract class ReadOnlySequenceFactory<T>
  {
  public static ReadOnlySequenceFactory<T> ArrayFactory { get; } = new ArrayTestSequenceFactory();
  public static ReadOnlySequenceFactory<T> MemoryFactory { get; } = new MemoryTestSequenceFactory();
+ public static ReadOnlySequenceFactory<T> MemoryManagerFactory { get; } = new MemoryManagerTestSequenceFactory();
  public static ReadOnlySequenceFactory<T> SingleSegmentFactory { get; } = new SingleSegmentTestSequenceFactory();
  public static ReadOnlySequenceFactory<T> SegmentPerItemFactory { get; } = new BytePerSegmentTestSequenceFactory();
  public static ReadOnlySequenceFactory<T> SplitInThree { get; } = new SegmentsTestSequenceFactory(3);
@@ -113,6 +116,49 @@ public override ReadOnlySequence<T> CreateWithContent(T[] data)
  }
  }
 
+ internal class MemoryManagerTestSequenceFactory : ReadOnlySequenceFactory<T>
+ {
+ public override ReadOnlySequence<T> CreateOfSize(int size)
+ {
+#if DEBUG
+ return new ReadOnlySequence<T>(new CustomMemoryManager(size + 1).Memory.Slice(1));
+#else
+ return new ReadOnlySequence<T>(new CustomMemoryManager(size).Memory);
+#endif
+ }
+
+ public override ReadOnlySequence<T> CreateWithContent(T[] data)
+ {
+ return new ReadOnlySequence<T>(new CustomMemoryManager(data).Memory);
+ }
+
+ private unsafe class CustomMemoryManager : MemoryManager<T>
+ {
+ private readonly T[] _buffer;
+
+ public CustomMemoryManager(int size) => _buffer = new T[size];
+
+ public CustomMemoryManager(T[] content) => _buffer = content;
+
+ public unsafe override Span<T> GetSpan() => _buffer;
+
+ public override unsafe MemoryHandle Pin(int elementIndex = 0)
+ {
+ if ((uint)elementIndex > (uint)_buffer.Length)
+ {
+ throw new ArgumentOutOfRangeException(nameof(elementIndex));
+ }
+
+ var handle = GCHandle.Alloc(_buffer, GCHandleType.Pinned);
+ return new MemoryHandle(Unsafe.Add<T>((void*)handle.AddrOfPinnedObject(), elementIndex), handle, this);
+ }
+
+ public override void Unpin() { }
+
+ protected override void Dispose(bool disposing) { }
+ }
+ }
+
  public static ReadOnlySequence<T> CreateSegments(params T[][] inputs) => CreateSegments(inputs.Select(input => (ReadOnlyMemory<T>)input.AsMemory()));
 
  public static ReadOnlySequence<T> CreateSegments(IEnumerable<ReadOnlyMemory<T>> inputs)

src/System.Memory/tests/ReadOnlyBuffer/ReadOnlySequenceTests.byte.cs

@@ -21,6 +21,11 @@ public class Memory : ReadOnlySequenceTestsByte
  public Memory() : base(ReadOnlySequenceFactory<byte>.MemoryFactory) { }
  }
 
+ public class MemoryManager : ReadOnlySequenceTestsByte
+ {
+ public MemoryManager() : base(ReadOnlySequenceFactory<byte>.MemoryManagerFactory) { }
+ }
+
  public class SingleSegment : ReadOnlySequenceTestsByte
  {
  public SingleSegment() : base(ReadOnlySequenceFactory<byte>.SingleSegmentFactory) { }