BufferSegment use ArrayPool for over-sized allocs (#13495)

Author: benaadams

src/Servers/Kestrel/Core/src/Internal/Infrastructure/PipeWriterHelpers/BufferSegment.cs

@@ -59,20 +59,16 @@ public void SetOwnedMemory(byte[] arrayPoolBuffer)
             AvailableMemory = arrayPoolBuffer;
         }
 
-        public void SetUnownedMemory(Memory<byte> memory)
-        {
-            AvailableMemory = memory;
-        }
-
         public void ResetMemory()
         {
             if (_memoryOwner is IMemoryOwner<byte> owner)
             {
                 owner.Dispose();
             }
-            else if (_memoryOwner is byte[] array)
+            else
             {
-                ArrayPool<byte>.Shared.Return(array);
+                byte[] poolArray = (byte[])_memoryOwner;
+                ArrayPool<byte>.Shared.Return(poolArray);
             }
 
             // Order of below field clears is significant as it clears in a sequential order

src/Servers/Kestrel/Core/src/Internal/Infrastructure/PipeWriterHelpers/ConcurrentPipeWriter.cs

@@ -341,8 +341,8 @@ private BufferSegment AllocateSegmentUnsynchronized(int sizeHint)
             }
             else
             {
-                // We can't use the pool so allocate an array
-                newSegment.SetUnownedMemory(new byte[sizeHint]);
+                // We can't use the recommended pool so use the ArrayPool
+                newSegment.SetOwnedMemory(ArrayPool<byte>.Shared.Rent(sizeHint));
             }
 
             _tailMemory = newSegment.AvailableMemory;