1 files changed, 159 insertions, 0 deletions
diff --git a/src/Mvc/src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/PagedCharBuffer.cs b/src/Mvc/src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/PagedCharBuffer.cs
new file mode 100644
index 0000000000..f086daf67b
--- /dev/null
+++ b/src/Mvc/src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/PagedCharBuffer.cs
@@ -0,0 +1,159 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
+{
+    public class PagedCharBuffer : IDisposable
+    {
+        public const int PageSize = 1024;
+        private int _charIndex;
+
+        public PagedCharBuffer(ICharBufferSource bufferSource)
+        {
+            BufferSource = bufferSource;
+        }
+
+        public ICharBufferSource BufferSource { get; }
+
+        public IList<char[]> Pages { get; } = new List<char[]>();
+
+        public int Length
+        {
+            get
+            {
+                var length = _charIndex;
+                for (var i = 0; i < Pages.Count - 1; i++)
+                {
+                    length += Pages[i].Length;
+                }
+
+                return length;
+            }
+        }
+
+        private char[] CurrentPage { get; set; }
+
+        public void Append(char value)
+        {
+            var page = GetCurrentPage();
+            page[_charIndex++] = value;
+        }
+
+        public void Append(string value)
+        {
+            if (value == null)
+            {
+                return;
+            }
+
+            var index = 0;
+            var count = value.Length;
+
+            while (count > 0)
+            {
+                var page = GetCurrentPage();
+                var copyLength = Math.Min(count, page.Length - _charIndex);
+                Debug.Assert(copyLength > 0);
+
+                value.CopyTo(
+                    index,
+                    page,
+                    _charIndex,
+                    copyLength);
+
+                _charIndex += copyLength;
+                index += copyLength;
+
+                count -= copyLength;
+            }
+        }
+
+        public void Append(char[] buffer, int index, int count)
+        {
+            while (count > 0)
+            {
+                var page = GetCurrentPage();
+                var copyLength = Math.Min(count, page.Length - _charIndex);
+                Debug.Assert(copyLength > 0);
+
+                Array.Copy(
+                    buffer,
+                    index,
+                    page,
+                    _charIndex,
+                    copyLength);
+
+                _charIndex += copyLength;
+                index += copyLength;
+                count -= copyLength;
+            }
+        }
+
+        /// <summary>
+        /// Return all but one of the pages to the <see cref="ICharBufferSource"/>.
+        /// This way if someone writes a large chunk of content, we can return those buffers and avoid holding them
+        /// for extended durations.
+        /// </summary>
+        public void Clear()
+        {
+            for (var i = Pages.Count - 1; i > 0; i--)
+            {
+                var page = Pages[i];
+
+                try
+                {
+                    Pages.RemoveAt(i);
+                }
+                finally
+                {
+                    BufferSource.Return(page);
+                }
+            }
+
+            _charIndex = 0;
+            CurrentPage = Pages.Count > 0 ? Pages[0] : null;
+        }
+
+        private char[] GetCurrentPage()
+        {
+            if (CurrentPage == null || _charIndex == CurrentPage.Length)
+            {
+                CurrentPage = NewPage();
+                _charIndex = 0;
+            }
+
+            return CurrentPage;
+        }
+
+        private char[] NewPage()
+        {
+            char[] page = null;
+            try
+            {
+                page = BufferSource.Rent(PageSize);
+                Pages.Add(page);
+            }
+            catch when (page != null)
+            {
+                BufferSource.Return(page);
+                throw;
+            }
+
+            return page;
+        }
+
+        public void Dispose()
+        {
+            for (var i = 0; i < Pages.Count; i++)
+            {
+                BufferSource.Return(Pages[i]);
+            }
+
+            Pages.Clear();
+        }
+    }
+}