Add HPack dynamic compression

Author: JamesNK

src/Servers/Kestrel/Core/src/Internal/Http2/HPack/HPackHeaderEntry.cs

@@ -0,0 +1,68 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using System.Net.Http.HPack;
+
+namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.HPack
+{
+    [DebuggerDisplay("Name = {Name} Value = {Value}")]
+    internal class HPackHeaderEntry
+    {
+        // Header name and value
+        public string Name;
+        public string Value;
+
+        // Chained list of headers in the same bucket
+        public HPackHeaderEntry Next;
+        public int Hash;
+
+        // Compute dynamic table index
+        public int Index;
+
+        // Doubly linked list
+        public HPackHeaderEntry Before;
+        public HPackHeaderEntry After;
+
+        /// <summary>
+        /// 
+        /// </summary>
+        public void Initialize(int hash, string name, string value, int index, HPackHeaderEntry next)
+        {
+            Debug.Assert(name != null);
+            Debug.Assert(value != null);
+
+            Name = name;
+            Value = value;
+            Index = index;
+            Hash = hash;
+            Next = next;
+        }
+
+        public uint CalculateSize()
+        {
+            return (uint)HeaderField.GetLength(Name.Length, Value.Length);
+        }
+
+        public void Remove()
+        {
+            Before.After = After;
+            After.Before = Before;
+            Before = null;
+            After = null;
+            Next = null;
+            Hash = 0;
+            Name = null;
+            Value = null;
+        }
+
+        public void AddBefore(HPackHeaderEntry existingEntry)
+        {
+            After = existingEntry;
+            Before = existingEntry.Before;
+            Before.After = this;
+            After.Before = this;
+        }
+    }
+}