Precompute Server and Date bytes

Author: benaadams

src/Microsoft.AspNet.Server.Kestrel/Http/DateHeaderValueManager.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Text;
 using System.Threading;
 using Microsoft.AspNet.Server.Kestrel.Infrastructure;
 
@@ -17,6 +18,9 @@ public class DateHeaderValueManager : IDisposable
         private readonly TimeSpan _timerInterval;
 
         private volatile string _dateValue;
+        private volatile int _activeDateBytes;
+        private byte[] _dateBytes0 = Encoding.ASCII.GetBytes("DDD, dd mmm yyyy hh:mm:ss GMT");
+        private byte[] _dateBytes1 = Encoding.ASCII.GetBytes("DDD, dd mmm yyyy hh:mm:ss GMT");
         private object _timerLocker = new object();
         private bool _isDisposed = false;
         private bool _hadRequestsSinceLastTimerTick = false;
@@ -62,6 +66,12 @@ public virtual string GetDateHeaderValue()
             return _dateValue ?? _systemClock.UtcNow.ToString(Constants.RFC1123DateFormat);
         }
 
+        public byte[] GetDateHeaderValueBytes()
+        {
+            PumpTimer();
+            return _activeDateBytes == 0 ? _dateBytes0 : _dateBytes1;
+        }
+
         /// <summary>
         /// Releases all resources used by the current instance of <see cref="DateHeaderValueManager"/>.
         /// </summary>
@@ -92,6 +102,8 @@ private void PumpTimer()
                         // here as the timer won't fire until the timer interval has passed and we want a value assigned
                         // inline now to serve requests that occur in the meantime.
                         _dateValue = _systemClock.UtcNow.ToString(Constants.RFC1123DateFormat);
+                        Encoding.ASCII.GetBytes(_dateValue, 0, _dateValue.Length, (_activeDateBytes ^ 1) == 0 ? _dateBytes0 : _dateBytes1, 0);
+                        _activeDateBytes ^= 1;
                         _dateValueTimer = new Timer(UpdateDateValue, state: null, dueTime: _timerInterval, period: _timerInterval);
                     }
                 }
@@ -105,6 +117,8 @@ private void UpdateDateValue(object state)
 
             // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.18 for required format of Date header
             _dateValue = now.ToString(Constants.RFC1123DateFormat);
+            Encoding.ASCII.GetBytes(_dateValue, 0, _dateValue.Length, (_activeDateBytes ^ 1) == 0 ? _dateBytes0 : _dateBytes1, 0);
+            _activeDateBytes ^= 1;
 
             if (_hadRequestsSinceLastTimerTick)
             {

src/Microsoft.AspNet.Server.Kestrel/Http/Frame.cs

@@ -36,6 +36,8 @@ public partial class Frame : FrameContext, IFrameControl
         private static readonly byte[] _bytesHttpVersion1_1 = Encoding.ASCII.GetBytes("HTTP/1.1 ");
         private static readonly byte[] _bytesContentLengthZero = Encoding.ASCII.GetBytes("Content-Length: 0\r\n");
         private static readonly byte[] _bytesSpace = Encoding.ASCII.GetBytes(" ");
+        private static readonly byte[] _bytesServer = Encoding.ASCII.GetBytes("Server: Kestrel\r\n");
+        private static readonly byte[] _bytesDate = Encoding.ASCII.GetBytes("Date: ");
 
         private readonly object _onStartingSync = new Object();
         private readonly object _onCompletedSync = new Object();
@@ -112,6 +114,7 @@ public string HttpVersion
                 }
             }
         }
+
         public IHeaderDictionary RequestHeaders { get; set; }
         public MessageBody MessageBody { get; set; }
         public Stream RequestBody { get; set; }
@@ -176,8 +179,8 @@ public void Reset()
         public void ResetResponseHeaders()
         {
             _responseHeaders.Reset();
-            _responseHeaders.HeaderServer = "Kestrel";
-            _responseHeaders.HeaderDate = DateHeaderValueManager.GetDateHeaderValue();
+            _responseHeaders.HasDefaultDate = true; 
+            _responseHeaders.HasDefaultServer = true;
         }
 
         /// <summary>
@@ -612,6 +615,13 @@ private Task CreateResponseHeader(
 
                 OutputAsciiBlock(statusBytes, memoryBlock, SocketOutput);
 
+                if (_responseHeaders.HasDefaultDate)
+                {
+                    OutputAsciiBlock(_bytesDate, memoryBlock, SocketOutput);
+                    OutputAsciiBlock(DateHeaderValueManager.GetDateHeaderValueBytes(), memoryBlock, SocketOutput);
+                    OutputAsciiBlock(_bytesEndLine, memoryBlock, SocketOutput);
+                }
+
                 foreach (var header in _responseHeaders.AsOutputEnumerable())
                 {
                     foreach (var value in header.Value)
@@ -625,7 +635,11 @@ private Task CreateResponseHeader(
                             _keepAlive = false;
                         }
                     }
+                }
 
+                if (_responseHeaders.HasDefaultServer)
+                {
+                    OutputAsciiBlock(_bytesServer, memoryBlock, SocketOutput);
                 }
 
                 if (_keepAlive && !_responseHeaders.HasTransferEncoding && !_responseHeaders.HasContentLength)