Pre-allocate standard method and version strings.

Author: Cesar Blum Silveira

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

@@ -702,7 +702,12 @@ protected bool TakeStartLine(SocketInput input)
                 {
                     return false;
                 }
-                var method = begin.GetAsciiString(scan);
+
+                string method;
+                if (!begin.GetKnownString(scan, out method))
+                {
+                    method = begin.GetAsciiString(scan);
+                }
 
                 scan.Take();
                 begin = scan;
@@ -735,7 +740,12 @@ protected bool TakeStartLine(SocketInput input)
                 {
                     return false;
                 }
-                var httpVersion = begin.GetAsciiString(scan);
+
+                string httpVersion;
+                if (!begin.GetKnownString(scan, out httpVersion))
+                {
+                    httpVersion = begin.GetAsciiString(scan);
+                }
 
                 scan.Take();
                 if (scan.Take() != '\n')

src/Microsoft.AspNet.Server.Kestrel/Infrastructure/MemoryPoolIterator2.cs

@@ -138,6 +138,49 @@ public int Peek()
             }
         }
 
+        public unsafe long PeekLong()
+        {
+            if (_block == null)
+            {
+                return -1;
+            }
+            else if (_block.End - _index >= sizeof(long))
+            {
+                fixed (byte* ptr = _block.Array)
+                {
+                    return *(long*)(ptr + _index);
+                }
+            }
+            else if (_block.Next == null)
+            {
+                return -1;
+            }
+            else
+            {
+                var blockBytes = _block.End - _index;
+                var nextBytes = sizeof(long) - blockBytes;
+
+                if (_block.Next.End - _block.Next.Start < nextBytes)
+                {
+                    return -1;
+                }
+
+                long blockLong;
+                fixed (byte* ptr = _block.Array)
+                {
+                    blockLong = *(long*)(ptr + _block.End - sizeof(long));
+                }
+
+                long nextLong;
+                fixed (byte* ptr = _block.Next.Array)
+                {
+                    nextLong = *(long*)(ptr + _block.Next.Start);
+                }
+
+                return (blockLong >> (sizeof(long) - blockBytes) * 8) | (nextLong << (sizeof(long) - nextBytes) * 8);
+            }
+        }
+
         public int Seek(int char0)
         {
             if (IsDefault)

src/Microsoft.AspNet.Server.Kestrel/Infrastructure/MemoryPoolIterator2Extensions.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.Diagnostics;
 using System.Text;
 
 namespace Microsoft.AspNet.Server.Kestrel.Infrastructure
@@ -12,6 +13,62 @@ public static class MemoryPoolIterator2Extensions
 
         private static Encoding _utf8 = Encoding.UTF8;
 
+        public const string HttpConnectMethod = "CONNECT";
+        public const string HttpDeleteMethod = "DELETE";
+        public const string HttpGetMethod = "GET";
+        public const string HttpHeadMethod = "HEAD";
+        public const string HttpPatchMethod = "PATCH";
+        public const string HttpPostMethod = "POST";
+        public const string HttpPutMethod = "PUT";
+        public const string HttpOptionsMethod = "OPTIONS";
+        public const string HttpTraceMethod = "TRACE";
+
+        public const string Http10Version = "HTTP/1.0";
+        public const string Http11Version = "HTTP/1.1";
+
+        private static long _httpConnectMethodLong = GetAsciiStringAsLong("CONNECT\0");
+        private static long _httpDeleteMethodLong = GetAsciiStringAsLong("DELETE\0\0");
+        private static long _httpGetMethodLong = GetAsciiStringAsLong("GET\0\0\0\0\0");
+        private static long _httpHeadMethodLong = GetAsciiStringAsLong("HEAD\0\0\0\0");
+        private static long _httpPatchMethodLong = GetAsciiStringAsLong("PATCH\0\0\0");
+        private static long _httpPostMethodLong = GetAsciiStringAsLong("POST\0\0\0\0");
+        private static long _httpPutMethodLong = GetAsciiStringAsLong("PUT\0\0\0\0\0");
+        private static long _httpOptionsMethodLong = GetAsciiStringAsLong("OPTIONS\0");
+        private static long _httpTraceMethodLong = GetAsciiStringAsLong("TRACE\0\0\0");
+
+        private static long _http10VersionLong = GetAsciiStringAsLong("HTTP/1.0");
+        private static long _http11VersionLong = GetAsciiStringAsLong("HTTP/1.1");
+
+        private const int PerfectHashDivisor = 37;
+        private static Tuple<long, string>[] _knownStrings = new Tuple<long, string>[PerfectHashDivisor];
+
+        static MemoryPoolIterator2Extensions()
+        {
+            _knownStrings[_httpConnectMethodLong % PerfectHashDivisor] = Tuple.Create(_httpConnectMethodLong, HttpConnectMethod);
+            _knownStrings[_httpDeleteMethodLong % PerfectHashDivisor] = Tuple.Create(_httpDeleteMethodLong, HttpDeleteMethod);
+            _knownStrings[_httpGetMethodLong % PerfectHashDivisor] = Tuple.Create(_httpGetMethodLong, HttpGetMethod);
+            _knownStrings[_httpHeadMethodLong % PerfectHashDivisor] = Tuple.Create(_httpHeadMethodLong, HttpHeadMethod);
+            _knownStrings[_httpPatchMethodLong % PerfectHashDivisor] = Tuple.Create(_httpPatchMethodLong, HttpPatchMethod);
+            _knownStrings[_httpPostMethodLong % PerfectHashDivisor] = Tuple.Create(_httpPostMethodLong, HttpPostMethod);
+            _knownStrings[_httpPutMethodLong % PerfectHashDivisor] = Tuple.Create(_httpPutMethodLong, HttpPutMethod);
+            _knownStrings[_httpOptionsMethodLong % PerfectHashDivisor] = Tuple.Create(_httpOptionsMethodLong, HttpOptionsMethod);
+            _knownStrings[_httpTraceMethodLong % PerfectHashDivisor] = Tuple.Create(_httpTraceMethodLong, HttpTraceMethod);
+            _knownStrings[_http10VersionLong % PerfectHashDivisor] = Tuple.Create(_http10VersionLong, Http10Version);
+            _knownStrings[_http11VersionLong % PerfectHashDivisor] = Tuple.Create(_http11VersionLong, Http11Version);
+        }
+
+        private unsafe static long GetAsciiStringAsLong(string str)
+        {
+            Debug.Assert(str.Length == 8, "String must be exactly 8 (ASCII) characters long.");
+
+            var bytes = Encoding.ASCII.GetBytes(str);
+
+            fixed (byte* ptr = bytes)
+            {
+                return *(long*)ptr;
+            }
+        }
+
         private static unsafe string GetAsciiStringStack(byte[] input, int inputOffset, int length)
         {
             // avoid declaring other local vars, or doing work with stackalloc
@@ -20,6 +77,7 @@ private static unsafe string GetAsciiStringStack(byte[] input, int inputOffset,
 
             return GetAsciiStringImplementation(output, input, inputOffset, length);
         }
+
         private static unsafe string GetAsciiStringImplementation(char* output, byte[] input, int inputOffset, int length)
         {
             for (var i = 0; i < length; i++)
@@ -203,5 +261,55 @@ public static ArraySegment<byte> GetArraySegment(this MemoryPoolIterator2 start,
             start.CopyTo(array, 0, length, out length);
             return new ArraySegment<byte>(array, 0, length);
         }
+
+        /// <summary>
+        /// Checks that up to 8 bytes between <paramref name="begin"/> and <paramref name="end"/> correspond to a known HTTP string.
+        /// </summary>
+        /// <remarks>
+        /// A "known HTTP string" can be an HTTP method name defined in the HTTP/1.1 RFC or an HTTP version (HTTP/1.0 or HTTP/1.1).
+        /// Since all of those fit in at most 8 bytes, they can be optimally looked up by reading those bytes as a long. Once
+        /// in that format, uninteresting bits are cleared and the remaining long modulo 37 is looked up in a table.
+        /// The number 37 was chosen because that number allows for a perfect hash of the set of
+        /// "known strings" (CONNECT, DELETE, GET, HEAD, PATCH, POST, PUT, OPTIONS, TRACE, HTTP/1.0 and HTTP/1.1, where strings
+        /// with less than 8 characters have 0s appended to their ends to fill for the missing bytes).
+        /// </remarks>
+        /// <param name="begin">The iterator from which to start the known string lookup.</param>
+        /// <param name="end">The iterator pointing to the end of the input string.</param>
+        /// <param name="knownString">A reference to a pre-allocated known string, if the input matches any.</param>
+        /// <returns><c>true</c> if the input matches a known string, <c>false</c> otherwise.</returns>
+        public static bool GetKnownString(this MemoryPoolIterator2 begin, MemoryPoolIterator2 end, out string knownString)
+        {
+            knownString = null;
+
+            // This optimization only works on little endian environments (for now).
+            if (!BitConverter.IsLittleEndian)
+            {
+                return false;
+            }
+
+            var inputLength = begin.GetLength(end);
+
+            if (inputLength > sizeof(long))
+            {
+                return false;
+            }
+
+            var inputLong = begin.PeekLong();
+
+            if (inputLong == -1)
+            {
+                return false;
+            }
+
+            inputLong &= (long)(unchecked((ulong)~0) >> ((sizeof(long) - inputLength) * 8));
+
+            var value = _knownStrings[inputLong % PerfectHashDivisor];
+            if (value != null && value.Item1 == inputLong)
+            {
+                knownString = value.Item2;
+            }
+
+            return knownString != null;
+        }
     }
 }

test/Microsoft.AspNet.Server.KestrelTests/MemoryPoolIterator2Tests.cs

@@ -128,5 +128,104 @@ public void Put()
             // Can't put anything by the end
             Assert.False(head.Put(0xFF));
         }
+
+        [Fact]
+        public void PeekLong()
+        {
+            // Arrange
+            var block = _pool.Lease();
+            var bytes = BitConverter.GetBytes(0x0102030405060708);
+            Buffer.BlockCopy(bytes, 0, block.Array, block.Start, bytes.Length);
+            block.End += bytes.Length;
+            var scan = block.GetIterator();
+            var originalIndex = scan.Index;
+
+            // Act
+            var result = scan.PeekLong();
+
+            // Assert
+            Assert.Equal(0x0102030405060708, result);
+            Assert.Equal(originalIndex, scan.Index);
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        [InlineData(4)]
+        [InlineData(5)]
+        [InlineData(6)]
+        [InlineData(7)]
+        public void PeekLongAtBlockBoundary(int blockBytes)
+        {
+            // Arrange
+            var nextBlockBytes = 8 - blockBytes;
+
+            var block = _pool.Lease();
+            block.End += blockBytes;
+            
+            var nextBlock = _pool.Lease();
+            nextBlock.End += nextBlockBytes;
+
+            block.Next = nextBlock;
+
+            var bytes = BitConverter.GetBytes(0x0102030405060708);
+            Buffer.BlockCopy(bytes, 0, block.Array, block.Start, blockBytes);
+            Buffer.BlockCopy(bytes, blockBytes, nextBlock.Array, nextBlock.Start, nextBlockBytes);
+
+            var scan = block.GetIterator();
+            var originalIndex = scan.Index;
+
+            // Act
+            var result = scan.PeekLong();
+
+            // Assert
+            Assert.Equal(0x0102030405060708, result);
+            Assert.Equal(originalIndex, scan.Index);
+        }
+
+        [Theory]
+        [InlineData("CONNECT / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpConnectMethod)]
+        [InlineData("DELETE / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpDeleteMethod)]
+        [InlineData("GET / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpGetMethod)]
+        [InlineData("HEAD / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpHeadMethod)]
+        [InlineData("PATCH / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpPatchMethod)]
+        [InlineData("POST / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpPostMethod)]
+        [InlineData("PUT / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpPutMethod)]
+        [InlineData("OPTIONS / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpOptionsMethod)]
+        [InlineData("TRACE / HTTP/1.1", ' ', true, MemoryPoolIterator2Extensions.HttpTraceMethod)]
+        [InlineData("HTTP/1.0\r", '\r', true, MemoryPoolIterator2Extensions.Http10Version)]
+        [InlineData("HTTP/1.1\r", '\r', true, MemoryPoolIterator2Extensions.Http11Version)]
+        [InlineData("GET/ HTTP/1.1", ' ', false, null)]
+        [InlineData("get / HTTP/1.1", ' ', false, null)]
+        [InlineData("GOT / HTTP/1.1", ' ', false, null)]
+        [InlineData("ABC / HTTP/1.1", ' ', false, null)]
+        [InlineData("PO / HTTP/1.1", ' ', false, null)]
+        [InlineData("PO ST / HTTP/1.1", ' ', false, null)]
+        [InlineData("HTTP/1.0_\r", '\r', false, null)]
+        [InlineData("HTTP/1.1_\r", '\r', false, null)]
+        [InlineData("HTTP/3.0\r", '\r', false, null)]
+        [InlineData("http/1.0\r", '\r', false, null)]
+        [InlineData("http/1.1\r", '\r', false, null)]
+        [InlineData("short ", ' ', false, null)]
+        public void GetsKnownString(string input, char endChar, bool expectedResult, string expectedKnownString)
+        {
+            // Arrange
+            var block = _pool.Lease();
+            var chars = input.ToCharArray().Select(c => (byte)c).ToArray();
+            Buffer.BlockCopy(chars, 0, block.Array, block.Start, chars.Length);
+            block.End += chars.Length;
+            var begin = block.GetIterator();
+            var end = begin;
+            end.Seek(endChar);
+            string knownString;
+
+            // Act
+            var result = begin.GetKnownString(end, out knownString);
+
+            // Assert
+            Assert.Equal(expectedResult, result);
+            Assert.Equal(expectedKnownString, knownString);
+        }
     }
 }