Don't add prefix padding in VectorArrayBuffer.

Author: scalablecory

NetworkToolkit/Http/Primitives/Http1Connection.Parsers.cs

@@ -15,7 +15,7 @@ namespace NetworkToolkitInternal.Http.Primitives
     public partial class Http1Connection
     {
         /// <summary>
-        /// The amount of padding, in terms of valid address space before and after the buffer header parsing is done from.
+        /// The amount of padding, in terms of valid address space after the buffer header parsing is done from.
         /// </summary>
         public static int HeaderBufferPadding => Vector256<byte>.Count - 1;
 
@@ -102,7 +102,8 @@ internal unsafe bool ReadHeadersPortable(Span<byte> buffer, IHttpHeadersSink hea
         }
 
         /// <remarks>
-        /// This method REQUIRES (32-1) bytes of valid address space in front of and after <paramref name="buffer"/>.
+        /// This method REQUIRES (32-1) bytes of valid address space after <paramref name="buffer"/>.
+        /// It also assumes that it can always step backwards to a 32-byte aligned address.
         /// It is built to be used with VectorArrayBuffer, which does this.
         /// </remarks>
         internal unsafe bool ReadHeadersAvx2(Span<byte> buffer, IHttpHeadersSink headersSink, object? state, out int bytesConsumed)
@@ -115,7 +116,6 @@ internal unsafe bool ReadHeadersAvx2(Span<byte> buffer, IHttpHeadersSink headers
             fixed (byte* vectorBegin = buffer)
             {
                 // align to a 32 byte address for optimal loads.
-                // This is why padding is required.
                 byte* vectorEnd = vectorBegin + buffer.Length;
                 byte* vectorIter = (byte*)((nint)vectorBegin & ~(32 - 1));
 

NetworkToolkit/VectorArrayBuffer.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 #nullable enable
+using NetworkToolkit.Http.Primitives;
 using System;
 using System.Buffers;
 using System.Diagnostics;
@@ -27,10 +28,13 @@ namespace NetworkToolkit
     [StructLayout(LayoutKind.Auto)]
     internal struct VectorArrayBuffer : IDisposable
     {
-        // Pad the front and back of the array with enough bytes to ensure we
+        // It is assumed that (due to how virtual memory works) we do
+        // not need to add padding to the front of the buffer.
+        private const int PrefixPaddingLength = 0;
+        // Pad the back of the array with enough bytes to ensure we
         // can always safely read an Vector256 at any index within returned spans.
-        private static int PerSidePaddingLength => Vector256<byte>.Count - 1;
-        private static int TotalPaddingLength => PerSidePaddingLength * 2;
+        private static int SuffixPaddingLength => Http1Connection.HeaderBufferPadding;
+        private static int TotalPaddingLength => PrefixPaddingLength + SuffixPaddingLength;
 
         private byte[] _bytes;
         private int _activeStart;
@@ -61,12 +65,12 @@ public void Dispose()
         }
 
         public int ActiveLength => _availableStart - _activeStart;
-        public Span<byte> ActiveSpan => new Span<byte>(_bytes, _activeStart + PerSidePaddingLength, ActiveLength);
-        public Memory<byte> ActiveMemory => new Memory<byte>(_bytes, _activeStart + PerSidePaddingLength, ActiveLength);
+        public Span<byte> ActiveSpan => new Span<byte>(_bytes, _activeStart + PrefixPaddingLength, ActiveLength);
+        public Memory<byte> ActiveMemory => new Memory<byte>(_bytes, _activeStart + PrefixPaddingLength, ActiveLength);
 
         public int AvailableLength => Capacity - _availableStart;
-        public Span<byte> AvailableSpan => new Span<byte>(_bytes, _availableStart + PerSidePaddingLength, AvailableLength);
-        public Memory<byte> AvailableMemory => new Memory<byte>(_bytes, _availableStart + PerSidePaddingLength, AvailableLength);
+        public Span<byte> AvailableSpan => new Span<byte>(_bytes, _availableStart + PrefixPaddingLength, AvailableLength);
+        public Memory<byte> AvailableMemory => new Memory<byte>(_bytes, _availableStart + PrefixPaddingLength, AvailableLength);
 
         public int Capacity => _bytes.Length - TotalPaddingLength;
 
@@ -76,8 +80,14 @@ private static byte[] Rent(int byteCount)
             array.AsSpan().Clear();
 
             // zero out the prefix and suffix padding, so they won't match any compares later on.
-            array.AsSpan(0, PerSidePaddingLength).Clear();
-            array.AsSpan(array.Length - PerSidePaddingLength, PerSidePaddingLength).Clear();
+            if(PrefixPaddingLength != 0)
+            {
+#pragma warning disable CS0162 // Unreachable code detected
+                array.AsSpan(0, PrefixPaddingLength).Clear();
+#pragma warning restore CS0162 // Unreachable code detected
+            }
+
+            array.AsSpan(array.Length - SuffixPaddingLength, SuffixPaddingLength).Clear();
 
             return array;
         }
@@ -115,7 +125,7 @@ private void EnsureAvailableSpaceSlow(int byteCount)
             if (byteCount <= totalFree)
             {
                 // We can free up enough space by just shifting the bytes down, so do so.
-                Buffer.BlockCopy(_bytes, _activeStart + PerSidePaddingLength, _bytes, PerSidePaddingLength, ActiveLength);
+                Buffer.BlockCopy(_bytes, _activeStart + PrefixPaddingLength, _bytes, PrefixPaddingLength, ActiveLength);
                 _availableStart = ActiveLength;
                 _activeStart = 0;
                 Debug.Assert(byteCount <= AvailableLength);
@@ -136,7 +146,7 @@ private void EnsureAvailableSpaceSlow(int byteCount)
 
             if (ActiveLength != 0)
             {
-                Buffer.BlockCopy(oldBytes, _activeStart + PerSidePaddingLength, newBytes, PerSidePaddingLength, ActiveLength);
+                Buffer.BlockCopy(oldBytes, _activeStart + PrefixPaddingLength, newBytes, PrefixPaddingLength, ActiveLength);
             }
 
             _availableStart = ActiveLength;

README.md

@@ -39,7 +39,7 @@ Avoid a connection pool to have exact control over connections.
 ```c#
 await using ConnectionFactory connectionFactory = new SocketConnectionFactory();
 await using Connection connection = await connectionFactory.ConnectAsync(new DnsEndPoint("microsoft.com", 80));
-await using HttpConnection httpConnection = new Http1Connection(connection);
+await using HttpConnection httpConnection = new Http1Connection(connection.Stream);
 await using ValueHttpRequest request = (await httpConnection.CreateNewRequestAsync(HttpPrimitiveVersion.Version11, HttpVersionPolicy.RequestVersionExact)).Value;
 
 request.ConfigureRequest(contentLength: 0, hasTrailingHeaders: false);