Use ulong.TryFormat for Content-Length values >= 1000 in Kestrel

src/Servers/Kestrel/perf/Microbenchmarks/BufferWriterExtensionsBenchmark.cs

@@ -0,0 +1,66 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Buffers;
+using System.IO.Pipelines;
+using BenchmarkDotNet.Attributes;
+
+namespace Microsoft.AspNetCore.Server.Kestrel.Microbenchmarks;
+
+public class BufferWriterWriteNumericBenchmark
+{
+    private const int Iterations = 1000;
+
+    private NullPipeWriter _pipeWriter;
+
+    [Params(5UL, 421UL, 4096UL, 1_048_576UL, 123_456_789_012UL)]
+    public ulong Number { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        _pipeWriter = new NullPipeWriter();
+    }
+
+    [Benchmark(OperationsPerInvoke = Iterations)]
+    public void WriteNumeric()
+    {
+        var writer = new BufferWriter<PipeWriter>(_pipeWriter);
+        var number = Number;
+        for (var i = 0; i < Iterations; i++)
+        {
+            writer.WriteNumeric(number);
+        }
+        writer.Commit();
+    }
+}
+
+public class BufferWriterWriteAsciiBenchmark
+{
+    private const int Iterations = 1000;
+
+    private NullPipeWriter _pipeWriter;
+    private string _asciiValue;
+
+    [Params(10, 30, 100)]
+    public int StringLength { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        _pipeWriter = new NullPipeWriter();
+        _asciiValue = new string('a', StringLength);
+    }
+
+    [Benchmark(OperationsPerInvoke = Iterations)]
+    public void WriteAscii()
+    {
+        var writer = new BufferWriter<PipeWriter>(_pipeWriter);
+        var value = _asciiValue;
+        for (var i = 0; i < Iterations; i++)
+        {
+            writer.WriteAscii(value);
+        }
+        writer.Commit();
+    }
+}

src/Shared/ServerInfrastructure/BufferExtensions.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Globalization;
 using System.IO.Pipelines;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -170,22 +171,24 @@ internal static void WriteNumeric(ref this BufferWriter<PipeWriter> bufferWriter
     [MethodImpl(MethodImplOptions.NoInlining)]
     private static void WriteNumericMultiWrite(ref this BufferWriter<PipeWriter> buffer, ulong number)
     {
-        const byte AsciiDigitStart = (byte)'0';
-
-        var value = number;
-        var position = _maxULongByteLength;
-        var byteBuffer = NumericBytesScratch;
-        do
+        // Fast path, format directly into the available memory
+        if (number.TryFormat(buffer.Span, out var bytesWritten, provider: CultureInfo.InvariantCulture))
         {
-            // Consider using Math.DivRem() if available
-            var quotient = value / 10;
-            byteBuffer[--position] = (byte)(AsciiDigitStart + (value - quotient * 10)); // 0x30 = '0'
-            value = quotient;
+            buffer.Advance(bytesWritten);
+            return;
         }
-        while (value != 0);
 
-        var length = _maxULongByteLength - position;
-        buffer.Write(new ReadOnlySpan<byte>(byteBuffer, position, length));
+        WriteNumericAcrossSpans(ref buffer, number);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void WriteNumericAcrossSpans(ref BufferWriter<PipeWriter> buffer, ulong number)
+    {
+        // Not enough space left in the current span, format to a scratch buffer and write it across spans
+        var byteBuffer = NumericBytesScratch;
+        var formatted = number.TryFormat(byteBuffer, out var bytesWritten, provider: CultureInfo.InvariantCulture);
+        Debug.Assert(formatted);
+        buffer.Write(new ReadOnlySpan<byte>(byteBuffer, 0, bytesWritten));
     }
 
     internal static void WriteEncoded(ref this BufferWriter<PipeWriter> buffer, string data, Encoding encoding)