Remove unsafe use ASCII.GetBytes for WriteAscii (#18404)

* Use ParallelBitExtract for EncodeAsciiCharsToBytes

* Use ASCII.GetBytes

* Use span overloads

* Betterize

* Remove old comment

src/Servers/Kestrel/Core/src/Internal/Http/HttpHeaders.Generated.cs

@@ -11538,7 +11538,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
                         if (value != null)
                         {
                             output.Write(headerKey);
-                            output.WriteAsciiNoValidation(value);
+                            output.WriteAscii(value);
                         }
                     }
                 }

src/Servers/Kestrel/Core/src/Internal/Http/HttpResponseHeaders.cs

@@ -48,9 +48,9 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http
                         if (value != null)
                         {
                             buffer.Write(CrLf);
-                            buffer.WriteAsciiNoValidation(kv.Key);
+                            buffer.WriteAscii(kv.Key);
                             buffer.Write(ColonSpace);
-                            buffer.WriteAsciiNoValidation(value);
+                            buffer.WriteAscii(value);
                         }
                     }
                 }

src/Servers/Kestrel/Core/test/PipelineExtensionTests.cs

@@ -87,7 +87,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
         {
             var pipeWriter = _pipe.Writer;
             var writer = new BufferWriter<PipeWriter>(pipeWriter);
-            writer.WriteAsciiNoValidation(input);
+            writer.WriteAscii(input);
             writer.Commit();
             pipeWriter.FlushAsync().GetAwaiter().GetResult();
             pipeWriter.Complete();
@@ -111,13 +111,13 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
         [InlineData("𤭢𐐝")]
         // non-ascii characters stored in 16 bits
         [InlineData("ñ٢⛄⛵")]
-        public void WriteAsciiNoValidationWritesOnlyOneBytePerChar(string input)
+        public void WriteAsciiWritesOnlyOneBytePerChar(string input)
         {
             // WriteAscii doesn't validate if characters are in the ASCII range
             // but it shouldn't produce more than one byte per character
             var writerBuffer = _pipe.Writer;
             var writer = new BufferWriter<PipeWriter>(writerBuffer);
-            writer.WriteAsciiNoValidation(input);
+            writer.WriteAscii(input);
             writer.Commit();
             writerBuffer.FlushAsync().GetAwaiter().GetResult();
             var reader = _pipe.Reader.ReadAsync().GetAwaiter().GetResult();
@@ -126,14 +126,14 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
         }
 
         [Fact]
-        public void WriteAsciiNoValidation()
+        public void WriteAscii()
         {
             const byte maxAscii = 0x7f;
             var writerBuffer = _pipe.Writer;
             var writer = new BufferWriter<PipeWriter>(writerBuffer);
             for (var i = 0; i < maxAscii; i++)
             {
-                writer.WriteAsciiNoValidation(new string((char)i, 1));
+                writer.WriteAscii(new string((char)i, 1));
             }
             writer.Commit();
             writerBuffer.FlushAsync().GetAwaiter().GetResult();
@@ -167,7 +167,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests
             Assert.Equal(gapSize, writer.Span.Length);
 
             var bufferLength = writer.Span.Length;
-            writer.WriteAsciiNoValidation(testString);
+            writer.WriteAscii(testString);
             Assert.NotEqual(bufferLength, writer.Span.Length);
             writer.Commit();
             writerBuffer.FlushAsync().GetAwaiter().GetResult();

src/Servers/Kestrel/shared/KnownHeaders.cs

@@ -945,7 +945,7 @@ $@"        private void Clear(long bitsToClear)
                         if (value != null)
                         {{
                             output.Write(headerKey);
-                            output.WriteAsciiNoValidation(value);
+                            output.WriteAscii(value);
                         }}
                     }}
                 }}

src/Shared/ServerInfrastructure/BufferExtensions.cs

@@ -1,11 +1,11 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // 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.Buffers;
 using System.IO.Pipelines;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace System.Buffers
 {
@@ -40,7 +40,7 @@ namespace System.Buffers
             return result;
         }
 
-        internal static unsafe void WriteAsciiNoValidation(ref this BufferWriter<PipeWriter> buffer, string data)
+        internal static void WriteAscii(ref this BufferWriter<PipeWriter> buffer, string data)
         {
             if (string.IsNullOrEmpty(data))
             {
@@ -48,18 +48,11 @@ namespace System.Buffers
             }
 
             var dest = buffer.Span;
-            var destLength = dest.Length;
             var sourceLength = data.Length;
-
+            // Fast path, try encoding to the available memory directly
-            // Fast path, try copying to the available memory directly
+            if (sourceLength <= dest.Length)
-            if (sourceLength <= destLength)
             {
-                fixed (char* input = data)
+                Encoding.ASCII.GetBytes(data, dest);
-                fixed (byte* output = dest)
-                {
-                    EncodeAsciiCharsToBytes(input, output, sourceLength);
-                }
-
                 buffer.Advance(sourceLength);
             }
             else
@@ -140,123 +133,31 @@ namespace System.Buffers
         }
 
         [MethodImpl(MethodImplOptions.NoInlining)]
-        private unsafe static void WriteAsciiMultiWrite(ref this BufferWriter<PipeWriter> buffer, string data)
+        private static void WriteAsciiMultiWrite(ref this BufferWriter<PipeWriter> buffer, string data)
         {
-            var remaining = data.Length;
+            var dataLength = data.Length;
-
+            var offset = 0;
-            fixed (char* input = data)
+            var bytes = buffer.Span;
+            do
             {
-                var inputSlice = input;
+                var writable = Math.Min(dataLength - offset, bytes.Length);
+                // Zero length spans are possible, though unlikely.
+                // ASCII.GetBytes and .Advance will both handle them so we won't special case for them.
+                Encoding.ASCII.GetBytes(data.AsSpan(offset, writable), bytes);
+                buffer.Advance(writable);
 
-                while (remaining > 0)
+                offset += writable;
+                if (offset >= dataLength)
                 {
-                    var writable = Math.Min(remaining, buffer.Span.Length);
+                    Debug.Assert(offset == dataLength);
-
+                    // Encoded everything
-                    if (writable == 0)
+                    break;
-                    {
-                        buffer.Ensure();
-                        continue;
-                    }
-
-                    fixed (byte* output = buffer.Span)
-                    {
-                        EncodeAsciiCharsToBytes(inputSlice, output, writable);
-                    }
-
-                    inputSlice += writable;
-                    remaining -= writable;
-
-                    buffer.Advance(writable);
-                }
-            }
-        }
-
-        private static unsafe void EncodeAsciiCharsToBytes(char* input, byte* output, int length)
-        {
-            // Note: Not BIGENDIAN or check for non-ascii
-            const int Shift16Shift24 = (1 << 16) | (1 << 24);
-            const int Shift8Identity = (1 << 8) | (1);
-
-            // Encode as bytes up to the first non-ASCII byte and return count encoded
-            int i = 0;
-            // Use Intrinsic switch
-            if (IntPtr.Size == 8) // 64 bit
-            {
-                if (length < 4) goto trailing;
-
-                int unaligned = (int)(((ulong)input) & 0x7) >> 1;
-                // Unaligned chars
-                for (; i < unaligned; i++)
-                {
-                    char ch = *(input + i);
-                    *(output + i) = (byte)ch; // Cast convert
                 }
 
-                // Aligned
+                // Get new span, more to encode.
-                int ulongDoubleCount = (length - i) & ~0x7;
+                buffer.Ensure();
-                for (; i < ulongDoubleCount; i += 8)
+                bytes = buffer.Span;
-                {
+            } while (true);
-                    ulong inputUlong0 = *(ulong*)(input + i);
-                    ulong inputUlong1 = *(ulong*)(input + i + 4);
-                    // Pack 16 ASCII chars into 16 bytes
-                    *(uint*)(output + i) =
-                        ((uint)((inputUlong0 * Shift16Shift24) >> 24) & 0xffff) |
-                        ((uint)((inputUlong0 * Shift8Identity) >> 24) & 0xffff0000);
-                    *(uint*)(output + i + 4) =
-                        ((uint)((inputUlong1 * Shift16Shift24) >> 24) & 0xffff) |
-                        ((uint)((inputUlong1 * Shift8Identity) >> 24) & 0xffff0000);
-                }
-                if (length - 4 > i)
-                {
-                    ulong inputUlong = *(ulong*)(input + i);
-                    // Pack 8 ASCII chars into 8 bytes
-                    *(uint*)(output + i) =
-                        ((uint)((inputUlong * Shift16Shift24) >> 24) & 0xffff) |
-                        ((uint)((inputUlong * Shift8Identity) >> 24) & 0xffff0000);
-                    i += 4;
-                }
-
-                trailing:
-                for (; i < length; i++)
-                {
-                    char ch = *(input + i);
-                    *(output + i) = (byte)ch; // Cast convert
-                }
-            }
-            else // 32 bit
-            {
-                // Unaligned chars
-                if ((unchecked((int)input) & 0x2) != 0)
-                {
-                    char ch = *input;
-                    i = 1;
-                    *(output) = (byte)ch; // Cast convert
-                }
-
-                // Aligned
-                int uintCount = (length - i) & ~0x3;
-                for (; i < uintCount; i += 4)
-                {
-                    uint inputUint0 = *(uint*)(input + i);
-                    uint inputUint1 = *(uint*)(input + i + 2);
-                    // Pack 4 ASCII chars into 4 bytes
-                    *(ushort*)(output + i) = (ushort)(inputUint0 | (inputUint0 >> 8));
-                    *(ushort*)(output + i + 2) = (ushort)(inputUint1 | (inputUint1 >> 8));
-                }
-                if (length - 1 > i)
-                {
-                    uint inputUint = *(uint*)(input + i);
-                    // Pack 2 ASCII chars into 2 bytes
-                    *(ushort*)(output + i) = (ushort)(inputUint | (inputUint >> 8));
-                    i += 2;
-                }
-
-                if (i < length)
-                {
-                    char ch = *(input + i);
-                    *(output + i) = (byte)ch; // Cast convert
-                }
-            }
         }
 
         private static byte[] NumericBytesScratch => _numericBytesScratch ?? CreateNumericBytesScratch();