use ArrayPool in Base64Encoder non-net6 branch to avoid per-chunk all…

src/Argon/Utilities/Base64Encoder.cs

@@ -24,15 +24,23 @@ public static void WriteBase64(this TextWriter writer, ReadOnlySpan<byte> buffer
     public static void WriteBase64(this TextWriter writer, ReadOnlySpan<byte> buffer)
     {
         var charsLine = new char[Base64LineSize];
-        var index = 0;
-        do
+        var bytesLine = ArrayPool<byte>.Shared.Rent(LineSizeInBytes);
+        try
         {
-            var min = Math.Min(LineSizeInBytes, buffer.Length - index);
-            var slice = buffer.Slice(index, min);
-            var written = Convert.ToBase64CharArray(slice.ToArray(), 0, min, charsLine, 0);
-            writer.Write(charsLine, 0, written);
-            index += LineSizeInBytes;
-        } while (index < buffer.Length);
+            var index = 0;
+            do
+            {
+                var min = Math.Min(LineSizeInBytes, buffer.Length - index);
+                buffer.Slice(index, min).CopyTo(bytesLine);
+                var written = Convert.ToBase64CharArray(bytesLine, 0, min, charsLine, 0);
+                writer.Write(charsLine, 0, written);
+                index += LineSizeInBytes;
+            } while (index < buffer.Length);
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(bytesLine);
+        }
     }
 #endif
 }

src/ArgonTests/Benchmarks/WriteBase64Benchmark.cs

@@ -0,0 +1,75 @@
+// Copyright (c) 2007 James Newton-King. All rights reserved.
+// Use of this source code is governed by The MIT License,
+// as found in the license.md file.
+
+using System.Buffers;
+using BenchmarkDotNet.Attributes;
+
+[MemoryDiagnoser]
+public class WriteBase64Benchmark
+{
+    const int Base64LineSize = 76;
+    const int LineSizeInBytes = 57;
+
+    byte[] data = null!;
+
+    [Params(57, 570, 5700, 57000)]
+    public int Size { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        data = new byte[Size];
+        new Random(42).NextBytes(data);
+    }
+
+    [Benchmark(Baseline = true)]
+    public void OldToArray()
+    {
+        using var writer = new StringWriter();
+        WriteBase64Old(writer, data);
+    }
+
+    [Benchmark]
+    public void NewArrayPool()
+    {
+        using var writer = new StringWriter();
+        WriteBase64New(writer, data);
+    }
+
+    static void WriteBase64Old(TextWriter writer, ReadOnlySpan<byte> buffer)
+    {
+        var charsLine = new char[Base64LineSize];
+        var index = 0;
+        do
+        {
+            var min = Math.Min(LineSizeInBytes, buffer.Length - index);
+            var slice = buffer.Slice(index, min);
+            var written = Convert.ToBase64CharArray(slice.ToArray(), 0, min, charsLine, 0);
+            writer.Write(charsLine, 0, written);
+            index += LineSizeInBytes;
+        } while (index < buffer.Length);
+    }
+
+    static void WriteBase64New(TextWriter writer, ReadOnlySpan<byte> buffer)
+    {
+        var charsLine = new char[Base64LineSize];
+        var bytesLine = ArrayPool<byte>.Shared.Rent(LineSizeInBytes);
+        try
+        {
+            var index = 0;
+            do
+            {
+                var min = Math.Min(LineSizeInBytes, buffer.Length - index);
+                buffer.Slice(index, min).CopyTo(bytesLine);
+                var written = Convert.ToBase64CharArray(bytesLine, 0, min, charsLine, 0);
+                writer.Write(charsLine, 0, written);
+                index += LineSizeInBytes;
+            } while (index < buffer.Length);
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(bytesLine);
+        }
+    }
+}

src/Benchmark.Tests/Program.cs

@@ -11,7 +11,7 @@ public static void Main(string[] args)
         var attribute = (AssemblyFileVersionAttribute)typeof(JsonConvert).Assembly.GetCustomAttribute(typeof(AssemblyFileVersionAttribute))!;
         Console.WriteLine($"Json.NET Version: {attribute.Version}");
 
-        var switcher = new BenchmarkSwitcher([typeof(WriteEscapedJavaScriptString), typeof(SerializeJTokenList), typeof(ReadQuotedNumbers)]);
+        var switcher = new BenchmarkSwitcher([typeof(WriteEscapedJavaScriptString), typeof(SerializeJTokenList), typeof(ReadQuotedNumbers), typeof(WriteBase64Benchmark)]);
         if (args.Length == 0)
         {
             switcher.Run(["*"]);