From 872de8d095ebe3126c4f03162ff2f64c62886f79 Mon Sep 17 00:00:00 2001
From: Kamron Batman <3953314+kamronbatman@users.noreply.github.com>
Date: Sat, 12 Apr 2025 12:42:15 -0700
Subject: [PATCH] fix: Optimizes GetString to eliminate allocations (#2154)

### Summary

* Optimized GetString by eliminating the intermediate string allocation.

** Note **: Encoding.GetChars() is still really inefficient, especially when strings are not aligned or have regular ascii/unicode characters. Thankfully we generally don't have to worry about these odd edge cases, but if they happen then GetChars can allocate hundreds of bytes.


This is a benchmark for just the related changes. NonSpecial are just ascii characters, while the other tests include control codes.
```cs
| Method                         | Mean     | Error   | StdDev  | Gen0   | Allocated |
|------------------------------- |---------:|--------:|--------:|-------:|----------:|
| GetString                      | 306.7 ns | 5.96 ns | 6.86 ns | 0.0124 |     200 B |
| GetStringNotSpecial            | 257.0 ns | 4.83 ns | 4.52 ns | 0.0114 |     184 B |
| GetStringSpanHelpers           | 166.4 ns | 3.26 ns | 3.48 ns |      - |         - |
| GetStringSpanHelpersNotSpecial | 137.3 ns | 1.57 ns | 1.22 ns |      - |         - |
```
---
 Projects/Server/Buffers/ValueStringBuilder.cs |  2 +-
 Projects/Server/Text/TextEncoding.cs          | 57 +++++++++++++------
 2 files changed, 41 insertions(+), 18 deletions(-)

diff --git a/Projects/Server/Buffers/ValueStringBuilder.cs b/Projects/Server/Buffers/ValueStringBuilder.cs
index 3196ca45e..b6d4ab2f1 100644
--- a/Projects/Server/Buffers/ValueStringBuilder.cs
+++ b/Projects/Server/Buffers/ValueStringBuilder.cs
@@ -309,7 +309,7 @@ public ref struct ValueStringBuilder
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void Append(ReadOnlySpan<char> value)
+    public void Append(scoped ReadOnlySpan<char> value)
     {
         int pos = _length;
         if (pos > _chars.Length - value.Length)
diff --git a/Projects/Server/Text/TextEncoding.cs b/Projects/Server/Text/TextEncoding.cs
index bf8051d71..77cc707c1 100644
--- a/Projects/Server/Text/TextEncoding.cs
+++ b/Projects/Server/Text/TextEncoding.cs
@@ -1,6 +1,6 @@
 /*************************************************************************
  * ModernUO                                                              *
- * Copyright 2019-2023 - ModernUO Development Team                       *
+ * Copyright 2019-2025 - ModernUO Development Team                       *
  * Email: hi@modernuo.com                                                *
  * File: TextEncoding.cs                                                 *
  *                                                                       *
@@ -16,6 +16,7 @@
 using System;
 using System.Runtime.CompilerServices;
 using System.Text;
+using Server.Buffers;
 
 namespace Server.Text;
 
@@ -114,33 +115,55 @@ public static class TextEncoding
             _          => 1
         };
 
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static bool IsSafeChar(ushort c) => c is >= 0x20 and < 0xFFFE;
-
     public static string GetString(ReadOnlySpan<byte> span, Encoding encoding, bool safeString = false)
     {
-        string s = encoding.GetString(span);
-
         if (!safeString)
         {
-            return s;
+            return encoding.GetString(span);
         }
 
-        ReadOnlySpan<char> chars = s.AsSpan();
+        var charCount = encoding.GetMaxCharCount(span.Length);
 
-        using var sb = new ValueStringBuilder(stackalloc char[256]);
-        var hasDoneAnyReplacements = false;
+        char[] rentedChars = null;
+        Span<char> chars = charCount <= 256
+            ? stackalloc char[charCount]
+            : rentedChars = STArrayPool<char>.Shared.Rent(charCount);
 
-        for (int i = 0, last = 0; i < chars.Length; i++)
+        try
         {
-            if (!IsSafeChar(chars[i]) && i == chars.Length - 1)
+            var length = encoding.GetChars(span, chars);
+            chars = chars[..length];
+
+            var index = chars.IndexOfAnyExceptInRange((char)0x20, (char)0xFFFD);
+            if (index == -1)
             {
-                hasDoneAnyReplacements = true;
-                sb.Append(chars.Slice(last, i - last));
-                last = i + 1; // Skip the unsafe char
+                return new string(chars);
+            }
+
+            using var sb = charCount <= 256
+                ? new ValueStringBuilder(stackalloc char[charCount])
+                : ValueStringBuilder.Create(charCount);
+
+            while (index != -1)
+            {
+                sb.Append(chars[..index]);
+                chars = chars[(index + 1)..];
+                index = chars.IndexOfAnyExceptInRange((char)0x20, (char)0xFFFD);
+            }
+
+            if (chars.Length > 0)
+            {
+                sb.Append(chars);
+            }
+
+            return sb.ToString();
+        }
+        finally
+        {
+            if (rentedChars != null)
+            {
+                STArrayPool<char>.Shared.Return(rentedChars);
             }
         }
-
-        return !hasDoneAnyReplacements ? s : sb.ToString();
     }
 }