Minor performance improvements on hot code paths (#1947)

* Fix broken HTML tag in README.md

* Remove HttpResponseMessage allocation in hot path

* Remove iterator allocation from Select() in hot path

* Replace allocating LINQ Reverse call with pre-sized reverse loop

* Optimize reverse lookup in query string parsing

* Use Convert.ToHexString (2x faster, 1/2 memory usage)

Author: bkoelman

README.md

@@ -303,7 +303,7 @@ We are grateful to the following sponsors, who provide the team with a no-cost l
   <a href="https://www.araxis.com">
     <img align="middle" src="docs/home/assets/img/araxis-logo.png" alt="Araxis Logo" style="width:150px">
   </a>
-<p/>
+</p>
 
 Do you like this project? Consider to [sponsor](https://github.com/sponsors/json-api-dotnet), or just reward us by
 giving our repository a star.

src/JsonApiDotNetCore/Queries/Parsing/QueryExpressionParser.cs

@@ -53,7 +53,20 @@ protected virtual void Tokenize(string source)
         Source = source;
 
         var tokenizer = new QueryTokenizer(source);
-        TokenStack = new Stack<Token>(tokenizer.EnumerateTokens().Reverse());
+        Token[] tokens = tokenizer.EnumerateTokens().ToArray();
+        TokenStack = TokensToStack(tokens);
+    }
+
+    private static Stack<Token> TokensToStack(Token[] tokens)
+    {
+        var stack = new Stack<Token>(tokens.Length);
+
+        for (int index = tokens.Length - 1; index >= 0; index--)
+        {
+            stack.Push(tokens[index]);
+        }
+
+        return stack;
     }
 
     /// <summary>
@@ -143,7 +156,11 @@ protected virtual void EatSingleCharacterToken(TokenKind kind)
     {
         if (!TokenStack.TryPop(out Token? token) || token.Kind != kind)
         {
-            char ch = QueryTokenizer.SingleCharacterToTokenKinds.Single(pair => pair.Value == kind).Key;
+            if (!QueryTokenizer.TokenKindToSingleCharacterLookup.TryGetValue(kind, out char ch))
+            {
+                throw new InvalidOperationException($"Token kind '{kind}' is not a single-character token.");
+            }
+
             int position = token?.Position ?? GetNextTokenPositionOrEnd();
             throw new QueryParseException($"{ch} expected.", position);
         }

src/JsonApiDotNetCore/Queries/Parsing/QueryTokenizer.cs

@@ -1,4 +1,3 @@
-using System.Collections.ObjectModel;
 using System.Text;
 using JetBrains.Annotations;
 
@@ -7,18 +6,20 @@ namespace JsonApiDotNetCore.Queries.Parsing;
 [PublicAPI]
 public sealed class QueryTokenizer
 {
-    public static readonly IReadOnlyDictionary<char, TokenKind> SingleCharacterToTokenKinds = new ReadOnlyDictionary<char, TokenKind>(
-        new Dictionary<char, TokenKind>
-        {
-            ['('] = TokenKind.OpenParen,
-            [')'] = TokenKind.CloseParen,
-            ['['] = TokenKind.OpenBracket,
-            [']'] = TokenKind.CloseBracket,
-            ['.'] = TokenKind.Period,
-            [','] = TokenKind.Comma,
-            [':'] = TokenKind.Colon,
-            ['-'] = TokenKind.Minus
-        });
+    public static readonly IReadOnlyDictionary<char, TokenKind> SingleCharacterToTokenKinds = new Dictionary<char, TokenKind>
+    {
+        ['('] = TokenKind.OpenParen,
+        [')'] = TokenKind.CloseParen,
+        ['['] = TokenKind.OpenBracket,
+        [']'] = TokenKind.CloseBracket,
+        ['.'] = TokenKind.Period,
+        [','] = TokenKind.Comma,
+        [':'] = TokenKind.Colon,
+        ['-'] = TokenKind.Minus
+    }.AsReadOnly();
+
+    internal static readonly IReadOnlyDictionary<TokenKind, char> TokenKindToSingleCharacterLookup =
+        SingleCharacterToTokenKinds.ToDictionary(pair => pair.Value, pair => pair.Key).AsReadOnly();
 
     private readonly string _source;
     private readonly StringBuilder _textBuffer = new();

src/JsonApiDotNetCore/Serialization/Response/FingerprintGenerator.cs

@@ -7,13 +7,6 @@ namespace JsonApiDotNetCore.Serialization.Response;
 internal sealed class FingerprintGenerator : IFingerprintGenerator
 {
     private static readonly byte[] Separator = "|"u8.ToArray();
-    private static readonly uint[] LookupTable = Enumerable.Range(0, 256).Select(ToLookupEntry).ToArray();
-
-    private static uint ToLookupEntry(int index)
-    {
-        string hex = index.ToString("X2");
-        return hex[0] + ((uint)hex[1] << 16);
-    }
 
     /// <inheritdoc />
     public string Generate(IEnumerable<string> elements)
@@ -30,22 +23,6 @@ public string Generate(IEnumerable<string> elements)
         }
 
         byte[] hash = hasher.GetHashAndReset();
-        return ByteArrayToHex(hash);
-    }
-
-    private static string ByteArrayToHex(byte[] bytes)
-    {
-        // https://stackoverflow.com/questions/311165/how-do-you-convert-a-byte-array-to-a-hexadecimal-string-and-vice-versa
-
-        char[] buffer = new char[bytes.Length * 2];
-
-        for (int index = 0; index < bytes.Length; index++)
-        {
-            uint value = LookupTable[bytes[index]];
-            buffer[2 * index] = (char)value;
-            buffer[2 * index + 1] = (char)(value >> 16);
-        }
-
-        return new string(buffer);
+        return Convert.ToHexString(hash);
     }
 }

src/JsonApiDotNetCore/Serialization/Response/JsonApiWriter.cs

@@ -118,7 +118,7 @@ private static bool CanWriteBody(HttpStatusCode statusCode)
 
     private static bool IsSuccessStatusCode(HttpStatusCode statusCode)
     {
-        return new HttpResponseMessage(statusCode).IsSuccessStatusCode;
+        return (int)statusCode is >= 200 and <= 299;
     }
 
     private string RenderModel(object? model)

src/JsonApiDotNetCore/Serialization/Response/ResourceObjectTreeNode.cs

@@ -184,11 +184,11 @@ public IList<ResourceObject> GetResponseIncluded()
         HashSet<ResourceObject> primaryResourceObjectSet = GetDirectChildren().Select(node => node.ResourceObject).ToHashSet(ResourceObjectComparer.Instance);
         List<ResourceObject> includes = [];
 
-        foreach (ResourceObject include in visited.Select(node => node.ResourceObject))
+        foreach (ResourceObjectTreeNode include in visited)
         {
-            if (!primaryResourceObjectSet.Contains(include))
+            if (!primaryResourceObjectSet.Contains(include.ResourceObject))
             {
-                includes.Add(include);
+                includes.Add(include.ResourceObject);
             }
         }