fix: enforce maximum expression length in MathParser

samples/SimpleMathParser/MathParser.cs

@@ -9,15 +9,22 @@ namespace SimpleMathParser;
 /// </summary>
 public class ArenaMathParser
 {
+    private const int MaxExpressionLength = 100_000;
+
     /// <summary>
     /// Tokenizes the given math expression into a list of tokens allocated in the provided arena.
     /// </summary>
     /// <param name="input">The math expression as a span of characters.</param>
     /// <param name="arena">The arena allocator to use for memory allocations.</param>
     /// <returns>A list of <see cref="Token"/> structures.</returns>
-    /// <exception cref="SyntaxErrorException">Thrown when an unknown character is encountered.</exception>
+    /// <exception cref="SyntaxErrorException">Thrown when an unknown character is encountered or if the expression exceeds the maximum length.</exception>
     public static ArenaList<Token> Tokenize(ReadOnlySpan<char> input, ArenaAllocator arena)
     {
+        if (input.Length > MaxExpressionLength)
+        {
+            throw new SyntaxErrorException("Expression too long.");
+        }
+
         var tokens = new ArenaList<Token>(arena);
 
         int i = 0;

tests/SimpleMathParser.Tests/SimpleMathParser.Tests.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector" Version="6.0.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="FluentAssertions" Version="6.12.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\SharpArena\SharpArena.csproj" />
+    <ProjectReference Include="..\..\samples\SimpleMathParser\SimpleMathParser.csproj" />
+  </ItemGroup>
+
+</Project>

tests/SimpleMathParser.Tests/TokenizationTests.cs

@@ -0,0 +1,44 @@
+using SharpArena.Allocators;
+using SimpleMathParser;
+using Xunit;
+using FluentAssertions;
+
+namespace SimpleMathParser.Tests;
+
+public class TokenizationTests : IDisposable
+{
+    private readonly ArenaAllocator _arena = new(1024);
+
+    [Fact]
+    public void Tokenize_WhenInputExceedsMaxLength_ShouldThrowSyntaxErrorException()
+    {
+        // Arrange
+        // We'll use a large string to exceed the planned 100,000 character limit.
+        string input = new string('1', 100_001);
+
+        // Act
+        Action act = () => ArenaMathParser.Tokenize(input.AsSpan(), _arena);
+
+        // Assert
+        act.Should().Throw<SyntaxErrorException>()
+           .WithMessage("Expression too long.");
+    }
+
+    [Fact]
+    public void Tokenize_WhenInputIsWithinLimit_ShouldSucceed()
+    {
+        // Arrange
+        string input = "1 + 2";
+
+        // Act
+        var tokens = ArenaMathParser.Tokenize(input.AsSpan(), _arena);
+
+        // Assert
+        tokens.Length.Should().Be(3);
+    }
+
+    public void Dispose()
+    {
+        _arena.Dispose();
+    }
+}