How to Safely Execute Dynamic C# Code at Runtime Using Roslyn

Executing dynamic C# code at runtime can be powerful but also comes with security and performance risks. Microsoft’s Roslyn compiler provides a way to compile and execute C# code dynamically while offering safety mechanisms.

This guide walks through how to use Roslyn to safely evaluate and run C# code at runtime.

Why Use Roslyn for Dynamic Code Execution?

Roslyn enables runtime compilation of C# code, making it useful for:

  • Scripting engines within applications.
  • Plugins and extensibility without recompiling the main application.
  • Interactive debugging and testing scenarios.
  • Custom formula evaluations in applications like rule engines.

Step 1: Install Roslyn Dependencies

To use Roslyn for dynamic execution, install the necessary NuGet packages:

Install-Package Microsoft.CodeAnalysis.CSharp.Scripting
Install-Package Microsoft.CodeAnalysis.Scripting

Step 2: Basic Execution of Dynamic Code

A simple way to execute dynamic C# code using Roslyn:

using System;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CSharp.Scripting;
using Microsoft.CodeAnalysis.Scripting;

class Program
{
    static async Task Main()
    {
        string code = "1 + 2";
        var result = await CSharpScript.EvaluateAsync<int>(code);
        Console.WriteLine("Result: " + result);
    }
}

Step 3: Providing Context for Execution

To allow dynamic scripts to use variables and functions from your main program, use a custom script state:

class ScriptGlobals
{
    public int X { get; set; } = 10;
}

var options = ScriptOptions.Default.AddReferences(typeof(ScriptGlobals).Assembly);
string code = "X * 2";
var result = await CSharpScript.EvaluateAsync<int>(code, options, new ScriptGlobals());
Console.WriteLine(result); // Output: 20

Step 4: Handling Exceptions in Dynamic Code

Since executing untrusted code can lead to runtime errors, wrap execution in try-catch:

try
{
    string invalidCode = "int x = 1 / 0;";
    await CSharpScript.EvaluateAsync(invalidCode);
}
catch (CompilationErrorException ex)
{
    Console.WriteLine("Compilation Error: " + string.Join("\n", ex.Diagnostics));
}
catch (Exception ex)
{
    Console.WriteLine("Runtime Error: " + ex.Message);
}

Step 5: Security Considerations

Executing user-provided code can be risky. Follow these best practices:

1. Use a Restricted Execution Context

Limit the namespaces and APIs available to the script:

var options = ScriptOptions.Default
    .AddReferences(typeof(object).Assembly) // Only essential assemblies
    .WithImports("System"); // Restrict available namespaces

2. Limit Execution Time

Run code in a separate thread with a timeout:

using System.Threading;
using System.Threading.Tasks;

var cts = new CancellationTokenSource(TimeSpan.FromSeconds(2));
try
{
    var task = CSharpScript.EvaluateAsync("while(true) {}", cancellationToken: cts.Token);
    await task;
}
catch (OperationCanceledException)
{
    Console.WriteLine("Execution Timed Out");
}

3. Use AppDomain Sandboxing (For Older .NET Versions)

In older .NET Framework applications, AppDomains can be used to isolate script execution. However, .NET Core and later versions no longer support AppDomains.

Step 6: Running More Complex Scripts with State

For multi-line scripts, use RunAsync instead of EvaluateAsync:

string script = @"
int Multiply(int a, int b) => a * b;
return Multiply(3, 4);
";
var result = await CSharpScript.RunAsync(script);
Console.WriteLine(result.ReturnValue); // Output: 12

Conclusion

Roslyn provides a powerful way to execute C# code dynamically while maintaining security and control. By following best practices such as limiting execution scope, handling errors, and enforcing timeouts, you can safely integrate dynamic scripting into your applications without exposing them to excessive risk.

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Related

String interpolation, introduced in C# 6.0, provides a more readable and concise way to format strings compared to traditional concatenation (+) or string.Format(). Instead of manually inserting variables or placeholders, you can use the $ symbol before a string to directly embed expressions inside brackets.

string name = "Walt";
string job = 'Software Engineer';

string message = $"Hello, my name is {name} and I am a {job}";
Console.WriteLine(message);

This would produce the final output of:

Hello, my name is Walt and I am a Software Engineer

String interpolation can also be chained together into a multiline string (@) for even cleaner more concise results:

string name = "Walt";
string html = $@"
    <div>
        <h1>Welcome, {name}!</h1>
    </div>";
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143

XML (Extensible Markup Language) is a widely used format for storing and transporting data.

In C#, you can create XML files efficiently using the XmlWriter and XDocument classes. This guide covers both methods with practical examples.

Writing XML Using XmlWriter

XmlWriter provides a fast and memory-efficient way to generate XML files by writing elements sequentially.

Example:

using System;
using System.Xml;

class Program
{
    static void Main()
    {
        using (XmlWriter writer = XmlWriter.Create("person.xml"))
        {
            writer.WriteStartDocument();
            writer.WriteStartElement("Person");

            writer.WriteElementString("FirstName", "John");
            writer.WriteElementString("LastName", "Doe");
            writer.WriteElementString("Age", "30");

            writer.WriteEndElement();
            writer.WriteEndDocument();
        }
        Console.WriteLine("XML file created successfully.");
    }
}

Output (person.xml):

<?xml version="1.0" encoding="utf-8"?>
<Person>
    <FirstName>John</FirstName>
    <LastName>Doe</LastName>
    <Age>30</Age>
</Person>

Writing XML Using XDocument

The XDocument class from LINQ to XML provides a more readable and flexible way to create XML files.

Example:

using System;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        XDocument doc = new XDocument(
            new XElement("Person",
                new XElement("FirstName", "John"),
                new XElement("LastName", "Doe"),
                new XElement("Age", "30")
            )
        );
        doc.Save("person.xml");
        Console.WriteLine("XML file created successfully.");
    }
}

This approach is ideal for working with complex XML structures and integrating LINQ queries.

When to Use Each Method

  • Use XmlWriter when performance is critical and you need to write XML sequentially.
  • Use XDocument when you need a more readable, maintainable, and flexible way to manipulate XML.

Conclusion

Writing XML files in C# is straightforward with XmlWriter and XDocument. Choose the method that best suits your needs for performance, readability, and maintainability.

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Slow initial load times can drive users away from your React application. One powerful technique to improve performance is lazy loading - loading components only when they're needed.

Let's explore how to implement this in React.

The Problem with Eager Loading

By default, React bundles all your components together, forcing users to download everything upfront. This makes navigation much quicker and more streamlined once this initial download is complete.

However, depending on the size of your application, it could also create a long initial load time.

import HeavyComponent from './HeavyComponent';
import AnotherHeavyComponent from './AnotherHeavyComponent';

function App() {
  return (
    <div>
      {/* These components load even if user never sees them */}
      <HeavyComponent />
      <AnotherHeavyComponent />
    </div>
  );
}

React.lazy() to the Rescue

React.lazy() lets you defer loading components until they're actually needed:

import React, { lazy, Suspense } from 'react';

// Components are now loaded only when rendered
const HeavyComponent = lazy(() => import('./HeavyComponent'));
const AnotherHeavyComponent = lazy(() => import('./AnotherHeavyComponent'));

function App() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <HeavyComponent />
        <AnotherHeavyComponent />
      </Suspense>
    </div>
  );
}

Route-Based Lazy Loading

Combine with React Router for even better performance:

import React, { lazy, Suspense } from 'react';
import { BrowserRouter, Routes, Route } from 'react-router-dom';

const Home = lazy(() => import('./pages/Home'));
const Dashboard = lazy(() => import('./pages/Dashboard'));
const Settings = lazy(() => import('./pages/Settings'));

function App() {
  return (
    <BrowserRouter>
      <Suspense fallback={<div>Loading...</div>}>
        <Routes>
          <Route path="/" element={<Home />} />
          <Route path="/dashboard" element={<Dashboard />} />
          <Route path="/settings" element={<Settings />} />
        </Routes>
      </Suspense>
    </BrowserRouter>
  );
}

Implement these techniques in your React application today and watch your load times improve dramatically!

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