🧩 Building Custom Middleware in ASP.NET Core – A Practical Guide

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Published on: June 5, 2025

Category: Real-World Use Case

Tags: ASP.NET Core, Middleware, .NET 8, Request Pipeline, Web API, Real World .NET, Coding Practices

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🧱 What is Middleware in ASP.NET Core?

Middleware is code that:

• Handles an incoming HTTP request
• Can pass the request to the next component in the pipeline
• Optionally does something after the next component completes

📌 Real-World Scenario: Execution Time Logger Middleware

You want to log how long each request takes to execute — useful for performance monitoring.

🔧 Step-by-Step: Create the Middleware

✅ 1. Create a Middleware Class

public class RequestTimingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestTimingMiddleware> _logger;

    public RequestTimingMiddleware(RequestDelegate next, ILogger<RequestTimingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var watch = Stopwatch.StartNew();
        await _next(context);
        watch.Stop();

        var elapsedMs = watch.ElapsedMilliseconds;
        _logger.LogInformation($"Request took {elapsedMs} ms");
    }
}

✅ 2. Register the Middleware in Program.cs

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.UseMiddleware<RequestTimingMiddleware>();

app.MapControllers();
app.Run();

🧠 Best Practices for Custom Middleware

• Keep it small and single-responsibility
• Always call _next(context) or the pipeline breaks
• Use ILogger instead of Console.WriteLine
• Avoid blocking operations; use async/await

🔍 Other Real-World Use Cases:

• Add custom headers
• Request/response transformation
• IP whitelisting or filtering
• Audit logging
• API key validation

🧠 Pro Tip

To conditionally apply middleware only in development:

if (env.IsDevelopment())
{
    app.UseMiddleware<SomeDebugMiddleware>();
}

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• 📧 Email: seajaygangwar@gmail.com

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