ASP.NET Core provides a plethora of built-in middleware components, sometimes you need to create your own to address specific requirements unique to your application. Custom middleware allows you to: Encapsulate logic: Bundle related operations (e.g., logging, security checks, custom headers) into a reusable component. Customize behavior: Tailor the request/response pipeline to precisely match your application’s needs. Improve code organization: Keep your middleware code clean and maintainable.
Anatomy of a Custom Middleware Class Implement IMiddleware: This interface requires a single method: InvokeAsync(HttpContext context, RequestDelegate next). This is the heart of your middleware’s logic. InvokeAsync or Invoke Method: context: The HttpContext provides access to the request and response objects. next: The RequestDelegate allows you to call the next middleware in the pipeline.
Code Explanation Let’s dissect the code you provided: // MyCustomMiddleware.cs namespace MiddlewareExample.CustomMiddleware { public class MyCustomMiddleware : IMiddleware { public async Task InvokeAsync(HttpContext context, RequestDelegate next) { await context.Response.WriteAsync(“My Custom Middleware – Starts\n”); await next(context); await context.Response.WriteAsync(“My Custom Middleware – Ends\n”); } }
// Extension method for easy registration public static class CustomMiddlewareExtension { public static IApplicationBuilder UseMyCustomMiddleware(this IApplicationBuilder app) { return app.UseMiddleware<MyCustomMiddleware>(); } } }
MyCustomMiddleware Class: This class implements IMiddleware. Its InvokeAsync method: Writes “My Custom Middleware – Starts” to the response. Calls next(context) to invoke the next middleware in the pipeline. Writes “My Custom Middleware – Ends” to the response after the next middleware has finished. CustomMiddlewareExtension Class: This provides a convenient extension method UseMyCustomMiddleware to register your middleware in the Startup.Configure method.
// Program.cs (or Startup.cs) using MiddlewareExample.CustomMiddleware;
// …
builder.Services.AddTransient<MyCustomMiddleware>(); // Register as transient
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Middleware app.Use vs. app.Run in Asp.net Core