How to create conventional middleware in C# ASP.NET Core
Middleware is a crucial component in ASP.NET Core applications. It allows us to handle requests and responses in a flexible and organized manner. We’ll explore how to create conventional middleware in C# ASP.NET Core, which enables us to intercept HTTP requests and responses.
Understanding middleware
Middleware in ASP.NET Core sits between the client and the server, processing requests and responses. It’s like a pipeline through which every request passes, allowing it to perform various tasks such as logging, authentication, authorization, and more.
Creating conventional middleware
Let’s dive into creating a conventional middleware component step by step.
Creating the middleware class
First, we need to create a class for our middleware. This class should have a method named InvokeAsync, which accepts HttpContext and RequestDelegate parameters. Here’s a simple example:
using Microsoft.AspNetCore.Builder;using Microsoft.AspNetCore.Http;using System;using System.Threading.Tasks;namespace CustomMiddleware{public class MyCustomMiddleware : IMiddleware{public async Task InvokeAsync(HttpContext context, RequestDelegate next){await context.Response.WriteAsync("Hello middleware\n");//Perform middleware logicawait next(context); // call the next middleware}}public static class MyCustomMiddlewareExtensions{public static IApplicationBuilder UseMyCustomMiddleware(this IApplicationBuilder app){return app.UseMiddleware<MyCustomMiddleware>();}}}
In the code, a class named MyCustomMiddleware is defined which has an inheritance from IMiddleware:
Line 8: The
MyCustomMiddlewareclass implements theIMiddlewareinterface, which requires the implementation of theInvokeAsyncmethod (line 10). This method is called to handle each HTTP request.Line 18: The
MyCustomMiddlewareExtensionsclass contains an extension methodUseMyCustomMiddlewarethat extends theIApplicationBuilderinterface (lines 20–23). This method adds theMyCustomMiddlewareto the middleware pipeline. It uses theUseMiddlewaremethod (line 22), passingMyCustomMiddlewareas the middleware type.
Implementing the middleware logic
Inside the InvokeAsync method of MyCustomMiddleware, we can implement the logic that needs to be executed before or after the next middleware. For example, we print “Hello middleware” on the browser:
public async Task InvokeAsync(HttpContext context, RequestDelegate next){await context.Response.WriteAsync("Hello middleware\n");//Perform middleware logicawait next(context); // call the next middleware}
Registering the middleware
Next, we need to register our middleware in the Program.cs file. Add the following line:
builder.Services.AddTransient<MyCustomMiddleware>(); // Register the middleware as service// Use the middleware using extension methodapp.UseMyCustomMiddleware();
Line 3 tells ASP.NET
Core to use our MyCustomMiddleware for processing requests.
Example code
Let’s create a simple middleware that prints “Hello Middleware” as an example. Press the “Run” button to execute the code:
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using System;
using System.Threading.Tasks;
namespace CustomMiddleware
{
public class MyCustomMiddleware : IMiddleware
{
public async Task InvokeAsync(HttpContext context, RequestDelegate next)
{
await context.Response.WriteAsync("Hello middleware\n");
//Perform middleware logic
await next(context); // call the next middleware
}
}
public static class MyCustomMiddlewareExtensions
{
public static IApplicationBuilder UseMyCustomMiddleware(this IApplicationBuilder app)
{
return app.UseMiddleware<MyCustomMiddleware>();
}
}
}
We can see that our custom middleware gets executed before the main logic ("Hello world" in this case) when the / request is executed by the browser.
Conclusion
Middleware is a powerful feature in ASP.NET Core that allows us to intercept and process HTTP requests and responses. By creating conventional middleware, we can easily add custom logic to our application’s request pipeline. We’ve covered the basics of creating and using middleware in ASP.NET Core. Experiment with different middleware components to enhance the functionality and behavior of your applications.
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