What is middleware in ASP.NET Core and how does it work?

Middleware in ASP.NET Core is software components that are placed in the request processing pipeline to handle requests and responses in a modular and composable way. Each middleware component in the pipeline performs a specific task, such as authentication, routing, logging, or caching, and can be added or removed as needed to create custom request processing pipelines.

The middleware pipeline in ASP.NET Core is composed of one or more middleware components that are executed sequentially in the order they are added. Each middleware component can perform some operation on the incoming request or outgoing response, such as modifying headers, redirecting requests, or returning a response directly.

Here's an example of how middleware works in ASP.NET Core:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)

{

if (env.IsDevelopment())

{

     app.UseDeveloperExceptionPage();

}

else

{

     app.UseExceptionHandler("/Error");

     app.UseHsts();

}

app.UseHttpsRedirection();

app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.UseEndpoints(endpoints =>

{

     endpoints.MapControllers();

});

}

In this example, the Configure method in the Startup class sets up the middleware pipeline for an

ASP.NET Core application. The first middleware component is the DeveloperExceptionPage middleware, which displays detailed error information in the response when running in development mode. This middleware is only added to the pipeline if the application is running in development mode.

The next middleware component is the ExceptionHandler middleware, which handles exceptions that occur during request processing and returns an error response. This middleware is added to the pipeline for all environments.

The HttpsRedirection middleware and StaticFiles middleware handle HTTP redirection and static file serving, respectively. These middleware components are added to the pipeline for all requests.

The Routing middleware and Authorization middleware handle routing and authentication/authorization, respectively. These middleware components are added to the pipeline for all requests.

Finally, the Endpoints middleware maps the incoming requests to the appropriate controller action method based on the route template. This middleware is added to the pipeline for all requests.

By composing middleware components in this way, you can build custom request processing pipelines that handle requests and responses in a flexible and modular way.