What is a Middleware?
A Middleware component is a custom component that encapsulates a specific functionality and executes during a request pipeline in an ASP.NET Core web application. A Middleware replaces a HttpModule and a HttpHandler of the .NET Framework in .NET Core.
A logical component (a class or a method) can be configured into a middleware by registering it under the Configure() method of the Startup class. It can be done as below.
How to configure a Middleware?
Logically, there are 3 ways in which you can configure a custom Middleware in an ASP.NET Core application.
Inline Middleware Definition
Takes a constructor parameter of RequestDelegate and uses it to navigate to next component, or a simple method delegate within the Configure method as below.
app.Use(async (context, next) =>
{
// Custom middleware logic
await context.Response.WriteAsync("Hello from Inline Middleware!\n");
// Call the next middleware in the pipeline
await next();
});Custom Middleware Class
If the logic to be implemented is complex or involves multiple services to be injected, we can create a custom class that encapsulates all the logic and register as a middleware – using the UseMiddleware generic method where the type of the middleware class is passed.
public class MyHelloMiddleware
{
private readonly RequestDelegate _next;
public MyHelloMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task InvokeAsync(HttpContext context)
{
// Custom middleware logic
await context.Response.WriteAsync("Hello from Middleware Class!\n");
// Call the next middleware in the pipeline
await _next(context);
}
}
// In the Configure method
app.UseMiddleware<MyHelloMiddleware>();Using Extension Method
You can further extend this by creating a separate extension method over the IApplicationBuilder interface and then calling the method directly.
public class MyHelloMiddleware
{
private readonly RequestDelegate _next;
public MyHelloMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task InvokeAsync(HttpContext context)
{
// Custom middleware logic
await context.Response.WriteAsync("Hello from Middleware Class!\n");
// Call the next middleware in the pipeline
await _next(context);
}
}
public static class CustomMiddlewareExtensions
{
public static IApplicationBuilder UseHello(this IApplicationBuilder builder)
{
return builder.UseMiddleware<MyHelloMiddleware>();
}
}
// In the Configure method
app.UseHello();
