.NET Middleware

Middleware is software assembled into a pipeline to handle request and responses. Each component:

  • Chooses if he passes the request to the next component.
  • Can perform work before and after the next component.

Common use cases:

  • Logging
  • Authentication & Authorization
  • Request/Response processing
  • Caching
  • Error handling

.NET middleware

Implementation w. DI

For more details check this project

We create our own custom middleware with an internal dependency, which is the class it’s going to process before/after our request.

// interface and its class, which do the processing
public interface IMiddlewareService
{
	Task ProcessRequest(string request);
}

// interface implementation
public class MiddlewareService : IMiddlewareService
{
	public async Task ProcessRequest(string request)
	{
		// do something with the request
		Console.WriteLine(request);
	}
}

Then we have our middleware class as such

public class CustomMiddleware(IMiddlewareService _service) : IMiddleware
{
	public async Task InvokeAsync(HttpContext context, RequestDelegate next)
	{
		// custom logic to be executed BEFORE next middleware
		await _service.ProcessRequest("middleware processing request");
		await next(context);
		// custom logic to be executed AFTER next middleware
	}
}

Declaration inside Startup.cs

public void ConfigureServices(IServiceCollection services)
{
	// ... whatever

	// register both: our custom middleware, and its internal dependency
	services.AddTransient<IMiddlewareService, MiddlewareService>();
	services.AddTransient<CustomMiddleware>();
	
	// ... whatever else
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
	// ... whatever

	// declaration to use middleware
	app.UseMiddleware<CustomMiddleware>();
	// if we use this, the middleware declaration has to be BEFORE or else it won't work
	app.UseEndpoints(endpoints => 
	{
		endpoints.MapControllers();
	})

	// ... whatever else
}

Reference(s)

https://medium.com/@dushyanthak/best-practices-for-writing-custom-middlewares-in-asp-net-core-97b58c50cf9c
https://learn.microsoft.com/es-es/aspnet/core/fundamentals/middleware/write?view=aspnetcore-8.0
https://sardarmudassaralikhan.medium.com/custom-middleware-in-asp-net-core-web-api-70c2ffbbc095