Adding a Custom Middleware with the IMiddleware Interface
This article is about how to add a custom middleware with the IMiddleware interface. We will take the .NET Core documentation example of setting the Spanish culture whenever an API call is fired.
Creating the Middleware
First, we need to create the middleware. Here is the code which runs perfectly:
public class RequestCultureMiddleware : IMiddleware
{
public Task InvokeAsync(HttpContext context, RequestDelegate next)
{
CultureInfo.CurrentCulture = new CultureInfo("es-ES");
CultureInfo.CurrentUICulture = new CultureInfo("es-ES");
// Call the next delegate/middleware in the pipeline
return next(context);
}
}
public static class RequestCultureMiddlewareExtensions
{
public static IApplicationBuilder UseRequestCulture(
this IApplicationBuilder builder)
{
return builder.UseMiddleware<RequestCultureMiddleware>();
}
}
Adding the Middleware to the Pipeline
Next, we need to add the middleware to the pipeline in the Startup class:
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
//here is our custom middleware!
app.UseRequestCulture();
app.UseHttpsRedirection();
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllers();
});
}
}
Registering the Middleware
Finally, we need to register the middleware. The IMiddleware interface is part of the Microsoft.AspNetCore.Http assembly. It looks like this:
namespace Microsoft.AspNetCore.Http
{
//
// Summary:
// Defines middleware that can be added to the application's request pipeline.
public interface IMiddleware
{
//
// Summary:
// Request handling method.
//
// Parameters:
// context:
// The Microsoft.AspNetCore.Http.HttpContext for the current request.
//
// next:
// The delegate representing the remaining middleware in the request pipeline.
//
// Returns:
// A System.Threading.Tasks.Task that represents the execution of this middleware.
Task InvokeAsync(HttpContext context, RequestDelegate next);
}
}
We can register the middleware using UseMiddleware:
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
//here is our custom middleware!
app.UseRequestCulture();
// ...
}
Error
But, when running the API, we get the following error at run-time:
System.InvalidOperationException: No service for type 'WebApplication1.RequestCultureMiddleware' has been registered.
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
at Microsoft.AspNetCore.Http.MiddlewareFactory.Create(Type middlewareType)
at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.<>c__DisplayClass5_1.<<UseMiddlewareInterface>b__1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
Solution
We need to register the middleware as a service using IServiceCollection.AddSingleton:
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers();
//add our custom middleware as a service
services.AddSingleton<RequestCultureMiddleware>();
}