Create a Custom Middleware in .NET

#dotnet #csharp #middleware

Creating custom middleware in .NET is straightforward and powerful. Here's a quick step-by-step guide to help you build and register your own middleware.

First, create a folder named Middlewares to store all your custom middleware classes. Inside this folder, create a middleware called RequestIPMiddleware which is encapsulated in a class. This middleware logs the user's IP address to the console.

Here's an example.

public class RequestIPMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger _logger;

    public RequestIPMiddleware(RequestDelegate next, ILoggerFactory loggerFactory)
    {
        _next = next;
        _logger = loggerFactory.CreateLogger<RequestIPMiddleware>();
    }

    public async Task Invoke(HttpContext context)
    {
        _logger.LogInformation($"User IP: {context.Connection.RemoteIpAddress}");

        await _next.Invoke(context);
    }
}

Second, create an Extensions folder to store your middleware extension methods. Inside it, add a new static class called RequestIPExtension. This extension method allows you to easily register the middleware in your application.

public static class RequestIPExtension
{
    public static IApplicationBuilder UseRequestIP(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<RequestIPMiddleware>();
    }
}

Third, open your Program.cs file and register the custom middleware, which is exposed via an extension method, like this:

var app = builder.Build();

// your custom middleware
app.UseRequestIP();
app.UseStaticFiles();

Run your application, and you should see the user's IP address logged in the console.

If your middleware is simple and you don't want to create a separate class or extension method, you can also define an inline middleware directly in Program.cs, like this:

app.Use(async (context, next) =>
{
    var logger = context.RequestServices.GetRequiredService<ILoggerFactory>().CreateLogger("RequestIPLogger");
    logger.LogInformation($"User IP: {context.Connection.RemoteIpAddress}");

    await next(context);
});