ASP.Net MVC:How to rewrite url by middleware in ASP.NET Core

You pretty much just need to move the code to a middleware class, and use the Core HttpContext instead of the System.Web one.

A class like that would look like this:

//RedirectMiddleware.cs

public class RedirectMiddleware
{
    private readonly RequestDelegate _next;

    public RedirectMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        string CountryCodeInUrl = "", redirectUrl = "";
        var countryCode = CookieSettings.ReadCookie();
        if (countryCode == "")
        {
            countryCode = "gb";
        }

        if (context.Request.Path.Value.Length >= 2)
        {
            CountryCodeInUrl = context.Request.Path.Value.Substring(1, 2);
        }

        if (countryCode != CountryCodeInUrl)
        {
            if (context.Request.Path.Value.Length >= 2)
            {
                if (context.Request.Path.Value.Substring(1, 2) != "")
                {
                    countryCode = context.Request.Path.Value.Substring(1, 2);
                }
            }
            if (!context.Request.Path.Value.Contains(countryCode))
            {
                redirectUrl = string.Format("/{0}{1}", countryCode, context.Request.Path.Value);
            }
            else
            {
                redirectUrl = context.Request.Path.Value;
            }
            CookieSettings.SaveCookie(countryCode);
            context.Response.Redirect(redirectUrl, true);
        }

        await _next.Invoke(context);
    }
}

To use it you then register it in you Startup.cs file, before you register the MVC middleware, like this:

app.UseMiddleware<RedirectMiddleware>();

app.UseMvc(routes =>
{
    routes.MapRoute(
        name: "default",
        template: "{controller=Home}/{action=Index}/{id?}");
});

I hope this'll get you started, you can see this blog post for more information on middleware.

As long as you insert the rewrite middleware before other middleware that fires you can re-write the Context.Request.Path in the middleware code.

The Path is writable and any subsequent code/middleware will use the new path to process the request.

Using self-contained (app.Use()) middleware you can do:

app.Use(async (context,next) =>
{
    var url = context.Request.Path.Value;

    // Rewrite privacy URL to index
    if (url.Contains("/home/privacy"))
    {
        // rewrite to index
        context.Request.Path = "/home/index";
    }

    await next();
});

Unlike the Repsonse.Redirect() (which fires a new server request) the URL of the original request is not changed by this operation.

More info in this blog post:

Back to Basics: URL Rewriting in ASP.NET Core