C# Asp.net core middleware for redirecting URLs

Question

I wrote a small middleware for redirecting between WWW URLs.

The most important thing that I want to change is to make it super fast.

Here's what it is doing:

If the host is localhost or mywebsite.com without any subdomains and without www, it will redirect to www.localhost or www.mywebsite.com.

If the host starts with www. AND has subdomains, it will redirect to a url without www.

using System;
using System.Threading.Tasks;
using System.Text.RegularExpressions;
 
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Builder;
 
using Microsoft.Extensions.Logging;
 
 
namespace Website.Middlewares
{
 
    public class WWWRedirectionMiddleware
    {
        private readonly RequestDelegate _next;
 
        private string _domain;
        private int _https_port;
 
        public WWWRedirectionMiddleware(RequestDelegate next)
        {
            _next = next;
        }
 
        public async Task InvokeAsync(HttpContext context)
        {
 
            var request = context.Request;
            var response = context.Response;
 
            var host = request.Host;
 
            if (Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") == "Development")
            {
                _domain = "localhost";
                _https_port = 5001;
            } 
            else
            {
                _domain = "seaoftools.com";
                _https_port = 80;
            }
 
            // Redirect to www domain if url is home page
            if (host.Host.Equals(_domain, StringComparison.OrdinalIgnoreCase))
            {
                host = new HostString("www." + host.Host, _https_port);
 
                var redirectUrl = UriHelper.BuildAbsolute(
                    "https", 
                    host,
                    request.PathBase,
                    request.Path,
                    request.QueryString);
 
                response.Redirect(redirectUrl, true);
                return;
            } // Redirect to non-www domain if url is with a subdomain 
            else if (host.Value.StartsWith("www.", StringComparison.OrdinalIgnoreCase)
                     && Regex.Replace(host.Host, @"www.|" + _domain, String.Empty) != String.Empty)
            { 
                host = new HostString(host.Host.Replace("www.", String.Empty), _https_port);
 
                var redirectUrl = UriHelper.BuildAbsolute(
                    "https", 
                    host,
                    request.PathBase,
                    request.Path,
                    request.QueryString);
 
                response.Redirect(redirectUrl, true);
                return;
            }
 
            await _next(context);
        }
    }
 
}

What should I change to make the middleware run faster?

Answer 1

Quick remarks:

• _https_port: do not use underscores in variable names etc., except at the start.

• _https_port = 80; The HTTPS port is most definitely not port 80.

• The logic to fill redirectUrl and then redirect is duplicated. It should be a method that gets called. I'd move the "compile new host value in these specific cases" logic to a method and return the resulting HostString, then compare that HostString to the existing host and execute the redirect if they're different.

• The string "www." is repeatedly used. It would be better to store it in a const string. Same for "https".

• In one if you say host.Host, yet in the other you say host.Value.

• Microsoft has guidelines against using more than three capital letters in a row. So "WWW" should become "Www" when it is part of a class name or method name etc.

Answer 2

If you add IWebHostEnvironment as a dependency to the middleware class, you can simplify the environment check by this:

if (webHostEnvironment.IsDevelopment())
{
        
}

Answer 3

My final code after all of the optimization:

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

namespace Website.Middlewares
{
    public class WwwRedirectionMiddleware
    {
        private readonly RequestDelegate _next;

        private string _domain;
        private int _httpsPort;

        public WwwRedirectionMiddleware(RequestDelegate next, IWebHostEnvironment webHostEnvironment)
        {
            _next = next;

            _domain = webHostEnvironment.IsDevelopment() ? "localhost" : "seaoftools.com";
            _httpsPort = webHostEnvironment.IsDevelopment() ? 5001 : 443;
        }

        public async Task InvokeAsync(HttpContext context)
        {
            bool IsRedirectNeeded = false;

            var request = context.Request;
            var response = context.Response;

            var host = request.Host;

            string WwwString = "www.";

            string HostWithoutWww = host.Host.Replace(WwwString, String.Empty);

            string HostWithWww = WwwString + host.Host;

            // Redirect to www domain if url is home page
            if (host.Host.Equals(_domain, StringComparison.OrdinalIgnoreCase))
            {
                host = new HostString(HostWithWww, _httpsPort);

                IsRedirectNeeded = true;
            } // Redirect to non-www domain if url is with a subdomain
            else if (host.Host.StartsWith(WwwString, StringComparison.OrdinalIgnoreCase) && host.Host.Split(".").Length > 2)
            {
                host = new HostString(HostWithoutWww, _httpsPort);

                IsRedirectNeeded = true;
            }

            if (IsRedirectNeeded)
            {
                var redirectUrl =
                    UriHelper
                        .BuildAbsolute("https",
                        host,
                        request.PathBase,
                        request.Path,
                        request.QueryString);

                response.Redirect(redirectUrl, true);
                return;
            }

            await _next(context);
        }
    }
}
```