最近有个客户要求开发一套短网址网站，小编现在都使用.net core进行网站开发了，以是厘厘思路，想想使用.net core 的中间件应该很容易实现。

1. 构建一个中间件，监测网站的响应状态，代码如下：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using NetCoreTFCMS.Domain.DbModel;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using TianFeng.FrameworkCore.DapperEx;
namespace NetCoreTFCMS.MiddleWare
{
    public static class RequestIPExtensions
    {
        public static IApplicationBuilder UseWatchNoFound(this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<WatchNoFoundMiddleWare>();
        }
    }
    public class WatchNoFoundMiddleWare
    {
        private readonly RequestDelegate _next;
        private readonly ILogger logger;
        public WatchNoFoundMiddleWare(RequestDelegate next, ILoggerFactory loggerFactory)
        {
            _next = next;
            logger = loggerFactory.CreateLogger<WatchNoFoundMiddleWare>();
        }
        public async Task Invoke(HttpContext context)
        {
            await _next.Invoke(context);
            var path = context.Request.Path.ToString().Trim();
            if (path.LastIndexOf("/") == 0)
            {
                var salt = path.Replace("/", "");
                if (Regex.IsMatch(salt, @"^[a-zA-Z0-9]{6}$"))
                {
                    var db = (IDbService)context.RequestServices.GetService(typeof(IDbService));
                    var model = await db.GetModelAsync<Link>(new { Salt = salt });
                    if (model != null)
                    {
                        if (!Regex.IsMatch(model.SiteUrl, "(file|gopher|news|nntp|telnet|http|ftp|https|ftps|sftp)://", RegexOptions.IgnoreCase))
                        {
                             model.SiteUrl = "http://" + model.SiteUrl;
                        }
                        context.Response.Redirect(model.SiteUrl, true);
                    }
                    else
                    {
                        logger.LogInformation(salt + "无匹配网址");
                    }
                }
            }
        }
    }
}