public class OuterImgMiddleware

    {

        public static string RootPath { get; set; } //配置文件读取绝对位置

        private readonly RequestDelegate _next;

        public OuterImgMiddleware(RequestDelegate next, IHostingEnvironment env)

        {

            _next = next;

        }

        public async Task Invoke(HttpContext context)

        {

            var path = context.Request.Path.ToString();

            var headersDictionary = context.Request.Headers;

            if (context.Request.Method == "GET")

                if (!string.IsNullOrEmpty(path) && path.Contains("/upload/logo"))

                {

                    var unauthorizedImagePath = RootPath + path;

                    context.Response.ContentType = "image/jpeg";

                    context.Response.Headers["Cache-Control"] = "public"; //指定客户端，服务器都处理缓存

                    int length = path.LastIndexOf(".") - path.LastIndexOf("/") - ;

                    context.Response.Headers["Etag"] = path.Substring(path.LastIndexOf("/") + , length);

                    context.Response.Headers["Last-Modified"] = new DateTime().ToString("r");

                    FileInfo file = new FileInfo(unauthorizedImagePath);

                    context.Response.Headers["Content-Length"] = file.Length.ToString();

                    context.Response.Headers["Accept-Ranges"] = "bytes";

                    //如果Transfer-Encoding =chunked 没有指定的话，SendFile 前台解析事变

                    //指定Content-Length 可以是 chunked 分块实效

                    //context.Response.Headers["Transfer-Encoding"] = "";

                    //Http 1.0 是使用Expires 属性

                    //context.Response.Headers["Expires"] = DateTime.Now.AddMonths(1).ToString("r");

                    await context.Response.SendFileAsync(unauthorizedImagePath);

                    return;

                }

            await _next(context);

        }

    }

    public static class MvcExtensions

    {

        public static IApplicationBuilder UseOutImg(this IApplicationBuilder builder)

        {

            return builder.UseMiddleware<OuterImgMiddleware>();

        }

    }