netcore 从api下载文件并直接返回

[HttpGet]
        public IActionResult HttpReturnFile()
        {
            string url = "http://localhost:99/api/HttpFile/GetFile";
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "GET";
            using (WebResponse webRes = request.GetResponse())
            {
                int length = (int)webRes.ContentLength;
                HttpWebResponse response = webRes as HttpWebResponse;
                Stream stream = response.GetResponseStream();
                var contentdisposition = response.Headers["Content-Disposition"];
                var filename = Util.Midstr(contentdisposition, "filename=", ";");
                var ext = "."+filename.Split('.')[1];
                new FileExtensionContentTypeProvider().Mappings.TryGetValue(ext, out var contenttype);
                //读取到内存
                MemoryStream stmMemory = new MemoryStream();
                byte[] buffer = new byte[length];
                int i;
                //将字节逐个放入到Byte中
                while ((i = stream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    stmMemory.Write(buffer, 0, i);
                }
                stmMemory.Close();
                return File(buffer, contenttype ?? "application/octet-stream",filename);
            }
        }

 url下载文件地址