.Net 5.0 从api下载文件到本地

       /// <summary>
        /// 从Http下载文件
        /// </summary>
        /// <param name="url">文件链接</param>
        /// <param name="fileName">保存文件路径名</param>
        /// <returns></returns>
        public static string HttpDownFile(string url,string fileName)
        {
           // url = "https://paper.ysbang.cn/data/img/report/user/2018/07/16/5b4c078549c55_6531.jpg";
            var request = (HttpWebRequest)WebRequest.Create(url);
            
            request.Method = "GET";
            using (var webRes = request.GetResponse())
            {
                var length = (int)webRes.ContentLength;
                var response = webRes as HttpWebResponse;
                var stream = response?.GetResponseStream();
                var contentDisposition = response?.Headers["Content-Disposition"];
                var match = Regex.Match(contentDisposition ?? string.Empty, @"(?is)filename=""([^""]+)""s*Content-Type:([^;]+)");
                fileName +="_"+ match.Groups[1].Value;

          
                //读取到内存
                var stmMemory = new MemoryStream();
                var buffer = new byte[length];
                int i;
                //将字节逐个放入到Byte中
                while (stream != null && (i = stream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    stmMemory.Write(buffer, 0, i);
                }
                stmMemory.ToArray();//文件流Byte
                var fs = new FileStream(fileName, FileMode.OpenOrCreate);
                stmMemory.WriteTo(fs);
                stmMemory.Close();
                fs.Close();
                return fileName;
            }
        }