一、维信支付退款错误：基础连接已经关闭的错误

原因：退款操作接口是https 的地址。

解决方案：发起请求时开启tls/ssl 通道，添加安全证书。

推荐示例代码1：

/// 
        /// 指定Post地址使用Get 方式获取全部字符串        /// 
        /// 请求后台地址        /// Post提交数据内容(utf-8编码的)        /// 
            public static string PostSsl3(string url, string content)        {            string result = "";            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);            req.Method = "POST";            req.ContentType = "application/x-www-form-urlencoded";            //添加证书            X509Certificate2 certificate = new X509Certificate2(@"F:\Mvc_Site\zzy\QL.MiniMall.LA_SZ\cert\apiclient_cert.p12", "1530564111", X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.MachineKeySet);            req.ClientCertificates.Add(certificate);            //设置安全模式            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls | SecurityProtocolType.Ssl3;            #region 添加Post 参数            byte[] data = Encoding.UTF8.GetBytes(content);            req.ContentLength = data.Length;            using (Stream reqStream = req.GetRequestStream())            {                reqStream.Write(data, 0, data.Length);                reqStream.Close();            }            #endregion            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();            Stream stream = resp.GetResponseStream();            //获取响应内容            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))            {                result = reader.ReadToEnd();            }            return result;        }

解决方案代码示例2：

public static string PostWebRequest(string postUrl, string paramData)        {            string ret = string.Empty;            try            {                X509Certificate2 certificate = new X509Certificate2(@"E:\工作项目\apiclient_cert.p12", "1519238551", X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.MachineKeySet);   //初始化证书                byte[] byteArray = Encoding.Default.GetBytes(paramData); //转化                HttpWebRequest webReq = (HttpWebRequest)WebRequest.Create(new Uri(postUrl));                webReq.Method = "POST";                webReq.ContentType = "application/x-www-form-urlencoded";                webReq.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)";                webReq.ClientCertificates.Add(certificate);     //添加证书                webReq.ContentLength = byteArray.Length;                                      Stream newStream = webReq.GetRequestStream();   //                newStream.Write(byteArray, 0, byteArray.Length);//写入参数                 ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls | SecurityProtocolType.Ssl3;                HttpWebResponse response = (HttpWebResponse)webReq.GetResponse();       //这里报错                StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);                ret = sr.ReadToEnd();                newStream.Close();                sr.Close();                response.Close();                newStream.Close();            }            catch (Exception ex)            {                return ex.Message;            }            return ret;         }