关于WebClient超时问题

在用C#实现一个Http消息推送时，用了WebClient.UpdateString，结果发现该函数在http消息没有返回时会被阻塞。

经测试，阻塞超时是100秒。如果使用默认超时，将会大大影响推送效率，经检索资料，发现WebClient类没有超时设置。

这里查到有两种方案解决。

方案1

 重写WebClient类，增加超时设置，实现起来还是比较简单

public class WebClientEx : WebClient {     public int Timeout {get; set;}     protected override WebRequest GetWebRequest(Uri address)     {        var request = base.GetWebRequest(address);        request.Timeout = Timeout;        return request;     } }

使用

var myClient = new WebClientEx(); myClient.Timeout = 900000 // Daft timeout period myClient.UploadData(myUri, myData);

方案2

使用异步方法 WebClient.UploadStringAsync (Uri, String) 

此方法的缺点是，一旦调用失败，无法直接获取调用的url，但也很容易解决，有两个办法

1）使用WebClient.UploadStringAsync (Uri, String, String, Object)这个方法，第三个参数可以存放自定义数据

然后在回调函数中从 e.UserState中获取；

2）同方案1中重写WebClient类，并添加成员变量m_url，调用时自己保存相关信息，等进入回调函数时可以使用。

相关代码：

private static void UploadStringCallback2(Object sender, UploadStringCompletedEventArgs e)        {            //string reply = (string)e.Result; 发生异常时Result是null，正常时是返回信息            WebClientEx wc = (WebClientEx)sender;            string str = wc.GetRequestURL();            string strlog = e.UserState.ToString();            strlog = e.Error.ToString();            }        }        public class WebClientEx : WebClient        {            public string m_strURL;            public int Timeout { get; set; }            protected override WebRequest GetWebRequest(Uri address)            {                var request = base.GetWebRequest(address);                request.Timeout = Timeout;                m_strURL = address.OriginalString;                return request;            }            public string GetRequestURL()            {                return m_strURL;            }        }//===使用WebClientEx wc = new WebClientEx();            //WebClient wc = new WebClientEx();            //wc.Timeout = 3000;            wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded");//可以post提交            wc.Encoding = Encoding.UTF8;            //string[] pinfo = ConfigurationManager.AppSettings["EnableProxy"].Split('|');            //if (pinfo[0].ToLower() == "true")            //{            //wc.Proxy = new WebProxy(pinfo[1], int.Parse(pinfo[2]));            //}            string postData = "a=12345&b=abcde";            string m_url = "http://localhost:16910/testpost.ashx";            wc.m_strURL = m_url;            string result = "";            Stopwatch timer = new Stopwatch();            wc.UploadStringCompleted += new UploadStringCompletedEventHandler(UploadStringCallback2);            timer.Start();            try            {                wc.UploadStringAsync(new Uri(m_url), "POST", postData, (object)m_url);                //wc.UploadString(m_url, postData);            }            catch (System.Exception ex)            {                result = ex.Message;            }            timer.Stop();            result +=" use:" +(timer.ElapsedMilliseconds / 1000).ToString();

另，在使用异步下载时，有朋友说网络中断会导致卡死，并给了解决方案，贴在这里备用

创建计时器监视响应情况，过期则取消下载

      

    public class Calculagraph
    {
        /// <summary>
        /// 时间到事件
        /// </summary>
        public event TimeoutCaller TimeOver;

        /// <summary>
        /// 开始时间
        /// </summary>
        private DateTime _startTime;
        private TimeSpan _timeout = new TimeSpan(0, 0, 10);
        private bool _hasStarted = false;
        object _userdata;

        /// <summary>
        /// 计时器构造方法
        /// </summary>
        /// <param name="userdata">计时结束时回调的用户数据</param>
        public Calculagraph(object userdata)
        {
            TimeOver += new TimeoutCaller(OnTimeOver);
            _userdata = userdata;
        }

        /// <summary>
        /// 超时退出
        /// </summary>
        /// <param name="userdata"></param>
        public virtual void OnTimeOver(object userdata)
        {
            Stop();
        }

        /// <summary>
        /// 过期时间(秒)
        /// </summary>
        public int Timeout
        {
            get
            {
                return _timeout.Seconds;
            }
            set
            {
                if (value <= 0)
                    return;
                _timeout = new TimeSpan(0, 0, value);
            }
        }

        /// <summary>
        /// 是否已经开始计时
        /// </summary>
        public bool HasStarted
        {
            get
            {
                return _hasStarted;
            }
        }

        /// <summary>
        /// 开始计时
        /// </summary>
        public void Start()
        {
            Reset();
            _hasStarted = true;
            Thread th = new Thread(WaitCall);
            th.IsBackground = true;
            th.Start();
        }

        /// <summary>
        /// 重置
        /// </summary>
        public void Reset()
        {
            _startTime = DateTime.Now;
        }

        /// <summary>
        /// 停止计时
        /// </summary>
        public void Stop()
        {
            _hasStarted = false;
        }

        /// <summary>
        /// 检查是否过期
        /// </summary>
        /// <returns></returns>
        private bool checkTimeout()
        {
            return (DateTime.Now - _startTime).Seconds >= Timeout;
        }

        private void WaitCall()
        {
            try
            {
                //循环检测是否过期
                while (_hasStarted && !checkTimeout())
                {
                    Thread.Sleep(1000);
                }
                if (TimeOver != null)
                    TimeOver(_userdata);
            }
            catch (Exception)
            {
                Stop();
            }
        }
    }

    /// <summary>
    /// 过期时回调委托
    /// </summary>
    /// <param name="userdata"></param>
    public delegate void TimeoutCaller(object userdata);

 

      

    public class CNNWebClient : WebClient
    {

        private Calculagraph _timer;
        private int _timeOut = 10;

        /// <summary>
        /// 过期时间
        /// </summary>
        public int Timeout
        {
            get
            {
                return _timeOut;
            }
            set
            {
                if (value <= 0)
                    _timeOut = 10;
                _timeOut = value;
            }
        }

        /// <summary>
        /// 重写GetWebRequest,添加WebRequest对象超时时间
        /// </summary>
        /// <param name="address"></param>
        /// <returns></returns>
        protected override WebRequest GetWebRequest(Uri address)
        {
            HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address);
            request.Timeout = 1000 * Timeout;
            request.ReadWriteTimeout = 1000 * Timeout;
            return request;
        }

        /// <summary>
        /// 带过期计时的下载
        /// </summary>
        public void DownloadFileAsyncWithTimeout(Uri address, string fileName, object userToken)
        {
            if (_timer == null)
            {
                _timer = new Calculagraph(this);
                _timer.Timeout = Timeout;
                _timer.TimeOver += new TimeoutCaller(_timer_TimeOver);
                this.DownloadProgressChanged += new DownloadProgressChangedEventHandler(CNNWebClient_DownloadProgressChanged);
            }

            DownloadFileAsync(address, fileName, userToken);
            _timer.Start();
        }

        /// <summary>
        /// WebClient下载过程事件，接收到数据时引发
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void CNNWebClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        {
            _timer.Reset();//重置计时器
        }

        /// <summary>
        /// 计时器过期
        /// </summary>
        /// <param name="userdata"></param>
        void _timer_TimeOver(object userdata)
        {
            this.CancelAsync();//取消下载
        }
    }

参考：

https://stackoverflow.com/questions/1237966/how-can-i-change-the-time-limit-for-webclient-uploaddata

http://www.cnblogs.com/heros/archive/2009/07/06/1517997.html