c#获取页面重定向url

/// <summary>
/// 获取页面重定向url
/// </summary>
/// <param name="url"></param>
/// <param name="referer"></param>
/// <param name="cookie"></param>
/// <returns></returns>
public static string GetRedirectUrl(string url, string referer = "", string cookie = "")
{
try
{
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
req.Method = "HEAD";
req.Referer = referer;
req.AllowAutoRedirect = false;
if (cookie.Length>0)
{
req.Headers.Add("Cookie:" + cookie);
}
WebResponse response = req.GetResponse();
return response.Headers["Location"];
}
catch (Exception e)
{
TextTool.Log(e,"获取url重定向地址错误");
return null;
}
}