如何在 c# 代码中处理来自 http 响应的重定向？

Question

I have a http request call that return a url . If I run this url in IE it returns a page that redirects to a another page and downloads the excel file.

How can I abstract this whole process in ac# Api tha will deal with http request + response + redirect + file_downlaod in a method and evetually return the file or the file stream.

thanks for the help.

Answer 1

Here is some [dated] code that follows all redirects until it hits a real page. You'll want to use more modern APIs to make web requests but the principle is the same.

/// \<summary\>
/// Follow any redirects to get back to the original URL
/// \</summary\>
private string UrlLengthen(string url)
{
    string newurl = url;
    bool redirecting = true;

    while (redirecting)
    {
        try
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(newurl);
            request.AllowAutoRedirect = false;
            request.UserAgent = "Mozilla/5.0 (Windows; U;Windows NT 6.1; en - US; rv: 1.9.1.3) Gecko / 20090824 Firefox / 3.5.3(.NET CLR 4.0.20506)";

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            if ((int)response.StatusCode == 301 || (int)response.StatusCode == 302)
            {
                string uriString = response.Headers["Location"];
                Log.Debug("Redirecting " + newurl + " to " + uriString + " because " + response.StatusCode);
                newurl = uriString;
                // and keep going
            }
            else
            {
                Log.Debug("Not redirecting " + url + " because " + response.StatusCode);
                redirecting = false;
            }
        }
        catch (Exception ex)
        {
            ex.Data.Add("url", newurl);
            Exceptions.ExceptionRecord.ReportCritical(ex);
            redirecting = false;
        }
    }
    return newurl;
}

Answer 2

You may consider using WebRequest / WebClient classes.

Here you have some examples.

http://msdn.microsoft.com/en-us/library/system.net.webrequest%28VS.80%29.aspx

http://www.c-sharpcorner.com/UploadFile/mahesh/WebRequestNResponseMDB12012005232323PM/WebRequestNResponseMDB.aspx