Question

I need to download a zip file created in realtime from a webservice.
Let me explain.
I am developing a web application that uses a SoapXml webservice. There is the Export function in the webservice that returns a temporary url to download the file. Upon request to download, the server creates the file and makes it available for download after a few seconds.
I’m trying to use

webClient.DownloadFile(url, @”c:/etc../”)

This function downloads the file and saves it to me 0kb. is too fast! The server does not have time to create the file. I also tried to put

webClient.OpenRead(url); 
System.Threading.Thread.Sleep(7000);
webClient.DownloadFile(url, @"c:/etc../");

but does not work.
In debug mode if I put a BREAK POINT on webClient.DownloadFile and I start again after 3, 4 seconds, the server have the time to create the file and I have a full download.

The developers of the webservice suggested me to use “polling” on the url until the file gets ready for the download. how does it work?

How can I do to solve my problem? (I also tried to DownloadFile Asynchronous mode )

Answer 1

I have similar mechanism in my application, and it works perfectly. WebClient does request, and waits, because server is creating response(file). If WebClient downloads 0kb that means that server responded to request with some empty response. This may not be a bug, but a design. If creating file takes long time, this method could result in timeouts. On the other hand if creating file takes short time, server side should respond with file(making WebClient hang on request, till the file is ready). I would try to discuss this matter with other developers and maybe redesign “file generator”.

EDIT: Pooling means making requests in loop, for example every 2 seconds. I’m using DownloadData because it’s useless, and resource consuming, to save empty file every time, which DownloadFile does.

        public void PoolAndDownloadFile(Uri uri, string filePath)
        {
            WebClient webClient = new WebClient();
            byte[] downloadedBytes = webClient.DownloadData(uri);
            while (downloadedBytes.Length == 0)
            {
                Thread.Sleep(2000);
                downloadedBytes = webClient.DownloadData(uri);
            }
            Stream file = File.Open(filePath, FileMode.Create);
            file.Write(downloadedBytes, 0, downloadedBytes.Length);
            file.Close();
        }