WebClient gives error when reading .dat file

Question

The following piece of code is used to read a file from server and download it to the client pc:

var webClient = new WebClient();
webClient.OpenReadCompleted += (s, e) =>
{
    using (var fs = (Stream) dialog.OpenFile())
    {
           e.Result.CopyTo(fs);
           fs.Flush();
           fs.Close();
    }
 };
 webClient.OpenReadAsync(GetFileUri(fileToDownload));

When downloading a .txt file everything is ok. But when I try to download a .dat file I get following exception: System.Reflection.TargetInvocationException with inner exception System.Net.WebException: The remote server returned an error: NotFound.The Uri is relative and doesn't present an issue with the .txt file.

I can't seem to find information if this should be possible or what the issue could be. The error itself also doesn't give me much. Any thoughts?

Well does the server definitely return the file for that URL? Does it work in a browser? — Jon Skeet
When I put the Url in the browser I get this: HTTP Error 404.3 - Not Found The page you are requesting cannot be served because of the extension configuration. If the page is a script, add a handler. If the file should be downloaded, add a MIME map. — LittleWhiteFairy
Right. So that's the problem - nothing to do with your client code. — Jon Skeet
".dat" is not a default MIME type. You have to configure your web server. — Jeroen Heier

LittleWhiteFairy LittleWhiteFairy · Accepted Answer · 2016-07-15T07:24:52

There was a setting missing in the config file. I needed to add the following:

<system.webServer>
  <staticContent>
    <mimeMap fileExtension=".dat" mimeType="application/octet-stream" />
  </staticContent>
</system.webServer>

WebClient gives error when reading .dat file

1 Answers