Exception in HttpResponseMessage for async POST method in .NET4.5

Question

I am developing an application for Windows 8 (Consumer Preview) in C#. It makes simple REST calls to the Last.fm API.

There is this exception which is bothering me since many days now. I am trying to send a POST call to a Last.fm API method. But whenever I send a call, I get the following mssg -

"An exception of type 'System.Net.Http.HttpRequestException' occurred in mscorlib.dll but was not handled in user code". Additional information: An error occurred while sending the request.

If I print out the exception it says -

System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The underlying connection was closed: The connection was closed unexpectedly.

at System.Net.HttpWebRequest.EndGeetResponse(IAsyncResult asyncResult)

at System.Net.Http.HttpClientHandler.GetResponseCallback(IAsyncResult ar)

My GET calls to the authentication API of last.fm are working fine.

I am attaching a code snippet:

private async void Collection_Click_1(object sender, RoutedEventArgs e)
{
    /* .
       .
       .
    */

HttpClient Cli = new HttpClient();
string track_updateNowPlaying = "method=track.updateNowPlaying&track=" + id3.Title + "&artist=" +id3.Artist + "&album=" + id3.Album + "&api_key=" + lfm_api_key + "&api_sig=" + updtrack_sig + "&sk=" + Globalv.session_key;

HttpContent tunp =new StringContent(track_updateNowPlaying);

try
{
    //getting exception in the following line
    HttpResponseMessage upd_now_playing = await cli.PostAsync(new Uri("http://ws.audioscrobbler.com/2.0/", UriKind.RelativeOrAbsolute), tunp);

}
catch(Exception ex) {textblock.text = ex.ToString();}
}

private async void LoginBtn_Click_1(object sender, RoutedEventArgs e) //this function is called before collection_click_1 function
{
    /* .
       .
       .
    */
HttpClient cli = new HttpClient();
string auth_request = "http://ws.audioscrobbler.com/2.0/?method=auth.getMobileSession&username=" + UsernameTBx.Text + "&authToken=" + lfm_authToken + "&api_key=" + lfm_api_key + "&api_sig=" + lfm_api_sig;

HttpResponseMessage auth = await cli.GetAsync(auth_request); //this works fine...

}

Please let me know if a stack trace would be necessary.

-Sagar

Answer 1

I guess I figured it out. I'm keeping the post for others to refer.

The case was that Last.fm servers do not accept Expect:100Continue in the header field. So I had to explicitly change it to false.

So had to add the following:

HttpClient cli = new HttpClient();
cli.DefaultRequestHeaders.ExpectContinue = false;