SSDP discovery on Windows Store App not reliable

Question

Hi,
I am having problem implementing SSDP discovery in windows 8 store program. Below is the code:
public async Task SearchForDevices()
var socket = new DatagramSocket();
socket.MessageReceived += async (sender, args) =>
Debug.WriteLine("Received data" + DateTime.Now);
DataReader reader = args.GetDataReader();
uint count = reader.UnconsumedBufferLength;
string data = reader.ReadString(count);
Debug.WriteLine(data);
var response = new Dictionary<string, string>();
foreach (
string x in
data.Split(new[] {"\r\n", "\n"}, StringSplitOptions.None))
if (x.Contains(":"))
string[] strings = x.Split(':');
response.Add(strings[0].ToLower(), x.Remove(0, strings[0].Length + 1));
Device device = await GetXml(response);
Debug.WriteLine("Device found");
if (DeviceFound != null)
DeviceFound(this, new DeviceFoundEventArgs(device));
await socket.BindEndpointAsync(null, "");
HostName hostName = new HostName("239.255.255.250");
socket.JoinMulticastGroup(hostName);
string message = "M-SEARCH * HTTP/1.1\r\n" +
"HOST: " + hostName.DisplayName + ":1900\r\n" +
"ST: upnp:rootdevice\r\n" +
"MAN: \"ssdp:discover\"\r\n" +
"MX: 3\r\n\r\n";
DateTime start = DateTime.Now;
TimeSpan interval = new TimeSpan(0, 0, 30);
Debug.WriteLine(start);
IOutputStream stream = await socket.GetOutputStreamAsync(hostName, "1900");
var writer = new DataWriter(stream) { UnicodeEncoding = UnicodeEncoding.Utf8 };
writer.WriteString(message);
await writer.StoreAsync();
await Task.Delay(1500);
This code is not reliable at all. About 50% times it can't find a connected device while other discover can find. But sometimes it works.
My network sniffer (SmartSniff) sometimes can't even capture its SSDP request even though I have made the call many times.
I don't think this is an async problem since it does work occasionally. Please help me. Thanks!

Answer 1

Hi Jeff,
I have an additional question to this thread.
I try to share code between WinRT and Windows Phone 8 using similar code.
Starting on Windows Phone 8 I ommited the following lines:
        await socket.BindEndpointAsync(null,
        socket.JoinMulticastGroup(hostName);
This worked fine on the Phone. MSDN mentions for BindEndpointAsync,
that  GetOutputStreamAsync also leads to a binding.
I could receive answers. but when I tried to use this on WinRT/Windows Shop I did not receive anything. I had to put in the two lines of code from above.
This is not how it is supposed to be, right?
Stefan