UWP RfComm - StreamSocketListener.BindServiceNameAsync throws exception - bluetooth

Question

I am trying to create a UWP app that listens for Bluetooth serial port connections. When I set up the listener in the application (via a button click) I get an exception at the line:
await socketListener.BindServiceNameAsync(
rfcommProvider.ServiceId.ToString(),
SocketProtectionLevel.BluetoothEncryptionAllowNullAuthentication);`
The exception message is:
System.ArgumentException: 'The parameter is incorrect.
'protectionLevel': Only plain sockets are allowed for IP StreamSocketListeners.'
Here is the code:
private async void btnBluetoothServerClick(object sender, RoutedEventArgs e)
{
var rfcommProvider =
await RfcommServiceProvider.CreateAsync(RfcommServiceId.SerialPort);
var socketListener = new StreamSocketListener();
socketListener.ConnectionReceived += OnConnectionReceived;
await socketListener.BindServiceNameAsync(
rfcommProvider.ServiceId.ToString(),
SocketProtectionLevel.BluetoothEncryptionAllowNullAuthentication);
rfcommProvider.StartAdvertising(socketListener);
}
When the protectionLevel parameter SocketProtectionLevel.BluetoothEncryptionAllowNullAuthentication, is changed to, SocketProtectionLevel.PlainSocketas the exception indicates, the new exception message is: System.Exception: 'The specified class was not found. (Exception from HRESULT: 0x8007277D)'.
The application manifest file includes:
<Capabilities>
<Capability Name="internetClient" />
<DeviceCapability Name="bluetooth" />
<DeviceCapability Name="proximity" />
<DeviceCapability Name="serialcommunication">
<Device Id="any">
<Function Type="name:serialPort" />
</Device>
</DeviceCapability>
<DeviceCapability Name="bluetooth.rfcomm">
<Device Id="any">
<Function Type="name:serialPort" />
</Device>
</DeviceCapability>
<DeviceCapability Name="wifiControl" />
</Capabilities>
It seems that this code should work according to the documentation at:
https://learn.microsoft.com/en-us/uwp/api/windows.networking.sockets.streamsocketlistener#Windows_Networking_Sockets_StreamSocketListener_BindServiceNameAsync_System_String_Windows_Networking_Sockets_SocketProtectionLevel_Windows_Networking_Connectivity_NetworkAdapter_
What am I doing wrong?

Answer 1

Just change parameter of the BindServiceNameAsync method,
rfcommProvider.ServiceId.ToString()
to
rfcommProvider.ServiceId.AsString()
then your code snippet will work.
The AsString() method of RfcommServiceId will convert the RfcommServiceId to a string.ToString will return the type which is not the correct parameter for BindServiceNameAsync.
More details please reference the official sample.